A background correction technique for double beam spectrophotometers and the analysis of microtrace
concentrations of silver using furnace atomic absorption spectroscopy
by Bruce Robert Culver
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in Chemistry
Montana State University
© Copyright by Bruce Robert Culver (1971)
Abstract:
Two aspects of furnace atomic absorption spectroscopy were studied.
The first involved the development of a background correction technique using plane polarized light.
Two perpendicularly polarized light beams were compared to one another — a continuous background
source and the hollow cathode radiation. Solid and liquid samples were run. The solid samples were
inserted into the furnace using a graphite cup and the liquid samples were ultrasonically nebulized into
the furnace. Calibration curves for Co, Cr, and Ag were run. Blank cups were inserted using: Al, Co,
Cr, Cu, Dy, Mg, and Mn hollow cathodes.
No blank reading was observed. An optical system employing a Glan-Taylor calcite polarizer was
used. A Beckman D. B. was used to compare the two polarized beams. Sensitivities ranged from about
10-11 g for solid samples and 10-10 g/ml for liquid samples.
c.
The second feature covered was the development of an analytical method for analyzing for microtrace
concentrations of Ag in snow, hail or water. The method involved preconcentratibn of the Ag by
solvent extraction and its subsequent analysis by furnace atomic absorption (FAA). The extractant was
a ditbizone-CCl4. solution. Two hundred twenty five snow and four hail samples were analyzed by this
method. A comparison between flame boat AA, neutron activation analysis and furnace AA was
presented. The results obtained by the boat technique were quite different than those obtained by the
other two methods. Where neutron activation analysis is +30% reproducible, FAA's reproducibility is
+5%. The concentration ranges involved were on the order of 5x10-11 gm/ ml. The sensitivity for the
FAA method was 5x10-13gm/ml.
STATEMENT OF PERMISSION TO COPY
In p re sen tin g th is th e s is in p a rtia l fu lfillm en t of the re q u ire m e n ts fo r an
advanced d eg ree at M ontana State U n iv ersity , I a g ree th a t the L ib ra ry sh all
m ake it fre e ly available fo r inspectio n .
I fu r th e r ag ree th a t p e rm is sio n fo r
extensive copying of th is th e s is fo r sch o la rly p u rp o ses m ay be g ran ted by my
m a jo r p ro fe s s o r, o r, in h is absen ce, by the D ire c to r of L ib ra r ie s .
It is u n d e r­
stood th a t any copying o r publication of th is th e s is fo r fin an cial gain sh all not be
allow ed w ithout my w ritte n p e rm issio n .
Signature
Date
%
f t S t Lf c*-
A BACKGROUND CORRECTION TECHNIQUE FOR
DOUBLE BEAM SPECTROPHOTOMETERS '
and
THE ANALYSIS OF MICROTRACE CONCENTRATIONS OF
SILVER USING FURNACE ATOMIC ABSORPTION SPECTROSCOPY
by
i/
BRUCE ROBERT CULVER
A th e s is subm itted to th e G raduate F aculty in p a rtia l
fulfillm ent of the re q u ire m e n ts fo r the deg ree
of
MASTER OF SCIENCE
,»
• C h em istry
A pproved:
W a d / M ajor D epartm ent
C h m rm a q /E x a m in in g C om m ittee
G raduate D ean
MONTANA STATE UNIVERSITY
B ozem an, M ontana
D ecem ber, 1971
- iii -
ACKNOWLEDGMENTS
I would like to thank M ontana State U n iv ersity and the N ational Science
Foundation fo r th e ir fin an cial a ss ista n c e during th e la s t two y e a r s .
I am. deeply indebted to D r. Ray W oodriff fo r his advice and in sp iratio n .
The help and advice of D r. A rlin Super is g re a tly a p p reciated .
And la s t, but f i r s t , I would like to thank my w ife, Lynn, w ithout whose
sup p o rt th is th e s is would not have been w ritten .
/
TABLE
OF
CONTENTS
page
LIST OF TABLES
v
LIST OF FIGURES
vi
ABSTRACT
I.
II.
IR.
INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . .
STATEMENT OF PROBLEM .
V.
VI.
VR
VIII.
IX.
vii
I
..............................3
EXPERIM ENTAL (Background C o rrectio n ) ...................... ...
A.
B.
C.
D.
E.
IV.
.
The F u rn ace ........................................................................................ .
The O ptical System ........................................
The D etection System
Sam ple P r e p a r a t i o n ....................................................; ... ..................
Sam ple N ebulization . . . . . . . . . . . . . . . . . . . . . .
7
7
10
12
13
14
RESULTS AND DISCUSSION (Background C o rrectio n ) . . . . . .
16
EXPERIM ENTAL (Silver A n a ly s is ) ..................
22
A.
B.
C.
D.
P re p a ra tio n of the^ G lassw are and R eagents . . . . . . . . .
The F u rn ac e .......................................................
The P r o c e d u re ...............................................
The D etection S y s te m ..................
22
23
23
26
RESULTS AND DISCUSSION (Silver A nalysis) . . . . . . . . . .
28
A.
30
Some R e su lts. . . . . . . . . . . . . . . . . . . . . . . . . .
CONCLUSIONS
37
NEED FOR FURTHER WORK
38
LITERATURE CITED
39
LIST OF TABLES
page
TABLE I.
S ensitivity D ata fo r El e me n t s . . . . . . . . . . . . . . . .
20
TABLE II.
C om parison of FAA w ith o th e r A nalytical M ethods . . . .
34
TABLE III.
C om parison of Some Sam ples Analyzed on D ifferent
D ays. . ...................... ........................................... ...
35
S ilv er in Hailt- Sam ples. . . . . . . . . . . . . . . . . . . . .
36
TABLE IV.
LIST
OF
FIGURES
page
F ig u re
I.
F ig u re
F ig u re
The F u rn ac e (a second g e n eratio n m o d e l)
............... ... „
2„ C opper Cooling Coil and E lectro d e Chuck
3.
8
9
' The O ptical S y ste m .
. 11
F ig u re
4. D ire c t Im pingem ent U ltraso n ic N ebulizer . . . . . . . . . .
15
F ig u re
5. T ypical R e c o rd e r T ra c e s . ................................................
17
F ig u re
6. C alib ra tio n C urves fo r Co, C r, and Ag . . . . . . . . . .
F ig u re
7. The F u rn a c e (a th ird g e n eratio n m odel) . . . . . . . . . . . .
24
F ig u re
8. A P ic tu re of the In stru m e n ta tio n . . . . . . . . . . . . . . .
27
F ig u re
9. T e m p e ra tu re C alib ratio n C urve fo r S ilv e r...........................
31
F ig u re
10. S ilv er S tandard C u rv e s . . „ . . .........................................
.
18
32
ABSTRACT
Two a sp e c ts of furnace atom ic ab so rp tio n sp ectro sco p y w ere studied.
The f ir s t involved the developm ent of a background c o rre c tio n technique using
plane p o la riz e d light. Two p e rp e n d icu la rly p o la riz ed light b eam s w ere com pared
to one another — a continuous background so u rce and the hollow cathode r a d i­
ation. Solid and liquid sam p les w ere ru n . The solid sam p les w e re in s e rte d into
th e fu rn ace using a g rap h ite cup and the liquid sam p les w ere u ltraso n ic ally nebu­
lized into the fu rn ace. C alib ratio n c u rv e s fo r Co, C r, and Ag w e re run. Blank
cups w e re 'in s e r te d using: A l, Co, C r, Cu, Dy, Mg, and Mn hollow cathodes.
