Development of techniques for non-flame spectroscopic determination of trace metals
by Darryl Duane Siemer
A thesis submitted in partial fulfillment of the requirements for the degree of DOCTOR OF
PHILOSOPHY in Chemistry
Montana State University
© Copyright by Darryl Duane Siemer (1974)
Abstract:
A mercury analysis system is presented which is adaptable to the determination of mercury in any type
of sample. Mercury vapor in air or other gases is captured by filtration through gold plated, porous
graphite carbon rod atomizer tubes. Mercury in solid samples is converted to the mtal vapor by burning
the sample in pure oxygen. Mercury in aqueous samples is reduced to the vapor with stannous chloride.
The gold plated porous tubes are placed between the rods of a carbon rod atomizer and the mercury
atomized and measured with an atomic absorption spectrometer. Substances which normally interfere
in the atomic absorption determination of mercury pass through the walls of the porous graphite tubes
and are not a problem. Operating parameters and some applications are discussed. Detecting limits in
the ppm to the ppb level with relative standard deviations of 4% to 10% range are achieved.
Porous graphite tubes are used as air filters. Particulate matter filtered from the air is analyzed for a
wide range of metallic elements by atomizing the material on the tubes directly into the light path of an
atomic absorption spectrometer with a carbon rod atomizer. The filtration characteristic of the tubes,
standardization, and the applications are discussed. The detection capabilities of the technique for most
elements are better than those of most other methods published to date.
A process for coating graphite objects with an impervious coating of pyrolytic carbon is described. The
method consists of passing natural gas over the object to be plated inside a wire-wound tubular quartz
furnace. The coating process and the properties of the pyrolytic carbon coating are discussed. The
pyrolytic carbon coatings are demonstrated to significantly improve flameless atomic absorption
atomizers. The process also allows construction of graphite objects useful for other purposes. DEVELOPMENT OF TECHNIQUES FOR NON-FLAME SPECTROSCOPIC
DETERMINATION OF TRACE METALS
by
DARRYL DUANE SIEMER
A t h e s i s su b m itte d - i n p a r t i a l f u l f i l l m e n t
o f th e re q u ire m e n ts f o r th e d egree
of
DOCTOR OF PHILOSOPHY
in
C hem istry
Approved:
Head, M ajor D epartm ent
G raduate Dean
MONTANA STATE UNIVERSITY
Bozeman, Montana
A ugust, 1974
ACKNOWLEDGEEMENT
I would l i k e t o th a n k ray w ife , Ju d y , f o r h e r su p p o rt and f o r h e r
p a tie n c e d u rin g ray y e a r s i n g ra d u a te school*
Dr* Ray W oodriff d e se rv e s s p e c ia l c r e d i t f o r su p p ly in g i n s p i r a t i o n
and a d v ic e , and f o r p ro v id in g a good environm ent f o r re se a rc h *
“ ivT A B L E OF CONTENTS
page
LIST OF TABLESeooooooooooooooooooooooooooooooooooooooooooooeoooooooooV
LIST OF FIGURESoeooooooooooeocoeeooeoooooo0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VX
ABSTRACT o o o o o o o e o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o e o o o e o o o o o o o o o
00 0 0 0 o V X H
GENERAL INTRODUCTIONoooooeoooeooeeoooooooooooeoooooooooeooooeoeoeoeool
0»V> V)
THE DETERMINATION OF MERCURY IN AIR, WATER, AND SOLID SAMPLES
WITH THE■CARBON ROD ATOMIZERoooeoeooooooooooeooooooooooooooooooooooeo
Introductionoo o o e o o e o o e o o o o o o o o o o o o o e o o o o o o o o o o o o 0 0 o o o o o e o o
General Outline of Experimental Techniquee o o e o o e o o o o o o o e o o e
Results and Discussion of Basic Procedure0oeooooooooooooool6
Application of the Technique to Air Samplingoooooo 00oo 000»28
Application of the Technique to Water ,SampMa;*o o o o o o o o o o o 033
Application of the Technique to Solid SampleSooooooooooooc41
Conclusionsoooocoooooooooooooooooeoooeoooooooooooooeooooo ©if7
DIRECT ATOMIC ABSORPTION DETERMINATION OF METALLIC POLLUTANTS
IN AIR WITH A CARBON ROD AT CMIZER ©©ooooooooooo©©©©©©©oo oooooooooooo©^9
,Introduction© ©©©©©©©©©©©©©o©©©©©©o©©©©©©©©©©©©©©©©©©©©©©© ©A*9
Experimental© ©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©SS
Results and Discussion©©©©©©©©©©©©©©©©©©©©©©©©©©o©©©©©©©©©$8
Conclusionsooeoooooooooooooooooooo©©©©©©©©©©©©©©©©©©©©©©©© 73
A SIMPLE TECHNIQUE FOR COATING GRAPHITE WITH PYROLYTIC CARBON©©©o©©©75
. t -Introduction© ©©©©©©©©©©©©©©©©©©©©©©©©©©©©©o©© ©©©o©©©©©©©© ©75
Experimental© o©o©oo©©©©©©o©o©©©©©©©©o©©©o©©©©©©o©©©o©©©©©o7^
Results and Dxscussxon©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©o©©©79
Conclusxons©©©©©©©©©o©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©©© 89
APPENDIX© o o o o o o o o e o o o o o o o o o o o d o o o o o o o o o o o o o o o o o p o o o © . © © © © © © © © © © © © © © © © 91
LITERATURE CITED© © © © © © © © © © © © © © © © © © © © © o o © © © © © © © © © © © © © © © © © © © © © © © © © © © © © 9A
-V -
LIS T OF T A BLES
Table
page
I.
M e rc u ry .C o lle c tio n E f f ic ie n c y o f Porous G ra p h ite T u b e s . . . ...1 7 .
II.
E f f e c t o f R epeated H eatin g on th e C o lle c tio n E f f ic ie n c y o f a
Gold P la te d G ra p h ite Tube. . . . . . . . . 6 * . o . . . . . . . . . . . . . . . . . . . . . . I^
. III.
M ercury C o lle c tio n a s a F u n c tio n o f th e Amount o f Gold
P la te d o n to T u b e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0
IV.
R e s u lts o f M ercury D e te rm in a tio n s i n th e A ir o f a Room
w ith V is ib le S p il le d M ercu ry ............................................. ............ . . . . 3 0
V.
Comparison o f D ire c t A to m izatio n t o Combustion f o r
S ta n d a r d iz a tio n .
. . . . . . . . . . . . . . . . . . oo.'44
V I.
F i l t r a t i o n E f f ic ie n c y o f Porous G ra p h ite F i l t e r s . . . . . . . . . ...59
V II.
S a lt E f f e c t on Lead D e te rm in a tio n .. . . . . .
...64
V III .
C om parison.of D ire c t t o I n d i r e c t Measurement o f C aptured
P a r t i c u l a t e S o . . . . . . . . * . . . . . . . . . . . . . * . . . . . . . * * . . . . . . * . . . . . ...66
IX.
Comparison o f M illip o r e F i l t e r t o Porous G ra p h ite f o r
Lead P a r t i c u l a t e s . e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OOO68
X.
T y p ic a l A n a ly tic a l P aram eters f o r th e D ire c t A n a l y s i s . . . . . . . 7 0
X I.
Comparison o f Coated and Uncoated Carbon Rod A tom izer
T u b e s ........................................... ..................... ............ ...............c o o . . . . .
.83
-v i LIST O F FIGURES
Figure
page
1.
Carbon Rod A tom izer. . . . . . .. . .
2.
Gold P la tin g Ap p a r a t u s o.ooooooooooo.oooooooooooooooo.ooo. . o i l
3.
F i l t e r A d ap to r.................... .....................
ko
S chem atic o f Atomic A b so rp tio n S p e c tr o m e te r ...o . . . . . . . . . . . . 14
5.
A pparatus f o r T e s tin g F i l t r a t i o n E f f i c i e n c y .. . . o . . . . . . . . . ..1 5
6»
F i l t r a t i o n E f f ic ie n c y a s a F u n c tio n o f th e Amount o f
M ercury and Goldoo.o.ooooo.ooooo.ooo.ooooooooooooooooooooooo21
7.
S tan d ard Curve f o r M ercury Based on Two Methods o f
S ta n d a r d iz a tio n ......... ............ ...... .................................ooooooo.ooooe.23
8.
Power In p u t V ersus Observed Atomic A b s o rp tio n ............................25
9.
A ir Flow w ith R espect t o P re s s u re D i r r e r e n t i a l o ooeoooeo.eoo27
OO
0 0 0 0 0 9 0 0 9 0 0 0 0 ' .
. 0 . 0 .
. 0 0 0 0 . 0 0 .
10. M ercury L ev el in Room 233 on December I , 1 9 7 3 .« .° .......... ooo.32
11.
M ercury i n W ater A p p a r a t u s . . . . . . . oooooooooooooooooooooooo. .35
12 . F lu sh in g Time V ersus Recovery. . . . . oooooooooooooooooooooooo. 37
13.
T y p ic a l A n a ly tic a l Curve f o r W ater A n a ly sis S y ste m ............ ..3 9
14.
S ta n d a rd A d d itio n s t o Langhor Mine W a t e r . . . . ......... . . . . . . . . . . A O
1 5 . M' ercury i n S o lid s Combustion Apparatusoeoeooeeoooooooeooeee42
16.
Beckman DB Flame P a r t i c u l a t e G e n e r a to r .. . . . . . . . . . . . . . . . . o . .5 4
17.
U ltra s o n ic N e b u liz e r P a r t i c u l a t e G e n e r a t o r . . . . . . . . . . . . . . . ..5 5
18.
Lead P a r t i c u l a t e G e n e ra tio n A p p a r a t u s . . . , . . . . . . . , . , . , o o o , . . 57
19.
M easured.P a r t i c u l a t e C o n c e n tra tio n a s a F u n c tio n o f
Sam pling R ate o o o . .oooooooooooooooooooooooo.o o . o . o o o o o , , , . O' . 61
-vii-
20*
S i l v e r S o ld e r Experiment/ W
21.
P y r o ly tic Carbon D e p o sitio n A p p a r a t u s .... . . . . . o c . . . . . . . . . . . 78
22.
D e p o sitio n R ate a s a F u n c tio n o f T e m p e ra tu re .. . . . . . . . . . . . . . . 8 1
23«
F i l t e r C ru c ib le C o n s t r u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24.
D ire c t' S o lu tio n P a r t i c u l a t e A n a ly s is .................
o e e e e e e e e e e d e e e e o e e e e o e e o o e o e e e e o e e rZ S
-viii"
ABSTRACT
A m ercury a n a ly s is system i s p re s e n te d which i s a d a p ta b le t o th e
d e te rm in a tio n o f m ercury in any ty p e o f sam pleo M ercury v ap o r in a i r
o r o th e r g a se s i s c a p tu re d by f i l t r a t i o n th ro u g h g o ld p la te d , porous
g r a p h ite carbon ro d a to m iz e r tu b e s . M ercury i n s o l i d sam ples i s con­
v e rte d to th e m ta l vapor by b u rn in g th e sample i n p u re oxygen. Mer­
cury i n aqueous sam ples i s red u ced t o th e v ap o r w ith stan n o u s c h lo r id e .
The g o ld p la te d porous tu b e s a re p la c e d betw een th e ro d s o f a carbon
rod a to m iz e r and th e m ercury ato m ized and measured w ith an atom ic
a b s o r p tio n s p e c tro m e te r. S u b stan ces which n o rm ally i n t e r f e r e in th e
atom ic a b s o r p tio n d e te rm in a tio n o f m ercury p a ss th ro u g h th e w a lls o f
th e porous g r a p h ite tu b e s and a re n o t a problem . O p e ratin g p a ra m ete rs
and some a p p lic a tio n s a re d is c u s s e d . D e te c tin g l i m i t s in th e ppm t o
th e ppb l e v e l w ith r e l a t i v e s ta n d a rd d e v ia tio n s o f k% t o 10% range a re
a c h ie v e d .
Porous g r a p h ite tu b e s a re used a s a i r f i l t e r s . P a r t i c u l a t e m a tte r
f i l t e r e d from th e a i r i s an aly zed f o r a wide ran g e o f m etal l i c elem en ts
by a to m iz in g th e m a te r ia l on th e tu b e s d i r e c t l y in to th e l i g h t p a th o f
an atom ic a b s o r p tio n s p e c tro m e te r w ith a carbon ro d a to m iz e r. The f i l ­
t r a t i o n c h a r a c t e r i s t i c o f th e tu b e s , s ta n d a r d iz a tio n , and th e a p p li­
c a tio n s a re d is c u s s e d . The d e te c tio n c a p a b i l i t i e s o f th e te c h n iq u e f o r
most elem en ts a re b e t t e r th a n th o s e o f most, o th e r methods p u b lish e d t o
d a te .
A p ro c e s s f o r c o a tin g g r a p h ite o b je c ts w ith an im p erv io u s c o a tin g
o f p y r o ly t ic carbon i s d e s c rib e d . The method c o n s is ts o f p a ss in g n a t­
u r a l gas o v e r th e o b je c t t o be p la te d in s id e a w ire-w ound tu b u la r
q u a rtz f u r n a c e . The c o a tin g p ro c e s s and th e p r o p e r tie s o f th e p y ro ly ­
t i c carbon c o a tin g a re d is c u s s e d . The p y r o ly tic carbon c o a tin g s a re
d e m o n strated t o s i g n i f i c a n t l y improve fla m e le s s atom ic a b s o r p tio n a t ­
o m iz e rs. The p ro c e s s a ls o a llo w s c o n s tr u c tio n o f g r a p h ite o b je c ts V..
u s e f u l f o r o th e r p u rp o s e s.
GENERAL INTRODUCTION
The use o f atom ic a b s o rp tio n s p e c tro sc o p y a s a r o u tin e a n a l y t i c a l
• :
t o o l began i n th e n in e te e n f o r t i e s , when i t was a p p lie d t o th e d e te r ­
m in a tio n o f m ercury i n a i r ( I ) .
I n 1954 a p a p er
was p u b lis h e d con­
c e rn in g th e u se o f atom ic a b s o r p tio n f o r th e a n a ly s e s o f gases®
Up t o
1955, th e u se o f atom ic a b s o rp tio n sp e c tro s c o p y f o r a n a ly s is work was
c o n fin e d t o th e a p p lic a tio n s d is c u s s e d i n th e s e referen ces®
The p rim ary re a so n f o r , t h i s d e a r th o f p ro g re s s i n th e l i g h t o f th e
burg eo n in g a p p lic a tio n o f v a rio u s atom ic e m issio n te c h n iq u e s was t h a t
none o f th e methods in w hich atom ic a b s o r p tio n m easurem ents had been
made by e x p e rim e n ta l p h y s ic i s ts s a t i s f i e d th e p r a c t i c a l re q u ire m e n ts
o f an a n a l y t i c a l t o o l from th e s ta n d p o i n ts :o f th e ran g e o f elem en ts em­
b ra c e d , s e n s i t i v i t y , and sim p lic ity ®
P erhaps even more im p o rta n t was
th e f a c t t h a t th e p o t e n t i a l a d v an ta g e s o f a b s o r p tio n methods o f a n a ly ­
s e s w ith r e s p e c t t o e m issio n methods had n o t been c l a r i f i e d t o th e ex­
t e n t t o promote r e s e a r c h in th e field ®
In 1955 W alsh ^ ^ and, in d e p e n d e n tly , Alkmade and M ila tz
p u b lis h e d p a p e rs in d ic a tin g s u b s t a n t i a l ad v an tag es o f a b s o r p tio n me­
th o d s o v er e m issio n te c h n iq u e s f o r q u a n t i t a t i v e s p e c tro c h e m ic a l a n a ly sis®
D uring th e e n su in g y e a rs s e v e r a l th o u san d works have been pub­
lis h e d on ato m ic absorption®
They w ere concerned b o th w ith r e s a rc h on
th e mechanisms in h e re n t t o th e a b s o r p tio n m easurem ents and on th e ex­
te n s io n o f th e f i e l d t o an e v e r in c r e a s in g ran g e o f substances®
The
method i s now w id e ly used in many c o u n tr ie s and has become th e most pop-
uI a r te c h n iq u e o f e le m e n ta l a n a ly s is f o r a wide range o f sample
ty p e so
The need f o r more s e n s i t i v e a n a l y t i c a l equipm ent sp u rre d r e ­
s e a rc h in nonflam e, p u lse d a to m iz e rs f o r atom ic a b s o r p tio n (5# 6, 7, 8)«
These a to m iz e rs a re much more s e n s i t i v e and, in some c a s e s , a llo w
chem ical a n a ly s is o f sam ples w ith no p re c o n c e n tra tio n o r s e p a ra tio n
s te p s .
S e v e ra l v e rs io n s o f th e s e a to m iz e rs have been made com m ercially
a v a il a b le by m ajor s c i e n t i f i c in s tru m e n ta tio n companies w ith in th e l a s t
th r e e y e a r s .
The purpose o f th e work d e s c rib e d in t h i s t h e s i s i s t o ex­
te n d th e a n a l y t i c a l c a p a b i l i t y o f th e s e a to m iz e rs in th e a r e a o f e n v i­
ro n m en tal a n a ly s is by im proving b o th th e a to m iz e rs th e m selv e s and th e
a n a l y t i c a l te c h n iq u e s f o r w hich th e y a re u s e d .
A w id e ly d i s t r i b u t e d
a to m iz e r, th e V arian T ech tro n Model 63, was chosen a s th e model t o be
used f o r t h i s re s e a rc h b o th b ecau se o f i t s a v a i l a b i l i t y t o a n a l y t i c a l
c h e m ists and i t s p o t e n t i a l v e r s a t i l i t y f o r d i f f e r e n t a to m iz a tio n
chamber m o d if ic a tio n .
THE DETERMINATION OF MERCURY IN AIR, WATER, AND SOLID SAMPLES
WITH THE CARBON ROD ATOMIZER
In tr o d u c tio n
The a n a ly s is o f sam ples f o r f r a c t i o n a l p a r t p e r m illio n l e v e l s o f
m ercury i s a common problem in a n a l y t i c a l la b o r a to r ie s =
S e v e ra l ex­
c e l l e n t re v ie w s have been p u b lis h e d r e c e n tly which d is c u s s th e e x te n t
o f th e c o n tam in atio n problem a s w e ll a s th e a n a l y t i c a l methodology
( 9 , 10, 11)
p r e s e n tly used*
There a r e th r e e b a s ic ap p ro ach es used f o r
th e a n a ly s is *
The f i r s t and o ld e s t te c h n iq u e in v o lv e s a c o n tr o lle d pH
d ith iz o n e e x tr a c ti o n o f m ercury from a s o lu tio n w ith su b seq u en t s p e c tr o m e tr ic a n a ly s is *
T h is a n a ly s is i s n e i t h e r a s s p e c i f i c n o r a s sen­
s i t i v e a s a re th e o th e r two approaches*
The second approach i s n e u tro n a c t i v a t i o n a n a ly s is *
The abso­
l u t e d e te c tio n l i m i t s a c h ie v a b le , on th e o rd e r o f 10"® gram a b s o lu te
( 12)
, a re v e ry good; how ever, i t s u f f e r s .f r o m poor r e p r o d u c i b i l i t y ,
v e ry h ig h c o s t, and g e n e r a lly in v o lv e s sen d in g sam ples o f f t o c e n t r a l
f a c i l i t i e s equipped w ith h ig h n e u tro n f lu x so u rces*
This, f e a tu r e
u s u a lly n e c e s s i t a t e s f a i r l y lo n g w a its f o r a n a l y t i c a l r e s u lts *
Atomic a b s o r p tio n , on th e o th e r hand, i s r e l a t i v e l y in e x p e n siv e and
can be accom plished w ith r e a d ily a v a il a b le equipm ent» A* A* a n a ly s is
f o r m ercury i s u s u a lly accom plished by ad d in g a re d u c in g a g e n t (u s u a l­
l y stan n o u s c h lo r id e ) t o a d ig e s t a t e and sw eeping th e ev o lv ed e le m e n ta l
m ercury o u t o f th e s o lu tio n i n t o a co ld v ap o r a b s o r p tio n tu b e in which
th e a b s o r p tio n o f th e Hg 2537 & reso n an ce l i n e i s measured*
The a n a ly ­
t i c a l s e n s i t i v i t y re p o rte d v a r ie s b u t i s u s u a lly on th e o rd e r o f I - 2
“4n g Hg f o r 1 % absorption.
