1766 Anal. Chem. 1987, 59, 1766-1770 LITERATURE CITED (1) Mlkkers. F. E. P.; Everaerts, F. M.; Verheggen, Th. P. E. M. J. zyxwvuts Chro- matogr. 1979, 769, 11-20, (2) Jorgenson, J. W.; Lukacs, K. D. J. Chromatogr. 1981, zyxwvutsr 218, 209-216. (3) Jorgenson, J. W.; Lukacs, K. D. Clln. Chem. (Winston-Salem, zyxwvutsrqp N.C.) 1981, 27. 1551-1553. (4) Jorgenson, J. W.; Lukacs, K. D. Anal. Chem. 1981, 53, 1298-1302. (5) Lauer, H. H: McManigill, D. Anal. Chem. 1986, 58, 165-170. (6) Tsuda. A.; Kazuhiro. N.; Nakagawa. G. J. Chromatogr. 1983, 264, (7) Green, J. zyxwvutsrqpo S.; Jorgenson, J. W. J. Chromatogr. 1986, 352, 337-343. (8) Walbroehl, Y.; Jorgenson, J. W. Anal. Chem. 1988, 58, 479-481. (9) Terabe, S.; Otsuka, K.; Ichikawa, K.; Tsuchlya, A; Ando, T. Anal. Chem. 1984, 56, 113-116. (IO) Otsuka, K.; Terabe, S.; Ando, T. J. Chromatogr. 1985, 348, 39-47. (11) Terabe, S.; Otsuka, K.; Ando T. Anal. Chem. 1985, 57, 834-841. (12) Burton, D. E.; Sepaniak, M. J.; Maskarinec, M. P. J. Chromatogr. Sci. 1986, 24, 347-351. (13) Jorgenson, J. W.; Lukacs, K. D. Science 1983, 222. 266-272. (14) Green, J. S.; Jorgenson, J. W. HRC CC. J. High Resolut. Chromatogr. Chromatogr. Common. 1984, 7, 529-531. (15) Gassman, E.; Kuo, J. E.; Zare, zyxwvutsrqpon R. N. Science 1985, 230. 813-814. (16) Gozel, P.; Gassmann, E.; Michelsen, H.; Zare, R. N. Anal. Chem. (17) Tsuda, S.; Nakagawa, G.; Sato, M.; Yagi, K. J. Appl. Biochem. 1983, 5, 530-336. (18) Walbroel, Y.; Jorgenson, J. W. J. Chromatogr. 1984, 375, 135-143. (19) Fujiwara, S.; Honda, S. Anal. Chem. 1986, 58, 1811-1814. 385-392. 1987. 59,44-49. (20) Waliingford, R. A.; Ewing, A. G. Anal. Chem. 1987, 59, 678-681. (21) Knecht, L. A.: Guthrie, E. J.; Jorgenson, J. W. Anal. Chern. 1964, 56, (22) St. Claire, R. L., 111; Jorgenson, J. W. J. Chromatogr. Sci. 1985, 23, 186-191. (23) White, J. G.; st. Claire, R. L., 111; Jorgenson, J. W. Anal. Chem. 1986, 58, 293-298. (24) Kaniansky, D.; Havasi, J.; Marak. J.; Sokoiik, R. J. Chromatogr. 1988, 366, 153-160. (25) Hood, H. P.; Nordberg, M. E. US. Patent 2 106744, Feb. 1, 1938. (26) Nordberg, M. E. J. Am. Ceram. SOC. 1944, 27(10), 299-305. (27) Elmer, T. H.; Nordberg, M. E.; Carrier, G. B.; Korda, E. J. J. Am. Ce- ram. SOC. 1970, 53(4), 171-175. (28) Elmer, T. H. J. Am. Ceram. SOC. 1983, 62(4), 513-516. (29) Pretorius, V.; Hopkins, B. J.; Shieke. J. D. J. Chromatogr. 1974, 132. 23-30. (30) Lukacs. K. D.; Jorgenson, J. W. HRC CC, J. High Resolut. Chroma- togr . Chromatogr . Commun . 1985, 8, 407-4 1 1. (31) Lauer, H. H.; McManigill, D. TrAC, Trends Anal. Chem. (Pers. Ed.) 1986, 5, 11-15. 479-482. RECEIVED for review January 20,1987. Accepted April 1,1987. This material is based upon work supported by the National Science Foundation under Grant No. BNS-8504292 and the National Institutes of Health under Grant No. 1 R01 GM37621-01. Liquid Chromatography/Electrochemical Detection of Carbohydrates at a Cobalt Phthalocyanine Containing Chemically Modified Electrode Leone1 M. Santos and Richard P. Baldwin* Department of Chemistry, University of Louisville, Louisville, Kentucky 40292 Numerous carbohydrates can be oxldlzed at low positive PO- tentlals at chemically modified carbon paste electrodes con- taining added cobalt phthaiocyanlne (CoPC). Although no response is observed at plain carbon paste electrodes, a diverse group of carbohydrates including