Indirect speciation of Cr(III) and Cr(VI) in water samples by selective separation and preconcentration on a newly synthesized chelating resin

Abstract

A new solid phase extraction method for the speciation, separation and preconcentration of Cr(III) and Cr(VI) was developed. As solid phase material, a new chelating resin, poly N-(4-bromophenyl)-2-methacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid-co-divinylbenzene was synthesized. Cr(III) was separated from Cr(VI) and preconcentrated by using a column containing chelating resin. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by hydroxylamine hydrochloride as a reducing agent. Then Cr(VI) was calculated by substracting Cr(III) concentration from the total chromium concentration. The parameters such as the effect of pH, eluent type, volume and concentration, flow rate of sample solution, sample volume and effect of interfering ions for the preconcentration of Cr(III) were investigated. The optimum pH was found to be 2. Eluent for quantitative elution was 10 mL of 1 mol L −1 HCl. The preconcentration factor of the method was 100. At the optimum conditions determined experimentally, the recovery for Cr(III) was found to be 95 ± 3%. The limit of detection (3 s/ b) of the method was 1.58 μg L −1. In order to determine the adsorption behaviour of chelating resin, the adsorption isotherm of Cr(III) was studied. Adsorption capacity and binding equilibrium constant were calculated to be 21.8 mg g −1 and 1.32 ×10 −2 L mg −1, respectively. The method was validated by analysing certified reference material (TMDA-54.4 a trace element fortified calibration standard). The proposed method was applied to the determination and speciation of chromium in tap water, lake water, spring water and wastewater samples with satisfactory results.