Anal. Chem. 1984, 56, 1041-1043
epoxy cement and Torr Seal masking were identical with a silver epoxy electrode itself. The point is that the contact material has no redox characteristics itself (such as the silver epoxy) and exhibits only a small background current for the solution redox system diffusing through the pores of the polymer electrode. Registry No. C, 7440-44-0. LITERATURE CITED (1) Heineman, W. R.; Kissinger, P. T. Anal. Chem. 1980, 52, 138R. (2) Rubinson, J. F.; Mark, H. E., Jr.; Diaz, A. F. I n “Extended Linear Chain Compounds”; Miller, J. S., Ed., Plenum: New York, in press. (3) Amer, A.; Zimmer, H.; Muiiigan, K. J.; Mark, H. B., Jr.; Pons, S.; McAleer, J. F. J. folym. Sci., folymn. Left. Ed., in press.
1041
(4) Amer, A.; Zimmer, H.;Muiligan, K. J.; Mark, H. B., Jr.; Pons, S.; McAleer, J. F., submitted for publication in J. f d y m . Sci., Polym. Len. Ed. (5) Nowak, R. J.; Mark, H. B., Jr.; Weber, D.; MacDiarmid, A. G. J. Chem. Soc., Chem. Commun. 1977, 9. (6) Nowak, R. J.; Kutner, W.; Mark, H. B., Jr.; MacDiarmid, A. G. J. Nectrochem. SOC.1978, 125, 232. (7) Nowak, R. J.; Rubinson, J. F.; Vouigaropoulus, A,; Kutner, W.; Mark, H. B.,Jr.; MacDiarmid, A. G. J. Nectrochem. SOC.1981, 128. 1927. (8) Amer, A.; Zimmer, H.; Mark, H. E., Jr., unpublished results, 1983. (9) Czerwinski, A.; Marassi, R.; Sobkowski, J., private communication, 1984.
RECEIVED for review December 14,1983. Accepted February 8,1984. This research was supported by the National Science Foundation, Grant No. CHE-8205873.
Liquid Chromatographic Cleanup Prior to Determination of Polychlorinated Biphenyls in Oil by Gas Chromatography/Mass Spectrometry Vincent P. Nero* a n d Robert D. Hudson Texaco, Inc., Teraco Research Center Beacon, Beacon, New York 12508 Polyclilorinated biphenyls (PCBs) had been commonly used in transformers, electromagnets, capacitors, hydraulic systems, and paints from 1930 until 1979, when the Environmental Protection Agency, under the Toxic Substances Control Act, restricted their use. The extensive application of PCBs, coupled with their chemical stability, has resulted in their permeation throughout the environment. Numerous analytical procedures have been devised to detect and measure the extent of PCB contamination in waste oils to permit proper disposal. Often, however, matrix interferences do not allow for the necessary sensitivity. These techniques and their associated problems have been previously reviewed (1). Enhanced detection of PCBs can be achieved either by using more complex instrumentation, which can discern the difference between the analyte and the potential interferences, or by previously removing the interferences. The most promising instrumental methods use specialized mass spectrometric approaches including gas chromatography/chemical ionization mass spectrometry (GC/CIMS) (21, mass spectrometry/mass spectrometry (MS/MS), and gas chromatography/high-resolution mass spectrometry (GC/ HRMS) (3). However, each of these alternatives requires more complex technique and instrumentation than conventional gas chromatography/mass spectrometry (GC/MS). The second approach is to employ various cleanup techniques to remove the interferences which complicate the GC/MS analysis. Florisil, alumina, silica gel, and gel permeation chromatography have been applied. Also sulfuric acid washing, acetonitrile partitioning, Florisil slurry, and alcoholic potassium hydroxide extractions have all been employed (4). These procedures tend to be lengthy and only partially effective. Often more than one technique may be required to remove interferences from the sample. The major mass spectrometric interferences masking PCBs in transformer or waste oils tend to be the hydrocarbons intrinsic to the oil. Transformer oils are composed of a complex mixture of aliphatic, alicyclic, and polynuclear aromatic hydrocarbons, all of which have possible alkyl substituents. The compositional analysis of the various classes of hydrocarbons present can be determined by established mass spectrometric methods (5,6). A typical composition has a wide range of paraffiis, cycloparaffins, and alkylpolycyclic aromatic hydrocarbons. Some of these compounds have the same masses and boiling ranges as the PCBs and therefore could
