Catalytic spectrophotometric determination of hexavalent chromium

A simple, highly selective and sensitive catalytic method is presented for the determination of Cr-VI in natural and highly polluted waste-waters. The method is based on the catalytic effect of Cr-VI on the oxidation of 2-aminophenol (AP) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 430 nm after 10 minutes of mixing the reagents. The optimum reaction conditions are 2 x 10(-3) mol l(-1) of AP, 0.3 mol l(-1) of H2O2 and 2.5 x 10(-2) mol l(-1) of phosphate buffer (pH 6.45 +/- 0.02), at 40 degreesC. The linear range of the calibration graph was up to 7.0 ng ml(-1) of Cr-VI and the detection limit (3S(b)) was 0.10 ng ml(-1). Interferences of Crm and Fe-III ions were eliminated by a quantitative co-precipitation with Al(OH)(3), rendering the method highly selective for Cr-VI. Spectrophotometric determination of as little as 1.0 ng ml(-1) of Cr-VI in aqueous solutions gave an average recovery of 99.5% with a relative standard deviation of 1.2% (n = 5). The implemented method was conveniently applied to natural and highly polluted industrial waste waters. A comparison of published catalytic-spectrophotometric methods is also presented.