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.