Combination of dispersive solid phase extraction with dispersive liquid-liquid microextraction for the sequential speciation and preconcentration of Cr(III) and Cr(VI) in water samples prior to graphite furnace atomic absorption spectrometry determination

In this study, the combination of dispersive solid phase extraction (DSPE) with dispersive liquid-liquid microextraction (DLLME) was proposed as a novel sequential speciation method for Cr determination by graphite furnace atomic absorption spectrometry. In the first step, the selective extraction of Cr(III) by DSPE was achieved using graphene oxide (GO) nanoparticles as the adsorbent. The difficulty of separation and collection of GO in analytical performance was solved by the introduction of the syringe nanofilter. Then Cr(VI) was enriched by DLLME using [Omim] [PF6] as the extraction solvent. The experimental parameters affecting the performance of both preconcentration methods were investigated and optimized. Under the optimal conditions including the initial pH value of 7, 150 mu g GO, 2 min ultrasound time, 210 mu L elution solvent (first step), secondary pH value of 4, 0.15% (m/v) Aliquat-336, 120 mu L of [Omim] [PF6] and 3 min ultrasound time (second step), the linear range of 0.06-5 ng/mL (R > 0.997), the limits of detection of 0.015 and 0.02 ng/mL were achieved for Cr(III) and Cr(VI), respectively. The relative standard deviations (n = 5) of 0.6 ng/mL Cr(III) and Cr(VI) were 3.2% and 4.6%, respectively. Finally, this newly developed method was applied for the speciation and determination of Cr species in different water samples and satisfactory results were obtained. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.