No blanlc read in g w as o b serv ed . An optical sy ste m em ploying a G lan -T ay lo r
c a lc ite p o la riz e r w as used. A Beclcman D. B. w as u sed to co m p are th e two
p o la riz e d b eam s. S en sitiv ities ranged fro m about 10“ "^ g fo r solid sam p les
and IO-10 g /m l fo r liquid sam p les.
c.
The second fe a tu re covered w as the developm ent of an an aly tical m ethod
fo r analyzing fo r m ic ro tra c e co n cen tratio n s of Ag in snow, h a il o r w a ter. The
m ethod involved p re c o n ce n tra tib n of the Ag by solvent e x tra c tio n and its su b se ­
quent a n aly sis by fu rn ace atom ic ab so rp tio n (FAA). The e x tra c ta n t w as a
ditbizone-CCLj. solution. Two hundred tw enty five snow and fo u r h ail sam p les
w e re analyzed by th is m ethod. A co m p ariso n betw een flam e boat AA, neutron
activ atio n a n aly sis and furnace AA w as p re se n te d . The re s u lts obtained by the
boat technique w ere quite differen t th an th o se obtained by th e o th e r two m ethods.
W here neu tro n activation a n aly sis is +30% re p ro d u c ib le , F A A 's rep ro d u cib ility
is +5%. The co n cen tratio n ra n g e s involved w ere on the o rd e r of 5x10""^ g m /
m l. The se n sitiv ity fo r th e FAA m ethod w as S x lO - -1-3 g m /m l.
INTRODUCTION
Our environm ent and the quality th e re o f is the co n cern of e v ery m an,
w om an, and child on th is planet.
W ith the developm ent and ap plication of r e l i ­
able and se n sitiv e an aly tical m ethods, c h e m ists have been able to m onitor tra c e
elem en t co n centrations and th e ir influence on the inhabitants of the e a rth .
F u r­
nace atom ic ab so rp tio n sp ectro sco p y (FAA) is p erh ap s one of the m ost re v o lu ­
tio n a ry an aly tical techniques at the p re s e n t tim e.
It has th e se n sitiv ity cap a­
b ility to com pete w ith neutron activation a n aly sis, w hile at th e sam e tim e being
a s rep ro d u cib le as flam e atom ic ab so rp tio n , th e se two fe a tu re s coupled w ith the
fact th at so lid , liquid, o r gas sam p les can be analyzed m ake FAA a potentially
pow erful tool in the field s of pollution co n tro l, w eath er m odification, m e d icin e,
and g e o ch e m istry as w ell as c h em istry .
W ithin the p a st two y e a r s , s e v e ra l la rg e in stru m e n t com panies have
m ade available non-flam e atom ic ab so rp tio n attach m en ts fo r th e ir co m m ercial
atom ic ab sorption sp ec tro p h o to m ete rs.
fe re n t th a n the fu rn ac e.
In g e n e ra l, th e se sy ste m a re quite d if­
M ost co m m e rcial m odels fla sh ev ap o rate the sam ple
by heating the e n tire sy ste m each tim e a sam p le is introduced.
The fu rn ace,
on the o th e r hand, re m a in s at a constant te m p e ra tu re as sam p les a re in se rte d
into it fo r atom ization.
The c o m m ercial non-flam e units a re about two o rd e rs
of m agnitude m o re sen sitiv e than flam e AA, w hile fu rn ac es a re about four
o rd e rs of m agnitude m o re sen sitiv e than flam e AA.
- 2 -
The m o re p ro m in en t w o rk e rs in the field of non-flam e AA a re : L'vov in
R u ssia ,
tr y ,
2 ’ 3) M assm an in W est G erm any, ^
^ Am os in A u stra lia , ^
Kahn and M anning in th is coun­
and W oodriff also in th is country.
The sy stem
developed by L 'vov is undisputedly the m o st se n sitiv e , but is n e ith e r p ra c tic a l
n o r convenient as f a r as the routin e a n aly sis of sam p les is concerned.
T his th e s is d e als p rim a rily w ith two a sp e c ts of FAA, the f ir s t being the
developm ent of a background c o rre c tio n technique which can be applied to any
double beam atom ic ab so rp tio n sy stem .
The second asp ect c o v ered is the ap p li­
cation of FAA to the a n aly sis of m e ta ls in r e a l sam p les, nam ely, s ilv e r in snow.
T his is c u rre n tly the b e st m ethod fo r analyzing fo r m ic ro tra c e co n cen tratio n s
of s ilv e r in e ith e r snow o r w ater.
■■ -v •-, •
STATEMENT OF THE PROBLEM
B ackground C o rre c tio n
In atom ic ab so rp tio n sp ectro p h o to m etry , background ab so rp tio n o ccu rs
fro m solvent m a trix e ffe c ts, fro m light s c a tte rin g in th e optical pathw ay, o r
anything e lse Other than th e sam p le w hich a b so rb s light fro m th e hollow cathode
so u rc e .
T h ere a re v a rio u s m ethods fo r elim in atin g the re la tiv e effects of b ack ­
ground abso rp tio n .
One of th e se techniques is to com pare the hollow cathode
(8 )
ra d ia tio n w ith som e continuous so u rc e such as a hydrogen o r d eu teriu m la m p ' .
T his is usually done in the ac m ode, th a t i s , th e pho to m u ltip lier alte rn ately d e­
te c ts the m onochrom atic ra d ia tio n and the continuous ra d ia tio n .
The output is
the net differen ce betw een th e tw o .. A second technique involves th e sam e p rin ­
ciple except th a t the photo m u ltip lier c o m p ares the line e m itte d fro m two d iffe r­
ent hollow cathodes o r elem en ts ^ \
A m o re re c e n t m ethod developed by R ain s,
involves a v ib ratin g s e c to r placed in sid e th e e n tra n ce s l i t ^ \
cally co m p ares the m onochrom atic ra d ia tio n on and off th e lin e.
The s e c to r opti­
This technique
is sim ple and holds g re a t p ro m ise .
It w as thought th a t a sy ste m using plane p o la riz ed lig h t could be u sed as
(11)
a background c o rre c tio n tech n iq u e' . If the re fe re n c e ra d ia tio n is p o la riz ed
p e rp e n d icu la r to the sam ple rad iatio n , th e two could be co m p ared e ith e r in th e
ac o r dc m ode.
s o u rc e s .
In the ac m ode, th e output is th e net d ifferen ce betw een the two
( 12 )
In the dc mode both so u rc e s can be o b serv ed in d ep en d en tly '
. The
- 4 -
sy ste m d isc u sse d involves the use of the ac m ode.
The technique w ill w ork
quite w ell if the two p o la riz e d beam s can be effectively se p a ra te d .
A nalysis of Silver
Seeding clouds w ith s ilv e r iodide c ry s ta ls is one of th e o ld est and m ost
w idely u sed ty p es of w e ath e r m odification.
In th e o ry , the s ilv e r iodide c ry s ta l
is quite s im ila r in s tru c tu re to a snow c ry s ta l.
It should th e re fo re serv e as a
nucleating agent fo r a snow c ry s ta l in a su p e rsa tu ra te d cloud.
