CONDUCTIVE CARBON CEMENT AS ELECTRODE MATRIX FOR COBALT PHTHALOCYANINE MODIFIED ELECTRODES FOR DETECTION IN FLOWING SOLUTIONS

A comparison has been made of the performance of electrodes modified with cobalt phthalocyanine catalyst prepared in different ways for use in flowing solutions. Because of leaching direct adsorption of cobalt phthalocyanine (CoPC) on a glassy carbon electrode surface had little analytical utility. Use of a polystyrene film prevents leaching of CoPC from the electrode surface to some extent, albeit at the expense of sensitivity. A new composite electrode with conductive carbon cement as electrode matrix was found to be comparable to a carbon paste electrode in terms of the electrocatalytic properties of CoPC towards thiol compounds (N-acetylcysteine, cysteine, glutathione and dithiothreitol) both in quiescent and flowing solutions, but is obviously superior in terms of long-term stability in flowing solutions. An advantage of the use of conductive carbon cement is that it can be repacked, so that the normal electrode body for carbon paste can be utilized. The modified electrode has been applied in liquid chromatography for the determination of cysteine in urine samples. The decrease of the electrode sensitivity over 5 h was about 5% at a flow-rate of 1.8 ml min-1 and a fixed potential of 0.7 V vs. Ag/AgCl.