Preconcentration and speciation of trace amounts of chromium in saline samples using temperature-controlled microextraction based on ionic liquid as extraction solvent and determination by electrothermal atomic absorption spectrometry

A sensitive and selective method for the preconcentration and speciation of sub ng L−1 levels of chromium species in aqueous solutions with high salt contents is described. The developed method is based on temperature-controlled microextraction of chromium species using the 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]) ionic liquid as an extractant followed by electrothermal atomic absorption spectrometry (ETAAS) determination. The extraction of chromium species from aqueous solution into the fine droplets of [HMIM][PF6] was performed with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent. Some predominant factors affecting the preconcentration and speciation of both Cr(III) and Cr(VI) species were evaluated and optimized. Under the optimum conditions, the calibration graphs were linear over the concentration ranges from 50 to 200 ng L−1 for Cr(III) and from 25 to 150 ng L−1 for Cr(VI). The limits of detection (LOD) of the developed method were 5.40 ng L−1 and 2.45 ng L−1 for Cr(III) and Cr(VI) ions, respectively. The enrichment factor for chromium species was found to be 42. The relative standard deviations for six replicate determinations of 100 ng L−1 of either Cr(VI) or Cr(III) were 4.24% and 3.05%, respectively. The developed method was successfully applied to the speciation and determination of chromium species in water and urine samples.