The fla m e le s s te c h n iq u e i s f e a s i b l e because m ercury p o s s e s s e s th e
p r o p e r tie s o f h av in g an a p p re c ia b le v ap o r p re s s u re a t room te m p e ra tu re
and o f n o t b e in g r e a d i l y o x id is e d by a i r .
e x p lo ite d by Woodson
These p r o p e r tie s were f i r s t
who d e s c rib e d in 1939 a sim p le in stru m e n t
f o r m easuring m ercury v ap o r in a i r .
th e method t o s o lu tio n a n a l y s i s .
B a lla rd e t a l (^4 -1 6 ) extended
They ra n th e s o lu tio n s th ro u g h a s ­
b e s to s pads soaked in cadmium s u l f i d e .
M ercury d is p la c e d th e cadmium
and was e f f e c t i v e l y f i l t e r e d from th e s o lu tio n s .
I t was su b se q u e n tly
d riv e n o f f in to th e a b s o rp tio n c e l l by th e a p p lic a tio n o f h e a t.
and R osenberg
Pappas
employed a m o d ific a tio n o f th e te c h n iq u e f o r th e
a n a ly s is o f s o l i d f o o d s tu f f s .
The sam ples were o x id iz e d in a combus­
t i o n f l a s k , and th e gaseous com bustion p ro d u c ts were ab so rb ed in 1 .2 N
HOI.
The pH was a d ju s te d t o 6 - 7 and th e s o lu tio n p a sse d th ro u g h CdS
im pregnated pads a s p re v io u s ly d e s c rib e d .
P o lu e k tov, B itk u n , and Zelyukova
w ere th e f i r s t t o u t i l i z e
'A .
d i r e c t re d u c tio n o f m ercury t o th e e le m e n ta l s t a t e by stan n o u s c h lo rid e
f o r c o ld v ap o r A. A. d e te rm in a tio n o f m ercury.
H atch and O tt
ap­
p lie d th e te c h n iq u e t o a c id d ig e s te d s o i l and c o b a lt and n ic k e l m e ta l
sam p les.
The m ost commonly used te c h n iq u e to d a y f o r m ercury d e te rm in a -
f 21)
t i o n in a w ide range o f o rg a n ic sam ples was d e sc rib e d by L in d s te d t v '
.
■
who a n aly z e d u r in e by com bining th e p o ta ssiu m p e rm a n g a n a te -s u lfu ric a c id
d ig e s tio n method o f Jaco b s and Singerm an
fo llo w e d by stan n o u s
-5-
c h lo rid e r e d u c tio n o f th e m ercu ry » The evolved m ercury i s swept from
th e s o lu tio n w ith a gas stre a m which c a r r i e s th e m ercury in to a
quartz-w indow ed flo w -th ro u g h c e l l mounted in an A0 Ae sp ec tro m e te r*
O
peak a b s o r p tio n o f th e 2537 A m ercury reso n an ce l i n e i s measured*
The
The r e d u c tio n - a e r a tio n te c h n iq u e i s f a i r l y r a p id , a d a p ta b le t o a
w ide range o f sam ples, and in e x p e n s iv e , b u t i t s u f f e r s from two m ajor
w eak n esses.
As th e a n a ly s is i s commonly perform ed, th e f i n a l m easur-
ment i s s u b je c t t o th e v a g a r ie s o f k i n e t i c s .
The r a t e o f flu s h in g gas
flow and th e r a t e o f m ercury r e d u c tio n by stan n o u s io n , which in tu r n
i s a f f e c te d by th e te m p e ra tu re , volum e, and ch em ical n a tu r e o f th e s o lu ­
t i o n , b o th a f f e c t th e peak atom ic a b s o r p tio n .
The second problem con­
c e rn s o th e r m a te r ia ls p re s e n t in th e sample w hich v o l a t i l i z e and sub­
s e q u e n tly ab so rb r a d i a t i o n a t th e m ercury 2537 & l i n e .
Among th e s e a re
c y c lic o rg a n ic compounds, s u l f i d e s , a c e to n e ,, and w a te r v a p o r.
There a r e s e v e r a l b a s ic ap p ro ach es t o s o lv in g th e s e p ro b lem s.
The
most obvious way t o so lv e th e problem s a s s o c ia te d w ith th e k i n e t i c s o f
th e re d u c tio n p ro c e s s i s t o in t e g r a t e th e atom ic a b s o r p tio n peak and
u se a peak a r e a in s te a d o f peak h e ig h t a s th e m easure o f m ercury.
How­
e v e r , most atom ic a b s o rp tio n in s tru m e n ts a re n o t c ap a b le o f t h i s .
S e v e ra l in g e n io u s te c h n iq u e s have been developed t o circum vent th e
problem o f n o n -ato m ic background a b s o r p tio n by compounds.
B a lla rd
to o k re a d in g s o f th e c e l l c o n ta in in g th e m ercury v ap o r on.tw o s e p a ra te
in s tru m e n ts , th e f i r s t b e in g a u n i t c o n ta in in g a m ercury lamp and th e
— 6—
second a s ta n d a rd sp e c tro p h o to m e te r h av in g a wide bandpass (32 A ) and a
continuum s o u rc e «
The d if f e r e n c e betw een th e two re a d in g s i s due o n ly
t o m ercuryo
B a rrin g e r (23) and Ling ^
com pensated f o r non atom ic ab­
s o rb e rs by u s in g th e w ings o f th e broadened 2537 A l i n e , th e c e n te r o f
w hich has been co m p le tely abso rb ed by p a s s in g th ro u g h an in te rm e d ia te
a b s o r p tio n c e l l s a tu r a te d w ith m ercury v a p o r»
T h is so u rc e i s in s e n ­
s i t i v e to .m e rc u ry b u t i s s e n s i t i v e t o o th e r s u b sta n c e s which ab so rb in
t h a t reg io n *
By com paring t h i s s i g n a l w ith t h a t o b ta in e d u sin g th e e -
m issio n l i n e o f th e m ercury lamp w ith no in te rm e d ia te m ercury f i l t e r , a
m easure o f m ercury v ap o r a lo n e i s made*
The background method d e s c rib e d by K oirtyohann and P ic k e tt (^6)
and a p p lie d by Kahn ^ 7 )
w hich l i g h t from a c o n tin u o u s so u rc e and a
m ercury lamp a r e a l t e r n a t i v e l y beamed th ro u g h th e a b s o r p tio n c e l l i s
a ls o u s e fu l*
Lech, S iem er, and W o o d riff (2 8 ) r a tio e d th e a b s o rp tio n
o f a n e arb y n o n -reso n an c e m ercury l i n e t o th e 2537 A l i n e a s a means o f
background c o rre c tio n *
These e x p e d ie n ts , w ith th e e x c e p tio n o f peak I n t e g r a t i o n , do n o t
e lim in a te th e k i n e t i c s d i f f i c u l t i e s *
I n o rd e r t o s o lv e t h i s problem
and t o e lim in a te th e b u l k .o f th e n o n -ato m ic a b s o rp tio n in te r f e r e n c e s ,
s e v e r a l means o f s e p a r a tin g and c o n c e n tra tin g th e m ercury a lo n e in a
s o lu tio n o r s tre a m o f g as have been u s e d .
W ith th e s e te c h n iq u e s , th e
m ercury i s c o lle c te d o v er a p e rio d o f tim e and r e le a s e d and m easured
under c a r e f u l l y c o n tr o lle d c o n d itio n s i n a s h o r t p e rio d o f tim e ,
M o ffit and Kupel (2 9 ) c o lle c te d m ercury i n g as stre a m s w ith spe­
c i a l l y im pregnated c h a rc o a l f i l t e r s .
The g r a p h ite was th e n p la ce d in to ,
a sam pling b o a t w hich was swung o v er a flam e in a s ta n d a rd A, A, s p e c tr o m e te r ,
The sam pling b o a t A, A, measurement d id n o t f u l l y r e a l i z e th e
p o t e n t i a l o f th e sy stem .
A nother method f o r th e d e te rm in a tio n o f m ercury i s d e p o s itio n from
s o lu tio n o nto a s i l v e r w ire o r s c r e e n , e i t h e r by ch em ical d e p o s itio n
(H in k le and L earned, 3 0 , 31) o r e l e c t r o l y s i s ( 6 ra n ^e n b e rSe r and B ader,
3 2, 3 3 ) e
The c o lle c te d m ercury was d riv e n o f f th e w ire by ra p id h e a t­
in g and th e m ercury in tro d u c e d i n t o and m easured i n an a b s o r p tio n c e l l
j u s t a s in th e a e r a tio n m ethod,
Vaughn and McCarthy ( ^ ) , U lfv a rso n (3 5 ), Lidduns and U lfv a rso n
( • ^ , and A nderson e t a l , (3 7 ) c o n c e n tra te d m ercury in stre am s o f gas
o n to f i n e l y d iv id e d g o ld by am algam ation.
A ll i n t e r f e r i n g s u b sta n c e s
p a sse d th ro u g h th e system and were v e n te d , a f t e r w hich th e m ercury was
d riv e n o f f th e g o ld by h e a tin g t o 400 - 500 °C i n t o th e a b s o rp tio n
c e ll.
Lech, S iem er, and W oodriff (^®» ^ ) used g o ld p la te d g r a p h ite t o
c o l l e c t m ercury i n a i r o r to r e t a i n th e m ercury from s o lu tio n s d rie d i n
p la te d c u p s.
The cups were th e n in s e r te d in to a W o o d riff fu rn ac e a -
to m iz e r f o r th e m ercury d e te rm in a tio n .
The s e n s i t i v i t y o f th e fu rn a c e te c h n iq u e o f Lech, S iem er, and Woodr i f f was b e t t e r by a f a c t o r o f two o r th r e e th a n t h a t o f any o th e r A, A,
method re p o rte d t o d ate*
The o n ly d isa d v a n ta g e o f th e system a s f a r a s
th e a v erag e a n a l y t i c a l chem ist i s concerned i s t h a t th e W oodriff f u r ­
nace a to m iz e r i s n o t w id e ly d is tr ib u te d ,,
The purpose o f th e re s e a rc h t o
be d is c u s s e d h e re was t o d ev elo p a com plete m ercury a n a ly s is system ap™
i
•
.
p l i c a b l e t o a com m ercially a v a il a b le n o n-flam e a to m iz e r— s p e c i f i c a l l y
th e carbon ro d atom izer*
An o u tlin e o f th e method i s a s fo llo w s 0
The m ercury i n th e sample
i s c o n v e rte d t o th e f r e e m e ta l v ap o r by stan n o u s c h lo r id e re d u c tio n o r
by com bustion in oxygen*
Then th e m ercury i s c a r r ie d by a stre am o f
g as i n t o a f i l t e r a d a p to r c o n ta in in g a g o ld - p la te d c y l i n d r i c a l tu b e o f
porous g ra p h ite *
The m ercury i s r e ta in e d on th e g o ld w h ile p o t e n t i a l l y
i n t e r f e r i n g g a se s p a ss th ro u g h th e tu b e*
The tu b e i s th e n p la c e d be­
tw een th e ro d s o f a carbon rod a to m iz e r s im ila r t o t h a t m arketed by
V a ria n T ech tro n and h e a te d t o ato m ize th e mercury®
The atom ic a b so rp ­
t i o n s p ik e i s th e n recorded®
G e n era l O u tlin e o f E x p e rim e n ta l Technique
The carbon rod. a to m iz e r (GRA) was c o n s tr u c te d a t t h i s la b o r a to r y
and i s d e p ic te d i n F ig u re I*
I t i s d esig n ed t o f i t i n t o a T ech tro n
b u rn e r-s p ra y chamber assem bly i n th e same manner t h a t a V arian T ech tro n
Model 63 CRA does*
The main f u n c tio n a l p o in ts o f d if f e r e n c e between
th e T e c h tro n CRA and our homemade v e r s io n i s t h a t o u r model i s some­
w hat l a r g e r ( t o accom odate s ta n d a rd s p e c tro g ra p h ic
ro d s and tu b e s )
and f e a t u r e s f l e x i b l e m ounting o f b o th ro d su p p o rt p o s ts and a s u p e r ! -
view of atomizer complete
with gas shield box
graphite
tube
graphite
rod
cooling water
inlet
brass post perforated
Al plate
Teflon
washer
/ Al base
block
power
cable
gum rubber
sle e v e
■ater outlet
adaptor to
fit burner mount
Figure I. Carbon Rod Atomizer
SAE
3 /8 "-2 4 nuts
T
— 10“
o r gas s h ie l d system®
N itro g e n g as i s u sed t o f lu s h th e a i r from a -
round th e h o t carbon when a sample i s atomized®
The CRA i s powered w ith a 5 KVA G® E® tra n s fo rm e r (9t21B1037G2)
c o n tr o lle d w ith a ty p e 242, 4®2 KVA P o w e rsta t au to tran sfo rm er®
T h is
power su p p ly p ro v id e s from O t o 13 rms v o l t s and can f u r n is h in ex­
c e s s o f 400 amps®
The te m p e ra tu re o f th e a to m iz a tio n tu b e i s measured
w ith a Pyro o p t i c a l pyrometer®
T em peratures i n e x ce ss o f 3000 °C a re
r e a d i l y o b ta in a b le w ith t h i s system®
The p orous g r a p h ite tu b e s a re made by d r i l l i n g a 4=5 mm h o le
(No® 13 d r i l l ) in 15 mm le n g th s o f 6=2 mm d ia m e te r N a tio n a l AGKSP o r
AGKS s p e c tro s c o p ic g r a p h ite rods®
Each tu b e i s p la te d on th e in s id e
w ith a b o u t I 05 mg o f g o ld in th e fo llo w in g manner?
One end i s s e a le d
o f f w ith a ru b b e r tu b e s e a le d w ith a g la s s b e ad ; 0=3 ml o f an a c i d i ­
f i e d g old c h lo r id e s o lu tio n i s p la c e d i n t o th e tu b e ; a p la tin u m w ire
anode i s i n s e r t e d ; and th e p l a t i n g c u r r e n t i s a p p lie d betw een th e tu b e
and th e anode f o r 4 - 5
m in u tes w ith a 12 V a u to m o b ile b a t t e r y in
s e r i e s w ith a 75 ohm re s is to r ®
mg/ml Auo
The g o ld s o lu tio n c o n ta in s ab o u t 5
F ig u re 2 s c h e m a tic a lly d e p ic ts th e process®
F ig u re 3 i l l u s t r a t e s th e f i l t r a t i o n a d a p to r u sed t o su p p o rt th e
g o ld p la te d tubes®
I t i s e s s e n t i a l l y s im ila r t o th e one d e s c rib e d by
W o o d riff and Lech ^ 8 ) Qx c Qpt t h a t th e s o f t e la s to m e r g a s k e ts s e a l b o th
ends o f th e tu b e w ith th e e x c e p tio n o f th e a i r in le t®
f i l t e r a d a p to r i s m achined from a c r y l i c p la stic ®
X
The body o f th e
The g a s k e t m a te r ia l
GOLD PLATING
5 mg A u / m l
Figure 2 . G old p la tin g a p p a r a tu s
in d i l u t e aqua r e gi a
^ 3 —
A IR
\
(I
F igure 3 . F ilte r a d a p te r
TO SYRINGE OR PUMP
-13”
was b u ty l o r n a t u r a l gum ru b b e r in th e o r i g i n a l m odels, b u t i t was l a t e r
d is c o v e re d t h a t s i l i c o n e ru b b e r o f th e ty p e used f o r gas chrom atograph
i n l e t s e p ta p ro v id e s a s u r e r s e a l arid i s c lea n e r.,
The ato m ic a b s o r p tio n in s tru m e n ta tio n used a re th o s e d e s c rib e d in
th e p a p e r by W oodriff e t a lo (39) w ith th e s u b s t i t u t i o n o f th e CRA f o r
th e fu rn a c e and th e a d d itio n o f a d e u te riu m lamp background c o r r e c tio n
sy ste m .
F ig u re 4 i s a sch em atic o f th e A, A0 s p e c tro m e te r w ith a l i s t ­
in g o f th e in d iv id u a l components u se d .
The CRA power su p p ly and th e
c o o lin g w a te r l i n e s have been d e le te d f o r c l a r i t y ,
A s h o r t (35 mm lo n g ) , quartz-w indow ed, co ld v ap o r a b s o rp tio n c e l l
was c o n s tr u c te d .
F ig u re 5 d e p ic ts how i t was used t o t e s t th e m ercury
f i l t r a t i o n e f f i c i e n c y o f th e g o ld p la te d tu b e s .
Ten cc o f a i r s a t u r a t ­
ed w ith m ercury v ap o r ( a t 24 eC) was drawn th ro u g h th e w a lls o f b o th
p la te d and u n p la te d p orous g r a p h ite tu b e s .
The f i l t e r e d a i r in th e
s y rin g e i s th e n e x p re sse d i n t o th e a b s o r p tio n c e l l and th e a b s o rp tio n
o f th e 2537 A l i n e i s m easured,
A sto p p e re d two l i t e r erh len m ey er
f l a s k c o n ta in in g a p p ro x im a te ly 5 g o f m ercury m e ta l se rv e d a s a
so u rc e o f m ercury v ap o r o f known c o n c e n tra tio n ,
A 1000 ppm s to c k m ercury s o lu tio n was made by d is s o lv in g Hg(NCy)^,
HgO in N/10 HNO^,
o f d ry KgCrgOy*
T h is s o lu tio n was s t a b i l i s e d by ad d in g 0 ,0 1 g/100 ml
D ilu tio n s o f t h i s s to c k were made d a i l y w ith N/100 .
HNOj o
E ppendorf p ip e ts o f 5» 10, 20, 50, and 100 m i c r o l i t e r c a p a c ity w ere
Beckman model 2965
power supply
Beckman D9 Lamp
Hollow Cathode
3 /4 meter SPEX monochrometer
Fluke 412 B power
X
supply
R 106
PM tube
PAR Model
JB 5 amplifier
Jarrell-Ash HG
power supply
Figure 4 . Schematic of AA spectrometer
Honeywell
"Electronlk 19
I
H
Vn
Absorbance
I
fxsTio tube
or unplated - 1
p la te d ~ .01 or.oz
/
Figure 5. Apparatus for testing filtration efficiency
-1 6 -
used t o make most o f th e d i l u t i o n s and sample a d d itio n s re q u ir e d .
A homemade n ic k e l-n ic h ro m e therm ocouple was used t o d eterm in e
te m p e ra tu re s low er th a n th o s e m easu reab le by th e o p t i c a l p y ro m eter.
The therm ocouple o u tp u t was a m p lifie d by a 741 o p e r a tio n a l a m p lif ie r
used i n a f o llb w e r- w ith -g a in c o n f ig u r a tio n and th e a m p lifie d o u tp u t
re a d w ith a VTVM0
R e s u lts and D isc u ssio n o f B asic Procedure
The f i r s t , c r i t e r i o n t o be met by a gas sam pling system i s a good
c o l le c tio n e f f ic ie n c y f o r what i s b e in g m easured.
T h is was te s t e d
(F ig u re 5) by com paring th e r e s u l t s o f t h i s experim ent perform ed w ith
e ig h t g r a p h ite tu b e s b o th b e fo re and a f t e r th e y were p la te d w ith g o ld .
T able I g iv e s th e r e s u l t s o f t h i s e x p e rim e n t.