have interfering mass fragments at a similar GC retention time. An HPLC procedure has been developed which quickly can eliminate these mass spectral interferences from transformer oils and related oil matrices. The resulting HPLC fraction is clean enough to be analyzed for PCBs by GC/EIMS down to the 100 ppb level. EXPERIMENTAL SECTION Reagents. All individual polychlorinated biphenyls, as well as 2,2/-dibromobiphenyl, were purchased from Ultra Scientific, Inc. (Hope, RI). Aroclor standards were obtained from Supelco, Inc., (Bellefonte, PA). Aroclor is a registered Monsanto Corp. trademark. Standard Reference Material 1581 (National Bureau of Standards, Washington, DC), which is 100 ppm Aroclor 1242 in transformer oil, was also used. Carbon-13-PCB recovery surrogates were obtained from the US. Environmental Protection Agency, (Washington,DC). Various commercial transformer oils and a NBS transformer oil from the SRM 1581 kit were used as dduents. All solvents were of HPLC quality (Burdick and Jackson Laboratories, Inc., Muskegon, MI) and were filtered through a 0.45-hm, filter (Millipore Corp., Bedford, MA) prior to use. Cleanup Procedure by High-Performance Liquid Chromatography. The cleanup procedure was carried out on a microprocessor-controlled gradient liquid chromatograph (Hewlett-Packard Model 1084B) equipped with a fraction collector (Hewlett-Packard Model 79825A) which is controlled by the microprocessor. The detector used was a multiwavelength UVvisible spectrophotometer (Hewlett-Packard Model 8450A), monitoring at 254 nm. A 25 cm long by 4.6 mm i.d. column, packed with Nucleosil 5 NOz, was purchased from Alltech Associates. Nucleosil5 NO2 is 3-(4-nitrophenyl)propyl bonded onto 5-ym spherical silica gel and is manufactured by Macherey-Nagel. Solvents used for the mobile phase include isooctane and tetrahydrofuran. A flow, as well as a solvent gradient, was employed, commencing with 100% isooctane at a flow rate of 1.0 mL/min and progressing to 100% tetrahydrofuran at a flow rate of 2.5 mL min-I (Figure 1). The chromatographic separations were run at room temperature. Aroclor standards as well as individual PCBs were dissolved in isooctane and injected onto the system to initially determine the retention time range for all PCB isomers. Aroclor standards and individual compounds were then diluted in various transformer oils at parts-per-million and parts-per-billion concentrations to determine retention times. In the initial investigations, each sample was spiked with 1ppm of 2,2’-dibromobiphenyl. In subsequent studies, EPA carbon-13 PCBs were used as recovery
0003-2700/84/0356-1041$01.50/00 1984 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL 56, NO. 6, MAY 1984
Table I. Retention Data for Model Compounds on NO,-Bonded Silica
11\11.!
00
33
retention time, min
no. of double bonds
3 5 7 7 9
2.71 3.12 4.14 5.51 13.02 13.07 19.90
0.15 0.52 1.04 3.82 3.82 6.37
3.5 7.0 25.8 25.8 43.0
6
Aroclor 1248
6
2,2'-dibromobiphenyl
5.709.60 6.10
1.112.55 1.26
7.517.2 8.5
0
167
k'
re1 retention vs. SAT
dead volume hexadecane toluene naphthalene phenanthrene anthracene fluoranthene
A
67 100 13.3 TIME MINUTES
capacity factor
1.0
200
Flgure 1. HPLC profile using ultraviolet detection at 254 nm: (a) PAHs in transformer oil, (b) Aroclor 1248 in hexane. Linear gradient conditions were 100% isooctane at 1 mL min-' for 5 min increasing to 1.5 mL min-' over a second 5-min period and followed by a solvent gradient change from 100% isooctane to 10% isooctane over an additional 5 min; then fl6w rate was increased to 2.5 mL min-' over a 5-min period and held for 5 min.
