Spectrophotometric determination of vanadium by oxidation of pyrogallol red

A spectrophotometric method of vanadium determination is described. It is based on the oxidation of Pyrogallol Red (PGR) and vanadium is determined by the decrease in absorbance of its characteristic band at 490 nm and at pH 4. This absorbance decrease is proportional to the concentration of vanadium(V). At a pH of 4, an ionic strength of 0.1 M, a temperature of 25 °C and a wavelength of 490 nm, there is a linear relationship between the absorbance of PGR (6 × 10–5M), at a fixed time, and the concentration of vanadium(V) over the range 0–1.83 p.p.m. The limit of detection of vanadium is found to be 0.05 p.p.m. In the presence of potassium bromate, the determination is possible at the parts per billion level. This paper describes studies of the selectivity of the method with respect to possible interference from 20 important species contained in ferrous and non-ferrous alloys, which have been classified according to their possible mechanism of interference. The precision and accuracy of the method at times of 5 and 10 min are also described.