Measurement of sulfite at oxide-coated copper electrodes

The amperometric determination of sulfite was performed using copper electrodes in alkaline media. A mechanism for the oxidation of sulfite at these electrodes is suggested, based on the formation of superficial CuO(.OH), which acted as an electron transfer mediator to the analyte. At 0.5 V versus SCE in 1 M NaOH, sulfite could be calibrated at a sensitivity of 0.2 A l mol^–1 cm^–2, with a response time for the steady state of 30 s. The limit of detection (three times the signal-to-noise ratio) was 2.5 × 10^–6M and the response was linear up to 5 × 10^–4M (r² = 0.9996, n = 15). The standard deviation (n = 10) at 1× 10^–5 and 1 × 10^–4M was 3.27 × 10^–7 A cm^–2 (mean = 3.62 × 10^–6 A cm^–2) and 1.07 × 10^–13 A cm^–2 (mean = 2.25 × 10^–5 A cm^–2), respectively.