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The determination of ultratrace concentrations of molybdenum(v1) by adsorptive cathodic stripping voltammetry on a glassy carbon mercury film electrode is described. The method involves a controlled preconcentration of the element by interfacial accumulation as molybdenum-8-hydroxyquinoline (oxine) complex on the electrode followed by a cathodic stripping voltammetric measurement. The optimum analytical conditions for the measurement of molybdenum by this method include the use of 0.20 M acetate buffer at pH 5.25, 1 mM oxine, an accumulation potential of -0.40V (vs. Ag/AgCl) and a rotated electrode at 3000 rpm. Under these conditions, the linear concentration range and lowest detectable concentration obtained with a 5-min accumulation were 0-300pg L-' (R2 = 0.997) and 0.5pgL-I [relative standard deviation (RSD) = 13.7%], respectively. The presence of most other metal ions do not interfere with the molybdenum determination, except for Pb" and Cd" which were successfully masked by addition of 3 pM EDTA, and Ti" and Wvl which were masked by 1 pM tartaric acid. The interference of surface-active substances, such as Triton X-100, is overcome by UV irradiation of the sample. The use of the adsorptive stripping voltammetric technique, after decomposition by dry ashing and UV treatment, is successfully demonstrated for the determination of molybdenum in biological and environmental materials.

A method involving a nonelectrolytic accumulation of a tin(rv)-catechol complex, followed by differential pulse cathodic voltammetric reduction of the tin-catechol complex and the direct reduction of lead(rr) ions, is described for the simultaneous determination of trace amounts of tin and lead on a glassy carbon mercury film electrode. The selective reaction of tin with catechol enables adequate resolution of its peak from the lead response. The resulting peaks which appeared at -0.39V, -0.50V and -0.66V (vs. Ag/AgCl), correspond to the reduction of Sn", Pb" and Sn", respectively. The lowest detectable concentrations in 0.10 M acetate buffer electrolyte (pH between 4.2 and 4.7) containing 5 x M catechol with an accumulation period of 300 s are l.0pg L-' and 0.5 pg L-' for lead and tin, respectively. The linear concentration range for lead and tin in the presence of 20 pg L-' of either element are 0-4mg L-' and 0-34 LLg L-' , respectively. The simultaneous determination of both elements was accomplished in solutions containing up to 4000-fold more lead than tin. The method is successfully demonstrated for the reliable simultaneous determination of lead and tin in some biological and environmental materials.