Spectrophotometric determination of trace amounts of vanadium by formation of the vanadium -4-(2-pyridylazo)resorcinol (PAR)-crystal violet complex: application to the analysis of plant materials

Abstract

The anionic complex of vanadium with 4-(2-pyridylazo)resorcinol (PAR), obtained at pH 4·6–5·1, forms an ion pair with Crystal Violet. This ion pair can be extracted with benzene-isobutyl methyl ketone (3 + 2). In the extracted ion pair the proportions of vanadium to PAR to Crystal Violet are 1:1:1. The coloured extract gives an absorption maximum at 585 nm, and Beer's law is obeyed in the concentration range 0·05–0·5 µg ml–1 of vanadium. The molar absorptivity is equal to 1·1 × 105 l mol–1 cm–1.The method was applied to the determination of trace amounts of vanadium in dried plant materials after wet ashing of the sample and extraction of the vanadium as the N-benzoyl-N-phenylhydroxylamine complex. The results obtained for the determination of vanadium in serradella, rye straw and grain and trefoil showed a relative standard deviation of 8–15 per cent. at the 0·1–0·25 p.p.m. level of vanadium and of about 25 per cent. at the 0·05 p.p.m. level.