Many m illio n s of
d o lla rs and m an h o u rs have been devoted to the study of s ilv e r iodide and its
e ffe ct on cloud ph y sics and p re c ip ita tio n .
U nder la b o ra to ry conditions in a cold
ch am b e r s e t up to m odel a s u p e rsa tu ra te d cloud, seeding w ith s ilv e r iodide is
quite e ffectiv e.
The technique involves counting snow flak es to d eterm in e if
seeding o c c u rre d .
T his m ethod when used in the field , although it is quite c u m -
(13)
ber som e and tim e consum ing, has had som e deg ree of s u c c e s s '
. A nother
m o re p ra c tic a l m ethod is to m e a su re th e s ilv e r co n cen tratio n in seeded and
unseeded snow and m ake som e s o rt of c o rre la tio n betw een in c re a s e d snow pack
and in c re a s e d s ilv e r concentratio n .
D uring the p a st five y e a r s th e re have been
two accepted techniques fo r m e asu rin g Ag in snow.
accepted is n eu tro n activation a n aly sis
(14)
The f i r s t and m o st widely
. T his technique re q u ire s la rg e
sam p les (I to 10 lite r s of m elted snow), a so u rc e of n eutron flux, m uch money
(ca $50 p e r sam ple), and has poor p re c isio n in the reg io n of the Ag co n cen tration
—
•5 ~
in snow.
A nother even le s s p re c is e m ethod has com e into e x isten ce re c en tly .
T his m ethod, how ever, is cheap.
It is a flam e atom ic ab so rp tio n technique
(15)
involving a m ic ro -sa m p lin g b o a t^ . The claim ed d etectio n lim it fo r th is te c h ­
nique ra n g e s fro m 10“ ^® g m /m l to 5 x l 0 ~ ^ g m /m l of s ilv e r.
T hese re p o rte d
lim its in c o rp o ra te a p re c o n c e n tra tio n step and a IOX re c o r d e r sc a le expansion.
O rdinary flam e AA has been used fo r the s ilv e r an aly sis in seed ed snow, but
th e p ro c e d u re lack s r e lia b ility ^ ^ ..
The v alu es re p o rte d by th e s e m ethods a re ,
to say the le a s t, quite questionable.
B ackground c o n cen tratio n s fo r s ilv e r in snow ran g e fro m 4 x IO- H g m / m l to 2 x IO- *2 g m /m l.. Seeded sam p les contain fro m 6 x 1 0 " ^ g m /m l to
6 x l 0 - 10 g m /m l of s ilv e r.
The se n sitiv ity of FAA fo r s ilv e r is on the o rd e r of 5 x 10""-^ g m /m l w ith
a 10X p re c o n c e n tra tio n ste p and no r e c o r d e r sc a le expansion.
The re p ro d u c i­
b ility of the m ethod in the S x lO - H g m /m l ran g e is +5% as co m p ared to +30%
w ith neutron activation a n aly sis.
tr a c e s ilv e r a n a l y s i s ^ \
FAA should be an ex cellen t m ethod fo r m ic ro -
T h e re a re , how ever, m any p ro b le m s involved in
handling such sm a ll co n cen tratio n s of s ilv e r.
U n treated aqueous s ilv e r so lu ­
tio n s a re u n stab le, e sp e c ia lly if the s ilv e r co n cen tratio n is below 10- 8 g m /m l.
S ilv er is ad so rb ed onto th e su rfa ce of the co n tain er Wall, th e re fo re the solution
m u st be.-stabilized.
C ontam ination is another p ro b lem .
M ost c o n tain ers,
- 6 -
so lv en ts, and re a g e n ts a re contam inated w ith s ilv e r at th is co ncentration
lev el.
The m ethod developed, and the p ro c e d u re used fo r handling the
sam p les w ill be d iscu ssed .
'•
'
•. , - I
EXPERIMENTAL
Background C o rre c tio n
The ap p aratu s used fo r th is study can be sep a ra te d into th re e c a te g o rie s:
the fu rn a c e , the optical sy ste m , and the detection sy stem .
The F u rn ac e ,
The fu rn ace design illu s tra te d in fig u re I depicts a second g en eratio n
fu rn ac e.
(VI 18)
T his furnace is som ew hat d ifferen t th an th at u sed p re v io u sly v
\
The h e a te r tubes a re 15.2 cm long, 10 m m o. d . , and 7 m m i .d .
The heat sink
X
in the c e n te r holds the h e a te r tu b es, the sh ield tube, and a lso a c ts as the s a m ­
ple in le t.
At the o u ter en d s, th e h e a te r tu b es a re held by co p p er chucks.
The
chuck is attach ed to a s p ira l copper tube (figure 2) w hich a c ts a s an end cooling
p la te .
The s p ira l tubing is flexible to allow fo r expansion of the h e a te r tubes.
The fu rn ace is flushed w ith argon gas to p rev en t the oxidation of th e g rap h ite.
The argon e n te rs at the sam ple p o rt, p a s s e s down the side tu b e, and out the
h e a te r tu b e s.
The hot gas e sc a p e s fro m th e fu rn ace through the copper cooling
co ils and is m on ito red w ith flow m e te rs .
Solid, liquid, and g as sam p les can be introduced into the furnace fo r
a n aly sis.
Solids a re p laced on a g rap h ite cup, ashed if n e c e s s a ry , screw ed on­
to an 1/8 in. g ra p h ite ro d and in s e rte d th ro u g h the side tube.
Liquid sam p les
can e ith e r be ev ap o rated on a cup, o r nebulized d ire c tly into the fu rn ace. G ases
could be analyzed by introducing the gas in place of the arg o n at a constant
INSULATOR
R U B B ER
INSULATION
30 cm
GR A PH IT E
IN SU IA TIO N
20 cm
H EA TER
TU BE
SIUELD
TU BE
HEAT
SINK *
G LAN- T A Y LOR
PO LA R IZE R
SIDE
LENS _
HOLDER
TUBE
CHUCK
RING "
SA M PLE
TJA
STA IN LESS S T E E L
H I GR A PH IT E
JlA
steel
TTA SILICA
PO RT
INSULATOR
TJA C O P P E R
Q
RU BBER
F ig u re I: The F u rn ace ( a second g en eratio n m odel )
END
PL A T E
SPIRA L H EATER
TU RE CONTACT
- 9 -
SPIRAL
HEATER
TUBE
CONTACT
F ig u re 2: C opper cooling coil and e le c tro d e chuck
- 10 I
flow.
Liquid sam p les w ere analyzed fo r th is study usin g both techniques m en­
tioned above.
A ttached to the sam ple p o rt is a V ycor 18/9 socket u sed to aid sam ple
introduction.
The fu rn ace te m p e ra tu re w as m e a su re d w ith an optical p y ro ­
m e te r.
The O ptical System
The optical sy ste m (figure 3) c o n sists of a G lan -T ay lo r a ir spaced c a lc ite light p o la riz e r, two G lan-type p ris m p o la riz e rs p laced in th e in stru m en t
sam ple com partm ent and a q u a rtz collim ating len s.
Two lig h t so u rc e s a re
needed: a hollow cathode and a hydrogen lam p which is u sed as a continuous
background so u rc e.
The hollow cathode light is p o la riz e d by the G lan -T ay lo r p o la riz e r b e ­
fo re it p a s s e s through the fu rn ace.
