Determination of vanadium as 4-(2-pyridylazo)resorcinol-hydrogen peroxide ternary complexes by ion-interaction reversed-phase liquid chromatography.

The separation and determination of the vanadium(V) ternary complex formed with 4-(2-pyridylazo)resorcinol (PAR) and hydrogen peroxide using ion-interaction reversed-phase high-performance liquid chromatography on a C18 column has been investigated. The optimal mobile phase was a methanol-water solution (32:68, v/v) containing 3 mM tetrabutylammonium bromide, 5 mM acetic acid and 5 mM citrate buffer at pH 7, with absorbance detection at 540 nm. The stoichiometry of the ternary complex of vanadium at pH 6 in 10 mM acetate buffer using the mole ratio and Job's method by HPLC indicated that the mole ratio of V(V):PAR:H2O2 was 1:1:1. The optimal conditions for precolumn formation of the ternary complex were 10 mM acetate, 7 mM H2O2, 0.3 mM PAR, and pH 6. The method gave relative standard deviations of retention time, peak area and peak height for the ternary complex of 0.187, 0.45 and 0.57%, respectively. The detection limit (at a signal-to-noise ratio of 3) for V(V) was 0.09 ng/ml in the digested sample using a 100-microl injection loop (or 0.09 microg/g in the solid fertiliser sample). The method was applied to the analysis of fertilisers (phosphate rocks and nitrogen, phosphorus and potassium fertiliser). The results for vanadium obtained by the HPLC method agreed well with those from magnetic sector inductively coupled plasma MS analysis.