Kinetic spectrophotometric determination of chromium(VI) by oxidation of sodium pyrogallol-5-sulphonate by hydrogen peroxide

A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437 nm within 1 min after addition of H2O2. The optimum reaction conditions are PS (1.32.10(-3) mol.dm(-3)), H2O2 (0.32 mol.dm(-3)), HClO4 (2.6.10(-3) mol.dm(-3)) at 25degreesC. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25 ng.cm(-3) and a detection limit of 0.024 ng.cm(-3), based on the 3sigma criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.