The hydrogen lam p light e n te rs the p o la ri­
z e r through the side window at a 7° angle to th e n o rm al to the optical axis. Two
p o la riz e d beam s fro m the hydrogen lam p e m e rg e fro m the p o la riz e r.
One is
p o la riz e d p e rp e n d ic u la r to the hollow cathode light while the o th e r is an e x tra ­
o rd in a ry ra y and is p o la riz e d p a ra lle l to the light fro m the hollow cathode.
The
e x tra o rd in a ry ra y is rem oved by m e re ly positioning the p o la riz e r so th at only
the beam w hich is p o la riz e d p e rp e n d icu la r to the hollow cathode light p a sse s
through the fu rn ace.
The e x tra o rd in a ry ra y is abso rb ed into the furnace w all.
BECKMAN
DB
APERATURE
SLIT
■POLARIZERS
I
M
I-1
I
F ig u re 3: The O ptical System
- 12 -
The angle betw een the two hydrogen lam p b eam s is about 10°.
The e x tra o rd in ­
a ry ra y fro m the hollow cathode, w hich is tra n s m itte d , is p o la riz e d p a ra lle l to
the optical axis of the c alc ite and the o rd in a ry ra y fro m the hydrogen lam p is
p o la riz e d p e rp e n d ic u la r to the c a lc ite 's optical axis.
Both co llim ated beam s p ro ceed th ro u g h the furnace and co m e to focus on
the a p e rtu re placed ju s t insid e the e n tran ce to the B eckm an D. B. sp ectro p h o to ­
m e te r.
The D etection System
The m o n o ch ro m ato r and re a d -o u t fo r th is sy stem is a B eckm an D .B .
sp ec tro p h o to m ete r.
A D .B . is a double beam ra tio re c o rd in g in stru m e n t. A fter
the two p o la riz e d b eam s go th ro u g h th e fu rn ace and com e to focus on the a p e r­
tu re in the. D. B. they p ro c e ed to the in stru m e n t s lit, th en on th ro u g h the m ono­
c h ro m a to r.
A fter p a ssin g throug h the m o n o ch ro m ato r the beam com es to focus
I
on a v ib ra tin g m ir r o r w hich a lte rn a te ly re fle c ts the light th ro u g h one of the two
p o la riz e rs lo cated in the sam ple co m p artm en t.
One p o la riz e r tra n s m its only
th e background light and the o th er only th e hollow cathode light.
A fter p assin g
through the p o la riz e rs the light fa lls on the p h o to m u ltip lier and th e net a b so r­
bance is re c o rd e d .
A B eckm an m odel 93506 lin e a r and log p o te n tio m e tric 6
in. re c o r d e r w as u sed to re c o rd the r e s u lts .
- 13 -
Sam ple P re p a ra tio n
The two types of stan d a rd solutions used w ere so lid and liquid stan d a rd s.
Solid sta n d a rd s a re stan d a rd s th a t have been ev ap o rated on a g rap h ite cup, and
liquid stan d a rd s a re nebulized d ire c tly into the fu rn ace.
The solid stan d ard s
w ere p re p a re d fro m s a lts of the m e ta l to be in v estig ated .
m ade by diluting a IO"7 g m /m l solution of th e m etal.
The stan d ard s w ere
F ifty pl p o rtio n s of the
sta n d a rd s w ere pipetted into a g rap h ite cup and ev ap o rated to d ry n e ss.
The
cups (6x11 mm) w ere screw ed onto a 1/8 in. g rap h ite ro d and in s e rte d into the
fu rn ace fo r a n aly sis.
A fter the signal w as re c o rd e d , the cup w as cooled in the
V ycor e n tra n ce tube befo re being p laced back in a d e s s ic a to r w here th e cups
re m a in e d when not being used.
Liquid sta n d a rd s, which a re to be nebulized, a re aqueous o r dilute acid
solutions of a s a lt of the m e ta l to be in v estig ated .
The solutions w ere diluted
to the w orking co n cen tratio n rang e w ith d is tille d m ethanol.
In th is c ase , the
w orking ran g e w as on th e o rd e r of IO""7 - IO- ^ gm of m e ta l/m l of m ethanol.
In
solutions containing le s s than 10-8 gm A g /m l the Ag exhibited a tendency to
becom e ad sorbed on the w alls of th e b eak er if the solution w as le ft to set in the
b e ak e r fo r m o re than 15 m inutes.
Com plexing th e s ilv e r w ith EDTA seem ed
to slow down the ra te of th is adsorption.
- 14 -
Sample N ebulization
N ebulization of the sam ple solution is c a r rie d out u sin g an u ltraso n ic
n e b u liz er
^
(figure 4).
The solution is pum ped a c ro s s the silv e re d face
of a v ib ratin g p ie z o e le c tric c ry s ta l (1.3 MHz) at a ra te of 2.32 m l/m in.
nebulized vapor is then pushed through th e fu rn ace w ith arg o n g a s.
of v ap o r flowing into the fu rn ace is .465 m l/m in .
sam ple g ets into the fu rn ac e.
The
The am ount
Tliis in d ic a tes th a t 20% of the
The rem ain in g 80% of the sam p le is d iscard ed .
The siz e of the m ethanol d ro p le ts is on th e o rd e r of 1.0
(19
V arious coatings fo r the p ie z o e le c tric tra n s d u c e r have been Studiedv ’
20)
At the p re s e n t tim e a coating w hich is capable of w ithstanding freq u en cies
on th e o rd e r of 1-5 MHz and is also re s is ta n t to co n cen trated acids a n d /o r
b a se s h as not been developed.
The flow m e te rs attach ed to the cooling co ils on th e o u te r ends of the
fu rn ace indicated th a t the arg o n flow out of the fu rn ace w as about I lite r/m in .
G as flow into the n eb u lizer ch am b er w as on the o rd e r of 500 m l/m in .
/ s*AtP i£
/
s oi a r/o s
I/H E .
F ig u re 4: A D irect Im pingem ent U ltraso n ic N ebulizer
/Z.E
/H P O T
RESULTS AND DISCUSSION
B ackground C o rre c tio n
The optical sy ste m using plane p o la riz e d light proved to be very, advan­
tageous in reducing the effects of the background absorption.
T ypical re c o rd e r
read in g s fo r solid sam p les and liquid sam p les a re shown in fig u re 5 (a) and (b).
C alib ratio n c u rv e s fo r Ag, C r, and Co w ere obtained (figure 6).
The la c k of rep ro d u c ib ility of the blank, e sp ecially w ith solid sam p les,
/
h as been a so u rc e of e r r o r in try in g to d e term in e the absolute sen sitiv ity fo r
elem en ts using g rap h ite tube furn ace technique
8\
When cups a re in s e rte d in ­
to the fu rn ace and butt against the re ta in e r inside the heat sink, sm all flakes of
carb o n occasionally w ill fall thro u g h the light path and cause ab so rp tio n of som e
of the hollow cathode ra d ia tio n .
If any org an ic m a tte r is on o r in th e cup, it
w ill p y ro lize to fo rm fre e carb o n p a rtic le s w hich also cau se background a b so rp ­
tio n .
U sing th e p o la riz ed light optical sy ste m , an equal am ount of the continu­
ous background light is also ab so rb ed , balancing out th e hollow cathode a b so rp ­
tio n so th a t th e net ab so rp tio n is z e ro .
