APPLICATION OF ADSORPTIVE STRIPPING VOLTAMMETRY TO TRACE MEASUREMENTS OF MOLYBDENUM IN PLANT MATERIALS

A procedure is presented for quantifying molybdenum in dry ashed plant samples. The determination is made by adsorptive stripping voltammetry in the differential pulse mode (DPAdSV). It is based on the adsorptive accumulation of the Mo(VI)-chloranilic acid complex on the surface of a hanging mercury drop, followed by the reduction of the adsorbed complex. Optimal conditions are stirred acidified supporting electrolyte solution (of pH 2-3), containing 10(-3) mol/L chloranilic acid and an accumulation potential of -0.20 V (vs. Ag/AgCl, 3 mol/L KCl). The height of the cathodic stripping peak around -0.60 V depends linearly on the molybdenum concentration and accumulation time (over the ranges 0-12 ng/ml and 0-300 seconds, respectively). For an accumulation period of 5 minutes, the detection limit is 0.02 ng/ml. Possible interferences by other trace metals are investigated. The proposed procedure has been applied to the determination of molybdenum traces in a variety of plants with good accuracy and precision. The results are in good agreement with those obtained by atomic absorption spectrometry.