The v a lu e f o r " F ra c tio n
Hg C o lle c te d " i n t h i s t a b l e i s d e fin e d a s one minus th e r a t i o o f th e
atom ic ab so rb an ce o f th e m ercury v ap o r in th e a i r p a sse d th ro u g h th e
w a lls o f a tu b e to ' th e atom ic ab so rb an ce o f th e same amount o f a i r
drawn th ro u g h th e f i l t r a t i o n a d a p to r w ith no tu b e i n p la c e .
I t is
c le a r t h a t e s s e n t i a l l y a l l o f th e m ercury i s c a p tu re d by th e p la te d
tu b e s .
I t i s a ls o a p p a re n t t h a t AGKSP g r a p h ite tu b e s n o t p la te d w ith
g old a re i n e f f e c t i v e f o r tr a p p in g mercuryj v a p o r.
DuriJig th e a c t u a l d e te rm in a tio n , t h e 1gold p la te d tu b e i s p la ce d
betw een th e ro d s o f th e CRA and r a p id ly h e a te d t o ato m ize th e m ercury.
To a s c e r t a i n w hether t h i s re p e a te d h e a tin g has any e f f e c t upon th e
t u b e f s a b i l i t y t o t r a p m ercury v a p o r, th e Hg f i l t r a t i o n e f f ic ie n c y .
-1 7 TABLE I
MERCURY COLLECTION EFFICIENCY OF POROUS GRAPHITE TUBES
Tube No.
Type o f Tube
I
■unplated
F r a c tio n Hg C o lle c te d *
- 0 .0 3 2
2
- 0.015
3
0.025
if
4
~0»015
5
0 .0 3 8
6
-0 .0 3 3
7
:
-0 .0 1 5
. 8
0 .050
A verage:
I
p la te d
0 .9 7 2
2
3
■
0.000375 ± 0.032**
0 .980
it
0 .9 8 6
4
0 .986
5
0 .9 9 4
6
0.986
7
0.986
8
0.986
* I - AA( t u b e )
AA(rio t u b e )
-:«(■ one s ta n d a rd d e v ia tio n
A verage:
'
0 .9 8 4 + 0.0063**
' -1 8 t e s t a s d e s c rib e d above was re p e a te d te n tim e s upon a s in g le tu b e ( d r i ­
v in g o f f th e m ercury each tim e between t e s t s ) .
s u l t s o f t h i s ex p erim en t,.
T able I I g iv e s th e r e ­
There was no d im u n itio n o f tr a p p in g e f f i c i e n ­
cy n o tic e d .
I n o rd e r to a s c e r t a i n how much g o ld i s r e q u ire d t o e f f e c t i v e l y
t r a p a l l o f th e m ercury in a i r p assed th ro u g h th e w a lls o f a p la te d
tu b e , a s e r i e s o f s ix AGKSP tu b e s were p la te d w ith d i f f e r i n g amounts o f.
g o ld .
The f r a c t i o n o f Hg r e t e n t i o n i n 10 cc o f s a tu r a te d a i r (24 °C)
was m easured (T able I I I ) .
From l i t e r a t u r e
v a lu e s o f th e vapor
p re s s u re o f m ercury and th e use o f th e i d e a l gas law , i t can be c a l­
c u la te d t h a t 10 cc. o f a i r s a tu r a te d a t 24 0C c o n ta in s 2 .0 x IO*"^ g o f
m ercury.
Because t h i s amount o f m ercury i s beyond th e u p p er range o f
th e a n a l y t i c a l curve r e s u l t i n g from d e te rm in a tio n o f m ercury in th e
CRA, i t i s a p p a re n t from th e t a b l e t h a t 10-4 g o r more g o ld i s s u f­
f i c i e n t f o r th e p l a t e .
A pproxim ately 1 .0 - 1 .5 mg g o ld was f i n a l l y
d e cid e d on f o r norm al u s e , b o th t o e n su re a h ealth y , e x c e ss and t o make
v i s u a l in s p e c tio n o f th e go ld p la te e a s i e r .
A s tu d y o f th e a b i l i t y o f tu b e s p la te d w ith d i f f e r i n g amounts o f
g o ld t o c a p tu re s u c c e s s iv e ly g r e a t e r amounts o f m ercury v ap o r was u n r
d e rta k e n ..
R epeated a liq u o ts o f 10 cc each o f . a i r s a tu r a te d a t 24 0C
w ith m ercury v ap o r were drawn th ro u g h p la te d tu b e s and th e Hg r e t e n I
t i o n e f f i c i e n c y m easured a f t e r each tim e .
o f f betw een each t e s t a s b e f o r e .
The m ercury was n o t d riv e n
F ig u re 6 d e p ic ts th e r e s u l t s .
-1 9 -
TABLE I I
EFFECT OF REPEATED HEATING ON A GOLD PLATED TUBEt S
ABILITY TO COLLECT MERCURY
T r i a l No.*
F r a c tio n Hg C o lle c te d
1
2 ’
0.980
■ 0 .983
0.986
3
4
.
0 .9 9 4
5
0 .9 9 4
6
0.986
7
0 .9 9 4
8
0.994
9
0.994
IO
0 .9 9 4
A verage:
-Ktube h e ate d to 900 0C betw een t r i a l s
-K-K- one s ta n d a rd d e v ia tio n
;
• •
0 .9 9 0 + 0.00554**
-20-
TABLE I I I
MERCURY COLLECTION AS A FUNCTION OF THE AMOUNT OF GOLD '
PLATED ONTO TUBES
Number
Amount o f Gold on Tube (g ) ■
F r a c tio n Hg C o lle c te d
I
2 .5 x 10-7
2
2 .5 x 10
3
1 .0 x IO"5.
0 .9 0 1
4
5 .0 x H f 5
0.970
5
5 .0 x IO"4
0 .9 8 7
6
1 .5 x 10“ 3
0 .9 9 4
-6
C o lle c tio n s from 10 ml a i r ( s a tu r a te d w ith Hg v ap o r)
0.561
0.808
-21-
Mercury Filtration Efficiency
1 .5 x 1 0
2 .5 x 10
0
Figure 6.
2
4
6
8
10
12
g . Au
14
16
18
20
22
24
Total Hg filtered
g x IO7
Filtration Efficiency as a Function of the Amount of Mercury
and Gold
-22-
A f t e r th e e f f e c t iv e n e s s o f th e tu b e s a s f i l t e r s was e s ta b lis h e d ,
i t rem ained t o determ in e s u ita b le c o n d itio n s f o r th e CRA a to m iz e r and
su b seq u en t d e te rm in a tio n o f m ercury.
F ig u re 7 shows th e r e s u l t s o f
e x p erim en ts t o d eterm in e an a n a l y t i c a l curve f o r m ercu ry .
V arious v o l-
xrnes o f a i r s a tu r a te d w ith m ercury in a la r g e f l a s k immersed in an i c e w a te r b a th a t 0 0C were drawn th ro u g h a s e r i e s o f p la te d tu b e s .
The
m ercury was atom ized a t a CRA power s e t t i n g r e s u l t i n g in a f i n a l te r n - .
p e r a tu r e o f 850 °C and m easured by th e A. A. s p e c tro m e te r.
shows d a ta from two methods o f s ta n d a r d iz a tio n .
The f ig u r e
The p o in ts denoted
w ith a t r i a n g l e a re based on f i l t r a t i o n o f th e a i r s a tu r a te d w ith mer­
cu ry a t 0 °C w ith c a lc u la tio n o f th e amount o f m ercury based on a I i t e r a tu r e v a lu e o f th e v ap o r p re s s u re x
.
Those denoted w ith a c i r c l e
a re b ased on th e d ry in g o f 5» 10, o r 15 m i c r o l i t e r a liq u o ts o f a f r e s h ­
ly p re p a re d 2 ppm m ercury s o lu tio n o n to th e tu b e s .
The r e l a t i v e s ta n d a rd d e v ia tio n f o r th e f i l t r a t i o n te c h n iq u e was
found to be 6.0% f o r a s e r i e s o f f iv e tu b e s each w ith 10 cc o f s a tu r a te d
a i r ( 3 .2 x 10""# g Hg) f i l t e r e d th ro u g h them .
The R. S . D6 f o r so lu ­
ti o n s p ip e te d d i r e c t l y i n t o th e tu b e s , d r ie d and atom ized was c o n s id e r­
a b ly p o o re r (9.6% f o r 7 r e p l i c a t e s o f 2 .0 x 10” ® g H g).
Because th e r e
i s no d em o n strab le d if f e r e n c e in th e s lo p e s o f a n a l y t i c a l cu rv es drawn
b ased on e i t h e r method o f s ta n d a r d iz a tio n and t h a t b a se d on f i l t r a t i o n
o f v ap o r is . more r e p ro d u c ib le , i t i s p ro b a b ly b e t t e r t o u se i t f o r
s ta n d a r d iz a tio n f o r r o u tin e a i r a n a ly s e s .
.
-23-
rbance
0.3C ,
A
points based on
saturated air
O
points based on
standard solutions
dried on the tube
0. 2 0
g Hg x 10
Figure 7.
Standard Curve for Mercury Based on Two Different Methods
of Standardization
— 24—
The c h o ice o f CRA power su p p ly a to m iz a tio n s e t t i n g s i s la r g e ly
a r b i t r a r y and th e f i n a l a n a l y t i c a l r e s u l t s depend more upon th e p a r­
t i c u l a r s e t t i n g th a n do th e r e s u l t s when s im i l a r l y p re p a re d cups a re
used in th e W oodriff fu rn a c e (^ 8 , 41# 42) &t d i f f e r e n t te m p e ra tu re s .
T his i s becau se th e absorbance peak h e ig h t i s what i s m easured—n o t th e
a re a .
When low a to m iz e r power s e t t i n g s a re u sed , th e f i r s t v o l a t i l i z e d
m ercury atom s have an o p p o rtu n ity t o d if f u s e o u t o f th e l i g h t p a th be­
f o r e th e l a s t o f th e m ercury i s d riv e n o f f o f th e tube®
In th e Wood-
r i f f fu rn a c e , th e atoms a re c o n fin e d t o th e o p t i c a l a x is f o r a lo n g e r
tim e and have l e s s chance t o escap e b e fo re com plete v o l a t i l i z a t i o n oc­
c u rs.
See Appendix I f o r c l a r i f i c a t i o n .
A s tu d y was made o f th e te m p e ra tu re t o which a p la te d tu b e could be
h e ate d b e fo re a p p re c ia b le m ercury was l o s t .
T his was done by f i l t e r i n g
2 cc o f s a tu r a te d a i r (27 0C) th ro u g h a tu b e and th e n p la c in g i t in to
th e CRA.
The power su pply was f i r s t tu rn e d on t o a low s e t t i n g f o r one
m inute, a f t e r which th e te m p e ra tu re o f th e tu b e was m easured w ith th e
th erm o co u p le.
Then th e
f lu s h in g gas was tu rn e d on, th e CRA power
su p p ly tu rn e d t o a h ig h e r s e t t i n g (450 w a t t s ) , and th e rem ain in g Hg,
atom ized and th e peak h e ig h t m e a su re d .. Up t o a f i n a l te m p e ra tu re o f
150°C no m ercury was l o s t from th e p la te d tu b e s .
At 230 0C a l l o f th e
m ercury was v a p o riz e d .
F ig u re 8 d e p ic ts r e s u l t s o f a stu d y t o a s c e r t a i n th e b e s t CRA
power s e t t i n g f o r a to m iz a tio n .
Two and one h a l f cc sam ples o f m ercury
bance
1.0
Power delivered to CRA (watts)
Figure 8. Power Input Versus Observed Atomic Absorbance
—26—
s a tu r a te d (27 °G) a i r was drawn th ro u g h a p o rous tu b e and th e m ercury
atom ized a t d i f f e r e n t power s e t t i n g s ,
As can be seen by th e f i g u r e , i t
i s im p o rta n t t o h e a t th e tu b e a s r a p id ly a s p o s s ib le .
I t i s a ls o v e ry
im p o rta n t t h a t th e tu b e n o t exceed 1100 0C a t any tim e d u rin g th e atom­
iz a tio n ,
I f t h i s i s done th e g o ld p l a t i n g m e lts (m, p , 10 6 0 ), ru n s
to g e th e r , and th e tu b e i s ru in e d f o r m ercury a n a l y s i s .
The a c tu a l
c y c le d e c id e d upon f o r most r o u tin e a n a ly s e s w ith th e homemade CRA was
a s h o r t p u ls e o f ab o u t 450 w a tts (50% o f a u to tra n s fo rm e r s e t t i n g ) f o l ­
lowed by a q u ic k cooldown t o a v o id o v e rh e a tin g .
E xperim ents done w ith th e V arian Model 63 a to m iz e r a t th e C hem istry
S ta tio n a t MSU re v e a le d t h a t a s a t i s f a c t o r y power s e t t i n g f o r g e n e r a l
a n a ly s is i s ”3 ,5 ” f o r 2 ,5 seconds w ith th e com m ercial CRA,
t i n g r e s u l t s i n a s e n s i t i v i t y o f 1 ,3 x 10"^® g ,
T his s e t ­
The autom ated power
su p p ly sh o u ld g iv e b e t t e r r e p r o d u c i b i l i t y th a n th e m anual one used
w ith th e homemade CRA,
To be r e a l l y u s e f u l a f i l t e r u sed f o r sam pling g a se s must a llo w a
f a i r l y la r g e sam ple t o be ta k e n in a re a so n a b le tim e .
The f i l t r a t i o n
r a t e o f a i r w ith r e s p e c t t o th e p re s s u re d i f f e r e n t i a l a c r o s s a tu b e was
s tu d ie d w ith a manometer and a G ilm ont flo w m e te r.
re s u lts ,
F ig u re 9 g iv e s th e
No m easurable d if f e r e n c e was n o tic e d w ith r e s p e c t t o w h eth er
o r n o t a porous g r a p h ite tu b e was p la te d w ith g o ld .
A p p a re n tly , g o ld ,
when p la te d u n d er th e h ig h c u r r e n t, h ig h a c id , c o n d itio n s used comes
o u t i n a form w hich does n o t p l a t e o v er th e p o re s in th e g r a p h ite .
1600
To pump
Flowmeter
Flow
cc/m in
Filter adaptor
P cm Hg
Figure 9 . Air flow with Respect to Pressure Differential
manometer
— 28-
A p p lic a tio n o f th e Technique t o A ir Sam pling
The s e n s i t i v i t y (1# a b s o r p tio n ) o f t h i s te c h n iq u e i s about
2 x 10-10 g (depending on a to m iz a tio n rate)®
To t r a n s l a t e t h i s f ig u r e
t o a " d e te c tio n l i m i t " i t i s n e c e s s a ry t o d e fin e w hat we mean by th e
te rm .
I t i s commonly (b u t n o t alw ay s) d e fin e d a s t h a t q u a n tity o f
a n a ly te which g iv e s an a n a l y t i c a l s i g n a l e q u iv a le n t t o tw ic e th e stan-*
d a rd d e v ia tio n o f th e b la n k .
B lank v a lu e s f o r t h i s te c h n iq u e a re made
by p la c in g a c le a n p la te d tu b e i n t o th e f i l t e r a d a p to r , l e t t i n g i t s i t
f o r a few sec o n d s, rem oving i t and ch eck in g i t f o r any m ercury t h a t i t
may have p ic k e d u p .
On d i f f e r e n t o c c a s io n s , w ith d i f f e r e n t f i l t e r ad-r­
a p to r s , d i f f e r e n t tu b e -tw e e z e r e t c . , mean b la n k ab so rb an c es co rresp o n d ­
in g t o 0 t o 4 x 10-10 g Hg w ith s ta n d a rd d e v ia tio n s o f 0 t o 2 x 10” 1° g
Hg have been m easured.
A t y p i c a l v a lu e o f 2 s ( d e te c ti o n l i m i t ) would
-1 0
be ab o u t I x IO*"
g«
(An A. A. s p e c tr o s c o p is t i s h a p p ie r sp eak in g of;,
" s e n s i t i v i t i e s " b ecau se th e y a r e r ig o r o u s ly d e fin e d and n o t s u b je c t t o
th e v a g a r ie s o f i n t e r p r e t a t i o n and o u tr i g h t fu d g in g a s a re " d e te c tio n
lim its " .)
The A m erican C onference o f G overnm ental I n d u s t r i a l H y g ie n ists has
adopted a th r e s h o ld l i m i t v a lu e f o r m ercury v ap o r and in o rg a n ic com­
pounds o f m ercury i n a i r o f 100 |tig/m3
^ 6) e
To d e te c t such a
l e v e l o f m ercury i n th e a i r w ith a d ith iz o n e method would r e q u ir e c o l­
l e c t i o n o f a t e n l i t e r sample ^ ^
i p u l a t i o n b e fo re a n a l y s i s .
P« 3 )
c o n s id e ra b le ch em ical man­
The method b ased on th e GRA would r e q u ir e
:
-
.
.
29a 2 cc sample a n d n o c h e mical p r e p a r a t i o n b e f o r e a n a l y s i s o
A ll t h a t i s needed t o sample m ercury l e v e l s i n a i r a r e a few
c le a n p la te d tu b e s , an a i r t i g h t c o n ta in e r t o c a r r y them i n , th e f i l t e r
a d a p to r , and a s y rin g e o r sim ple pump t o draw a i r th ro u g h th e tu b e s .
I '
A
■
s y rin g e i s a d eq u a te f o r l e v e l s o f m ercury down t o a b o u t I pg/m3; a t
low er l e v e l s i t i s h a n d ie r t o u se a pump.
We have u sed Nalgene s in k
a s p i r a t o r s in th e la b o r a to r y t o sample f o r low, background le v e l s and
a m e ch an ical pump e lse w h e re .
An i n t e r e s t i n g s e r i e s o f sam ples was ru n on June 10, 1973 in room
I
328 around S h e rry Farwe11*s p o la ro g ra p h ic a p p a r a tu s .
th e r e s u l t s .
T ab le IV g iv e s
S ix ty cc sam ples o f a i r a t v a rio u s p o in ts around th e room
w ere ta k e n e x c e p t t h a t 120 cc w ere ta k e n n e a r th e open window.
I t is
easy t o see t h a t a v e ry s m a ll q u a n tity o f s p i l l e d m ercury can r e s u l t in
a p p re c ia b le l e v e l s in th e a i r .
To a s c e r t a i n th e d e g re e o f r e p r o d u c i b i l i t y p o s s ib le when sam pling
low am bient l e v e l s o f m ercury, r e l a t i v e l y la r g e ( 6 .5 - 7«5 l i t e r ) sam­
p le s o f a i r w ere ta k e n in a w e l l - v e n t i l a t e d room (room 233) by draw ing
a i r th ro u g h a s e r i e s o f f o u r tu b e s f o r f iv e m inutes each u s in g a fa u c e t
a s p i r a t o r a s a pump.
o f sam p lin g .
I
A G ilm ont flo w m eter was used t o m easure th e r a t e
A mean v a lu e o f 0 .2 4 |ug/m? and a RSD o f 7.8% were th e r e ­
s u l t s a c h ie v e d .
On S a tu rd a y , December I , 1973, a m ercury s p i l l o c c u r r e d . in th e
hood in room 221.
When i t was c le a n e d up, a t e s t o f th e a i r i n th e hood
-30“
TABLE IV .
RESULTS OF MERCURY DETERMINATIONS IN THE AIR OF A ROOM WITH
VISIBLE SPILLED MERCURY
Tube Number
L o c a tio n
Hg jug/nP
I
to p o f equipm ent bench
38
2
under p o la ro g ra p h
43
3
f l o o r by e a s te r n w a ll
18
4
f l o o r by w e ste rn w a ll
32
5
n e a r open window
ACGIH l i m i t 100 ug/m3
5
•**
re v e a le d 147 Ug/m^ o f m ercury .
