Journul of Chromatography , 5 14 (1990) 1 II-1 78 Elsevier Science Publishers B.V., Amsterdam CHROM. 22 566 Electrochemical detection for high-performance liquid chromatography using a Kel-F wax-graphite electrode JULIE WANGSA and NEIL D. DANIELSON* Department qf Chemistry. Miami University. O.xford, OH 45056 (U.S.A.) (First received October 3rd, 1989; revised manuscript received April 24th, 1990) ABSTRACT A carbon paste electrode using Kel-F wax as the binder was characterized for electrochemical detection in high-performance liquid chromatography. The resulting electrode was stable in solutions with high organic content and possessed good repro- ducibility and detection limit. The amperometric response of the Kel-F wax carbon paste electrode by flow injection analysis was about 26% higher than that of Kel-F oil carbon paste electrode in an acetonitrile-water (70:30) solution. This represented a two-fold improvement over the Nujol oil carbon paste electrode. Cyclic voltammetric data indicated the greater response of the Kel-F wax carbon paste electrode in high- acetonitrile-containing solutions was due to a higher surface area caused in part by solvent swelling of the electrode. Three unconjugated estrogens were separated and detected satisfactorily at the pg level using this Kel-F wax carbon paste electrode. INTRODUCTION The most common electrodes used for electrochemical detection in high- performance liquid chromatography (HPLC) are based on various types of carbon such as glassy carbon, pyrolytic graphite, and numerous kinds of carbon pastelp5. Carbon paste electrodes (CPEs) can be advantageous because they are cheap, easy to prepare and replace, and modifiable to suit the required electrode potential. These CPEs, however, suffer from several drawbacks. The most severe limitation of the CPE is the tendency for the binder (such as Nujol) to dissolve in solutions containing an appreciable content of organic solvent. To overcome this problem, a variety of composite electrodes such as graphiteeKe’-F particle6 and graphite-epoxy electrodes’ have been developed. In our previous work’, we have compared the performance of Nujol and Kel-F oil-based CPEs. The response of identically prepared Kel-F and Nujol oil CPEs to estriol was evaluated by flow injection analysis (FIA) using mobile phases of various acetonitrile content. An enhancement factor of about 1.7 over the response of the Nujol oil CPE was obtained for the Kel-F oil CPE as the acetonitrile content in the 0021-9673/90/$03.50 li‘, 1990 Elsevier Science Publishers B.V.