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

A procedure is presented for quantifying molybdenum in dry ashed plant samples. The determination is made by adsorptive stripping voltammetr y in the differential pulse mode (DPAdSV). It is based on the adsorpti ve accumulation of the Mo(VI)-chloranilic acid complex on the surface of a hanging mercury drop, followed by the reduction of the adsorbed c omplex. Optimal conditions are stirred acidified supporting electrolyt e solution (of pH 2-3), containing 10(-3) mol/L chloranilic acid and a n accumulation potential of -0.20 V (vs. Ag/AgCl, 3 mol/L KCl). The he ight 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 interferenc es 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 agre ement with those obtained by atomic absorption spectrometry.