2-(5-bromo-2-pyridylazo)-5-diethylaminophenol as a photometric reagent for the spectrophotometric determination of chromium(III) and/or chromium(VI) and its application to the sequential determination of chromium(III) and chromium(VI) in mixtures

Abstract

Three simple, rapid and accurate spectrophotometric procedures are described for the individual determination of chromium(III) and chromium(VI) and the sequential determination of chromium(III) and chromium(VI) in mixtures. The first two procedures are based on measuring the absorbance (ε= 2.64 × 10⁴ at 580 nm) of the coloured product as formed by the reaction between chromium(III or VI) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP); these two procedures are suitable for the individual determination of chromium(III) or chromium(VI), respectively, in amounts up to about 50 µg per 50 ml when either of them is present in the sample without prior conversion of the valence state of the chromium by additional oxidation or reduction. The third procedure, for the sequential analysis of chromium(VI) and chromium(III), involves the determination of the total amount of chromium with 5-Br-PADAP after the determination of chromium(VI) with diphenylcarbazide [without interference from chromium(III)] and destruction (by boiling) of the excess of diphenylcarbazide and the chromium(III)-diphenylcarbazone complex.

The procedures have been applied to the determination of chromium(VI) and chromium(III) in three water samples containing both chromium(III) and chromium(VI) without the need for any additional separation process, masking or solving of simultaneous equations.