Analysis of Total PCB Content by Reductive
Dechlorination to Biphenyl
John G. Doyle, TeriAnn Miles, Erik Parker,
I. Francis Cheng
Department of Chemistry
University of Idaho
Moscow, Idaho 83844-2343 ifcheng@uidaho.edu
(208) 885-6387

Outline
1.
Short History of PCBs
2.
Present state of PCB analysis
Multi-component – 209 congeners
Associated problems with GC-ECD
3.
Chemical Reaction to Single Species
Carbon Skeleton
Perchlorination
4.
Complete dechlorination at RTP.
Pd/Mg bimetallic particles
Performance with Arochlor

1221
5.
Elimination of Interferences by other Halocarbons
Mixtures of DDT and Arochlor 1260

PCB history
Clx Cly
10

x + y
Industrial uses 1930 – 1977

Dielectric fluids, capacitors and transformers

Printing inks

Paints

Pesticides
Health and Environmental Risks

Occupational exposure (1936)

Bio-accumulative (low water solubility)

Banned by TSCA 1977
EPA policy
Soils: nonrestricted access areas must 10 ppm or less

PCB analyses
Clx
Cly
209 possible congeners
GC-FID of a PCB mixture

Complicating Features
CG-ECD analysis based on pattern recognition of key congener peaks.
1.
Matrix effects
-DDT/DDE metabolites
-Other Halocarbons
2.
Environmental aging
-Different rates of dechlorination for each congener
-Volatility differences for each congener
3.
ECD response
-Varies with each congener
“
Sources and Magnitude of Bias Associated with Determination of
Polychlorinated Biphenyls in Environmental Samples”
Analytical Chemistry ,
1991 , 63 , 2130-2137.

Chemical Reaction of PCBs
To one predominate species
1. Reductive Dechlorination:
Clx
+ 2(x+y) e -
+ (x+y) Cl -
Cly
2. Perchlorination:
Clx
Cly
+ 2 (10-x+y) Cl -
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
+ (10-x+y) H + + (10-x+y) e -
Cl

Requirements for Chemical Reaction to Single
Species
1.
Reproducible and Quantitative
100% Yield
2.
Rapid
R oom Temperature and Pressure
3.Simple minimal work-up

Literature methods
Reductive Dechlorination:
Procedure Analysis Detection
Limit
150 ng H
2
reduction on Pd catalyst @ 305 0 C
GC-FID
Heated Pd catalysts GC-FID
Na reduction Cl ISE
10 ng
10 mg
LiAlH
4
HPLC UV@248 nm 100 ng
Perchlorination
SbCl
5
@ 205 0 C GC-ECD ?
Most of the above involve extensive procedures.

Rapid reductive dechlorination under mild conditions
1. Standard Reduction Potential of PCBs
Clx
+ 2(x+y) e -
+ (x+y) Cl -
Cly
E 0 red
= 0.5 to 1.0 volts
2. Reducing Agents (aqueous)
Fe

Fe 2+ + 2e -0.44 V
Cr

Cr 3+ + 3e -0.74 V
Mn

Mn 2+ + 2e -1.182 V
Mg

Mg 2+ + 2e -2.36 V
E 0 red

Complete dechlorination of PCB by zero-valent metals is slow.
1.
Most congeners are completely stable in presence of metal reducing agents at RTP.
2.
Requires catalyst.
Pd/Fe bimetallic system*.
2 g, 10
 m, 99.9% Fe particles
0.05 % Pd w/w
5 ml 20 ppm Arochlor 1260
(30% MeOH , 20% acetone, 50% water)
Complete dechlorination in 10 minutes
Majority product, biphenyl
*C. Grittini, M. Malcomson, Q. Fernando, N. Korte
Environ. Sci. & Tech., 1995 , 29 , 2898-2900.

