Role of acid-base equilibria in the reduction of selenious(IV) acid

Electroanalytical methods have been widely used for determination of Se(IV) , but the nature of the reduction processes involved is not well understood . Polargraphic reduction occurs in three waves (i(1), i(2), and i(3)) the h eight of which changes with pH. We proved that in wave i(1) H3SeO3+ is redu ced, in i(2) H2SeO3, and in i(3) HSeO3- SeO32- is not reducible. All reduct ions involve a transfer of six electrons and yield selenides. Limiting curr ents are controlled by the rate of protonation. As proton donors, in additi on to H3O+, the acid forms of the buffer present also act. Limiting current s increase markedly with increasing concentration of the buffer. Tenfold in crease in buffer concentration can result in up to 200% increase in limitin g current.