Automated salting-out assisted single-phase liquid–liquid extraction of Cr(vi) from river water samples prior to its atomic absorption spectrometric determination

Abstract

A new automated method was developed combining the features of the salting-out effect, single-phase liquid–liquid extraction (SPLLE), and flow-batch analysis to determine Cr(VI) in river water samples by graphite furnace atomic absorption spectrometry. A water–ethanol–amyl alcohol mixture containing sodium diethyldithiocarbamate (NaDDTC) as the chelating agent was also employed. Before spectrometric measurements, the salting-out effect allowed fast single-phase separation and preconcentration of the complex Cr(VI)-DDTC. The extraction procedure was performed inside the mixing chamber of the flow-batch analyzer, simplifying the overall design. Less sample dilution and reduced volume of the organic phase were achieved by studying the phase diagram of the ternary system. Spectrometric operational parameters, the composition of the water–ethanol–amyl alcohol mixture, the concentration of the chelating agent, the concentration of the saline solution, and the parameters of the flow-batch system were optimized. Characteristic mass, sample throughput, limit of detection, limit of quantification, and enrichment factor were 0.33 pg, 129 samples h⁻¹, 0.05 μg L⁻¹, 0.17 μg L⁻¹, and 7.3, respectively. The proposed method's accuracy was evaluated by analysis of a certified reference material and recovery tests, which resulted in a relative error of 2.94% and recovery rates ranging from 96 to 102%. The proposed method proved to be simple and effective for determining Cr(VI) in river water samples and could be used in further investigations regarding the determination/speciation of other chemical elements.