Determination of trivalent and hexavalent chromium in waste water by flow injection chemiluminescence analysis

Flow injection analysis (FIA) has been applied to the determination of both Cr(III) and Cr(VI) in waste water. The method is based on the measurement of Cr(III)-catalyzed light emission from luminol oxidation by hydrogen peroxide and the apparatus consists of a FIA system with a flow cell suitable for chemiluminescence detection. Cr(III) is determined directly by the chemiluminescence, meanwhile Cr(VI) is reduced previously to Cr(III) by H2O2 in acidic medium and then the total amount of chromium is determined. The concentration of Cr(VI) is obtained by the difference between the Cr(III) and Cr(VI) determinations. We have analyzed synthetic mixtures of both species, Cr(VI) and Cr(III), using this method and its application to waste water has been shown to be very efficient. The method is simple, inexpensive, sensitive (subnanomolar concentrations), selective and rapid. Tens of samples per hour can be performed with tolerance to potential interferants.