BLOCKING OF CHEMICALLY MODIFIED GRAPHITE-ELECTRODES BY SURFACTANTS

The blocking effect of selected surfactants on phenoxazine-modified graphite electrodes was studied by amperometry and cyclic voltammetry. Non-ionic surfactants such as Tween 20, 60 and 80 caused an almost irreversible blocking of NADH oxidation at the electrode. Hexacyanoferrate(II)/(III) and protons, however, could penetrate the adsorbed surfactant layer. Cationic and anionic surfactants produced reversible blocking, i.e. the current was depressed when the surfactants were present, but returned to its original value after the system had been flushed with pure buffer. Adsorbed non-ionic surfactants could easily be removed by a solution of SDS at a concentration above cmc, thus restoring the original current for NADH oxidation.