31
"
T his was n o t s u r p r is in g in view o f th e
s i t u a t i o n b u t su b seq u en t t e s t s re v e a le d t h a t a i r sam ples ta k e n on a l l
f o u r f l o o r s o f G aines H a ll c o n ta in e d from 17 t o 30 ng/n? o f m ercury.
F ig u re 10 d e p ic ts th e r e s u l t s o f d e te rm in a tio n s ru n i n room 233 a t
v a rio u s tim e s d u rin g t h a t d ay .
The. windows were opened a t ab o u t 10:30
A, M, upon th e d is c o v e ry o f th e s e h ig h l e v e l s ,
A s e r i e s o f 360 cc
sam ples ta k e n o v e r a f i v e m inute p e rio d in room 234 gave a mean co n cen t
t r a t i o n o f 23 pg/rn^ and a r e l a t i v e s ta n d a rd d e v ia tio n o f 10$,
A
s y rin g e was u sed f o r a l l o f th e sam p lin g done on t h a t d ay .
Follow up d e te rm in a tio n s were made from 9 :3 0 t o 1 0 :0 0 A, M, on th e
fo llo w in g Monday,
S an p les ta k e n in th e h a l l s on a l l fo u r f lo o r s o f th e
b u ild in g c o n ta in e d from 4 t o 7 jig/m
se v e ra l a u th o ritie s
3
m ercu ry .
In view o f th e f a c t t h a t
” ^ 7 ) have recommended maximum en­
v iro n m e n ta l m ercury l e v e l s a s low a s 0 ,3 pg/m ?, th e l e v e l s en co u n tered
in th e b u ild in g a r e o f some concern t o th e a u th o r .
These l e v e l s were
p ro b a b ly th e r e s u l t s o f b o th a la r g e number o f m ercury s p i l l s o v er
th e y e a rs and th e f a c t t h a t , due t o th e w e a th e r, th e b u ild in g had
been s e a le d up w ith r e l a t i v e l y l i t t l e v e n t i l a t i o n ,
As compared t o com m ercially a v a il a b le m ercury d e te c to r s ( most
o f w hich u t i l i z e a crude form o f ato m ic a b s o rp tio n measurement ) t h i s
te c h n iq u e h as s e v e r a l a d v a n ta g e s. F i r s t o f a l l , i t c a p tu re s and mea-,
s u re s b o th p a r t i c u l a t e and gaseous m ercu ry . The g r a p h ite tu b e s a re
e f f e c t i v e f i l t e r s f o r p a r t i c u l a t e m a tte r down t o 0 ,0 1 6 pm i n d i a ■1 ■
i
10:00
12:00
Time
Figure 10.
Mercury Levels in Room 233 on December I, 1973
-33"
m eter
T his s iz e i s c o n sid e ra b ly s m a lle r th a n t h a t o f th e b u lk o f
a irb o u rh e p a r t i c u l a t e m a tte r
so p a r t i c u l a t e m ercury i s e f f e c t i v e l y
tr a p p e d .
A nother adv an tag e o f th e g o ld p la te d g ra p h ite f i l t e r s i s t h a t th e y
do no c o l l e c t and su b se q u e n tly measure SO2, b enzene, a c e to n e , e t c . a s
do most o f th e common m ercury m o n ito rin g equipm ent (Beckman In stru m e n ts
I n c . ; G e n era l E l e c t r i c j Sunshine S c i e n t i f i c In s tru m e n ts , I n c . ; e t c . ) .
E xperim ents were perform ed by draw ing a i r s a tu r a te d w ith benzene o r
a c e to n e th ro u g h th e s e tu b e s and s e e in g i f a n o tic e a b le " b la n k " r e s u l t e d .
None d id .
L a te r e x p erim en ts w ith g a se s r e s u l t i n g from com bustion o f
h ig h s u l f u r c o a ls a ls o re v e a le d no i n te r f e r e n c e s from COg, SO2, o r NO2 .
N on-atom ic a b s o r p tio n a s measured by use o f a d e u teriu m lamp has
n e v e r been observed in a i r sam ples ta k e n i n th e Bozeman a r e a .
However,
i t i s c o n c e iv a b le t h a t an in te r f e r e n c e would be n o ted i n a sample o f a i r
c o n ta in in g v e ry hig h c o n c e n tra tio n s o f t a r r y smoke r e s u l t i n g from in ­
com plete b u rn in g o f o rg a n ic m a te r ia ls .
I f t h i s should o c c u r, some mod­
i f i c a t i o n o f th e m e rc u ry -in - s o lid s com bustion a p p a ra tu s t o be d is c u s s e d
l a t e r in t h i s t h e s i s sh ould e lim in a te th e problem .
P o rtio n s, o f t h i s s e c tio n o f th e t h e s i s have been p u b lis h e d .
A p p lic a tio n o f th e Technique t o W ater Samples
The most commonly u t i l i z e d method f o r th e a n a ly s is o f m ercury in
aqueous s o lu tio n s i s th e s tr a ig h tf o r w a r d a d d itio n o f stan n o u s c h lo rid e
to th e sam ple, whereupon th e m ercury i s red u ced t o th e m e ta l and i s
c a r r ie d a s a v ap o r in to a co ld v ap o r a b s o r p tio n tu b e by a c a r r i e r gas
bubbled th ro u g h th e s o lu tio n .
M ercury in o rg a n ic form s i s f i r s t con­
v e rte d t o th e io n ic form by p re tre a tm e n t o f th e sample w ith H2SO^ and
KMMO^0
The m ain problem s a s s o c ia te d w ith th e te c h n iq u e a r e th o s e r e ­
l a t e d t o th e k i n e t i c s o f th e r e d u c tio n - a e r a tio n p ro c e ss a s enum erated
b e fo re .
W ater vapor a lo n g w ith v o l a t i l e o rg a n ic compounds i n t e r f e r e
w ith th e f i n a l measurement and must be e i t h e r removed from th e gas
stre am o r t h e i r e f f e c t s c o rre c te d f o r .
F ig u re 11 i s a diagram o f th e f i n a l v e rs io n o f s e v e r a l a p p a ra ta
made t o a llo w a p p lic a tio n o f th e p la te d - g r a p h ite CRA te c h n iq u e t o
w a te r a n a l y s i s .
The b u b b lin g f l a s k was made o f a 125 cc erlenm eyer
f l a s k t o which was added a lo n g e r n eck , an e n tra n c e p o r t s e a le d w ith
a ru b b e r septum , a s id e tu b e , and a d r a in tu b e in th e b o tto m ,
A
t h i s t l e tu b e w ith a g la s s f r i t gas d i f f u s o r i s mounted i n a ru b b e r s to p ­
p e r o f a s iz e t o f i t th e neck o f th e f l a s k ,
A gold p la te d porous
g r a p h ite a i r f i l t e r mounted on a s to p p e r t o f i t th e t h i s t l e tu b e was
used (when n e c e s s a ry ) t o reduce " b la n k ” l e v e l s r e s u l t i n g from m easure­
ment o f th e m ercury i n th e a i r used t o c a r r y th e red u ced m ercury from
th e s o l u t i o n .
The b ottom o f th e f l a s k was drawn t o a s l i g h t l y c o n ic a l
shape and th e d r a in was s e a le d o f f w ith ru b b e r tu b in g and a g la s s b ead .
By sq u eezin g th e tu b in g o v er th e b ead , i t i s p o s s ib le t o d r a in th e f l a s k
in a few sec o n d s.
The f i l t e r a d a p to r i s mounted on th e s id e tu b e and a i r i s drawn
-35-
gold plated,
cleaner
O O
TO
ASPIRATOR
Figure 11.
Mercury In Water
Apparatus
TO DRAIN
O
-36-
t h rough b o th i t and th e r e s t o f th e system w ith a s in k a s p i r a t o r a t a
flow r a t e o f 400 t o 500 c c /m in u te .
The o n ly re a g e n t used was 20% SnClg
(B-A re a g e n t g ra d e ) i n 6 F HCl.
The p ro c e d u re used t o a n aly z e a sample i s a s f o llo w s e
t o r i s tu rn e d on and a i r drawn th ro u g h th e system®
p la te d tu b e i s p la c e d in th e f i l t e r adaptor®
c h lo r id e re a g e n t i s added t o th e f l a s k .
The aspira**
I n i t i a l l y , no gold
One o r two ml o f stan n o u s
T his i s u s u a lly done by p i p e t -
in g i t i n t o th e t h i s t l e tu b e and w ashing i t down w ith a few ml o f
water®
The system i s allo w ed t o b ubble f o r a m inute o r so t o f lu s h o u t
any m ercury p re s e n t in th e stan n o u s c h lo rid e o r d i s t i l l e d water®
Then
a gold p la te d f i l t e r tu b e i s p u t in to th e a d a p to r and th e w a te r sample
added.
I f th e sample i s tu r b i d , i t i s added th ro u g h th e f u n n e l; i f . .
c l e a r , i t i s p la c e d i n t o th e t h i s t l e tu b e .
The purpose o f adding tu r b i d
sam ples th ro u g h th e fu n n e l i s t o p re v e n t c lo g g in g th e gas d i f f u s e r f r i t
on th e end o f th e t h i s t l e tu b e .
The system i s allow ed t o b ubble th r e e
o r fo u r m in u te s b e fo re th e go ld p la te d tu b e i s removed and th e evolved
m ercury determined®
To d e term in e th e b u b b lin g tim e r e q u ir e d t o e n su re com plete red u c­
t i o n and su b seq u en t m ercury c o l l e c t i o n , a s e r i e s o f t e s t s was run w ith
_8
1 .5 x 10
g m ercury a s Hg+* i n 10 ml o f w a te r .
The p la te d tu b e s were
removed and a n aly z e d fo llo w in g d i f f e r e n t i n t e r v a l s a f t e r th e sample was
added and th e observed atom ic ab so rb an c es were p l o t t e d a g a in s t th e bub­
b lin g tim e (F ig u re 1 2 ).
The shape o f th e r e s u l t i n g curve was c a lc u la te d
-37-
irbance
A
calculated from
flushing equation
observed
0
Figure 12.
1
2
Flushing Time (minutes)
Flushing Time Versus Recovery
3
-3 8 -
u t i l i z i n g th e " f lu s h in g e q u a tio n " (3 6 , p„ 199) ,
The b u b b lin g r a t e was
470 c c /m in ,
I n Cn = V
Cm Vq
Vq = volume of system (200 cc)
V — volume o f f lu s h in g gas (v o l/m in x t )
Cq = i n i t i a l l e v e l o f Hg i n f l a s k
Ct ~ l e v e l o f Hg i n f l a s k a t tim e " t "
Because th e observed f lu s h in g r a t e i s so w e ll acco u n ted f o r by th e
e q u a tio n , th e a c t u a l r e d u c tio n tim e f o r m ercury i n th e sim p le s o lu tio n
used must be v e ry s m a ll.
A t y p i c a l a n a l y t i c a l curve f o r t h i s system
i s g iv e n i n F ig u re 13.
A s ta n d a rd a d d itio n experim en t was perform ed on a sample re c e iv e d
from th e U. S . F o r e s t S e rv ic e o f d ra in a g e w a te r from a le a d mine i n
Langhor Canyon.
D if f e r in g amounts o f I ppm Hg s o lu tio n w ere added t o 5
m i l l i l i t e r sam ples o f th e w a te r and th e t o t a l m ercury r e s u l t s compared
t o th o s e o f s im ila r a li q u o t s o f th e s ta n d a rd a lo n e .
A r a t h e r su b sta n ­
t i a l b la n k (SE = 0 .0 6 3 , n = 5) has n o t been s u b tr a c te d from a ry o f th e
p o in ts p l o t t e d i n F ig u re 14.
F iv e more sam ples were ru n o f ta p w a te r ta k e n .a t v a rio u s p o in ts in
th e c i t y o f Bozeman.
m easured.
T here was l i t t l e v a r i a t i o n in th e m ercury le v e l s
The c o n c e n tra tio n s ra n from 0 .0 1 8 t o 0 .025 ppb— a l l f a r
below th e USPHS l i m i t o f 5 ppb.
T here h as been o n ly a lim ite d amount o f a p p lic a tio n work done t o
d a te w ith t h i s te c h n iq u e .
The te c h n iq u e i s v e ry f a s t ( 4 - 5 m in u te s ),
s e n s i t i v e (4 x 10“3 ppb in a 50 ml sam ple) and sh o u ld be u s e f u l i n geo­
ch em ical p ro s p e c tin g a s w e ll a s in r o u tin e t r a c e l e v e l w a te r a n a ly s is .
Absorbance
~39“
g . Hg x 10
Figure 13.
Typical Analytical Curve for Water Analysis System
Absorbance
—4 0 —
A Standard addition curve
Standards alone
( Mine water contained 1.0 ppb
mercury.)
0
5
10
gl5
20
g Hg added x 10
Figure 14. Standard Additions to Langhor Mine Water
-41-
A p p lic a tio n o f th e Technique t o S o lid Samples
D ire c t com bustion o f s o lid s a s a means o f r e le a s in g th e m ercury
i n t o a gas s tre a m f o r sub seq u en t a n a ly s is has been u t i l i z e d in some
form o r a n o th e r f o r s e v e r a l y e a rs
48 - 49) #
Q0I d o r s i l ­
v e r was used by most o f th e s e w orkers t o c o n c e n tra te th e m ercury and
t o e lim in a te in t e r f e r e n c e s .
The a p p a ra tu s t h a t was used t o a d a p t g o ld p la te d CRA tu b e s t o th e
d i r e c t d e te rm in a tio n o f m ercury i n s o l i d s i s shown i n F ig u re 1$.
i s th e l a t e s t o f s e v e r a l v e rs io n s t h a t have been t r i e d .
T h is
B a s ic a lly , i t
i s sim ply a nichrom e w ire-w rapped Vycor com bustion tu b e w ith two oxygen
i n l e t s and an e n tra n c e p o r t .
The tu b e has two main s e c tio n s :
th e com­
b u s tio n chamber p ro p e r and a fo llo w in g " a f te r b u r n e r " s e c tio n lo o s e ly
f i l l e d w ith a g ra n u la te d fu s io n mass o f 4 p a r t s CaO t o I p a r t NagCO^.
Oxygen flow, i s c o n tr o lle d and m easured by a p a i r o f G ilm ont flow gauges
and n e e d le v a lv e s .
The com bustion b o a t i s made from a s h o r t s e c tio n o f
10 mm d ia m e te r q u a rtz tu b in g which h as been s p l i t i n h a l f and s e a le d t o
a le n g th o f 4 mm q u a rtz ro d .
An e a r l i e r v e rs io n (50) in c o rp o ra te d a
c o ld f in g e r i n th e t r a i n t o remove w a te r v a p o r; however, i t i s n o t
g e n e r a lly n e c e s s a ry t o do s o .
A b a llo o n on th e f i r s t oxygen i n l e t tu b e
s e rv e s a s a p r e s s u r e i n d i c a t o r . As i n th e b u b b lin g a p p a ra tu s d is c u s s e d
' ;
"
"
'
i n th e l a s t s e c tio n , a fa u c e t a s p i r a t o r i s u t i l i z e d t o draw th e ev o lv ed
.
g a se s th ro u g h th e w a lls o f th e g r a p h ite tu b e s .
Sample a n a ly s is i s perform ed a s fo llo w s .
The power i s a p p lie d t o
balloon pressure sensor
20 gauge
nichrome
Filter adaptor
combustion
boat
combustion
to aspirator
afterburner"
To HO V A. C
Figure 15. Mercury In Solids Combustion Auparatus
To O- regulator
z and tank
-4 3 -
h e a t th e tu b e and th e a s p i r a t o r tu rn e d on.
( I t i s l e f t ru n n in g f o r as
lo n g a s any sam ples o r s ta n d a rd s a re b e in g r u n .)
p la te d tu b e i s p la c e d in to th e f i l t e r a d a p to r .
Then a c le a n , gold
The sample ( I - 100 mg)
i s weighed i n th e com bustion b o a t and th e n th e b o a t i s in s e r te d in to th e
I
com bustion cham ber. The oxygen flo w i s a d ju s te d t o th e maximum which
'
p e rm its a n e t t o t a l p re s s u re in th e com bustion tu b e o f l e s s th a n one
atm osphere ( u s u a lly a b o u t 200 c c /m in . f o r each o f th e two i n l e t s ) . . The
purpose o f t h i s i s t o a s s u re t h a t a le a k in th e sy stem r e s u l t s i n no :
lo s s o f m ercury v a p o r.
ab o u t a m in u te .
Complete com bustion ta k e s from 10 seconds t o
The system i s allo w ed t o f lu s h f o r two o r th r e e min­
u te s more and th e n th e CRA tu b e i s removed and th e c a p tu re d m ercury
d eterm in ed a s p re v io u s ly d e s c rib e d .
The method i s c a l i b r a t e d by p la c in g v a rio u s volumes o f m ercury
s ta n d a rd s o lu tio n s i n t o th e com bustion b o a ts and t r e a t i n g them e x a c tly
l i k e s o l i d sam p les.
A com parison was made o f t h i s method o f s ta n d a rd ­
i z a t i o n w ith r e s p e c t t o t h a t o f ad d in g th e same amount o f s ta n d a rd mer­
cury s o lu tio n d i r e c t l y t o th e p la te d CRA tu b e , d ry in g i t , and f i n a l l y
a to m iz in g i t .
F iv e m i c r o l i t e r s o f a fo u r ppm Hg s o lu tio n (20 ng Hg)
were a l t e r n a t i v e l y p la c e d in to e i t h e r th e com bustion b o a t (and "burned” )
o r d i r e c t l y i n t o a , CRA tu b e .
The r e s u l t s a re g iv e n i n T able 7 .
The
d a ta s u p p o rt th o s e g iv en on F ig u re 7 and th e c o n c lu s io n i s th e same;
i . e . , m ercury vap o r s ta n d a r d iz a tio n i s more re p ro d u c ib le th a n s o lu tio n
s ta n d a r d iz a tio n , b u t th e r e i s no o th e rw is e s i g n i f i c a n t d if f e r e n c e i n r e - .
-4 4 TABLE V
COMPARISON OF DIRECT AT.CMIZATION TO COMBUSTION
FOR STANDARDIZATION
Combustion Boat
Number o f d e te rm in a tio n s (n)
Mean A bsorbance (X)
S tan d ard D e v ia tio n ( s )
.8
8
0 .4 1 8
0 .4 0 6
0.0126
0.0295
R e la tiv e S ta n d a rd D e v ia tio n (RSD)
3 .0 #
■ t - 1.0.5
t^ c g (14 d e g re es o f freedom )
= 2 .1 0
no s i g n i f i c a n t d if f e r e n c e betw een means a t 95#
co n fid e n ce l e v e l
F - 4 .8 5
F (0 . 0 5 )
CRA Tub,
(7 & 7 d e g re es o f freedom )
= 3 .7 9
There i s a s i g n i f i c a n t improvement in r e p r o d u c i b i l i t y
. when s ta n d a rd s a re "b u rn ed ".
7 .4 #
-45“
s u i t s w ith r e s p e c t t o m ethod.
Because m ercury i s u s u a lly found in th e p re se n c e o f s u l f u r in o r­
g a n ic a s w e ll a s m in e ra l m a tric e s a t e s t was ru n t o see i f n e t re c o v e ry
o f m ercury was a f f e c t e d by an e x c e ss o f s u lp h id e .
The a d d itio n o f a
th o u s a n d -fo ld e x c e ss o f (NH^) 2S t o 2 x 10"® g o f m ercury i n a s ta n d a rd
s o lu tio n p la c e d i n t o th e com bustion b o a t had no e f f e c t on e i t h e r th e
re c o v e ry o f m ercury o r on th e background.
S e v e ra l d i f f e r e n t ty p e s o f o rg a n ic sam ples were a n a ly z e d .
I t was
n e c e s s a ry t o g rin d th e sam ple t o l e s s th a n 100 mesh t o g e t re p ro d u c ib le
r e s u l t s i n some c a s e s .