The optics m u st be aligned so that the
two co llim ated p o la riz e d beam s coincide throughout th e e n tire length of th e f u r ­
nace.
If th is is not the c a s e , unequal p o rtio n s of the p o la riz e d beam s w ill be
ab so rb ed , m aking th e technique le s s efficient.
Blank cups w ere in s e rte d into the fu rn ace using the following hollow
cathodes: Cu, Co, C r, Mn, Mg, Al, and Dy.
No net blank w as ob serv ed fo r
SOLID SAMPLES
LIQUID
SAMPLES
ONE MINUTE
ONE MINUTE
TYPICAL PEAK FOR
SAMPLES HAVING
LOW VAPOR
PRESSURE
TYPICAL PEAK FOR
SAMPLES HAVING
HIGH VAPOR
PRESSURE
L_-L_
TIME
F ig u re 5: Typical R e c o rd e r T ra c e s
TIME
ABSORBANCE
GRAMS
X
10
F ig u re 6: C alib ratio n c u rv es
C M / ML
X
10
- 19 -
any of th e se e lem en ts.
It should be em p h asized , how ever, th at because of the
r a th e r crude in stru m e n ta tio n 100% sca le d eflection was not alw ays obtainable.
Below 2400 A the c alc ite in the G lan -T ay lo r p o la riz e r began absorbing light and,
due to alignm ent d ifficu lties, above 4100
w alls in te rfe re d .
X blackbody ra d ia tio n fro m the furnace
U sing b e tte r in stru m e n ta tio n and re c o rd in g technique coupled
w ith im proved o p tic s, th e se p ro b lem s could be allev iated .
C alib ratio n cu rv es
fo r Co and C r using the cup technique a re p re se n te d in fig u re 6 (a).
N ebulizing liquid sam p les into the atom ization s o u rc e , w h eth er it be a
fla m e , p la sm a , o r fu rn ac e, is of g re a te r in te re s t to an aly tical ch em ists th an
introducing solid sam p les into the atom ization so u rc e.
The technique d e sc rib e d
looks v e ry p ro m isin g fo r ro u tin e a n aly sis of tr a c e elem en ts.
fo r Ag and C r w e re obtained (figure 6 (b)).
C alib ratio n c u rv e s
Once the sam ple solution is pumped
o v er the face of the p ie z o e le c tric c ry s ta l it re q u ire s approxim ately 3 seconds
to re a c h m axim um absorption.
A steady s ta te condition is th en reach ed .
It w as o bserved th a t the tim e constant of the sam ple decay cu rv es could
be d ire c tly re la te d to sam ple co n cen tratio n .
fa ll off exponentially and a re quite co n sisten t.
T his is b ecau se th e decay cu rv es
The decay cu rv e is dependent
upon: furnace te m p e ra tu re , the vapor p r e s s u r e of the e lem en t, and som ew hat
on g as flow ra te .
If the f i r s t and la s t of th e se p a ra m e te rs a re held constant, it
is re aso n ab le th a t a stan d a rd curve (concentration v s. tim e constant) could be
- 20 -
obtained.
At high c o n cen tratio n s of sam ple (95% scale d eflectio n +) a sa tu ra tio n
point is re a ch e d and a B e e r 's law plot begins to flatten out-m aking peak height a
le s s re lia b le m e a s u re of concen tratio n .
At th e se h ig h er co n cen tratio n s the tim e
constant could be a m o re p re c is e m e a s u re of co n cen tratio n .
c en tratio n s
F o r s m a lle r con­
how ever, the tim e constant is usually too sh o rt to get p re c ise
m e a su re m e n ts.
TABLE I:
Sensitivity D ata fo r E lem ents
A
Sample
P hase
F u rn ace
T e m p e ra tu re
(°C)
Co
2407.3
solid
2400
l . l x l O 'l O gm
Cr
3578.7
solid
2200
8 .0 x l0 " " H gm
Cr
3578.7
liquid
1850
3 .Ox 10-10 g m /m l
Ag
3280.7
liquid
1600
4 .5 x 1 0 " ^ ^ g m /m l
W avelengthE lem ent
Sensitivity
The s e n s itiv itie s of the c a lib ra tio n c u rv e s obtained a re lis te d in T able I.
C alculated absorbance re a d in g s c o rresp o n d in g to 1% ab so rp tio n d eterm in e the
s e n s itiv itie s fo r the e lem en ts te ste d .
The sy ste m d e sc rib e d can be applied to any double beam s p e c tro m e te r.
- 21 —
It should w ork quite w ell w ith flam e atom ic ab so rp tio n in s tru m e n ts .
F u r­
nace atom ic ab so rp tio n is m o re advantageous th an flam e atom ic absorption,
because it confines the sam ple in a sm a ll volume of lo n g er path length w ith
a nonturbulent in e rt a tm o sp h ere in w hich ab so rp tio n can take p lace.
W ith
im proved in stru m e n ta tio n tra c e elem en t a n aly sis down to IO- -^ g /m l fo r
som e elem en ts could be com m onplace.
I
EXPERIM ENTAL
Silver A nalysis
T his sectio n can be sep a ra te d into four m ain c a te g o rie s: p re p a ra tio n of
the g la ssw a re and re a g e n ts, the fu rn a c e , th e p ro c e d u re , and the d etectio n s y s ­
te m .
P re p a ra tio n of the G lassw are and R eagents
One s e t of P y re x g la ssw a re is kept sp ecifically fo r the a n aly sis of s ilv e r.
It c o n sists of: 6-400 m l b e a k e rs , 6-150 m l Teflon sto p p ered se p a ra to ry funnels,
1-100 m l g rad u ated cy lin d e r, 1-50 m l g rad u ated cy lin d er, 1-10 m l graduated
cy lin d e r, and 2-500X p ip e tte s.
u sed fo r any o th e r p u rp o se.
All the g la ssw a re w as p u rc h a se d new, and not
A solution co n sistin g of:
I lite r of d istille d w a te r
I lite r of co n cen trated h y d ro ch lo ric acid
50 m l of c o n cen trated hydrofluoric acid
50 m l of 30% hydrogen peroxide
w as used fo r cleaning all the g la ssw a re .
tio n .
The g la ssw a re w as rin se d in th is so lu ­
A fter th is in itia l cleaning, th e s e p a ra to ry funnels w e re kept filled with
I . ON HNOg betw een u se s.
The b eak ers and g rad u ated c y lin d e rs w ere p e rio d i­
cally soaked in I N HNOg, th en rin se d 6 to 8 tim e s w ith doubly d istille d w a ter.
The re a g e n ts u sed w ere dithizone (diethylthiocarbazone), carb o n t e t r a ­
c h lo rid e , and n itric acid.
The dithizone is reag en t g rad e and w as re c ry s ta lliz e d
-
five tim e s to in su re its p u rity .
the n itric acid.
23
-
The carbon te tra c h lo rid e w as d istille d as w as -
All re a g e n ts w ere independently checked fo r s ilv e r.
The w a te r
u sed fo r rin sin g the g la ss w a re and m aking dilutions was doubly d istille d in
P yrex.
The F u rn ac e
The fu rn ace u sed in th is study w as a th ir d g en eratio n fu rn ace (figure 7).
It is e ss e n tia lly the sam e b a sic design as a second g e n eratio n fu rn ace w ith one
m a jo r exception — the outside jack et is double w alled s ta in le s s s te e l fo r w a ter
cooling.
ite .
