Anal. Chem. 1984, 56, 1039-1041
3
Br-
O.2ppm
4
NO;
12.2ppm
5
50-:
22.5ppm
volume this equates to a detection limit of 1 pg on the filter. This is more than adequate for the concentration of ionic species present in atmospheric aerosols which occur at the two sampling sites even on the least polluted days. Detection limits could be improved if necessary by increasing the injection volume or decreasing the extraction volume. Repeated analysis of a single coarse particle filter sample gave the results shown in (Table 11) in terms of solution concentration (ppm). This indicates that the precision of the analysis is of the order of f2-3%. In conclusion, with a relatively small investment in a conductivity detector and appropriate columns, existing HPLC equipment was adapted to provide a satisfactory ion chromatography system. Application to the analysis of atmospheric aerosols collected on filters requires extraction of the sample with the eluent solution and choice of a suitable pH to give adequate C1-, NO3- resolution while not giving too long a retention time for Sod2-.pH 5 was M phthalate eluent. generally found to be suitable with a The detection limit was about 0.1 ppm or 1 pg of C1-, NOS-, or Sod2on the filter. Registry No. C1-, 16887-00-6; NO3-, 14797-55-8; Sod2-, 14808-79-8.
1
5
I
I
1
I
20
15
10
5
1
0
TIME(rninutes1
LITERATURE CITED
Figure 4. Chromatogram of fine aerosol filter extract at pH 5.5.
Table 11. Analysis of a Single Coarse Particle Filter Sample
max min mean(N = 10)
1.99 1.86 1.91
NO;, ppm 4.82 4.39 4.59
std dev
0.05
0.14
Cl-, ppm
1039
SO,'-, PP m
0.15
7.30 6.83
7.08
mulation of lead antiknock additives. It seems unlikely that the nitrite originates in the aerosol since analysis of a clean filter from a freshly opened box shows a similar peak corresponding to about 5 wg of N02-/filter. For a 1OO-wL sample and use of the optimum operating conditions, 0.1 ppm can be readily detected. This is equivalent to injecting 10 ng onto the column. For a 10-mL extraction
(1) Mulik, J. D.; Puckett, R.; Wllilams, D.; Sawlcki, E. Anal. Lett. 1976, 9, 653. (2) Sawicki, E., Mulik, J. D., Wittgenstein, E., Eds. "Ion Chromatographic Analysis of Environmental Pollutants"; Ann Arbor Science Publishers: Ann Arbor, MI, 1978; Vol. 1. (3) Harrison, K. and Burge, D.,Paper presented at the Pittsburgh Conference on Applied Spectroscopy; Cleveland, OH, March 1979; Paper 301. (4) Glatz, J. A.; Girard, J. E. J. Chromatogr. Sci. 1982, 2 0 , 266. (5) Dogan, S.; Haerdi, W. Chimia 1981, 35, 339. (6) Girard, J. E.; Glatz, J. A. Am. Lab. (Fairfield, Conn.) 1981, 13 (lo), 26. (7) Clarke, A. G.; Willison, M. J., submitted to Atmos. Envlron. (6) Gjerde, D.J.; Fritz, J. S. Anal. Chem. 1981, 53, 2324. (9) Herschovitz, H.; Yarnltzky, Ch.; Schmuckler, G. J. Chromafogr. 1962, 244, 217. (10) Molnar, I.; Knauer, H.; Wilk, D. J. Cbromatogr. 1980, 201, 225-240.
RECEIVED for review August 25,1983. Resubmitted November 17, 1983. Accepted January 9, 1984. Financial support for this work was provided by the Science and Engineering Research Council in the form of a research grant and a fellowship to M. J. Willison.
Mounting Assembly for Preparation of Electrodes from Totally Insoluble Conducting Polymers Andrzej Czerwinski,' J o h n R. Schrader, a n d H a r r y B. Mark, Jr.* Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221 In the past few years, there has been an increasing interest in the study of surface-modified (1) and polymer electrodes (2). Such exotic electrode materials have significant fundamental properties and have considerable potential for practical applications in electrocatalysis. Very recently, several papers have reported the application of various conducting polymers as electrodes (2). In our laboratory we have been synthesizing a variety of substituted polyacetylenes and polythienylenes for study as electrode materials (3, 4 ) . In cases where the polymer material either is soluble in a nonaqueous solvent or can be obtained in a high density nonporous form, preparing it as an electrode is relatively simple. In the first case, a drop leave from the University of Warsaw, Warsaw, Poland.
