Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

Abstract

Cloud point extraction (CPE) was applied as a preconcentration step for HPLC speciation of chromium in aqueous solutions. Simultanous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by CPE with diethyldithiocarbamate (DDTC) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the DDTC chelates of Cr(III) and Cr(VI) was realized on a RP-C 18 column with the use of a mixture of methanol–water–acetonitrile (65:21:14, v/v) buffered with 0.05 M NaAc–HAc solution (pH 3.6) as the mobile phase at a flow rate of 1.0 ml min −1. The precision (R.S.D.) for eight replicate injections of a mixture of 100 μg l −1 of Cr(III) and Cr(VI) were 0.6 and 0.5% for the retention time, 4.1 and 4.6% for the peak area measurement, respectively. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for HPLC separation and in the initial solution, was 65 for Cr(III) and 19 for Cr(VI). The linear concentration range was from 50 to 1000 μg l −1 for Cr(III) and 50–2000 μg l −1 for Cr(VI). The detection limits of Cr(III) and Cr(VI) were 3.4 and 5.2 μg l −1, respectively. The developed method was applied to the speciation of Cr(III) and Cr(VI) in snow water, river water, seawater and wastewater samples.