In a l l c a se s s tu d ie d , s ta n d a rd a d d itio n s o f mer­
cury s o lu tio n t o th e sam ples gave a n a l y t i c a l c u rv e s p a r a l l e l t o c u rv es
p re p a re d w ith s o lu tio n s a lo n e .
The amount o f sam ple was chosen to
g iv e on th e o rd e r o f te n t o f i f t y nanograms o f m ercury c o lle c te d on th e
tu b e .
M o lecu lar a b s o r p tio n due t o in co m p lete o x id a tio n o f t a r s was a
problem i n p re lim in a ry w ork. . However, changing th e p o s itio n o f th e
com bustion b o a t in th e com bustion chamber, o r th e Og flo w s, o r, i f
n e c e s s a ry , re d u c in g th e s iz e o f sample burned has e lim in a te d t h i s prob­
lem i n e v e ry ty p e o f sample s tu d ie d .
A sim u lta n eo u s background c o r r e c t­
io n system would e lim in a te some problem s a lo n g t h i s l i n e i f one were
a v a ila b le .
Ground o rc h a rd le a v e s (NBS n o . 1571) were th e o n ly sam ples a n aly z e d
w ith a known m ercury c o n te n t.
The r e s u l t s o b ta in e d w ith seven r e p l i ­
c a te s q£ ab o u t 50 mg le a v e s each tim e were a mean v a lu e o f 0 .1 6 ppm and
-46-
a r e l a t i v e s ta n d a rd d e v ia tio n o f 7 .8 # .
The a c c e p te d v a lu e f o r th e s e
le a v e s i s 0 .1 6 ppm.
A la r g e number o f c o a l sam ples were th e p rim ary re a so n f o r b eg in ­
n in g re s e a rc h on a q u ic k , r e l i a b l e method f o r d e te rm in in g m ercury.
Re­
c e n t developm ent o f low s u l f u r c o a l d e p o s i t s . i n e a s te r n Montana has
sp ark ed c o n s id e ra b le i n t e r e s t in p o s s ib le t r a c e m e ta l c o n tam in atio n o f
th e environm ent r e s u l t i n g from u se o f th e c o a l.
V alues f o r a s e r i e s o f
f o r t y - t h r e e such c o a ls ranged from 0 .0 6 t o a h ig h o f 0 .6 ppm w ith r e l ­
a t i v e s ta n d a rd d e v ia tio n s o f ab o u t 7# f o r r e p l i c a t e s on in d iv id u a l
sam p les.
Very f i n e l y ground sam ples were r e q u ire d f o r good re p ro d u c i­
b i l i t y w ith c o a l.
H air and t o e n a i l sam ples from a number o f in d iv id u a ls were a n a ly ­
zed.
A pproxim ately 3 - 5
te s ts .
m illig ra m s o f sample i s r e q u ire d f o r th e s e
V alues ranged from 0 .8 ppm t o 3»0 ppm f o r h a i r and somewhat l e s s
th a n t h i s f o r th e n a i l sam p les.
R e la tiv e s ta n d a rd d e v ia tio n s f o r
chopped h a i r sam ples were 8# .
At t h i s w r iti n g th r e e o f th e s e m ercury d e te rm in a tio n system s
have been b u i l t f o r .u s e i n a n a l y t i c a l l a b o r a t o r i e s .
The C hem istry
S ta tio n u s e s one on a r o u tin e b a s is f o r a wide v a r i e t y o f sam ples.
Mr.
L a szlo Torma h a s re q u e s te d p e rm is sio n t o p re s e n t th e r e s u l t s o f h is
f in d in g s co n ce rn in g th e te c h n iq u e a t a n a tio n a l A. 0 . A. C. m eetin g .
D r. Frank Munshower p u rch ased one f o r h is la b o r a to r y f o r fe e d and f o r ­
age a n a l y s i s .
The D epartm ent o f H e alth and E n v iro n m en tal S c ie n ce s in
-47-
H elena i s p r e s e n tly g e t t i n g one s e t up f o r com parative t e s t s .
A ll o f
th e s e l a b o r a t o r i e s have V arian model 63 carbon rod a to m iz e rs .
C o n clu sio n s
The b a s ic approach s tu d ie d has proven t o be a p p lic a b le t o th e de­
te rm in a tio n o f m ercury in th e e n t i r e ran g e o f sample ty p e s normally sub­
m itte d t o a n a l y t i c a l l a b o r a t o r i e s ,
The d eg ree o f fre e d o n from i n t e r ­
fe re n c e s and s e n s i t i v i t y i s u n u su a l f o r so sim ple an a n a l y t i c a l ap­
p ro a c h ,
The m ain problem s a s s o c ia te d w ith i t have been w ith im p e rfe c t
s e a lin g o f th e tu b e s in th e f i l t e r a d a p to rs a llo w in g th e g a se s sampled
to go around and th e re b y c a u s in g a lo s s o f s i g n a l .
T h is i s p r im a r ily
due t o roughness on th e ends o f th e f i l t e r tu b e s caused by norm al w ear
a s w e ll a s by d ro p p in g , e t c .
The s i l i c o n e ru b b e r g a s k e ts have been
h e lp f u l i n t h i s r e s p e c t because t h a t m a te r ia l " u p s e ts ” t o f i l l (and
s e a l ) s u rfa c e im p e rfe c tio n s b e t t e r th a n d id th e e a r l i e r m a te r ia ls
u se d .
An im proved model o f th e f i l t e r a d a p to r u t i l i z i n g a f r e e l y -
tu r n in g r e a r g a s k e t has shown prom ise o f re d u c in g w ear on b o th th e gas­
k e ts and th e tu b e s .
A nother problem seen o nly w ith th e com m ercial (V a ria n Model 6 3)
CRA i s w ith b reakage o f th e porous tu b e s .
The p o ro u s tu b e s a re f r a g i l e
a s compared t o th e th ic k - w a lle d , im p erv io u s g r a p h ite tu b e s t h a t th e CRA
i s d e sig n e d t o u s e , and th e s p rin g te n s io n on th e carbon ro d s must be
a d ju s te d w ith in narrow l i m i t s ,
A w eaker (a lth o u g h e n t i r e l y s tro n g e -
nough f o r e i t h e r ty p e o f tu b e ) s p rin g would a l l e v i a t e t h i s problem .
—48—
The work t o d a te has been w ith th e carbon ro d ty p e o f a to m iz e r and
W o o d riff fu r n a c e j how ever, th e b a s ic te c h n iq u e sh o u ld be a p p lic a b le t o
any o f th e s e v e r a l carbon tu b e a to m iz e rs p r e s e n tly on th e market*
r
DIRECT A. A. DETERMINATION .OF METALLIC POLLUTANTS IN AIR
WITH A CARBON ROD ATOMIZER
I n tr o d u c tio n
The e f f e c t i v e c o n tr o l o f a irb d u rn e p a r t i c u l a t e m a tte r r e q u ir e s th e
c a p a b i l i t y o f a n a ly z in g a irb o u rn e p a r t i c u l a t e s e
For t h i s purpose op­
t i c a l em issio n s p e c tro sc o p y h as been e x te n s iv e ly used t o o b ta in most o f
th e d a ta .
A r e l a t i v e l y la r g e number o f elem en ts can be determ in ed s i ­
m u lta n e o u sly by t h i s te c h n iq u e .
However, th e te c h n iq u e i s n e ith e r a s
s e n s i t i v e n o r a s a c c u ra te a s atom ic a b s o r p tio n and i t a l s o re q u ire s
b o th more ex p en siv e equipm ent and more h ig h ly tr a in e d p e rs o n n e l th a n
does A. A.
I n t e r n a l s ta n d a r d iz a tio n ^ l ) im proves th e p r e c is io n and
a c c u ra c y b u t does n o th in g t o a l l e v i a t e th e o th e r p ro b lem s.
X ra y
flu o re s c e n c e sp e c tro m e try i s sometimes used b u t i t s u f f e r s to an even
g r e a t e r d eg ree from most o f th e same problem s a s does atom ic em issio n
a n a ly s is .
I t i s even more e x p e n siv e , prone t o in te re le m e n t i n t e r f e r ­
e n c e s , and th e p r e p a r a tio n o f p ro p e r s ta n d a rd s i s v e ry d i f f i c u l t ^ 2 ) o
I n re c e n t y e a rs atom ic a b s o rp tio n a n a ly s is has been w id e ly used
f o r th e a n a ly s is o f t r a c e m e ta ls in a tm o sp h eric p a r t i c u l a t e s ^ 3 ~ 59)„
The c h ie f re a so n s f o r t h i s tr e n d in c lu d e good s e l e c t i v i t y , s e n s i t i v i t y ,
sim ple o p e ra tin g te c h n iq u e s , and low i n i t i a l equipm ent c o s t s .
The con­
v e n tio n a l flam e A. A. system s u f f e r s from two m ajor d is a d v a n ta g e s .
It
has a la r g e consum ption ( I — 2 m l/m in u te ) o f sample s o lu tio n , and i t
la c k s th e s e n s i t i v i t y t o perfo rm u l t r a t r a c e a n a ly s e s u n le s s v e ry la r g e
-5 0 -
a i r sam ples a re ta k e n e
T his volume re q u ire m e n t can be d r a s t i c a l l y r e ­
duced by u sin g non-flam e atom ic a b s o r p tio n because o f i t s in h e r e n tly
g re a te r' s e n s itiv ity .
C o lle c tio n o f le a d p a r t i c u l a t e s on a f i l t e r from a i r volumes as
sm a ll a s t e n l i t e r s fo llo w ed by ch em ical d ig e s tio rl and non-flam e
atom ic a b s o r p tio n had been re p o rte d by Qmang
T h e.c o n tin u o u s
d e te rm in a tio n o f a tm o sp h eric le a d by an in d u c tio n h e a te d carbon tu b e
fu rn a c e has been re p o rte d by L o f tin e t a l .
Much o f th e d i f f i c u l t y in a c h ie v in g good d e te c tio n l i m i t s i s as
much due t o th e sample c o l le c tio n and ch em ical p re tre a tm e n t s te p s as
t o th e a c t u a l s e n s i t i v i t y o f th e a n a l y t i c a l t o o l used f o r th e f i n a l
a n a ly s e s .
tic u la te s .
A t y p i c a l example would be the. a n a ly s is o f b e ry lliu m p a r­
A commonly a c c e p te d approach would be t o draw a i r th ro u g h
a m iilip o r e f i l t e r , d ig e s t th e f i l t e r in a c id , and b r in g th e s o lu tio n
volume up t o 50 o r 100 ml p r i o r to a n a l y s i s .
I f b e ry lliu m p a r t i c u l a t e s
a t th e maximum l e v e l a c c e p te d by law i n Montana (0 .0 1 ug/m?) were t o be
d e te c te d i n t h i s manner, even w ith a v e ry s e n s i t i v e non-flam e atom ic
a b s o r p tio n te c h n iq u e ^ 2 ) , a t o t a l o f s ix ty cu b ic m e te rs o f a i r would
need t o be sam pled.
A sample t h i s s iz e ;would r e q u ir e ab o u t a day t o
I
c o l l e c t on a m iilip o r e f i l t e r .
The f a c t o r lim i t i n g th e s e n s i t i v i t y in
t h i s case i s th e sample p re tre a tm e n t s te p w ith i t s a tte n d a n t d i l u t i o n ,
n o t th e a c t u a l a n a ly s is s t e p .
-■
.
To m inim ize sample p re tre a tm e n t and d i l u t i o n , M atpusek and B rodie
-51-
used Varian Techtron carbon cup atomizer for direct air sam­
pling of lead*
An essentially standard cup is perforated through the
bottom with many small holes*
A small disk of millipore acetate filter
is placed in the cup (a la Buchner funnel) and the air to be sampled is
drawn through*
The filter material is burned off slowly firstj then the
lead is atomized in normal fashion.
lead in the millipore disks
Because there is a large amount of
they were pro-cleaned by soaking in
nitric acid to minimize blanks*
Lech and W oodriff (3 0 ) were th e f i r s t t o r e p o r t on th e f i l t r a t i o n
o f le a d p a r t i c u l a t e s by g r a p h ite fu rn a c e a to m iz e r cups*
A ir was
drawn th ro u g h th e w a lls o f porous g r a p h ite cups w hich were in s e r te d
i n t o a W oodriff fu rn a c e w ith no p re tre a tm e n t w hatsoever*
The s e n s i t i ­
v i t i e s r e p o rte d a re th e b e s t in te rm s o f amount o f le a d d e te c ta b le , p e r
u n i t volume o f a i r o f any te c h n iq u e c i t e d t o date*
S e e le y and Skogerboe
(6 4 ) fo llo w e d up on L ech9S work by u s in g an em issio n s p e c tro g ra p h ic
te c h n iq u e t o d eterm in e m e ta ls c a p tu re d in porous g r a p h ite e le c tr o d e
f i l t e r s * The s e n s i t i v i t y o f th e e m issio n method i s g e n e r a lly c o n sid e r­
a b ly i n f e r i o r t o t h a t o f th e atom ic a b s o r p tio n method o f Lech b u t i t
does have th e ad v an tag e o f th e sim u lta n eo u s d e te rm in a tio n o f s e v e r a l
e lem en ts on th e same f i l t e r .
The Woodriff furnace is not yet widely used in analytical labor­
atories while the Varian Techtron type of carbon rod atomizer (CRA)
is*
The CRA has absolute sensitivities generally comparable to the
-
52 -
W oodriff fu rn a c e and p o s s e s s e s th e e a s i l y rem ovable, a to m iz e r tu b e s
n e c e s s a ry f o r s u c c e s s f u l a d a p ta tio n t o f i l t e r s o A f l e x i b l e power sup­
p ly a llo w s sample p re -a s h in g d i r e c t l y in th e a to m iz e r tu b e s so no
re a g e n ts a re n eed ed e . For th e s e re a so n s th e a u th o r d e cid e d t o i n v e s t i ­
g a te th e u se o f t h i s ty p e o f a to m iz e r f o r th e d i r e c t a n a ly s is o f a
wide ran g e o f p a r t i c u l a t e m a tte r in a i r .
E x p e rim e n ta l
The s p e c tro s c o p ic a p p a r a tu s , th e carbon ro d a to m iz e r, and th e f i l ­
t r a t i o n a d a p to r u sed have a lre a d y been d e s c rib e d i n t h i s t h e s i s .
The
porous g r a p h ite tu b e s a r e i d e n t i c a l t o th o s e used f o r th e work on mer­
cury e x ce p t th e y a re n o t p la te d w ith g o ld f o r p a r t i c u l a t e an alysis®
N a tio n a l AGKS o r AGKSP proved t o be e q u a lly s a t i s f a c t o r y f o r g ra p h ite
f i l t e r s w ith th e nod going t o th e f i r s t because o f i t s lo w er p r i c e ,
C o n tra ry t o L echvS fin d in g s (41) i t was found by t h i s a u th o r t h a t
f i l t r a t i o n a d a p to rs m achined from L u c ite were f u l l y a s d e s ir a b le a s
th o s e made from T e flo n .
The L u c ite i s much ch eap er and e a s i e r to
machine th a n T e flo n and seems t o be a s e asy t o c le a n .
The contam ina­
t i o n problem s t h a t Lech e x p e rie n c e d were l i k e l y due t o th e n a tu re o f th e
g a sk e t m a te r ia l he used r a t h e r th a n t o th e m a te r ia l o f th e body o f th e
f i l t e r a d a p to r .
S ilic o n e ru b b e r has proven t o be a s a t i s f a c t o r y gas­
k e t m a te r ia l i n L u c ite f i l t e r a d a p to rs w ith no c o n ta m in a tio n problem s
f o r th e d e te rm in a tio n o f Pb, Ag, Cd, Be, Se, As o r Hg,
P a r t i c u l a t e s were g e n e ra te d i n th e la b o r a to r y i n a v a r i e t y o f
-53-
w ays.
An approach used in s e v e r a l in s ta n c e s in v o lv e d a s p i r a t i n g s o lu ­
t i o n s in to s p e c tro s c o p ic prem ix o r t o t a l consum ption b u rn ers,,
The
d r o p le ts o f s o lu tio n c o n ta in in g a s a l t o f th e elem ent o f i n t e r e s t were
c a r r ie d in to th e flam e where th e y were decomposede
The g a se s above
th e flam e c o n ta in p a r t i c u l a t e s r e s u l t i n g from re c o m b in atio n o f th e e l e ­
m ents e n te r in g th e fla m e .
These system s f e a tu r e a re p ro d u c ib le con­
c e n tr a ti o n o f p a r t i c u l a t e s p e r u n it volume o f gas b u t g iv e an unknown
p a r t i c l e s iz e d i s t r i b u t i o n and c o m p o sitio n .
A Beckman double s l o t
C H ^/air A. A. b u rn e r f i t t e d w ith a prem ix d e s o lv a tio n chamber i s p ic ­
tu r e d in F ig u re 1 6.
A Beckman CgHg/Og t o t a l consum ption b u rn e r was
used f o r g e n e r a tin g Cd c o n ta in in g p a r t i c l e s .
An u l t r a s o n i c n e b u liz e r (Tomorrow E n te r p r iz e s 1, P o rtsm o u th , Ohio)
f i t t e d w ith a d e s o lv a tio n system and a d ilu tio n /m ix in g chamber was used
to produce re p ro d u c ib le c o n c e n tra tio n s o f p a r t i c l e s o f ro u g h ly known
dim ension f o r c o l l e c t i o n e f f ic ie n c y s t u d i e s .
apparatus®
F ig u re 17 d e p ic ts th e
S o lu tio n d r o p le ts o f mean d ia m e te r 2 .5 pm a r e g e n e ra te d by
th e u l t r a s o n i c n e b u liz e r and a re c a r r ie d by a flo w o f 90 cc/m in u te o f
a i r i n t o a nichrom e w ire h e ate d des o lv a tio n tu b e in w hich tiie - s o lv e n t
(m ethanol) i s d riv e n o f f .
w ith a co ld f i n g e r .
The e x c e ss m ethanol i s condensed and removed
The d e s o lv a te d p a r t i c l e s a re th e n mixed w ith a
la r g e volume o f a i r and blown down th e le n g th o f a m ixing tu b e b e fo re
th e y a r e sam pled.
A m o to rcy cle b u rn in g r e g u la r g as was used t o g e n e ra te le a d - c o n ta in -
F ig u re 16. B eckm an DB flam e p a r t i c u l a t e g e n e r a to r
cold finger
4 .7 1/min
desolvator
ultrasonic nebulizer
I
Vl
Vt
sample
inlet
I
RF power &
cooling lines
dilution/m ixing tube
filter adaptor & syringe
Figure 17. Ultrasonic nebulizer particulate generator
™56in g p a r t i c u l a t e s f o r a com parison s tu d y o f m illip o r e v e rs u s g ra p h ite ;
filtra tio n ®
F ig u re 18 shows th e e n t i r e a p p a r a tu s .
A f r a c t i o n o f th e
e x h au st g a se s a re d ilu te d and mixed w ith com pressed a i r p r i o r t o sam­
p lin g i n a m ixing chamber s im ila r t o t h a t used w ith th e u ltr a s o n ic
n e b u liz e r d e s c rib e d above.
S e v e ra l o th e r system s w hich g e n e ra te d p a r t i c l e s c o n ta in in g m e tals
hazardous t o human h e a lth were in v e s t ig a te d .
In c lu d e d in t h i s c a te g o ry
a re c i g a r e t t e s , c e r t a i n ty p e s o f c a n d le s , and g a s o lin e lamp m a n tle s.
A
more com plete d is c u s s io n o f th e s e w i l l be g iv en in th e fo llo w in g sec­
tio n s .
F or m ost o f t h i s w ork, a 60 cc d is p o s a b le sy rin g e was used to
draw a i r sam ples th ro u g h th e w a lls o f th e f i l t e r tu b e s .
(1 .3 5 l i t e r ) homemade s y rin g e was used in some c a s e s .