surrogates. Five microliters of each sample was introduced into the liquid chromatograph without further dilution. The column eluent, approximately 4.5 mL, was collected for the retention time window previously determined. The collected fraction was then transferred to a conical shaped vial and the mobile phase solvent was allowed to evapbrate just to dryness with a very light nitrogen flow. The PCB residue with the dibromobiphenyl surrogate was then taken up by carefully washing down the sides of the conical vial with 25 p L of methylene chloride. The PCB residue with the EPA carbon-13 recovery eurrogate was taken up in 25 p L of methylene chloride spiked with 1 ppm dibromobiphenyl as an internal standard. Samples were then analyzed by GC/MS. After each HPbCC collection,the injection system was flushed three times with tetrahydrofuran to prevent any contamination. Transformer oil blanks spiked at 1 ppm with dibromobiphenyl were run periodically to ensure against carry-over. GC/MS Analysis. A 2.0-pL sample of the isolated PCB fraction was then analyzed on a Hewlett-Packard 5730 gas chromatograph by splitless injection with a 35-5 delay. The GC was equipped with a methyl silicone, 25 m X 0.2 mm fused silica column, inserted directly into the mass spectrometer source. The injector was 250 "C. The oven temperatuie was programmed from 100 "C to 300 "C at 8 "C/min with a 16-min hold at 300 "C. A VG Analytical 7070HS mass spectrometer was operated at an initial 4-kV accelerating voltage, 1000 resolution (10% valley), 200-pA trap current, 70-eV electron energy, and a source temperature of 250 "C. Ion abundances were selectively recorded by voltage using the VG 2000 data system equipped with a digital scanner unit. A 1700 ppm window was scanned for each monitored ion. Ion abundances for 222.00,224.00, 255.96,257.96,289.92, and 291.92 daltons were continuously measured for 50 ms each during retention times between 7 and 12 min. Ion abundances for 289.92, 291.92,303.96, 311.90, 323.88, 325.88, 359.84, and 361.84 daltons were obtained during retention times between 12 and 20 min. Total cycle times were less than 1 s each. RESULTS A N D DISCUSSION HPLC Separation Procedure. Various polar bonded stationary phases have been evaluated for their ability to perform separations of polycyclic aromatic hydrocarbons (PAH) by normal-phase HPLC which, unlike reversed-phase procedures, uses volatile mobile phases that can be easily removed from fractions collected for further analysis (7,8). The 3-(4-nitrophenyl)propyl bonded silica stationary phase has a high affinity for double bonds when used with nonpolar
m/z 324
m/z 326
RETENTION TIME
Flgure 2. Reconstructed ion chromatograms for Aroclor 1016 spiked
at 2 ppm into transformer oil. Dibromobiphenyi was added at 1 ppm as a recovery surrogate. mobile phases. This property is applicable to the separation of saturated hydrocarbons from aromatics, as well as the separation of the aromatics by increasing ring number. Various organic compounds have retention times directly related to their respective number of double bonds (Table I). PCBs and dibromobiphenyl (an internal standard used in this study) eluted in the range appropriate for biphenyls or other PAHs with six double bonds (Figure 1). This column effectively isolated the PCBs from most of the matrix, removing approximately 96% of the oil content with its inherent interferences. The mobile phase gradients were designed to enhance separation of the PCBs followed by a strong increase in solvent flow and polarity to flush off any remaining oil prior to reequilibration. This program was found to maintain constant retention properties. GC/MS Results. The six double bond HPLC fraction, which primarily contains alkyl biphenyls and possible PCBs, was separated by gas chromatography. The PCB molecular ion chlorine isotopes were selectively recorded. In the resulting chromatograms, the GC retention time frame of the PCBs is not significantly complicated by extraneous peaks (Figure 2).
