Direct voltammetric determination of Mo(VI) in plants: the need for a multivariate study of interferences

A multivariate modelling procedure using a second order composite design showed that the adsorptive stripping voltammetry (AdSV) technique used for molybdenum determination in a N,N-dimethylformamide (DMF)-ethanol-water homogeneous ternary solvent system (HTSS) using alpha-benzoinoxime (alphaBO) as the complexing agent and a sodium acetate-acetic acid buffer as the supporting electrolyte is much more tolerant to the presence of phosphorous (as phosphate) and iron than it could be presumed. Instead of the concentration ratios of P/Mo = 100 and Fe/Mo = 500, determined by univariate experiments, these values were respectively raised to 97,500 and 4200 when the phosphate and Fe(III) levels are varied simultaneously from 0.625 to 2.500 and from 0.006 to 0.150 mg 1(-1), respectively, in the voltammetric cell, keeping the molybdenum concentration constant at 3.00 mug 1(-1). This allowed us to propose a straightforward AdSV-HTSS procedure for the determination of Mo(VI) in plants. The AdSV results compared favourably with those obtained by using graphite furnace atomic absorption spectrometry (GFAAS) and with the results of samples from the International Plant-Analytical Exchange (IPE) programme of Wageningen University (The Netherlands). (C) 2003 Elsevier Science B.V. All rights reserved.