SIMULTANEOUS DETERMINATION OF TETRATHIOMOLYBDATES AND MOLYBDATES IN SPIKED BLOOD-PLASMA BY DIFFERENTIAL-PULSE VOLTAMMETRY AND THEIR SPECIATION

A selective, sensitive and reliable voltametric method for the simulta neous determination of MoS42- and MoO42- has been developed. The reduc tion of HgMoS4 at - 0.43 V and the reduction of Mo as complex of MoO2- oxine(2) at - 0.63 V in acetate buffer at pH 4.9 are utilized for the simultaneous determination by differential pulse cathodic stripping vo ltametry (DPCSV). Cadmium and lead form complexes with MoS42-, but do not interfere with the determination. The limit of detection is 0.59 m u g/l Mo for MoS42- and 1.8 mu g/l for MoO42-. The R.S.D at a concentr ation level of 20 mu g/l is 4.7% for MoO42- and 3.6% for MoS42-. The m ethod is applied to spiked blood plasma samples for the determination of free tetrathiomolybdates and molybdates. Additionally, labile tetra thiomolybdates and molybdates can be determined in spiked blood plasma after treatment of the sample with 0.15 mol/l KCN and ultrafiltration .