An electrocatalytic approach for the measurement of chlorophenols

An electrocatalytic approach using an enzymatic reaction for the regeneration of analytes has been developed for the measurement of chlorophenols. Chlorophenols were oxidized to quinoid compounds by ceric sulfate or chloroperoxidase and the resulting oxidation products were measured in an amperometric system using glucose oxidase immobilized on a glassy carbon electrode. In this system, glucose oxidase was readily reduced by its substrate, glucose, to provide a non-rate-limiting source of electron flow towards the electrode. The quinoid products of chlorophenols then recycled the reduced enzyme to its original active form, i.e., mediating the rate-limiting electron transfer from the enzyme to the electrode. Analytical selectivity resulted from both the production of quinoid products and their electrocatalytic specificity for glucose oxidase, while high sensitivity was obtained from the amplified redox cycling of the analyte electrocatalyst. While this method was able to differentiate para-chlorinated chlorophenols from other chlorophenols, its selectivity for 2,4,6-trichlorophenol was uniquely high. The detection limit of this method was about 1 nM and the detection principle was easily integrated into flow injection analysis for a sample throughput as high as one per min.