The sh ield tube and heat sin k w as co n stru cted fro m one piece of g ra p h ­
T hese two fe a tu re s seem ed to have g re a tly in c re a s e d the lifetim e of the
h e a te r tu b e s.
One p a rtic u la r p a ir la ste d 10 m onths w ithout burning out.
ous to th a t, the expected lifetim e w as one o r two m onths.
The fu rn ace te m p e ra ­
tu re w as m e a su re d through the side tube w ith an o ptical p y ro m e te r.
te m p e ra tu re s can be v a rie d fro m 200°C to 2800°C.
s ilv e r a n aly sis w as e ith e r 1650°C o r ISOO0C.
P r e v i­
F u rn ace
The te m p e ra tu re fo r the
The pow er d issip a te d to acq u ire
th e se te m p e ra tu re s w as about 2500 to 3000 w a tts.
The fu rn ace is pow ered w ith
a GE dc a rc w eld er.
The P ro c e d u re
The snow sam p les w ere co llected in p la stic bags p laced at the v a rio u s
co llectio n s ite s .
They w ere kept fro ze n at a ll tim e s until ju s t p rio r to the
0
S T A IN L E S S
H
g r a p h it e
E 3 QUARTZ
STEEL
U
RUBBER
M
CO PPER
□
g r a p h it e
SAM PLE
IN S U L A T IO N
F ig u re 7: The F u rn ace ( a th ird g en eratio n m odel )
PO R T-
—25 —
. e x tra c tio n step .
The m en collectin g the sam p les w ere carefu lly in stru c te d how
to handle the bags to avoid any p o ssib ility of contam ination.
M ost of the s a m ­
p le s w ere co llected w eekly e ith e r by snowm obile o r h e lic o p ter.
siz e v a rie d fro m 500 m l of snow up to 4 o r 5 lite r s .
The sam ple
The m ethod is as fo llo w s:
1.
B re ak up sam ple in bag and m ix thoroughly.
2.
F ill a 400 m l b e ak e r w ith snow and m elt on a hot p late.
3.
Im m ediately a fte r the snow has m elted add I m l of . 1 N HNOs to
100 m l of the m elted snow sam ple (sam ple is at pH 3).
4. . P o u r the sam ple into a s e p a ra to ry funnel and add 5 m l of IO- ^ m
d ithizone-C C l4 solution.
Shake the funnel vigorously fo r about
45 seconds.
5.
A fter th e la y e rs have se p a ra te d , tr a n s f e r a p o rtio n of the organic
■phase to a 5 m l holding bottle.
The sam ple may. be sto re d fo r one
day in the bottle in a r e f r ig e r a to r w ith no a p p reciab le lo s se s of Ag.
6.
U sing a 100X E ppendorf p ip ette, ev ap o rate 500X of the organic
phase onto a g rap h ite cup under an in fr a - re d lam p .
The volume
of a cup is about 120X. D uplicate cups fo r e ac h sam p le a re run.
7.
A fter the sam ple is on the cup, it can be analyzed im m ediately o r
s e v e ra l days la te r .
The cups a re sto re d in a d e s s ic a to r.
To a n a l-
ze, the cups a re screw ed onto a 1 /8 inch g rap h ite ro d and in s e rte d
r
■
—26 —
into the fu rn ace.
The r e s u lts a re re p o rte d as g ra m s of A g/m l of m elted snow.
The n o r­
m a l co n cen tratio n ra n g e fo r s ilv e r in snow is on th e o rd e r of IO-11 g m /m l,
(10~® g m /m l = I ppm).
The D etection System
A p ic tu re of the in stru m e n ta tio n is on page 27.
The. m a jo r com ponents
of the sy ste m a re : the fu rn ac e, a Spex 3 /4 m e te r C z e rn y -T u rn e r Spectrophoto­
m e te r, a P rin c e to n A pplied R e s e a rc h (PAR) HR8 lo ck -in a m p lifie r and light
chopper, a Honeywell 6 inch re c o rd e r , and th e a sso c ia te d e le c tro n ic s (Hewlett
P a c k ard and Fluke pow er su p p lies, T ek tro n ix o scillo sco p e, e t c . ).
The Spex m onochrom ato r w as s e t on th e m o st se n sitiv e of th e two s ilv e r
re so n an c e lin e s.
RCA IP28.
The line is at 3280
The p h o to m u ltip lier in the Spex is an
The hollow cathode light w as chopped at 400 h e rtz , and the PAR
a m p lifie r w as lo ck ed -in on th a t frequency.
The signal fro m th e p h o to m u ltip lier
w as m on ito red by the o scillo sco p e as it went into th e PAR.
The re c o r d e r re c o rd s the sig n al, and its c h a rt speed w as s e t at 2 m in /in .
F ig u re 5 shows a ty p ical tr a c e .
F igure 8:
P ic tu re of the instru m en tatio n
1.
The hollow cathode
2.
PAR m odel B Z -I light chopper
3.
The F u rn ace - a th ird g en eratio n model
4.
Spex 3 /4 m e te r C ze rn y -T u rn e r sp ectro p h o to m eter
5.
Honeywell 6 inch re c o rd e r
6.
T ech tro n ics type RM 503 oscilloscope
7.
PAR HR8 lo ck -in am p lifier
RESULTS AND DISCUSSION
S ilv er A nalysis
S ev eral p o ssib le m ethods of sam ple p re p a ra tio n fo r s ilv e r co n cen tratio n s
in the p ico g ram to nanogram ran g e have been studied by w o rk e rs in o ur la b o ra ­
tory^2"^ as w ell as o th e rs
15 ’ 16\
Some of the m ethods w ere- co p recip itatio n
of the s ilv e r w ith a c a r r i e r and subsequent cen trifu g atio n into a cup fo r a n aly sis,
(14)
p re c o n ce n tra tio n of the s ilv e r using an anion-exchange co lu m n '
elec tro p latin g
the s ilv e r onto a P t o r I r filam en t fo r e m issio n s p e c tro a n a ly sis in a R F induced
(2i)
d isc h a rg e , ' J and e x tra c tio n of the s ilv e r into an organic solvent w ith som e
chelating agent fo r p re c o n ce n tra tio n .
A fter c arefu lly studying th e se m ethods,
th e la tte r w as chosen as the sim p le st, m o st re lia b le , and p ra c tic a l method.
Dithizone (diethyIth io c a rb azone) w as chosen as the b e st chelating agent
fo r s ilv e r b ecause it has a high deg ree of sp ecificity fo r s ilv e r o v er a wide pH
ran g e.
The p rim a ry s ilv e r dithizonate, which is fo rm ed at pH 's below 7, is
soluble in organic so lv en ts and p ra c tic a lly insoluble in xyater.
C hloroform is
th e u sual solvent fo r dithizone b ecau se m e ta l d ith izo n ates a re m o st soluble in
c h lo ro fo rm .
The s ilv e r co n cen tratio n in ch lo ro fo rm , how ever, w as too high
(ca. IO-9 g m /m l) fo r it to be used.
S ev eral attem p ts w ere m ade to rem ove the
Ag fro m th e ch lo ro fo rm , but none w ere su cc e ssfu l.
C arbon te tra c h lo rid e w as
then se le c te d as a solvent, and proved to be quite fre e fro m s ilv e r a fte r being
d is tille d once.
