Visible spectrophotometric determination of tantalum in soil, sediment, minerals, and alloys

A new, sensitive, and selective method is described for the spectrophotomet ric determination of Ta(V). The method is based on the extraction of the Ta (V)-F -CV+ complex (CV+ = crystal violet cation) with a benzene solution of imidoyl derivatives (ID), i.e., N,N ' -diphenylbenzamidine (DPBA), N-hydro xy-N,N ' -diphenylbenzamidine, and N(2,5-dimethyl)phenyl-p-tolylimidoylphen ylhydrazine, from sulfuric acid solution; DPBA was selected for detailed st udy. The molar absorptivities of the Ta(V)-F-CV+ -ID complexes in the benze ne solution were in the range of (1.00-1.65) x 10(5) L/mol(.)cm at 600 nm. The limit of detection was 7 ng Ta/mL (which had an absorbance greater than that of the blank + 3 standard deviations). The optimization of the analyt ical variables, the composition of the complex, and the effect of diverse i ons in the determination of Ta are discussed. The present method was applie d to the determination of Ta in environmental samples, i.e,, soil, sediment , minerals, and alloys.