A much l a r g e r
A Nalgene
f a u c e t a s p i r a t o r was u sed in th e la b o r a to r y f o r h ig h e r volume sam p lin g .
A s m a ll b a tte ry -p o w e re d a i r com pressor (Auto F l a t o r , W. R. Brown C o rp .,
Chicago 1 1 1 .) was m o d ified f o r u se f o r h ig h volume sam pling o u ts id e th e
b u ild in g .
The a n a l y t i c a l te c h n iq u e i s s im ila r t o t h a t a lre a d y d e sc rib e d f o r
th e d e te rm in a tio n o f m ercury i n a i r .
A p re -h e a te d CRA tu b e i s p laced
i n t o th e f i l t e r a d a p to r and a m easured volume o f a i r i s drawn th ro u g h
th e w a lls o f th e tu b e .
Then th e tu b e i s removed, p la c e d betw een th e
ro d s o f th e carbon rod a to m iz e r, p re -h e a te d t o 400 - 500 °C f o r a few
seconds t o d e s tr o y t a r s , smoke, e t c = , and f i n a l l y h e a te d t o a p r e - d e te r -
S
compressed air
Hood
Figure 18. Lead Particulate Generation Apparatus
— $8—
mined te m p e ra tu re h igh enough t o atom ize th e a n a ly te »
I n most c a s e s ,
th e p re -a s h ste p , i s n o t n e c e s sa ry f o r am bient a i r sam p lese
The atom ic absorbance v a lu e s o f th e elem en ts in th e m a te r ia l f i l ­
te r e d from a i r a re compared t o th o s e o f an a liq u o t o f a s ta n d a rd s o lu ­
t i o n o f th e elem ent o f i n t e r e s t p ip e te d in to and atom ized in th e same
tu b e in o rd e r t o c a lc u la te th e amount o f m a te r ia l c a p tu re d 0
. .
R e s u lts and D iscu ssio n
The e f f ic ie n c y o f porous g r a p h ite f i l t e r s f o r t i n y p a r t i c l e s has
/
I “i
been e s ta b lis h e d by Lech '
\
'„
Lech g e n e ra te d p a r t i c l e s o f a known
s iz e i n a stre a m o f gas and measured th e t o t a l m e ta l c o n c e n tra tio n o f
th e gas b o th b e fo re and a f t e r f i l t r a t i o n by. i n j e c t i n g m easured q u a n ti­
t i e s i n t o a W oodriff fu rn a c e f i t t e d w ith a s id e tu b e
The atom ic
a b s o r p tio n s ig n a ls r e s u l t i n g from th e i n j e c t i o n o f f i l t e r e d and u n f i l ­
te r e d gas were compared t o a s s e s s th e e f f i c i e n c y o
T able VI gaves th e
r e t e n t i o n e f f i c i e n c i e s o f f i l t e r s made o f N a tio n a l AGKSP g ra p h ite f o r
p a rtic le s of d iffe re n t s iz e s .
Some p re lim in a ry work was done w ith b e ry lliu m c o n ta in in g p a r t i c l e s
g e n e ra te d by a s p i r a t i n g b e ry lliu m s o lu tio n s in to a Beckman A. A. b u rn e r
and sam pling th e g a se s above th e flam e
A c u rre n t s u f f ic ie n t to
r a i s e th e te m p e ra tu re o f th e tu b e t o 2800 0C was a p p lie d and th e peak
atom ic absorbance m easured.
When th e b u rn e r was a s p i r a t i n g a 10 ppm
Be s o lu tio n , a s e r i e s o f seven sam ples o f th e b e ry lliu m p a r t i c u l a t e s
gave a mean atom ic absorbance o f 0 ol $8 and a c o e f f i c i e n t o f v a r i a t i o n
-5 9 table-
VI
FILTRATION EFFICIENCY OF POROUS GRAPHITE FILTERS
P a rtic le
Mean D iam eter (um)
Pb(NO3 ) 2
0 .1 5
9 9 .2
Pb(NO3 ) 2
0 .0 9
98.6
AgNO3
0.076
9 9 .4
Pb(NO3 ) 2
0 .0 7 7
9'7.9
AgNO3
0.037
97 . 7
-6 0 -
o f 14«5^®
The same f i l t e r tu b e s , when 5 u l o f a 0«1 ppm Be s o lu tio n
(5 x I O " ^ g Be) was d rie d and atom ized in them , gave an absorbance o f
0«443 w ith a c o e f f i c i e n t o f v a r i a t i o n o f 4«9%»
The s e n s i t i v i t y o f th e
method i s such t h a t a sample o f o n ly two l i t e r s o f a i r c o n ta in in g Be
( a t th e maximum allow ed l e v e l , 0«01wg/nP in M ontana) would be re q u ire d
f o r d e te c tio n *
A sample o f t h i s s iz e would r e q u ir e one and one h a lf
m in u tes t o c o l l e c t .
In o rd e r t o a s c e r t a i n th e e f f ic ie n c y o f AGKSP porous tu b e s w ith
r e s p e c t t o th e r a t e o f f i l t r a t i o n th e a p p a r a tu s . d e p ic te d i n F ig u re I ?
was u s e d ,
D eso lv ated p a r t i c l e s o f s i l v e r n i t r a t e a re mixed w ith a
la r g e volume o f a i r and blown down th e le n g th o f a m ixing tu b e p r i o r t o
sam p lin g .
The h ig h t o t a l flow in th e system ( 4 ,8 l i t e r / m i n , ) a llo w s a
much h ig h e r sam pling r a t e t o be used th a n i s p o s s ib le w ith Lech9S sys«*
tern.
A s o lu tio n o f s i l v e r n i t r a t e in m ethanol (2 x IO"''7 g Ag/ml) was
pumped i n t o th e u l t r a s o n i c h e b u liz e r r e s u l t i n g i n a c a lc u la te d p a r t i c l e
s iz e o f 0 ,0 1 4 pm,
A s e r i e s o f 60 cc sam ples o f th e m ix e d /d ilu te d p a r­
t i c l e b e a rin g gas stre a m was drawn th ro u g h th e w a lls o f porous g ra p h ite
tu b e s a t w id e ly d i f f e r i n g sam pling r a t e s .
The. c o n c e n tra tio n o f s i l v e r
i n th e 60 cc o f g a se s sampled by th e tu b e s i s p l o tte d a g a in s t th e sam­
p lin g r a t e in F ig u re 19«
There i s no lo s s in f i l t r a t i o n e f f ic ie n c y a s
th e r a t e o f sam pling i s changed.
T h is i s im p o rta n t because in some
s i t u a t i o n s i t i s d e s ir a b le to g e t an a n a ly s is in a s s h o r t a tim e a s
p o s s ib le ; e . g», a f t e r an i n d u s t r i a l a c c id e n t.
I n o th e r c a s e s , i t i s
8
7
.
2
I
.
1.6
1.8
2.0
2.2
2.4
LogiQ ( s a m p l i n g r a t e in cm'Vmin)
2.6
Figure 19. M e a s u r e d P a r t i c u l a t e C o n c e n t r a t i o n a s a Fu nc tio n of Sa m plin g Rate
—6 2 -
more d e s ir a b le to a s c e r t a i n a mean am bient l e v e l av erag ed over a
r e l a t i v e l y lo n g sam pling tim e .
There was some q u e s tio n a s t o w h eth er a s ta n d a rd s o lu tio n d rie d
and atom ized i n a carbon tu b e would be a v a lid way t o q u a n tita te p a r­
t i c u l a t e m a tte r f i l t e r e d by such a tu b e .
not be.
There a re two re a so n s i t m ight
F i r s t , th e geom etry i s d i f f e r e n t .
P a r t i c l e s f i l t e r e d by th e
a p p a ra tu s d e s c rib e d a re f a i r l y u n ifo rm ly d i s t r i b u t e d o v er th e in n e r s u r­
fa c e o f th e tu b e s .
T h e re fo re , when th e tu b e i s h e a te d , sample atoms en­
t e r th e o p t i c a l p a th from a l l s id e s and n o t from a s in g le s p o t on one
s id e a s i s th e case when a d r o p le t o f s o lu tio n i s d r ie d i n th e tu b e .
Second, th e m a te r ia l f i l t e r e d i s o f unknown co m p o sitio n .
D if f e r e n t
s a l t s o f th e same elem ent sh o u ld v o l a t i l i z e a t d i f f e r e n t tim e s d u rin g
th e a to m iz a tio n c y c le and d is s o c ia te t o a g r e a te r o r l e s s e r d e g re e .
T h is would r e s u l t in d i f f e r e n t f r e e atom p o p u la tio n s and a c o n se q u e n tly
d if f e r e n t a n a ly tic a l s ig n a l.
L eVOV (35? PP« 236 - 245) in d ic a te s t h a t th e f a c t t h a t an elem ent
i s p re s e n t i n d i f f e r e n t forms a c t u a l l y makes l i t t l e d if f e r e n c e in c a r­
bon fu rn a c e atom ic a b s o r p tio n .
i n th e W oodriff f u r n a c e .
In d eed , t h i s has proven t o be th e case
A t e s t o f t h i s p ro p o s itio n was made w ith th e
carbon ro d a to m iz e r in th e fo llo w in g m anner.
Five m i c r o l i t e r a liq u o ts
o f a 2 .0 x 10"7 s/ro l ( 10“ ^ M) le a d s o lu tio n (le a d a s n i t r a t e s a l t in
d i s t i l l e d w a te r) were d r ie d i n an a to m iz e r tu b e .
Then, f iv e m ic r o lit­
e r s o f 0 .1 M HOI, HNO3 , o r HgSO^ were p ip e te d i n t o th e tu b e and d rie d
-63-
o v er th e le a d .
The a p p ro x im a te ly IO^ f o ld e x cess o f a c id should con­
v e r t th e m e ta l t o th e r e s p e c tiv e le a d s a l t .
When th e le a d was atom ized,
th e r e was no d if f e r e n c e i n th e a n a l y t i c a l s ig n a l from le a d t r e a t e d w ith
th e d i f f e r e n t a c i d s .
T ab le V II g iv e s th e r e s u l t s »
The g e o m e tric a l a s p e c t o f th e s ta n d a r d iz a tio n q u e s tio n was s tu d ie d
by a n a ly z in g cadmium p a r t i c u l a t e s c a p tu re d on porous g r a p h ite tu b e s by
an in d ep en d en t method and com paring th e r e s u l t s w ith th o s e ach iev ed w ith
d i r e c t a to m iz a tio n and s o lu tio n s ta n d a r d iz a tio n .
F o rty cc o f th e g a se s above a Beckman Og, CgHg, b u rn e r a s p ir a ti n g
1000 ppm cadmium s o lu tio n were drawn th ro u g h each o f tw elve, porous CRA
tu b e s .
S ix o f th e s e tu b e s were p la c e d i n t o sm all t e s t tu b e s which had
c a l i b r a t i o n marks a t two m i l l i l i t e r s .
Ten m i c r o l i t e r s o f a s o lu tio n
c o n ta in in g 4 x 10"°8 g o f cadmium were p la c e d in to each o f th r e e more
porous CRA tu b e s and d r i e d .
These “ s ta n d a rd ” CRA tu b e s were a ls o p la ­
ced i n t o c a l i b r a t e d t e s t tu b e s .
One m i c r o l i t e r o f 1 :1 0 n i t r i c a c id was
added t o each o f th e n in e t e s t tu b e s and th e cadmium s a l t s d is s o lv e d by
p la c in g th e tu b e s in a h o t w a te r b a th o v e rn ig h t.
The t e s t tu b e s were
each f i l l e d t o 2 .0 ml w ith d i s t i l l e d w a te r and th e c o n te n ts mixed.
Ten m i c r o l i t e r a li q u o t s o f each s o lu tio n were a n aly z e d in an im per­
v io u s CRA tu b e u s in g th e 228.8 nm re so n an c e l i n e .
The atom ic absorb­
a n ces from a n a ly s is o f th e s o lu tio n s from th e s i x CRA tu b e s used a s f i l ­
t e r s were compared t o th o s e o f th e s o lu tio n s from th e th r e e sta n d a rd
tu b e s t o c a lc u la te th e amount o f Cd i n th e p a r t i c u l a t e m a tte r f i l t e r e d .
— 64— ■
TABLE VII
SALT EFFECT ON LEAD DETERMINATION
CONDITIONS:
5 u l o f 2 x K T ? g /m l Pb, 283,3 nm l i n e , 3400 W atts,
5 u l of. O el M HC1, HgSO^, o r HNO3 , p re -a s h to $00 °C
a f t e r d ry in g
MEAN ABSORBANCE
COEFFICIENT OF.VARIATION
NUMBER OF RUNS
W ith HCl
W ith HNO3
W ith H2SO4
0 .2 4 7
0 .2 4 0
0.246
' 4 .3 *
4
7 .3 *
4
3 .6 *
'
4
:
There i s no s i g n i f i c a n t d if f e r e n c e i n
th e mean v a lu e s a t th e 95% co n fid en ce
le v e l
— 65—
The mean v a lu e c a lc u la te d f o r t h i s i n d i r e c t a n a l y t i c a l approach was
2«80 x 10""® g p e r tu b e .
The o th e r s i x tu b e s c o n ta in in g f i l t e r e d Cd p a r t i c l e s were an aly zed
d i r e c t l y on th e carbon rod u sin g th e f a r l e s s s e n s itiv e 3 2 6 .1 run
reso n an ce l i n e .
The atom ic ab so rb an ces observed were compared w ith
th o s e m easured when aqueous s ta n d a rd s o lu tio n s o f cadmium were p ip e te d
i n t o and atom ized in th e same tu b e s .
Two s ta n d a rd s o lu tio n s were u sed ;
th e f i r s t c o n ta in e d 3 .0 x 10” ® g Cd i n 10 m i c r o l i t e r s and th e second
3 .0 x 10” ® g Cd in I m i c r o l i t e r .
The mean v a lu e s by t h i s d i r e c t ap­
proach f o r th e t o t a l cadmium f i l t e r e d by th e s ix porous tu b e s were
2 .8 1 x 10” ® g and 2 .7 9 x 10” ® g based on th e atom ic ab so rb an ces o f th e
10 m i c r o l i t e r and I m i c r o l i t e r s ta n d a rd s r e s p e c tiv e ly .
T able V III summarized th e r e s u l t s .
B asing a measurement o f th e
m e ta l c o n ta in e d in p a r t i c u l a t e m a tte r f i l t e r e d from a i r
upon th e atom ic
ab so rb an ce o f I p i s ta n d a rd s o lu tio n s d r ie d i n th e same tu b e s ap p ears t o
be v a lid w ith a p o s s ib le 16% e r r o r ( t o r i t x RSD (A method) a t th e 95%
c o n fid e n ce l e v e l ) .
A c tu a lly th e e x p e rie n c e g o tte n w ith m ercury s ta n ­
d a r d iz a tio n in which th e g e o m e tric a l c o n s id e ra tio n s a re th e same in ­
d ic a t e s t h a t th e p ro b a b le e r r o r due t o t h i s e f f e c t i s l i k e l y l e s s th a n
5%.
A com parison o f th e r e s u l t s o f le a d a n a ly s is u s in g c o n v e n tio n a l
m illip o r e f i l t r a t i o n w ith su b seq u en t d i s s o l x t t i o n o f th e membrane f i l ­
t e r and a n a ly s is o f a f r a c t i o n o f th e r e s u ltin g , s o lu tio n and th e d i r e c t
-6 6 TABLE VIII
COMPARISON OF DIRECT TO INDIRECT MEASUREMENT OF CAPTURED PARTICULATES
C a lc u la te d
Mean Value (g )
RSD %
D egrees
of
Freedom
D ire c t ( I u l s ta n d a rd ) ,
2 .7 9 x 10-8
18
D ire c t (10 u l s ta n d a r d )
2 .8 1 x 10-8
23
9
In d ire c t
2 .8 0 x IQ"#
13
7
RSD (am ethod)
U
RSD o f th e s t a t i s t i c ( ^ d i r e c t - X in d ir0)
e q u a ls /(1 8 )2
v 11
C r i t i c a l , v a lu e o f
+
=
7
(11 + 7 - 2 ) d e g re es o f freedom
e q u als. 2«13
-6 ? -
porous tu b e approach was made u sin g a m o to rcy cle b u rn in g re g u la r
g a s o lin e a s a p a r t i c u l a t e so u rce (F ig u re IS)®
A f r a c t i o n o f th e ex­
h a u s t from th e m o to rcy cle was d ilu te d w ith com pressed a i r t o b rin g th e
le a d l e v e l down t o m anageable l e v e l s w ith a system s im ila r to t h a t
d e p ic te d i n F ig u re 17®
A s e r i e s o f f i v e 20 cc sam ples was ta k en th ro u g h
porous g r a p h ite tu b e s and two 1350 cc sam ples were drawn th ro u g h 13 mm
d ia m e te r d is k s o f 0 .4 5 pm m illip o r e membranes®
The membranes were d i s ­
so lv e d by h e a tin g w ith 100 u l o f HNO^ and th e s o lu tio n d ilu te d t o 1 .0 ml
b e fo re a n a ly s is on th e CRA® F iv e m i c r o l i t e r s o f 5 x IO"? g/m l Pb
s o lu tio n was p ip e tte d in to porous tu b e s t o s ta n d a rd iz e th e d i r e c t
a n a ly s is .
The r e s u l t s a re g iv en in T ab le IX .
I t would have been d e s ir a b le
to c o l l e c t a g r e a t e r number o f sam ples b u t th e m o to rcy cle cb u ld n * t ru n
f o r more th a n t e n m inutes in a s t a t i o n a r y s t a t e w ith o u t o v e rh e a tin g .
I t to o k a p p ro x im a te ly fo u r m in u tes t o draw each sam p le.th ro u g h th e
m illip o r e f i l t e r s compared t o ab o u t f iv e seconds each f o r th e porous
tu b e s .
F i l t r a t i o n o f th e g a se s above b u rn e rs a s p i r a t i n g s o lu tio n s c o n ta in ­
in g m e ta l io n s w ith su bsequen t a to m iz a tio n and atom ic a b s o rp tio n d e te r ­
m in a tio n of. th e c o lle c te d m e ta ls was u n d e rta k en w ith sele n iu m , b e r y l l i ­
um, le a d , and cadmium.
In a l l c a s e , p l o t s o f th e re c o rd e d atom ic a b -
s o r p tio n v e rs u s e i t h e r th e volume o f gas sampled o r th e c o n c e n tra tio n
o f th e s o lu tio n s a s p ir a te d were lin e a r®
The r e l a t i v e s ta n d a rd d e v ia tio n
—6 8 “
TABLE H
COMPARISON OF MILLIPORE FILTER TO POROUS GRAPHITE FOR
LEAD PARTICULATES
CONDITIONS:
Pb 283»3 nm l i n e , 2800 w a tts power
FILTER
VOLUME SAMPLED
NUMBER OF DETERMINATIONS
MEAN VALUE (ug/m3)
STANDARD DEVIATION (ug/m3)
MILLIPORE
GRAPHITE
1350 cc
20 cc
2
5
205
173
30
9 .3
More sam ples would have been ru n , e s p e c ia ll y w ith th e
m illip o r e f i l t e r s , i f th e m o to rcy cle had n o t o v erh eated
and th r e a te n e d t o s t a l l *
—69“
o f such e x p erim en ts ranged from 10 - 15$ .
T ab le X l i s t s some o f th e im p o rta n t f e a tu r e s o f th e m ethod.
The
p e n u ltim a te column g iv e s th e volume o f a i r t o be sam pled t o g e t an ab­
so rb an ce s i g n a l e q u a l t o te n tim e s th e s e n s i t i v i t y o f th e method p ro­
v id e d t h a t th e a i r sampled c o n ta in s l e v e l s a t th e re c o g n iz e d l i m i t s .
I t i s c l e a r t h a t f o r s i t u a t i o n s in v o lv in g p o s s ib ly dangerous le v e l s o f
a i r c o n tam in an ts ( e . g . a m ercury s p i l l ) a d e te rm in a tio n can be made
w ith on ly a v e ry sm a ll sample ta k e n in a few sec o n d s.
