Spectrophotometric method of chromium (III) by 4-(2-pyridylazo)-resorcinol in the presence of hydrogen peroxide

Abstract

We found that the reactivity of chromium (III) with complexing agents was accelerated when the oxidation state of chromium (III) was turned to change to (IV) or (V) in the presence of hydrogen peroxide. Consequentry, we applied the finding to the reaction of chromium (III) and 4-(2-pyridylazo)-resorcinol (PAR) to obtain more sensitive and simple method for the determination of chromium (III). A given quantity of chromium (III), 2 ml of 5.00 × 10^-3 M PAR, 2 ml of 2 M acetic acid-sodium acetate buffer solution, and 3 ml of 1 M hydrogen peroxide were pipetted into a 100 ml Erlenmeyer flask fitted with a plug. The final volume was brought to 50 ml by the addition of redistilled water. The solution was warmed for 20 min at 40°C in a thermostatically-controlled water bath. After cooling to room temperature, a portion of the solution was then transferred into a cell. The measurements of absorbance were made at 530 nm. The calibration curve was obtained by the above procedure for the concentration range of (0.100.52) μg ml^-1 of chromium (III). The molar absorptivity at 530 nm was calculated to be 5.1 × 10⁴ 1 mol^-1 cm^-1. The method is very sensitive and simple.