Thiosulfate (S2O32-) can be quantitatively oxidized to sulfate (SO42-)
without production of elemental sulfur (S-o) by a two-step anodic pro
cess at glassy carbon electrodes in 1.0M NaOAc/1.0M HOAc buffer (pH 5)
. The first step, at 1.0 V vs. SCE, converts S2O32- to tetrathionate (
S4O62-). The second step, at 1.6 V vs. SCE, converts S4O62- to S4O2-.
Addition of bromide (Br-) to S2O32- solutions expedites the desired co
nversion, presumably because of homogeneous oxidations by bromine (Br-
2) generated by anodic oxidation of Br-.