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Catalytic effect of mercury(II) on the photo-oxidation of EDTA by iodine: kinetic determination of mercury.

A kinetic method for the determination of trace amounts of mercury based on the marked catalytic effect exerted by HgII on the photochemical reaction between iodine and EDTA is proposed. The reaction, involving 6 × 10–5M l2 and 2 × 10–4M EDTA, is carried out by irradiation with 2000 lux at pH 5 and 30 °C. The rate of the reaction is monitored amperometrically by measuring the time required for cancellation of the reduction current of iodine, measured with a Pt reference electrode maintained at –100 mV vs. SCE. Mercury can be determined in the range 0.4–6 ng ml–1 by irradiation at pH 3 and 40 °C, and between 4 and 42 ng ml–1 at pH 5 and 40 °C, using 2000 lux radiation in both instances. The proposed method has been applied with excellent results to the determination of mercury in zinc concentrates and in contact lens cleaning solutions.