A comparative study of some phenoxazine and phenothiazine modified carbon paste electrodes for ethanol determination

An amperometric ethanol electrode is described based on carbon paste modified with alcohol dehydrogenase (ADH) and a mediator. The possibility of coupling this enzymatic system with some commercially available phenoxazines [Meldola Blue (MB), Nile Blue (NB) and Brilliant Cresyl Blue (BCB)] and phenothiazines [Toluidine Blue O (TBO)], that allows the electrocatalytic oxidation of NADH, was investigated. Different strategies of mediator immobilization in the carbon paste were compared. The most suitable immobilization technique was the coverage of the modified carbon paste surface with a dialysis membrane and the best electrocatalytic structure was the phenothiazine TBO. The TBO(10%)-ADH(5%)-modified carbon paste electrode shows steady state signals for ethanol within 30 s. The influence of various experimental conditions was explored for optimum analytical performance. Amperometric detection of ethanol at an applied potential of 50 mV (Ag/AgCl) gives linear responses over the concentration range of 10-100 mu M, with a detection limit of 5 x 10(-6) M. The modified electrode was applied to the determination of ethanol in wine.