A Spectrophotometric Determination of Chromium and Vanadium

Abstract

A very simple, selective and sensitive method is developed for the spectrophotometric determination of Cr^VI and/or V^V based on their reactions with perphenazine to instantaneously give a red colored product exhibiting a maximum absorbance at 526 nm. Following the recommended procedure, chromium and vanadium can be determined with linear calibration graphs up to 0.40 and 1.00 µg ml^-1 and detection limits of 3 and 5 ng ml^-1, respectively. The molar absorptivities are 1.87×10⁴ and 1.20×10⁴ l mol^-1 cm^-1 with Sandell sensitivity indexes of 2.8 and 4.2 ng cm^-2 for Cr and V, respectively. Analyses of mixtures of Cr^VI and V^V in the ratios of 1:100 to 100:1, following the recommended procedure gave recoveries of 97 - 102% with relative standard deviations of ≤1.4% for both Cr^VI and V^V. The total Cr and V was determined first; then, V was determined after addition of As^III to reduce Cr^VI that was calculated by the difference. Statistical treatment of the analytical results did not detect any systematic error and showed the high accuracy and precision of the method. The unique selectivity and sensitivity of the method allowed its direct application to the determination of Cr and V in complex matrices of certified reference materials and synthetic mixtures. The results obtained are in excellent agreements with the nominal values.