The l a s t column g iv e s th e s e n s i t i v i t y o f th e te c h n iq u e i n term s o f
th e c o n c e n tra tio n
th e s e m e ta ls b ased on a te n l i t e r a i r sam-
p ie r e q u ir in g ab o u t e ig h t m inutes t o c o l l e c t .
These s e n s i t i v i t i e s com-
p a re fa v o ra b ly w ith th o s e g iv en by Thompson e t a l .
who re p o rte d
t h e i r d e te c tio n l i m i t s on th e b a s is o f a 2000 cu b ic m eter sample c o l­
le c t e d on a f i b e r g l a s s f i l t e r over a p e rio d o f tw e n ty -fo u r ho u rs!
The am bient l e v e l o f le a d i n a la b o r a to r y in th e c h e m istry b u ild ­
in g a t MSU was m easured t o a s s e s s th e d eg ree o f r e p r o d u c i b i l i t y p o s s ib le
a t f a i r l y low l e v e l s .
A ir was drawn th ro u g h a s e r i e s o f porous tu b e s
f o r f iv e m in u tes a t flow r a t e s ra n g in g from 220 - 1400 c c/m in u te u sin g
a fa u c e t a s p i r a t o r f o r a pump.
A mean
v a lu e o f
0 .1 4 4 pg/m? w ith
a re l­
a t i v e s ta n d a rd d e v ia tio n o f 13$ was a ch ie v e d f o r n in e le a d d eterm in a­
tio n s .
High volume sam ples (14 - 29 l i t e r s ) ta k e n from th e
ro o f o f th e
same b u ild in g on a h o lid a y gave a mean
v a lu e o f
0 .0 5 2 pg/m^ w ith
RSD o f 7$ f o r th r e e le a d d e te r m in a tio n s .
Samples ta k e n on th e same o c -
an
T A B L E X;
Elem ent
Line
nm
TYPICAL ANALYTICAL PARAMETERS FOR THE DIRECT ANALYSIS
A to m izatio n Temp®*
S a fe ty Lim its*
Volume^
S e n s itiv ity ^
Co
240® 7
3000
Mn
279.5
3000
5000
Hg
253.7
900
100
Se
1 96.0
3000
—=”=
Be
234.9
3000
2
Cd
2 2 8 .8
2000
200
0®04 .
0.0001
Pb
217.0
2200
200
0 .7
0 .0 0 1
Cu
3 24.7
3000
*” •=*
—«="
0 .0 0 4
Ag
3 2 8 .1
2200
——
—=”=
0.0004
Cr
3 5 7 .8
3000
100
2
0 .0 0 2
—=”■
=~~"
0 .0 1
0 .0 0 9
0.0004
22
="=■"
22
0 .0 2
0 .0 2
0.0004
I®
T em perature o f a to m iz a tio n i s o n ly approximate® V alues g iv en were measured w ith an o p t i c a l
pyrom eter a p p ro x im a te ly f iv e seconds a f t e r th e power was tu rn e d on®
2o
ACG-IH l i m i t s ta k e n from J a e Hwang, Anal®'Chem0, AAn No® 14, 20A(19?2)®
3®
Volume o f a i r sample a t th e ACGIH l i m i t n e c e s s a ry t o g iv e an absorbance s ig n a l te n tim e s
th e s e n s i t i v i t y (ato m ic absorbance o f 0 ®044) i .
4®
S e n s i t i v i t y o f th e method (1% a b s o rp tio n ) in term s o f jug/nP based on 10 l i t e r a i r sample
-7 1 -
c a s io n f o r b e ry lliu m and chromium in d ic a te d t h a t th e s e elem en ts w ere a t
l e v e l s below 0.0003 and 0.0007 >ig/m^ r e s p e c tiv e ly .
A common cause o f cadmium in h a la tio n i s th e use o f s i l v e r b ra z in g
a llo y s i n p o o rly v e n t i l a t e d a r e a s .
In o rd e r t o s im u la te such a c o n d i-
t i o n , a p p ro x im a te ly two m illig ra m s o f s i l v e r s o ld e r were b razed to in ­
candescence i n th e g la ssb lo w in g la b o r a to r y .
F i f t y cc sam ples o f th e a i r
in th e room were ta k e n p e r i o d i c a l l y and th e cadmium c o n c e n tra tio n de­
te rm in e d .
F ig u re 20 i l l u s t r a t e s th e r e s u l t s . . In an i n d u s t r i a l s i t u a ­
t i o n Cd l e v e l s could ru n much h ig h e r.
A d d itio n a l e x p erim en ts were perform ed in a l i t t l e u sed la b o ra to ry
room.
Ah u h c o lo re d c an d le o f a common d e c o ra tiv e v a r i e t y having a t i n y
le a d w ire in th e w ick t o s t i f f e n i t was lig h te d and th e a i r sampled f o r
le a d .
A s in g le can d le succeeded i n r a i s i n g am bient l e v e l s o f le a d from
0 .1 4 to 1 .5 Ug/m^ in an h o u r.
In a n o th e r t e s t in th e same room, a p ro­
pane gas m antle lamp r a is e d th e b e ry lliu m l e v e l from n i l t o 0 .8 ug/m^
in seven m in u te s.
Most o f th e b e ry lliu m was g iv en o f f i n th e f i r s t few.
m in u tes a f t e r a f r e s h m antle was f i r s t l i t .
Im m ediately above th e lam p,
l e v e l s ex ceed in g 30 jug/m3 (15 and 3000 tim e s th e ACGIH and Montana s t a t e
l i m i t s r e s p e c tiv e ly ) were o b serv ed .
T h is in d ic a te s t h a t l i g h t i n g such
a lamp equipped w ith a new m antle in an e n clo se d space such, a s a t e n t
would be in a d v is a b le .
The o n ly sam ples checked which gave an a p p re c ia b le non-atom ic in ­
te r f e r e n c e peak were o f u n d ilu te d c i g a r e t t e smoke.
A p y rex c i g a r e t t e
72-
Time after heating silver solder (min)
Figure 20. Silver solder experiment
-73-
h o ld e r was made and th e f i l t e r a d a p to r was connected t o i t w ith a
s h o r t p ie c e o f ru b b e r tubing®
T w en ty -fiv e cc sam ples o f th e smoke from
two u n f i l t e r e d Camel c i g a r e t t e s were drawn th ro u g h p o ro u s tubes®
The
t a r s were ashed by h e a tin g th e tu b e s t o a v e ry d u l l re d in th e carbon
ro d atomizer®
W ith le a d th e r e was no problem in rem oving th e t a r s
w ith o u t lo s in g le a d ; how ever, w ith cadmium, because o f i t s g r e a te r v o l­
a t i l i t y , i t was n e c e s s a ry t o ad h ere t o a c a r e f u l a sh in g sequence o f
t h i r t y seconds a t 450 - 475 °C t o e f f e c t i v e l y remove t a r s w ith o u t lo s s
o f th e metal®
The cadmium l e v e l av erag ed about $ pg/m^ and th e le a d
about 50 pg/m^ w ith th e f i n a l sam ples (ta k e n from th e c i g a r e t t e b u t t )
b e in g h ig h e r th a n th e fir s t®
C o n clu sio n s
T h is te c h n iq u e f e a tu r e s v e ry low d e te c tio n l e v e l s f o r a wide ran g e
o f elem en ts in a i r samples®
The c h ie f re a so n f o r t h i s i s t h a t a l l o f
th e c o lle c te d m a te r ia l i s atom ized and m easured in one i n s t a n t ® An­
o th e r c o n tr ib u to r to i t s s e n s i t i v i t y i s th e low ’’b la n k s ” a s s o c ia te d
w ith it®
High re a g e n t o r f i l t e r b la n k s u n av io d ab le i n many a n a l y t i c a l
te c h n iq u e s d r a s t i c a l l y l i m i t th e d e te c tio n c a p a b i l i t i e s possible®
For
exam ple, a s in g le sq u are c e n tim e te r o f common o rg a n ic membrane f i l t e r
c o n ta in s an a v erag e o f 8 ng o f le a d
T h is b la n k amount o f le a d
i s 800 tim e s t h a t a s s o c ia te d w ith m e ta l p ick ed up in h a n d lin g th e
porous tu b e s , c o n ta c t w ith th e f i l t e r a d a p to r, s to r a g e , etc® , i s u s u a l­
l y l e s s th a n th e s e n s i t i v i t y o f th e f i n a l a n a l y s i s ; i® e®, f o r le a d
- rJUt h i s b la n k i s on th e o rd e r o f 10” ^
g o r le s s *
The d i r e c t te c h n iq u e i s b e s t used where speed o f a n a ly s is o r ex­
trem e s e n s i t i v i t y i s re q u ire d * Examples a re s tu d ie s o f th e d if f u s io n
o f p a r t i c l e s from a so u rce o r f o r r a p id d e te rm in a tio n o f p o s s ib ly dan­
g ero u s l e v e l s o f co n tam in an ts in a w orking space*
I t sh o u ld a ls o prove
u s e f u l f o r th e d e te rm in a tio n o f background l e v e l s f o r some elem ents
w hich a re a t l e v e l s to o low f o r d e te c tio n by th e more common a n a l y t i c a l
a p p ro ach es ( 62) e
A p p lic a tio n s t o which i t i s n o t i d e a l l y s u ite d a re th o s e in which
th e s m a ll sample s iz e and s in g le elem ent c a p a b ility a r e lim ita tio n s *
An example o f t h i s would be th e d e te rm in a tio n o f th e av erag e amount of
le a d over a tw e n ty -fo u r hour p e rio d i n th e a i r i n a c a r p a rk in g l o t .
A nother example would be th e d e te rm in a tio n o f th e a v erag e l e v e l o f ir o n ,
m anganese, chromium, and n ic k e l in th e a i r over G ary, In d ian a*
The method i s cheap, sim p le , s e n s i t i v e , and r e a d i l y a d a p ta b le to
com m ercially a v a il a b le in s tru m e n ta tio n *
The b a s ic ap p ro ach has proven
t o work w e ll w ith th e W oodriff fu rn a c e and th e carbon ro d and should be
a p p lic a b le t o any carbon fu rn a c e w ith e a s i l y changed a to m iz a tio n tu b es*
Much o f th e m a te r ia l in t h i s s e c tio n has been a c c e p te d f o r pub­
l i c a t i o n in S p ectro ch em ica A cta ^®^*
A SIMPLE TECHNIQUE FOR COATING GRAPHITE WITH PYROLYTIC CARBON
I n tr o d u c tio n
R ecent l i t e r a t u r e i s r e p l e t e w ith ev id en ce t h a t carbon non-flam e
a to m iz e rs used f o r atom ic a b s o r p tio n o r atom ic flo u re s c e n c e a re improved
by th e use o f non-porous p y r o l y t i c a l l y c o ate d g r a p h ite o r v itr e o u s c a r­
bon in l i e u o f th e more common and ch eap er form s o f carbon ^
5
^Oil
The re a s o n s l i e i n th e p e rm e a b ility o f th e u s u a l g ra d e s o f spec­
tr o s c o p ic g r a p h ite s and "c a rb o n s” t o g a se s and s o l u t i o n s .
T h is perme­
a b i l i t y a llo w s a c t u a l l o s s o f sample atoms th ro u g h th e w a lls o f th e
a to m iz a tio n chamber and s h o rte n s th e e f f e c t i v e re s id e n c e tim e o f atoms
w ith in th e o p t i c a l p a th .
A naly te m a te r ia l from s o lu tio n p a r t i a l l y ab­
sorbed i n t o th e g r a p h ite s u b s tr a te b e fo re d ry in g e n te r s th e o p t i c a l p a th
more slo w ly upon h e a tin g th a n does m a te r ia l d rie d on th e s u rfa c e o f th e
g r a p h ite .
T h is cau ses a b ro ad en in g and lo w erin g o f th e peak atom ic
a b s o r p tio n s i g n a l t h a t i s m easured.
T his la b o r a to r y has been concerned w ith r e s e a r c h on fla m e le s s atom­
i c a b s o r p tio n a to m iz e rs such a s homemade v a r i e t i e s , o f th e Massman f u r ­
nace
y ears.
carbon ro d and, o f c o u rs e , th e W oodriff fu rn a c e f o r s e v e r a l
Over a y e a r ago we became i n t e r e s t e d in u s in g e i t h e r p y r o ly tic
g r a p h ite o r v itr e o u s carbon because o f th e low p o r o s ity o f th e s e m a te ri­
a ls .
However, i t q u ic k ly became a p p a re n t t h a t making th e re q u ire d atom ­
i z e r p a r t s o f com m ercially a v a il a b le v a r i e t i e s o f th o s e m a te r ia ls would
be p r o h i b i t i v e l y e x p e n s iv e .
A lso , th e d i f f i c u l t y e x p e rie n c e d in machin­
in g a sample o f v itr e o u s carbon made i t a p p a re n t t h a t , even i f t h a t
-76-
m a te r ia l were a v a il a b le in b u lk a t re a so n a b le c o s t, c o n s tr u c tio n o f a t ­
o m izatio n fu rn a c e p a r t s would be a m ajor u n d e rta k in g «, W ith th e s e p ra c ­
t i c a l c o n s t r a i n t s i n mind we d e cid e d t o d e v ise a system t o c o a t r e a d ily
a v a il a b le (and m ach in ab le) form s o f g r a p h ite w ith an im pervious c o a tin g .
The Super Temp Company o f S a n ta Fe S p rin g s, C a l if o r n ia , g ra c io u s ly
p ro v id ed us w ith th e m a te r ia l t h a t g o t u s s t a r t e d (73 - 76)«
At e l e ­
v a te d te m p e ra tu re s , methane w i l l decompose in s e v e r a l s t e p s , e v e n tu a lly
form ing hydrogen gas and c arb o n .
I f a s u ita b le s u rfa c e i s p r e s e n t, th e
carbon w i l l be d e p o s ite d upon i t .
The p h y s ic a l c h a r a c t e r i s t i c s o f th e
r e s u l t i n g c o a tin g a r e dependent b o th upon th e te m p e ra tu re o f d e p o s itio n
and th e p re s s u re o f th e m ethane.
At low (1000 °C) and h ig h (> 2 1 0 0 °C)
te m p e ra tu re s , dense carbon c o a tin g s a re formed r e g a r d le s s o f p re s s u re
At in te rm e d ia te te m p e ra tu re s from 1300 °C t o 2100°C reduced,
p re s s u re s oh th e o rd e r o f a t o r r o f methane a re n e c e s s a ry t o avoid i s o - .
t r o p i c , so o ty d e p o s it s .
C om m ercially, th e c o a tin g o f g r a p h ite i s done
a t around 2100 °C a t reduced p re s s u re s w ith in d u c tio n h e a tin g o f th e
g ra p h ite s u b s t r a t e .
We s e t o u t t o d ev elo p a p ro c e s s w ith which u s e f u l
p y r o ly tic carbon c o a tin g s could be produced ch eap ly w ith equipment
a v a ila b le in a g e n e r a l s p e c tro s c o p ic la b o r a to r y .
E x p e rim en ta l
To s im p lif y th e com m ercial p ro c e s s , we used a sim p le tu b e fu rn a c e
in s te a d o f an RF in d u c tio n h e a tin g a p p a ra tu s and no vacuum sy stem .
The
re a so n t h a t th e s e s u b s t i t u t i o n s a re p o s s ib le i s t h a t we u t i l i z e d r e l a -
-7 7 -
t i v e l y low te m p e ra tu re s in th e ran g e o f 950 t o 1150 °C f o r th e d e p o s itio n ,
P re lim in a ry e x p erim en ts were perform ed by p a s s in g methane gas
th ro u g h a q u a rtz tu b e h e a te d t o a b o u t 1000 °C i n th e flam e o f a
to rc h used f o r w orking glass®
A h a rd , sh in y c o a tin g o f carbon was de­
p o s ite d i n th e h e ate d p o r tio n o f th e tube®
By w rapping th e q u a rtz tu b e
w ith a c o i l o f nichrom e w ire , much more uniform h e a tin g and, consequent­
l y , b e t t e r c o a tin g s , resu lted ®
From t h a t p o in t th e developm ent o f th e
a p p a ra tu s t h a t we a r e p r e s e n tly u s in g fo llo w ed n a t u r a l l y (F ig u re 21)®
This a p p a ra tu s i s sim ply a I ? mm Vycor tu b e wrapped w ith ab o u t f i f t y
tu r n s o f 18 gauge nichrom e w ire and in s u la te d w ith a lo o s e ly wrapped
la y e r o f q u a r tz wool®
A la r g e (4=2 KVA) P o w erstat v a r ia b le a u to tr a n s ­
form er s u p p lie s th e h e a tin g current®
A th re e -w ay v a lv e a llo w s e i t h e r
n itr o g e n o r n a t u r a l gas to p a ss th ro u g h th e tube®
The e x i t tu b e i s
p la ce d i n a pan o f w a te r ( o r t u r p e n tin e ) t o p re v e n t oxygen d if f u s io n
in to th e system®
T h is pan should be i n a hood t o sweep away th e p o s s ib ­
l y t o x i c , h ig h ly u n s a tu r a te d hydrocarbon fumes exhausted®
The c o a tin g p ro c e s s i s simple®
The v a lv e i s a d ju s te d t o p ass Ng
th ro u g h th e system and th e power i s tu rn e d on®
Then th e o b je c t t o be
p la te d i s p la c e d i n t o th e r i g h t end o f th e tu b e fu rn a c e and pushed i n t o
th e c e n te r o f th e h e a te d zone w ith a q u a rtz rod®
and th e e n tra n c e p o r t restoppered®
methane th ro u g h th e tu b e .
The ro d i s removed
Then th e v a lv e i s tu rn e d t o p a ss
When th e p l a t i n g tim e h as e la p s e d , n itr o g e n
i s a g a in a d m itte d , and th e o b je c t i s moved w ith th e q u a rtz rod t o one
to natural gas
N0 tank
support rod
valve
30 cm.
to autotransformer
Figure 2 1 . Pyrolytic Carbon Deposition Aoparatus
entrance port
-79- .
o f th e c o o l ends o f th e tu b e .
When th e p la te d o b je c t has cooled i t i s
pushed o u t o f th e end o f th e tu b e .
The te m p e ra tu re o f d e p o s itio n i s measured w ith an o p t i c a l pyro­
m eter fo c u sse d on th e o b je c t b e in g p l a t e d .
The flo w r a t e o f th e n a tu ­
r a l gas i s from 50 t o 200 cc/m in u te a s measured by a G ilm ont flo w m eter.
There must be s u f f i c i e n t flow t o a s s u re a f a i r l y u n ifo rm b a th in g o f
p a r t s to be p la te d w ith th e n a t u r a l g a s .
tem e x c e s s iv e ly .
Top h ig h flo w s c o o l th e sy s­
Power in p u t t o th e tu b e i s on th e o rd e r o f 1400
w a tts .
The carbon rod a to m iz e r d e s c rib e d p re v io u s ly in t h i s t h e s i s and a
W oodriff fu rn a c e were used t o compare g ra p h ite a to m iz e r components
b o th b e fo re and a f t e r d e p o s itio n o f p y r o ly tic carbon c o a tin g s .
R e s u lts and D isc u ssio n
The p y r o ly tic carbon c o a tin g s a re m e ta llic g rey i n ap p earan ce,
hydrophobic, and v e ry h a rd .
Depending on th e s iz e and shape o f th e ob­
j e c t and th e te m p e ra tu re , th e r a t e s o f d e p o s itio n v a ry , b u t a re u s u a lly
in th e range o f 0 .0 1 t o 0 .3 mm/hour.
Even th e low er f ig u r e i s two o r­
d e rs o f m agnitude g r e a t e r th a n th e r a t e quoted by K o tlen sk y ^73) f o r
d e p o s itio n s a t s im ila r te m p e ra tu re s .
