Selective measurement of chromium(VI) by fluorescence quenching of ruthenium.

A flow injection method is described for the selective measurement of chromium(VI) in aqueous solutions. This method is based on the dynamic quenching of ruthenium(II) fluorescence. The detection limit is 0.43 ppm and 40 samples can be analyzed per hour. Selectivity is demonstrated over ferrous, nickel, cupric and zinc cations and no effect is observed from sulfate, chloride, borate and phosphate. Some interference quenching was measured for cyanide and nitrate, but the method is more responsive to chromium(VI) by factors of 10.2 and 82, respectively. The effects of solution pH, carrier stream flow rate and ruthenium concentration are demonstrated. Results indicate the method is suitable for measuring chromium(VI) in effluents from electroplating baths.