Coulometric stripping potentiometry for arsenic( III )

Calibration‐free determination of As III in the presence of As V using coulometric stripping potentiometry is described. As III , in the concentration range 0.01‐2 mg/L, is quantitatively reduced to elemental arsenic and simultaneously dissolved in gold codeposited onto a glassy carbon substrate by electrolysis for 4 minutes at −0.50 V (vs. Ag/AgCl (0.01 MCl − )) in 12 μL samples containing 3 M hydrochloric acid and 10 mg/L gold(III). Selectivity between arsenic(III) and (V) is achieved by proper control of the deposition potential and by minimizing the gold(III) concentration and the time between addition of gold(III) and commencement of analysis.