of the dissolved polymer solution is placed on a platinum, carbon, or other conducting substrate and the solvent is evaporated (1). In the second case, the polymer material is glued to a metal wire with a silver conducting epoxy cement and the contact area masked with an inert epoxy cement such as Torr Seal (5-7). However, most of the new conducting polymers that have been synthesized in our laboratory are amorphous, highly porous, and totally insoluble in all solvents. Although these materials can be pressed into a pellet, this has presented a major problem in the construction of an electrode for the study of these materials. For example, poly(p-nitrophenylacetylene) is produced as totally insoluble, highly porous hard grains (8). They are easily connected to a metal wire with a conducting silver epoxy and the connection is well
0003-2700/84/0356-1039$01.50/00 1984 American Chemical Society
1040
ANALYTICAL CHEMISTRY, VOL. 56, NO. 6, MAY 1984 i, mA e
cathodic 06
04
Figure 1. Electrode hokler assembly: (a) Teflon rod, (b) vitreous
carbon contact, (c) platinum wire, (d) Teflon bolt, (e) brass ring cap.
covered with Torr Seal. Because of the high porosity of the polymer, the electrochemical behavior of this mounting is essentially that of a silver epoxy electrode alone. A further complication was found in that the solvent or components of the freshly mixed Torr Seal react in some way with the polymer material itself. Thus, it has become necessary to design a simple method of mounting these materials to study their electrode characteristics which is described here.
EXPERIMENTAL SECTION Electrode-Holder Construction. The body (a) of this electrode holder was constructed from a Teflon rod (d = 16 mm) as shown in Figure 1. A small hole was drilled along the length of the Teflon rod and a platinum wire (c) inserted which makes electrical contact with a small rod of vitreous carbon (b) which was pressed into the hole drilled in the Teflon rod as shown. The vitreous carbon (Gallard Schlesinger Atomergic) was chosen as a contact material as it has been shown to have no electrochemical influence on the behavior of any material deposited on its surface (9). The polymer electrode material is inserted in the slot in the bottom of the electrode and was held in place and in contact with the vitreous carbon surface by applying pressure with the Teflon screw (d). For amorphous insoluble palymers, the material was pressed into a disk with a standard IR pellet dye and press. For polymers that formed single crystals or large mechanically hard grains, the particles were used as is. In all cases, the area of the vitreous carbon contact was smaller than the polymer material. The brass ring (e) and Teflon screw were used simply to ensure good electricity of the platinum (or silver) wire and the potentiostate alligator clip.
anodic
Figure 2. Cyclic voltammograms for electrode holder system in 0.1
M KCI supporting electrolyte: (a) electrode assembly (vitreous carbon exposed) alone; (b) single crystal (SN), electrode mounted. Scan rate was 10 mV/s. i.mA
RESULTS ANb DISCUSSION Single crystals of poly(su1fur nitride), (SN),, were used to test the applicability of the electrode holder, since the electrochemical behavior of this polymer has been well characterized ( 5 ) . Curve a of Figure 2 shows the cyclic voltammetric background current for the electrode holder (vitreous carbon surface) alone using a 0.1 M KCl supporting electrolyte. Curve b is the background current obtained for a single crystal (SN), mounted in the holder as an electrode. The cyclic voltammogram is typical for an (SN), crystal mounted on a silver wire with Ag conducting epoxy and Torr Seal epoxy to mask the contact point (5-7). Clearly any background current arising from potential (if any) exposed vitreous carbon is negligible compared to that arising from the redox process occurring at surface functional groups of the (SN),. A more significant test of the electrode holder is its response to a redox system. Figure 3, curve a, is the cyclic voltammogram obtained with the electrode holder alone (thus, a vitreous carbon electrode) for a M ferricyanide, 0.1 M KC1 solution. Curve b of Figure 3 is the cyclic voltammogram
Figure 3. Cyclic voltammograms of a 1.0 X
M ferricyanide, 0.1 M KCI solution: (a) electrode assembly (vitreous carbon exposed) alone; (b) single crystal (SN), electrode mounted. Scan rate was 100 mV/s.
obtained with a single crystal of (SN), mounted in the holder assembly. Again there is no measurable current contribution to the voltammogram from a redox process at the vitreous carbon as the curve is similar to that obtained for (SN), crystals mounted as previously described (5-7). Similar experiments with pressed pellets made in a standard IR dye of porous amorphous polythienylene yielded cyclic voltammograms characteristic of polymer alone. The working surface areas of the electrodes were determined experimentally with M ferricyanide, 0.1 M KC1 solution. Previous results obtained for the polymer mounted on silver wire with Ag
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 C I T E D (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 commercialtransformer oils and a NBS transformer oil from the SRM 1581kit 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)propylbonded 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-13PCBs were used as recovery
0003-2700/84/0356-1041$01.50/00 1984 American Chemical Society