-
29
-
The f ir s t attem p ts to e x tra c t the s ilv e r involved e x tra c tin g 50 m l of
m elted snow into 5 m l of IO- ^ M dithizone in carbon te tra c h lo rid e and ev ap o ra ­
ting all 5 m l on a g ra p h ite cup.
technique.
The background peaks w ere off scale using th is
The sam ple siz e w as cut in half to 25 m l, but the background peaks
w e re s till too high.
A nother problem encountered w ith th is technique w as high
blanks due to the contam ination of the g la ssw a re .
and 50% sca le deflection and w ere in co n sisten t.
BlanIc peaks ra n betw een 20%
The g la ssw a re could not be
com pletely cleaned of s ilv e r.
Silver see m s to slowly le ac h out of the g la ss o v er
a p e rio d of w eeks o r m onths.
T his p ro b lem p e rta in e d m o stly to th e sep a ra to ry
funnels.
Keeping the funnels filled w ith I IjI HNOg betw een u ses seem ed to d e '
c re a s e the pro b lem ov er a p erio d of tim e , but did not e n tire ly e lim in a te it.
The two m ethods m entioned above w e re in esse n ce putting 50 and 25 m l
of m elted snow on the cup.
m ethod w as developed.
The Ag co n cen tratio n was too high.
An a ltern ativ e
This, new m ethod not only d e c re a se d the Ag c o n cen tra­
tio n to w ithin the rig h t range but also elim in ated the blank p ro b lem fro m the
g la ss w a re , and saved tim e .
The m ethod involved taking a la r g e r sam ple (100 m l), but only evaporating
i / 1 0 of the e x tra c ta n t onto a cup (.5 m l).
T his technique is equivalent to e v a p o ra ­
tin g 10 m l of ,m elted snow on a cup while at the sam e tim e cutting th e blank one .. :
o rd e r of m agnitude.
The w orking range w as 3 x l0 ~ 1 2 g m /m l up to about 3 x IO- ^-O
- 30 <
g m /m l.
Some highly seeded sam p les s till went off sc a le , but a s m a lle r p o rtio n
of the e x tra c ta n t (200X), which was held in the holding b o ttle, w as ev ap o rated on
another p a ir of cups and re ru n im m ed iately .
A nother p ro b lem encoun tered in handling sam p les containing such m inute
q u an tities of s ilv e r is th a t of su rfa ce ad so rp tio n .
S ilv er has a tendency to ad -
(22 23)
so rb onto c o n tain er w alls if the solution is not p ro p e rly tre a te d ^ ’
. This is
why it is n e c e s sa ry to acidify the sam ple as quickly as p o ssib le a fte r it has
m elted .
Once the sam ple is acidified the s ilv e r w ill stay in solution fo r a sh o rt
tim e (ca. 1 /2 hour).
The s ilv e r w as alw ays e x tra c te d im m ed iately to avoid th is
p ro b lem .
The optim um fu rn ace te m p e ra tu re to analyze s ilv e r w as determ in ed .
F ig u re 9 shows th a t m axim um sen sitiv ity is achieved som ew here betw een 140CPC
and 1800°C.
Two Ag stan d a rd c u rv e s w e re ru n , one at 1650°C and the o th e r at
ISOO0C fig u r e 10).
Although th e IGSO0C cu rv e is obviously m o re sen sitiv e ,
th e ISOO0C curve is m o re lin e a r over a w id er co n cen tratio n ran g e.
Both c u rv e s
w ere m ade by running stan d a rd s ilv e r solutions through the e x tra c tio n p ro ced ­
u re .
Some R esu lts
O ver 225 snow sam p les and 4 hail sam p les w ere analyzed using the
above m entioned m ethod.
N ineteen of th e se sam p les w ere trip lic a te d and sent
1.0
-10
gram s
of Ag
a b s o r b a n c e
8x10
1200
1600
1400
TEMPERATURE
1800
( 0 C)
F ig u re 9: T e m p e ra tu re C alib ratio n Curve fo r Silver
2000
0
1650° C
a b s o r b a n c e
1800°C
g ram s^,x
F ig u re 10: S ilver Standard C urves
of
Ag
-
33
-
to two o th e r la b o ra to rie s , B ureau of R eclam atio n L ab o rato ry in D enver, Colo­
ra d o , and D e se rt R e s e a rc h In stitu te n e a r R eno, Nevada.
In D enver, the sa m ­
p le s w ere analyzed using a flam e AA boat-technique., The sam p les sent to DRI
w ere done by W arburton using neutron activ atio n a n aly sis. ' T able II shows som e
re s u lts of th e se m ethods as com p ared to the fu rn ace technique.
th e sam p les done in D enver a re q uestionable.
The re s u lts of
In m ost c a se s th e sam p les an aly ­
zed at DRI a re in good ag reem en t w ith th e fu rn ace m ethod.
U sing the fu rn ace,
som e sam p les w e re found to have a 35% s ilv e r g rad ien t fro m one end of the
sam p le to the o th er.
T his n e c e s s ita te s thorough sam ple m ixing.
The tr i p li­
c a te sam p les sen t to th e v a rio u s m entioned la b o ra to rie s w e re not th e sam e s a m ­
ple.
They w ere c arefu lly tak en fro m the sam e location, but w e re not portions
of the sam e sam ple.
T hese two facts could account fo r som e of the v a ria tio n
betw een th is m ethod and th a t done by neu tro n activ atio n a n a ly sis.
The boat
technique is not even com petitive w ith th e o th e r m ethods.
Of the sam p les analyzed, 22 w e re u n sa tisfa c to ry (i. e . , th e d u plicates
w ere quite d ifferent).
shown on ta b le III.
c h em ist.
T hese sam p les w e re rean aly zed .
Some of the re s u lts a re
The tag s w ere changed to in su re honesty on th e p a rt of the
E very one of th e re an aly zed sam p les w ere e ith e r a lm o st equal to one
of the o th e r two e a r lie r r e s u lts o r fell betw een th e two e a r lie r re s u lts .
- 34 -
TABLE II:
•
Snow Sample
C om parison of FAA w ith o th er A nalytical Methods
(re su lts in g m /m lx lO - "*;0 of Ag)
boat AA (Salman)
NAA (W arburton)
FAA (Culver)
301
3.7
0.6
0.5
302
2.4
0.4.
0.3
303
1.5
0.9
0.7
.304
1.0
0.8
0.6
305
13.0
0.3
0.3
307
lo s t
0.2
0.8
308
0.6
0.2
0.5
309
3.8
1.7
0.8
310
lo st
0.3
0.7
311
1.4
lo st
0.1
312
lo st
0.2
0.5
313
0.6
0.1
0.5
314
1.4
0.5
0.6
315
0.7
0.2
0.5
316
11.0
24.8
2.6
317
2 0 .0
27.9
4.2
■ 318
0,6
0.1
0.1
''
.
