The addition of methyl viologen (MV2+) accelerates the reduction of Na2SeO3 not only in 0.1 moldm-3 sodium phosphate buffer (PBS, pH 7) but also in 0.22 moldm-3 sodium acetate buffer (pH 4). Water-insoluble red Se is dispersed in the vicinity of the electrode surface as the reduced product. Michaelis-Menten-type relationship is obtained between the reduction current and the concentration of Na 2SeO3, suggesting that MV2+ molecules mediate the electron transfer from the electrode to HSeO3- or SeO3 2- dissolved in PBS. MV2+ is also effective in accelerating the reduction of SeO42-, which has already been reported to be electrochemically inactive.
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