Spectrofluorometric determination and chemical speciation of trace concentrations of chromium (III & VI) species in water using the ion pairing reagent tetraphenyl-phosphonium bromide

A highly selective, and low cost extractive spectrofluorometric method has been developed for determination of trace concentrations of chromium (III & VI) in water samples using the fluorescent reagent tetraphenylphosphonium bromide (TPP+·Br−). The method was based upon solvent extraction of the produced ion associate [TPP+·CrO3Cl−] of TPP+·Br− and halochromate in aqueous HCl and measuring the fluorescence quenching of TPP+·Br− in chloroform at λex/em = 242/305 nm. The fluorescence intensity of TPP+Br− decreased linearly on increasing the chromium (VI) concentration in the range of 1–114 μg L−1. The limits of detection (LOD) and quantification (LOQ) of chromium (VI) were 0.43 and 1.42 μg L−1, respectively. Chromium (III) species after oxidation to chromium (VI) with H2O2 in alkaline solution were also determined. Chemical speciation of chromium (III & VI) species at trace levels was achieved. The method was applied for analysis of chromium in certified reference material (IAEA Soil-7) and in tap- and wastewater samples and compared successfully (>95%) with the inductively coupled plasma-mass spectrometry (ICP-MS) results.