- 35 -
TABLE IIL
C om parison of Some Sam ples Analyzed on D ifferent Days
(re su lts in g m /m lx lO " ^ ^ of Ag)
Sam ple
A nalyses
#1
date
#2
date
105
0.17
2 /1 9 /7 1
0.53
6 /2 4 /7 1
*0.44
7 /1 3 /7 1
106
0.46
2 /1 7 /7 1
0.70
6 /2 9 /7 1
*0.63
7 /1 3 /7 1
108
0.81
5 /2 2 /7 1
0.46
6 /2 3 /7 1
0.56
7 /1 3 /7 1
109
0.23
2 /1 9 /7 1
0.61
6 /2 4 /7 1
0.20
7 /1 3 /7 1
111
0.29
2 /2 0 /7 1
0.57
6 /2 4 /7 1
0.52
7 /1 3 /7 1
116
1.10
6 /2 4 /7 1
0.90
7 /1 3 /7 1
120
0.32
6 /2 4 /7 1
0.45
7 /1 3 /7 1
#3
date
^ re s u lts a re the av erag e of trip lic a te d eterm in atio n s
F o u r fro ze n hail sam p les tak en in conjunction w ith the N o rth east Colo­
rad o Hail E xperim ent (NECHE) w ere analyzed fo r background s ilv e r concen­
tra tio n .
The r e s u lts a re lis te d in ta b le IV.
The s ilv e r background in hail
a p p ea rs to be one to tw o o rd e rs of m agnitude higher than th a t of the snow, and
v a rie s so m uch th a t not m uch useful in fo rm atio n could be obtained by analyzing
h a il fo r s ilv e r.
w ork.
S ilver iodide is u sed by m e te o ro lo g ists fo r h a il su p p ressio n
The re a so n fo r the high background could be b ecau se hail sto rm s a re
- 36 -
g e n e ra lly quite tu rb u len t and dust could e a s ily contam inate the sam p les even
though they a re taken 30 feet above the ground.
M ost so il contains about .1 ppm
of s ilv e r ^24\
TABLE IV:
S ilv er in H ail Sam ples
Sample
D ate Taken
I
July 9, 1971
22 x IO-11 g m /m l
2
July 9, 1971
16 x IO- ^ g m /m l
3
June 30, 1971
7x10""H g m /m l
4
June 21, 1971
11x10""H g m /m l
Note:
S ilv er C oncentration
Sam ples I and 2 w e re ta k en d u ring th e sam e
s to rm .
CONCLUSIONS
T hese in v estig atio n s w ere u ndertaken to d eterm in e if:
1.
P o la riz e d light could be effectively used fo r a background
c o rre c tio n technique using double beam sp ec tro p h o to m e te rs.
2.
A p ra c tic a l, re lia b le , and inexpensive m ethod fo r the silv e r
■ a n aly sis of snow could be developed.
The re s u lts show th a t p o la riz ed lig h t can be used as a background c o r­
r e c to r .
C om paring a continuous background so u rce of an elem en ta l o r hollow
cathode so u rc e has been an effective way of rem oving the re la tiv e effects of
e x tran eo u s light ab so rp tio n a n d /o r sc a tte rin g .
The p o la riz e d light technique
proved to be a potentially useful ex ten sio n of th e m ethod.
The m ethod developed fo r analyzing s ilv e r in the p ico g ram range proved
not only to be p ra c tic a l, re lia b le , and inexpensive, but it is a lso fa st and sim p le.
T his m ethod is c u rre n tly the b e st m ethod fo r s ilv e r a n aly sis in snow, hail, o r
w a te r fo r co n centrations below the n a n o g ra m /m l range.
NEED FOR FURTHER WORK
As w as m entioned in the intro d u ctio n , furnace atom ic ab so rp tio n is one
of the m o st p ro m isin g an aly tical to o ls fo r tr a c e and m ic ro tra c e m etal an aly sis
at the p re s e n t tim e .
In m edicine: It is conceivable to be able to do 50 quantitative
e lem en tal an aly ses on I m l of whole blood.
It is known
th a t m any tr a c e m e ta ls a re in stru m e n ta l in th e cause or
p rev en tio n of many hum an ailm en ts.
In g e o ch e m istry : O re dep o sits could be lo cated by carefu lly
analyzing ground w ater.
In w eath er m odification: A nalysis of elem en ts in s to rm s for
p o ssib le contro l o v er h u rric a n e s, h a il o r draught.
\
In pollution co n tro l: M onitoring tr a c e elem en ts in th e a ir , w a te r,
anim al and vegetable tis s u e .
W ith th e sen sitiv ity capability th a t th e fu rn ace h a s, m any p ro b lem s can
be overcom e by m e re ly going around th em as w as done w ith the Ag in snow
m ethod.
The fu rn ace o ffers an inexpensive alte rn ativ e to n eu tro n activation
a n a ly sis, w hile at the sam e tim e being sim p le if p ro p e r p re c au tio n s a re tak en
w ith re a g e n ts and handling technique.
LITERATURE CITED
1.
B. V. L 'vov,
SpectrocMmo A cta 17_, 761 (1961).
2.
B„ V. L 'vov,
A tom ic A bsorption A nalysis (Nauka, M oscow, USSR, 1966).
3.
B„ V. L 'vov,
SpectrocM m . A cta 24B , 53 (1968).
4.
H. M assm an, SpectrocM m . A cta 23B , 215 (1968).
5.
D. C. Manning, P a p e r at E a s te rn A nalytical Sym posium , in New Y ork,
D ecem ber 1969.
6.
H. L„ Kahn, A„ A. N ew sletter, 7_40 (1968).
7.
M. Do A m os, P„ A. B ennett, K„ G. B ro d ie , P . W. Y. Lung and J . P,
M ato n se ls, Anal. Chem . , 43, 211 (1971).
8.
S. R. K oirtyohann and E . E. P ick ett, Anal. C hem . , 37_, 601 (1965).
9.
P . B. Z eem an and J . A. B rink, A nalyst, 93_, 388 (1968).
10.
T . C. R ains, NBS unpublished w ork.
11.
R„ W oodrift, B. R. C ulver, and K. O lsen, Appl. S p ectro sc. 24, 530
(1970).
12.
R . W oodriff, D„ S h rad e r, Anal. Ch e m ., 43_, Nov. (1971).
13.
V. S chaefer, J . Appl. M e te o r., 7_, 452 (1968).
14.
J . A. W arburton, L . G. Young, J. A ppl. M e te o r., 7_, 433 (1968).
15.
M eeting on "The analy sis of s ilv e r in te r r e s t r i a l and aquatic e c o sy ste m s"
held in D enver, C olorado, on May 18, 1971, th e r e s u lts of wMch
w e re subm itted to the W ater R e so u rc e s b u lletin fo r publication.
- 40 -
16.
F . P . P aru n g o , C. E. R ob ertso n , J . Appl. M eteor. , 8_, 315 (1969).
17.
R . W oodriff and R 0 Stone, Appl. O p t., 7_, 1337 (1968).
18.
R. W oodriff, R. Stone, and A. M. Held, Appl. S p ectro sc. , 22_, 408 (1968).
19.
L 0 E.
Owen, A ir F o rc e M at. Lab. , A FM L -T R -67-400 (1967).
20.
L 0 E.
Owen, A ir F o rc e M at. Lab. , A FM L -T R -68-354 (1968).
21.
R. W oodriff and D. S ie m e r, A ppl0 S p e c tro s c ., 23_, 38 (1969).
22.
F . K.
W est, P . W0 W est, and T. V. R am ak rish n a, E n v ir. Sci. and T e c h 0,
I , 717 (1967).
23.
F . K. W est, P 0 W. W est, and F . A 0 Id d in g s, Anal. C hem . , 38, 1566
(1966).
24.
J . A. W arburton, P e rs o n a l C om m unication, May 18, 1971.
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