Anal. Chem. 1982, 5 4 , 1169-1174
specificity procedures for establishing standard reference material (SRM) values of phenols and miscellaneous hydrocarbons in shale oil. With LCEC, simpler procedures may be followed to profile electroactive solutes. The selectivity of LCEC for trace phenols is exemplified in Figure 7. The base line shift with LCEC is iminimal since the detector is operated a t low gain. Of course, the selectivity prevents the determination of important polyaromatic hydrocarbons. The choice of methodology is dependent on the goals desired. Provided that the solutes are electroactive, simpler manipulations as described here enable the analyst to shorten analysis times and improve method reliability. LITERATURE C I T E D (1) Rand, M. C., Cireenberg, A. E., Taras, M. J., Ed. "Standard Methods for the Examlnation of Waste and Wastewater", 14th ed.; American Public Health Association: Washington, DC, 1976. (2) Edgerton, T. I?.; Moseman, R. F.; Lores, E. M.; Wrlght, L. H. Anal. Chem. 1980, 5 2 , 1774-1777. (3) McKague, A. B. J. Chromatogr. 1981, 208, 287-293. (4) fed. Regist. 1979, 4 4 , (Dec. 3), 69464-69575. (5) Ogan, K.; Katz, E. Anel. Chem. 1981, 5 3 , 160-163. (6) Kuwata, K.; Ueborl, M.; Yamazaki, Y. Anal. Chem. 1981, 5 3 ,
1531-1534.
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(7) Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1979, 51, 1426-1 433. (8) Ugiand, K.; Lundanes, E.; Grelbrokk, T. J. Chromatogr. 1981, 213, 63-90. (9) Sparacino, C. M.; Minick, D. J. Environ. Sci. Technol. 1980, 14, 860-882. (10) Shoup, R. E. "Bibliography of Recent Reports on Liquid ChromatographylEiectrochemistry"; Bioanalytlcal Systems Inc.: West Lafayette, IN, 1980. (11) Armentrout, D. N.; McLean, J. D.; Long, M. W. Anal. Chem. 1979, 5 1 , 1039-1045. (12) Weisshaar, D. E.; Tallman, D. E.; Anderson, J. L. Anal. Chem. 1981, 5 3 , 1809-1813. (13) Shoup, R. E., unpublished results. (14) Schauwecker, P.; Frei, R. W.; Ernl, F. J. Chromatogr. 1977, 136, 63. (15) Bushway, R. J. J. Chromatogr. 1981, 211, 135-143. (16) Werkhoven-Goewle, C. E.; Brinkman, U. A. Th.; Frei, R. W. Anal. Chem. 1981, 5 3 , 2072-2080. (17) Hackman, M. R.; Brooks, M. A. J . Chromatogr. Blomed. Applications 1981,22, 179-190. (18) Lund, U. J. Liq. Chromatogr. 1981, 4 , 1933-1945. (19) Hertz, H. S.;Brown, J. M.; Cheder, S. N.;Guenther, F. R.; Hiipert, L. R.; May, W. E.; Parris, R. M.; Wise, S . A. Anal. Chem. 1980, 52,
1650.
RECEIVED for review December 18,1981. Accepted March 24, 1982.
Carbon Electrodes for Liquid Chromatography Detection J. D. McLean Dow Chemical U.S.A., Michigan Dlvision Analytical Laboratories, 1602 Building, Midland, Michigan 48640
Graphlte electrodes wore treated wlth various lmpregnatlng agents to Improve signal-to-nolse ratios for analytical measurements, and surface morphology was examlned by scannlng electron microscopy. Electrodes were formulated from carbon black and various polymeric blndlng agents and found to possess superior qualltles for use as worklng electrodes for llquld chromalography cletectors. Parameters evaluated were percent carbon loading, type of blndlng agent, method of electrode fabrlcatlon, and preparatlon of electrode surface. The electrodes were applled to the detection of halogenated phenols and lnhlbltors In monomer systems.
Wax impregnation has been the method of choice to improve the performance of graphite electrodes for analytical electrochemical measurements. A detailed study of various waxes was reported by Gaylor ( I ) . Adams (2) described the preparation of the carbon-paste electrode and Kissinger ( 3 ) has applied this electrode to the detection of species eluting from liquid chromatography (LC) columns. The electrochemical detection of various halogenated phenols was studied ai, several electrode materials after appropriate LC separation. Carbon paste and wax-impregnated graphite were found to be unsuitable, as a result of dissolution of the binder in acetonitrile solvents and loss of performance, respectively. Previously, a carbon black polyethylene combination was found to plossess unique and desirable properties ( 4 ) . While the polyethylene carbon black (PECB) electrode material outperformed all other forms of carbon tested, only one composition (50/50 by weight) was evaluated. This paper
reports a detailed study of a variety of carbon black polymer electrodes. EXPERIMENTAL SECTION Apparatus. The LC equipment employed consisted of an Altex Model l1OA pump, a Chromatronix Model R6031V6K rotary injection valve with a 250-pL injection loop, a Laboratory Data Control (LDC) 12.7 X 330 mm Cheminert glass column with movable Teflon plungers to permit adjustment of the column bed length, and a tubular anode electrochemical detector ( 4 ) employing a Ag/AgCl reference electrode. The scanning potentiostat employed was designed by J. Holland of Michigan State University. A Varian Model (2-2500 variable range recorder was employed to record all chromatograms. The various carbon electrodes were prepared as previously described ( 4 ) and machined to 3/16 in. 0.d. X 3/16 in. long tubular electrodes with 1/16 in. diameter bores. Carbon black anodes are the subject of pending patents. An electrochemical LC detector employing a similar cell design and a carbon black polyethylene working electrode has recently become available from Chromatix of Sunnyvale, CA, as the Model CMX-20. A Cambridge Mark IIA scanning electron microscope was employed for surface morphology studies. Electrodes were mounted so that the inside surface of the bore could be observed. By use of a magnification of 50X, the edges of the in. bore could be kept in the field of view. Reagents. The LC column was slurry packed with Aminex 50W-X4, 20-30 pm particle size strong cation exchange resin available from Bio-Rad Laboratories, Richmond, CA. Fresh resin was washed in the column with UV grade acetonitrile and then with 1 N sulfuric acid prior to use. Because of the strong acid eluent, the Delrin column end fittings normally supplied with the column were replaced with ones machined from stainless steel. The eluent employed was a 29% acetonitrile-water mixture containing 0.05 N sulfuric acid to suppress phenol ionization and to provide supporting electrolyte for the electrochemicaldetector.
0003-2700/82/0354-1 169$01.25/0 0 1982 American Chemical Society
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ANALYTICAL
CHEMISTRY, VOL. 54,
NO. 7, JUNE 1982
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