Analysis of total PCB by reductive dechlorination with Pd/Mg bimetal.
1.
Mg vs. Fe
Fe surface requires extensive pretreatment
Anaerobic acid washing
Air sensitive
Mg requires no special treatment
2.
Deposition of Pd onto Mg
Untreated 0.5 grams 20 mesh Mg
(98%, Aldrich)
20 mg K
2
PdCl
6
PdCl
6
2 + 2Mg = Pd + 6Cl + 2Mg 2+
Pd
Mg

PCB dechlorination
Analyte solution

3-5 ml of 50/50 v/v 2-propanol/water

1 – 60

M Arochlor 1221

0.5 grams 20 mesh Mg particles

20 mg K
2
PdCl
6
powder
reaction complete in 5 minutes
Preparation for HPLC
 syringe filter 0.2 ml of above

Role of Pd in the catalysis of zero-valent metal reduction of halocarbons.
R-H + H + + Cl -
Mg 2+ 2H +
Pd
.
H
Pd island
H
H
R-Cl
Metal surface
2e -

Pd is a catalytic surface for hydrogen evolution

Increases Mg dissolution (galvanic corrosion)

Hydrogen intercalates in bulk Pd

May result in excellent surface for hydrodehalogenation

Pt fails as hydrodehalogenation catalyst
I.F. Cheng, Q. Fernando, N. Korte, Environmental
Science and Technology, 1997, 31 (4) 1074-1078.

Analytical performance of Mg/Pd reductive dechlorination system
HPLC analysis

50 uL sampling loop

UV absorbance detector 200 nm (HP 79853C)

Isocratic 65/35 v/v acetonitrile/water

C-8 Zorbax column

Arochlor 1221 biphenyl content, 3.3%

Biphenyl Calibration Curve
Biphenyl
4.50E+07
4.00E+07
3.50E+07
3.00E+07
2.50E+07
2.00E+07
1.50E+07
1.00E+07 y = 7.95E+11x + 3.59E+05
R
2
= 9.99E-01
5.00E+06
0.00E+00
0.00E+00 1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05 6.00E-05
Concentration (M)

Biphenyl from Arochlor 1221 dechlorination
Biphenyl From Arochlor 1221 with Mg/Pd
4.50E+07
4.00E+07
3.50E+07
3.00E+07
2.50E+07
2.00E+07
1.50E+07
1.00E+07
5.00E+06 y = 7.76E+11x - 1.53E+06
R
2
= 9.97E-01
0.00E+00
0.00E+00 1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05 6.00E-05
Concentration (M)

Biphenyl yield = 98% (from slopes)

Chemical Interferences

DDT and major impurities and metabolites

10 major GC-FID peaks

Co-elute with PCBs
DDT
Cl Cl
CCl
3
DDE
Cl Cl
CCl
2
DDO
Cl Cl
CH
3
DDNS
CCl
3

Cl
Reductive dechlorination of DDT/metabolites by
Pd/Mg.

RTP reaction completed in 10 minutes

Only demonstrated method for the complete and rapid dechlorination of DDT at RTP
Procedure as with PCB dechlorination
Cl
Pd/Mg
+ 5 Cl -
CCl
3
CH
3
Major product of DDT/metabolite reductive dechlorination

GC-FID of PCB & DDT mixtures

Illustrates DDT interference
Top 50 ppm PCB (Arochlor 1260) and 50 ppm DDT
Bottom 50 ppm DDT

Pd/Mg Treatment of DDT/PCB mixtures

GC-FID

Conclusions and Future Work
Advantages
PCB reductive dechlorination by Pd/Mg to biphenyl

Rapid (< 5mins)

Reproducible (98% yield)

Detection Limit (no sample preconcentration)
5 x 10 -6 M
100 ppb
5 ng
Disadvantages

Loss of congener specific information

Requires analysis for biphenyl background
Future

Elimination of halocarbon interferences (DDT)

Acknowledgements
Co-authors
John G. Doyle
TeriAnn Miles
Erik Parker
Other Contributors
Mark Engelmann
Kristy Henscheid
Keri Colvin
Roshan Koshravi
Josh Linard
University of Idaho Research start-up funds
Contact Information:
Frank Cheng
Department of Chemistry
University of Idaho
Moscow, Idaho 83844-2343 ifcheng@uidaho.edu
(208) 885-6387