Chromogenic reaction of bromopyrogallol red with tri- and hexavalent chromium in the presence of cetyltrimethyl ammonium bromide and its application in Cr speciation

Abstract

The coordination reactions of bromopyrogallol red (BPR) with tri- and hexavalent chromium in the presence of cetyltrimethylammonium bromide (CTAB) have been studied by absorption spectrometry. Results show that the reactions of Cr(VI) and Cr(III) with BPR in the absence or presence of CTAB have different temperature dependences. The reaction mechanism of Cr(VI) is that Cr(VI) is first reduced by BPR to Cr(III) and then the Cr(III) produced reacts with BPR. Based on the study on the coordination reactions and the effects of surfactants upon them, a simple, rapid, sensitive and accurate method for Cr speciation has been developed. Over the range of 0–8 μg Cr(VI) or 0–12μg Cr(III) per 25ml final volume, the calibration curve is linear with a detection limit of 3.5 × 10−7 mol/1 for Cr(VI) or 4.4 × 10−7 mol/1 for Cr(III).