Kinetic-spectrophotometric determination of chromium(VI) by the oxidation of pyrogallol red

Abstract

A spectrophotometric method is described for the determination of chromium(VI), which is based on the ability of chromium(VI) to oxidise Pyrogallol Red (PGR). For a fixed time the decrease in absorbance of the characteristic band of PGR (with λ_max. at 490 nm and at pH 4) is proportional to the concentration of chromium(VI) in the range of 0–1.00 p.p.m. The limit of detection of chromium is found to be 0.05 p.p.m. using 6 × 10^–5M PGR at pH of 4, an ionic strength of 0.1 M, a temperature of 25 °C and a wavelength of 490 nm.

The oxidation of PGR by Cr(VI) is first order with respect to Cr(VI). This paper describes studies of the selectivity of the method with respect to possible interferences from 22 species, which have been classified according to their possible interference mechanism. The precision and accuracy of the method for times of between 5 and 20 min are also described.