The only e x p la n a tio n t h a t I can
o f f e r f o r t h i s i s t h a t th e com m ercial p ro c e ss u t i l i z e s reduced p re s ­
s u re s o f methane w h ile o urs does n o t.
The r a t e o f d e p o s itio n a s a fu n c tio n o f th e te m p e ra tu re o f de­
p o s itio n was determ ined by c o a tin g a W oodriff fu rn ac e h e a te r tu b e, a t
- 80“
d i f f e r e n t te m p e ra tu re s .
These tu b e s a re made o f R in g sd o rff g ra p h ite
ty p e R W 105 and a re 1 4 .9 cm lo n g w ith an o u ts id e d ia m e te r o f 1 .0 cm
and an in s id e d ia m e te r o f 80 mm.
The methane flow r a t e was a p p ro x im a te ly 120 c c /m in u te .
F ig u re 22
i s a p lo t o f th e lo g a rith m o f th e g a in i n mass o f th e s e tu b e s in m i l l i ­
grams p e r m inute v e rs u s l / T .
The f a c t t h a t th e d a ta d e f i n i t e l y in d ic a te
a curved l i n e p ro b a b ly in d ic a te s t h a t more th a n one in te rm e d ia te s p e c ie s
i s im p o rta n t in d e te rm in in g th e o v e r a ll d e p o s itio n r a t e .
A check o f d e p o s itio n r a t e w ith r e s p e c t t o th e flo w r a t e o f methane
gas was made.
A W oodriff fu rn a c e h e a te r tu b e s im ila r t o th e ones used
f o r th e te m p e ra tu re e f f e c t e x p erim en ts serv ed as th e s u b s t r a t e .
At a
te m p e ra tu re o f 1040 0Cs, flow r a t e s from 50 t o 200 cc/m in gave s im ila r
r e s u l t s (a b o u t 5 mg d e p o s ite d /m in u te ) .
At low er flo w r a t e s th e carbon
d e p o s it was n o t un ifo rm , w h ile a t flow r a t e s in e x ce ss o f 200 cc/m in u te
th e d e p o s itio n was s lo w e r.
T h is was p ro b a b ly due t o th e c o o lin g e f f e c t
o f th e e x ce ss g a s .
The d e n s ity o f th e d e p o s ite d carbon was m easured by m easuring th e
mass and volume o f low p o r o s ity g r a p h ite o b je c ts b o th b e fo re and a f t e r
p la tin g .
The d e n s ity o f c r y s t a l l i n e g r a p h ite i s 2 .2 6 * ^ 6 ) e
T h is f i g ­
u re i s commonly approached in com m ercially, d e p o s ite d p y r o ly tic g r a p h ite .
The m easured d e n s ity o f th e carbon d e p o s ite d by o ur ,a p p a ra tu s ran g es
*Commercial g ra d e s o f g r a p h ite c o n ta in a c o n sid e ra b le number o f v o id s ,
r e s u l t i n g i n a c t u a l d e n s i t i e s from 0 .9 t o 1 .9 .
— 81—
l/T
x 10
Figure 22. Deposition Rate as a Function of Temperature
-82-
from 2»28 t o 2.43 g /c c in d ic a tin g t h a t some i n f i l t r a t i o n o f th e sub­
s t r a t e g r a p h i t e vs s u rfa c e ta k e s p la c e d u rin g d e p o s itio n o f th e pyro­
l y t i c c o a tin g .
A ir was drawn th ro u g h th e w a lls o f porous g r a p h ite tu b e s u sin g th e
a p p a ra tu s shown in F ig u re 9»
An uncoated N a tio n a l AGKSP tu b e , 14 mm
lo n g , 6 .2 mm o . d . and 4 .7 mm i . d . w i l l p a ss about 1400 cc/m in u te o f
a i r w ith a p re s s u re d i f f e r e n t i a l o f 30 cm o f m ercury a c r o s s it®
The
a i r flo w ( i . e . , th e p o r o s ity o f th e g r a p h ite ) o f such a tu b e i s r e ­
duced t o e s s e n t i a l l y z ero a f t e r a f o r t y m inute p l a t i n g p e r io d .
A com parison o f carbon rod a to m iz e r tu b e s o f th e s e dim ensions un­
d e r c o n d itio n s o f a c c e le r a te d o x id a tio n gave ev id en ce o f th e s u p e r io r ity
o f tu b e s, p la te d w ith p y r o ly tic carbon t o th o s e t h a t a r e n o t .
a re g iv e n i n T able X I.
The d a ta
Two tu b e s were made? th e f i r s t was d r i l l e d w ith
a #13 d r i l l and th e second w ith a #12 d r i l l (T h is r e s u l t s in a 0.1 3 mm
l a r g e r d ia m e te r h o le th a n th e f i r s t d o e s .) .
When th e second tu b e was
p la te d f o r one h a l f h o u r, i t s mass and i n t e r n a l d ia m e te r matched th e un­
c o ate d t u b e vs q u ite c lo s e ly .*
The tu b e s were a l t e r n a t i v e l y p la ce d be­
tw een th e ro d s o f th e CRA and h e a te d t o a p p ro x im a te ly 3000 0C f o r fo u r
seconds each tim e f o r s e v e r a l t r i a l s .
The amount o f Ng flu s h in g gas
was red u ced in s te p s from 20 t o 0 fo o t^ /h o u r a s th e t e s t p ro ceed ed .
* I t i s im p o rta n t t o m atch th e s iz e and mass o f carbon ro d a to m iz er tu b e s
q u ite c lo s e ly t o a c h ie v e s im ila r r e s u l t s w ith d i f f e r e n t tu b e s . T h is i s
because th e a n a l y t i c a l s ig n a l depends s tr o n g ly on th e r a t e o f atom iza­
t i o n , hen ce, upon th e e l e c t r i c a l r e s i s t a n c e and h e a t c a p a c ity o f th e
tu b e .
"
83
"
TABLE XI
COMPARISON OF COATED AND UNCOATED CRA TUBES
no.
N2
9
of CVclesj' flow (cfh;
Tube
coated
initial
coated
2
5
mass
A. A?
flow (cc/min)^
copper
O
50
0.059
1.2
50
0.065
O
1300
5
3=2
1400
0.048
5
3
3 .6
75
0.061
uncoated
■5
3
7=8
. 1500
0.031
coated
3
O
16.2
250
. 0.054
uncoated
3
O
30.0
1900
0.029
uncoated
initial
uncoated
2
coated
=OESOMt*
.
0.050
I0
A ll h e a tin g c y c le s were t o a p p ro x im a te ly 3000 0C f o r 4 seconds
(4100 w a tts a to m iz a tio n pow er)«,
2,
The u s u a l f lu s h in g gas flow i s 20 cfh*
3,
C um ulative mass l o s s from i n i t i a l weighing®
4,
A measure o f tu b e p o r o s ity ; th e l a r g e r th e flo w , th e more p o r­
ous th e tu b e 0
5„
324=7 run l i n e , 5 x 10” 10 g Cu in 5 u l aqueous, s o lu tio n , 4100
w a tts a to m iz a tio n power, 20 c fh f lu s h in g r a t e e
— 84"
A fte r s e v e r a l h e a tin g c y c le s , th e p o r o s ity (a s measured by th e a i r
flo w s th ro u g h th e w a lls o f th e tu b e s w ith a p re s s u re d i f f e r e n t i a l o f
25 cm Hg), th e lo s s i n mass due t o o x id a tio n , and th e atom ic absorp­
t i o n o f 5 x lO” -*-® g o f copper were m easured e
The p la te d tu b e o x id iz e d
o n ly one h a l f a s f a s t and gave h ig h e r and more re p ro d u c ib le atom ic ab­
sorbance v a lu e s th ro u g h o u t th e t e s t e
S im ila r t e s t s were perform ed com paring co ated and uncoated CRA
tu b e s f o r th e d e te rm in a tio n s o f Be, Co, Mn, and Pb w ith th e carbon ro d
a to m iz e r.
I n a l l c a s e s th e co ated tu b e s gave b o th more s e n s itiv e and
more re p ro d u c ib le a n a l y t i c a l r e s u l t s .
C oating th e h e a te r tu b e s o f a
W oodriff fu rn a c e a to m iz e r improved th e s e n s i t i v i t y f o r copper alm ost
tw o -f o ld .
These h e a te r tu b e s were d r i l l e d fro m ' R in g s d o rff ty p e R W
105 s p e c tro g ra p h ic g r a p h ite and were t e s t e d b e fo re and a f t e r c o a tin g
f o r an hour in th e p l a t i n g a p p a r a tu s .
A nother a p p lic a tio n o f th e te c h n iq u e i s in jo in in g p ie c e s o f
g r a p h ite to g e th e r .
I f th e item s t o be bonded a re p la c e d in in tim a te
c o n ta c t, th e y w i l l be q u ite s e c u re ly w elded a f t e r ab o u t an h o u r’ s
tre a tm e n t i n th e tu b e fu r n a c e .
The th re a d s o f g r a p h ite screw s and
o th e r components o f th e h ig h te m p e ra tu re a to m iz e rs used in t h i s la b o r­
a to r y a r e s tre n g th e n e d and t h e i r u s e f u l l i f e extended by c o a tin g them .
Some f r i t t e d carbon f i l t e r c r u c ib le s were made u s in g t h i s p ro c e s s .
G ra p h ite powder from 80 t o 150 mesh was w e tte d w ith a two p e rc e n t s o lu ­
t i o n o f Duco cement i n benzene and packed in to a 2 - 3 m illim e te r
-8 5 -
th ic k la y e r a t one end o f a s h o r t g r a p h ite tu b e (F ig u re 2 3 ).
The r e ­
s u l t i n g assem bly was d r ie d f o r a few m in u tes and th e n i n s e r te d in to th e
tu b e fu rn a c e f o r f i f t e e n m in u te s .
D e p o sitio n o f p y r o l y t i c carbon i n th e
c lo s e ly packed f r i t s e a le d th e p a r t i c l e s to g e th e r and t o th e g ra p h ite
c y lin d e r .
The r e s u l t i n g f i l t e r c r u c ib le s a re b o th p h y s ic a lly s tro n g and
h ig h ly r e s i s t a n t t o chem ical a t t a c k .
They f i l t e r a t a h ig h r a t e (60
m l/m inute/ cm2 f i l t e r a r e a ) and w i l l q u a n t i t a t i v e l y f i l t e r f in e BaSO^
p re c ip ita te s .
They sh o u ld prove u s e f u l i n th e f i l t r a t i o n o f s o lu tio n s
which a re h ig h ly c o rro s iv e t o th e u s u a l f r i t t e d g la s s o r p o r c e la in
c r u c ib le s .
The f in e n e s s o f th e f r i t can be e a s i l y c o n tr o lle d by u s in g
carbon powders o f d i f f e r e n t s i z e s .
Some p re lim in a ry ex p erim en ts w ere perform ed u s in g a f r i t t e d bottom
carbon ro d a to m iz e r cup ( i n l i e u o f th e CRA tu b e used f o r a i r p a r tic u ­
l a t e a n a ly s is ) f o r th e d i r e c t a n a ly s is o f suspended m a tte r in n a tu r a l '
w a te r s .
The f i l t r a t i o n a p p a ra tu s i s d e p ic te d i n F ig u re 2 4 .
Tygon
tu b in g s u p p o rts th e CRA cup and s e a l s th e s id e s from vacuum o r w ater
le a k s .
A measured q u a n tity o f pond w a te r i s poured i n t o th e fu n n e l on
to p and drawn th ro u g h th e f r i t t e d cu p .
Then th e cup i s p la c e d betw een
th e ro d s on th e CRA and th e c o n te n ts f i r s t d r ie d 9 th e n a sh e d , and.
f i n a l l y a to m iz e d .
A p o r tio n o r a l l o f th e f i l t r a t e can be caught in a
t e s t tu b e suspended in th e s u c tio n f l a s k .
A few ex p erim en ts were perform ed a tte m p tin g t o r e l a t e th e r a t i o
o f d is s o lv e d to suspended le a d in th e w a te r i n th e f i s h pond a d ja c e n t
)
-8 6 -
g la ss rod tamper
graphite cylinder
sh eet of
aluminum foil
carbon granules
Figure 23. Filter Crucible Construction
- 87~
A.A. light path
rods of the
CRA
fritted - bottom
CRA cup
Tygon s*
tubing
suction flask
filtrate
Figure 24. Direct solution particulate analysis
88-
t o th e m usic b u ild in g a t MSU.
A p lo t o f volume f i l t e r e d v e rs u s t o t a l
le a d r e ta in e d by th e cup i s ro u g h ly a s t r a i g h t I i n e 0
However, i t was
soon a p p a re n t t h a t th e f r i t t e d carbon c a p tu re s io n s from s o lu tio n a s
w e ll a s th o s e i n p a r t i c u l a t e m a tte r o
T he.cup ab so rb ed ap p ro x im ately
two p e rc e n t o f th e le a d in two m i l l i l i t e r s o f 2»0 x 10"? g/m l Pb s o l u - t i o n which was f i l t e r e d e
In a n o th e r experim ent w ith a more d i l u t e
le a d s o lu tio n (10 ml o f 8 x 10“ 9 g /m l Pb) th e cup a b so rb ed a p p ro x im ately
5% o f th e lead®
T h is was n o t e n t i r e l y u n ex p ected , a s some ex perim ents
in a n o th e r s tu d y t e s t i n g d i f f e r e n t a b s o rb e rs in c lu d in g g r a p h ite f o r
s o i l s o lu tio n a n a ly s is in d ic a te d t h a t alm o st e v e ry th in g a c t s a s a con­
c e n t r a t o r o f io n s from e x tre m ely d i l u t e s o lu tio n s *
A ttem pts were made
to p r e - s a t u r a t e s o r p tio n s i t e s in th e f r i t t e d cup w ith io n s such as
Ba
and La
b e fo re p a s s in g le a d s o lu tio n s th ro u g h th e cup®
These
io n s were i n e f f e c t i v e f o r t h i s purpose ®
For th e s e re a s o n s I f e e l t h a t a s im ila r a p p lic a tio n proposed by
Wang (77) w i l l be u n s u c c e s s fu l f o r s o lu tio n /s u s p e n d e d m a tte r d if f e r e n ­
tia tio n ®
However, t h i s approach sh o u ld prove t o be u s e f u l on a semi­
m icro l e v e l i n which th e q u a n t i t i e s o f m a te r ia ls a n aly z e d a re a t th e
m icrogram r a t h e r th a n th e nano and p ic o gram le v e l s u s u a lly measured
w ith fla m e le s s atom ic absorption®
At th e s e r e l a t i v e l y h ig h c o n ce n tra ­
t i o n l e v e l s th e amount o f le a d ab so rb ed by g ra p h ite i s i n s i g n i f i c a n t
compared t o th e q u a n tity analyzed®
These d i r e c t f i l t r a t i o n te c h n iq u e s
sh o u ld a ls o prove u s e f u l f o r th e d e te rm in a tio n o f io n s w hich can be
-8 9 -
quant i t a t i v e l y c o p r e c ip ita te d w ith a s u ita b le c a r r i e r from r e l a t i v e l y
la r g e amounts o f s o lu tio n *
C onclusions
The p y r o ly tic carbon d e p o s itio n p ro c e ss d e s c rib e d i s c e r t a i n l y n o t
a t i t s peak o f p o t e n t i a l developm ent* how ever, i t s e rv e s th e purpose
f o r w hich i t was in te n d e d a d m ira b ly .
I t allo w s an e x p e rim e n te r t o s ig ­
n i f i c a n t l y improve h i s s p e c tro s c o p ic a p p a ra tu s q u ic k ly and a t low c o s t .
What i s more im p o rta n t, i t a llo w s a d eg ree o f freedom i n f a b r ic a tin g
new equipm ent (su ch a s th e f r i t t e d - b o t t o m carbon c r u c ib le s ) which i s
n o t com m ercially a v a i l a b l e .
The p o t e n t i a l u s e d .in f i e l d s o f ch em istry
o th e r th a n s p e c tro sc o p y a re m a n ifo ld .
porous g r a p h ite e le c tr o d e s .
E le c tro c h e m is ts o f te n use non-
P y r o ly tic g ra p h ite r e a c tio n v e s s e ls may
prove u s e f u l f o r s y n th e s is o r a n a l y s i s .
Much o f t h i s work has been a c c e p te d f o r p u b lic a tio n i n A pplied
S p e c tro sc o p y .
APPENDIX
APPENDIX
A good estimate of the theoretical sensitivity of the CRA for mer­
cury if all of the mercury atoms could be atomized into the light path
before any loss through diffusion occurs can be made with standard cal­
culations.
The experimental evidence (p.24 , this thesis) indicates
that the mercury is volatilized from the plated graphite in the temper­
ature range of 200 - 300 °C.
At these temperatures and at atmospheric
pressure of nitrogen the width of the absorption line is determined
primarily by Lorentz broadening.
chell and Zemansky
(eq. I)
vT = 2 £ x
K
The following equation is from Mit­
:
N 2 RTfl + I
.
. [M1
M 2J
cr L - Lorentz broadening collision cross section of N2 gas
molecules with Hg atoms
N = Number of N 2 molecules/cc in the absorption cell
M^ + Mg - molecular wts of Hg and N2 respectively
putting in Mitchell & ZemanskytS value of
for nitrogen - Hg and
573 bK for Ts
V t = 2(64.8
x 10-16)(9.740 x
103) (6.40 x 10%)
(5.73 x IO2 )
(IO1^) •
2 (8 .3 1 x IO7 ) 573 a
+ l j
[201
28J
Vl = 4.64 x IO^ sec
Atomic absorption follows an exponential law for the intensity I of
transmitted light against absorbing length I:
(eq. 2)
I - I0e“Kvl
When the absorption line profile of the Hg atoms in the CRA tube is
-9 2 much wider than that of the emission profile of the hollow cathode
lamp (as is the case in our technique) it is permissible to use the
absorption coefficient at the center of the absorption line K q ^ in­
stead of Kv in equation 2«
gives an equation for Kq1j on page 12:
L Jvov
(e q . 3)
K0L - 2g2 + Nf
me
vL
Substituting into this equation the number of atoms/cm? (N) re­
sulting when 2 x 10""® g of mercury is atomized in a GRA tube (inner
diameter 4*6 mm and length 15 mm) and literature values for e (charge
of an electron), c (speed of light), m (mass of an electron), f (the
oscillator strength of the 2537 A Hg line), and our calculated value of
L
vL, we obtain a Kq
as follows:
K01, = 2(4.8 x 10-10)2
+ (2.4 x 101^)(3.Q x 10“ 2)
(9.1 x I(T28) O x IO1 0 )
4.64 % IO9
K0L = 2.6 x IO1
T
Substituting this value of Kq into equation 2 using a 1 .5 cm path Ien
length, we expect to see:
I
=
i 0 e ” 2 6 ( l.,5 )
I -= I0l(f(e434)(26)(le5)
Abs = (.434)(26)(1.5) = 17 ■
The absorbance actually observed when 2 x ICf*8 g of mercury is at­
omized in the rod is about 0.4.
This indicated that at no time is more
-93-
than a small fraction (l7 ) of the total mercury atoms in the optical
beam.
The results of similar calculations based on the dimensions and
instrumental conditions in the Woodriff furnace agree with the ac­
tually observed absorbances measured to within a factor, of two or
three.
This indicates the greater atomization efficiency of the fur­
nace as compared to the carbon rod atomizer.
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-9 7 -
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tio n .
-3 P
‘7 T
[i- >,<
v 7
S il5
c o p .2
DATE
S ie m e r, D a rry l Dueune
Development o f te c h ­
n iq u es f o r non-flam e
s p e c tro s c o p ic d e term in a ­
t i o n o f t r a c e m e ta ls .
ISSUED TO
/ k/
jUK3 0
M - I l # # # etA.VA.es
/
WAS %
I-
H V O \k^ %
-
vf
^
Cf