Electrochemical detection of Se (IV) and (VI) was investigated at gold-modified boron-doped diamond electrodes. Cyclic voltammetry in acid condition showed that the onset of current flows of Se (IV) and Se (VI) occurred at almost similar potentials. Furthermore, the currents at the peak potential of ∼0.9 V (vs. Ag/AgCl) showed high linearity against concentrations of both Se (IV) and Se (VI) with estimated limits of detection (S/N = 3) of 20 and 50 ppb, respectively. However, whereas oxidation peaks of Se (IV) and Se (VI) can be observed in acid and neutral pH, only oxidation peak of Se (IV) appeared in high pH. The possibility to differentiate a mixture of Se (IV) and Se (VI) by applying cyclic voltammogram (CV) at acidic and basic conditions was discussed, and it was promising, especially because, previously, it always stated that Se (VI) was not electrochemically active.
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