DETERMINATION OF ULTRA-TRACE CONCENTRATIONS OF TIN BY ADSORPTIVE CATHODIC STRIPPING VOLTAMMETRY ON A GLASSY-CARBON MERCURY FILM ELECTRODE

A sensitive and selective method is described for the determination of ultra-trace concentrations of tin by adsorptive cathodic stripping voltammetry on a glassy carbon mercury film electrode. The method involves a controlled preconcentration by accumulation of tin-catechol complexes on the electrode followed by stripping voltammetric measurement in the cathodic direction. The optimum conditions for the determination of tin by this method include the use of a rotated electrode at 1920 rpm, 0.10 M acetate buffer electrolyte (pH 4.2-4.7), 5 x 10(-4) M catechol and an accumulation potential of -0.20 V vs. Ag/AgCl. A linear concentration range is obtained from 0 to 35 mug l-1 and the limit of detection is 0.5 mug l-1 for an accumulation period of 300 s. An interference study with various metal ions indicated that these substances generally do not interfere with the tin determination, except for Cu, Cd and Cr. The interference of Cu and Cd is eliminated by the addition of 1 x 10(-6) M EDTA into the solution. The interference of surface-active organic substances, e.g., Triton X-100, is overcome by UV irradiation of the sample for at least 2 h. The method was successfully employed for the determination of tin in fruit juices. Comparison of the results obtained for the juices demonstrated reasonable agreement with those obtained by atomic absorption spectrometry.