Anal. Chem. 1984, 56, 1043-1046
m/z 290
7MIN
RETENTION TIME
18 MIN
Figure 3. Reconstructed ion chromatograms for Aroclor 1242 and surrogate at 250 ppb in NBS transformer oil. Dibromobiphenyl was added at 1 ppm as an internal standard. Selected ion chromatograms for tri-, tetra-, and pentachlorobiphenyl isomers, as well as the 2,2'-dibromobiphenyl recovery surrogate standard, clearly reveal characteristic peak profiles free of interferences. These chromatograms have very similar isomer distribution patterns and relative intensities to that of 2 ppm Aroclor 1016 in hexane. The only interferences observed arise in the latter portion of the trichlorobiphenyl chromatograms, mlz 256 and mlz 258 (Figure 21, beyond the retention region of the respective PCBs. This interference can be easily differentiated from PCBs not only by its longer retention time but also by its lack of consistently corresponding isotope peaks at mlz 256 and m/z 258. These data resulted from spiking 2 ppm Aroclor 1016 and 1 ppm 2,2'-dibromobiphenyl into a transformer oil. The various PCBs which comprise Aroclor 1016 are of course present in lesser amounts. For example, the total tetrachlorobiphenyl isomers represent only 12% of total Aroclor and therefore are present at 240 ppb. The individual peaks detected are within
1043
the 100 ppb range (Figure 2, m/z 290, 292). In a second case a mixture of Aroclor 1242 from SRM 1581 was diluted to 2 ppm with the corresponding NBS transformer oil and was then spiked at 250 ppb with [l3CI2]-3,3',4,4'tetrachlorobiphenyl as a recovery surrogate. Dibromobiphenyl was added to the cleaned HPLC fraction at the 1 ppm level as an internal standard. A comparison of the [13C]tetrachlorobiphenyl recovery surrogate chromatogram, m / z 312, with the chromatogram of the tetrachlorobiphenyl in Aroclor 1242, m / z 292 (Figure 3), indicates clearly individual isomers at approximately 80-150 ppb. Exact quantitation would require the determination of response factors between individual PCB chromatogram peaks and the surrogate peaks as described by Erickson et al. (4). Interfering background noise is more pronounced but is beyond the expected GC retention time for tetrachlorobiphenyl. The major advantage of this method is first that it permits at least a 100 ng detection in the trichloro- to hexachlorobiphenyl range using [13C]tetrachlorobiphenylas a surrogate. To preclude the effect of any possible PCB fractionation during the recovery process, the lower and higher PCB ranges would best be quantitated against [13C]chlorobiphenyl, [13C]octachlorobiphenyl,and [13CJdecachlorobiphenyl,which are also included in the EPA surrogate package. The second advantage is that the HPLC fraction collection procedure is fully automated. Although the GC/MS runs were performed on an individual basis, this step also could be made more efficient by using an automated GC/MS inlet system. Furthermore, even though the mass spectrometric analysis was carried out on a high-resolution instrument, it was operated under low-resolution conditions and ions were monitored over approximately half of an atomic mass unit. Therefore a mass spectrometer having unit resolution with good sensitivity could have been substituted.
LITERATURE CITED Cairns, T.; Slegmund, E. G. Anal. Chem. 1981, 53. 1183A. Cairns, T.; Siegmund, E. G. Anal. Chem. 1981, 53, 1599, Voyksner, R. D.; Hass, J. R . ; Sovocool, G. W.; Bursey, M. M. Anal. Chem. 1983, 55, 744. Erlckson, M. D.; Stanley, J. S.; Turman, K.; Radolovich, G.; Bauer, K.; Onstof, J.; Rose, D.; Wlckham, M. "Analytical Methods for By-products PCB's"; Literature Review and Preliminary Recommendations; Interim Report No. 1 ; Office of TOXICSubstances, U S . Environmental Protection Agency: Washington, D.C.; EPA-560/5-82-005, 1982. "ASTM Method D-2786,ASTM Standards, Part 24"; American Society for Testing and Materials: Philadelphia, PA, 1981. ASTM Method D-3239,ASTM Standards, Part 25"; American Society for Testing and Materlals: Philadelphia, PA, 1981. Chmlelowlec, J.; George, A. E. Anal. Chem. 1980, 52, 1154. Bluemer, 0. P.; Zander, M. Fresenius' 2. Anal. Chem. f977, 288, 277.
RECEIVED for review October 28,1983.
Accepted January 25,
1984.
Gas Transfer Device Utilizing a Mechanlcai Piston Compressor Eric R. Sirkin' Department of Chemistry, University of California-Berkeley, Berkeley, California 94720 Quantitative analyses of gases produced by chemical reactions generally involve collections and analysis of only small portions of the total sample. For some applications it is desirable to abstract all, or nearly all, the sample for analysis. 'presentaddress: CA 94086.
vale,
zorancarp., 710 Lakeway, Suite 170, sunny-
When the gases cannot be readily condensed by liquid N2,this can be a considerable problem. Previously a Toepler pump has been employed in such applications, however, this device suffers from the necessity of using large quantities of Hg in a fragile glass collection vessel, thereby providing an unwieldy system with a considerable safety risk and little portability. In addition some applications such as organometallic photo-
0003-2700/84/0356-1043$01.50/00 1984 American Chemical Society
