Kinetic-spectrophotometric determination of manganese and vanadium + manganese by oxidation of pyrogallol red

Abstract

Spectrophotometric methods for the determination of manganese and the simultaneous determination of vanadium + manganese, based on the oxidation of Pyrogallol Red (PGR), are described. Manganese or vanadium + manganese are determined by the decrease in the absorbance of the characteristic band at 490 nm at pH 4. At pH 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 manganese(VII) over the range 0–1.10 p.p.m. The limit of detection of manganese is 0.03 p.p.m. Studies were made of the selectivity of the method with respect to possible interferences from 22 species, which have been classified according to their possible mechanism of interference. The precision and accuracy of the method using a fixed time of 5 min were also determined. The simultaneous determination of vanadium in the range 0.20–1.83 p.p.m. and manganese(VII) in the range 0.11–1.10 p.p.m. by using a system of equations in which the absorbance at a fixed time is considered to be proportional to the total concentration of the two elements and their effects on the absorbance of PGR are additive, is described.