VOLTAMMETRIC DETERMINATION OF TETRATHIOMOLYBDATES, AN EFFECTIVE ANTIDOTE IN ACUTE INTOXICATION BY COPPER(II) AND OTHER TOXIC METAL-IONS

A selective, sensitive and reliable voltammetric method for the determ ination of free tetrathiomolybdates, an antidote in acute intoxication by copper(II) and other toxic metal ions, is developed. Cyclic voltam metry of tetrathiomolybdates in aqueous solutions reveals a substantia lly different behaviour with respect to dimethylformamide solutions. T he irreversible kinetically controlled reduction of HgMoS4 in aqueous solutions is exploited to determine MoS42- by differentical pulse volt ammetry (DPV). MoS42- and MoO42- show quite different electrochemical behaviour and the reduction peak of HgMoS4 at - 0.43 V in acetate buff er at pH 4.9 is well separated from the peaks of MoO42-; on the other hand, in phosphate buffer of pH 7.3 MoO42- did not give any peak, whil e HgMoS4 gave one at - 0.67 V. The hydrolysis of MoS42- is also studie d. CadMiUM Complexes with MoS42-, but does not interfere in the determ ination of free tetrathiomolybdates. The determination limit is 0.02 m ug ml -1 for DPV and can be lowered to 1 ng ml-1 by employing differen tial pulse adsorptive stripping voltammetry; the relative standard dev iation is less than 4%.