Cr speciation in water samples by dispersive liquid-liquid microextraction combined with total reflection X-ray fluorescence spectrometry

A novel method based on dispersive liquid-liquid microextraction (DLLME) and total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for the determination and preconcentration of inorganic Cr species (Cr(VI) and Cr(III)) in water samples. Parameters affecting the extraction procedure for Cr speciation (pH, sample volume, disperser solvent, complexing agent, organic solvent, temperature) and TXRF conditions (sample volume, drying mode, measurement time, internal standardization) have been carefully evaluated to ensure the highest sensitivity for Cr determination. It was found that the minimum Cr content that can be detected was 0.8 μg L- 1. This value is significantly lower than the maximum Cr content permissible in drinking waters and it is better or comparable with those obtained in other published works based on the use of solid phase extraction or liquid phase microextraction in combination with atomic absorption spectrometry techniques. A good linearity (R2 = 0.9937) was obtained in the range of 5 to 4000 μg L- 1 demonstrating the suitability of the DLLME + TXRF for both the analysis of drinking and waste water samples. Additional advantages of the DLLME-TXRF systems include the use of very small amount of reagents and the simplicity and low cost of operation of the benchtop instrument used (no cooling media and gas consumption are needed)The authorswant to thank the financial support for this project from the Spanish National Research Program (Project ref. CGL2010-22168-C03-01 and Project ref. CGL2013-48802-C3-2-R