mono- and di- saccharides, pyranose and furanose rings, and reduclng and nonreducing sugars are readily oxldlzed at the modlfled electrode surface. I n 0.15 M NaOH, the oxldatlons exhlblt a cyclic voltammetric peak potential of 4-0.40 V vs. Ag/AgCI, the waves decreasing In magnltude and shiftlng to more posltlve potentials at less baslc pH. The CoPC electrodes can be used for electrochemical detectlon of the carbohydrates In liquid chromatography as long as the applled potentlal Is regularly pulsed to -0.3 V or lower. Detection Umlts obtained in this manner range from 100 pmol injected for glucose and maltose to 500 pmoi Injected for fructose and sucrose. In recent years, several electrochemical approaches have been proposed for use in the flow injection or high-perform- ance liquid chromatographic (HPLC) analysis of carbohy- drates (1-15). These approaches are of particular interest because carbohydrates do not exhibit significant absorption at wavelengths above 210 nm and thus are not well suited for the absorption and fluorescence detection methods most commonly employed in HPLC. As a consequence, monitoring of sugars has ordinarily been performed either by refractive index detection of the intact carbohydrates or by chemical derivatization with strongly absorbing or fluorescing groups. Many carbohydrates-most notably, the reducing sugars-are known for the ease with which their chemical oxidation can be made to take place (16). Thus, it might be expected that electrochemical detection following liquid chromatography (LCEC) should provide a relatively straightforward monitoring approach. Unfortunately, utili- zation of such an approach has been stymied by the fact that carbohydrates, including the reducing sugars, have a large overpotential toward electrooxidation at the glassy carbon or carbon paste electrodes most commonly used in LCEC. As a consequence, inordinately high detector potentials are re- quired for the redox processes to occur to an appreciable extent. Thus, direct electrochemical detection is not a viable option for these compounds when carried out at conventional electrodes in the ordinary manner. Alternatively, several new electrochemical detection schemes have been developed for carbohydrates. These schemes have been of two varieties. In the first, metallic sensing electrodes such as platinum zyxwvu (1-3)) gold (4-61, and nickel (7-9) have been used in place of the usual glassy carbon or carbon paste. Although the mechanism involved in carbohydrate oxidation appears to be somewhat different at each of these surfaces, each permits the oxidation to occur at modest potentials (-0.2 to -0.8 V vs. Ag/AgCl for Pt, +0.15 V for Au, and +0.45 V for Ni) and thereby provides very sensitive LCEC detection of these compounds. However, with Pt and Au, where the electrocatalysis proceeds with adsorption of the starting carbohydrate (Pt) or of resulting oxidation products (Pt and Au), stable response is obtained only if appropriate cycles of oxidative cleaning of adsorbed material and reductive removal of the resulting oxide layer are applied between detection intervals. Thus, the use of dual- or triple-pulse potential waveforms is generally required for operation of these elec- trode materials to be practical (3, 6). With Ni, where the 0003-2700/87/0359-1766$01.50/0 0 1987 American Chemical Society