Speciation analysis of chromium in water samples using nanometer zirconium dioxide and direct ultrasonic slurry sampling with electrothermal atomic absorption spectrometry

Abstract

ABSTRACTA new analytical procedure for the determination of chromium Cr(III) and Cr(VI) species in different water samples was developed. The method involves solid-phase extraction (SPE), direct ultrasonic slurry sampling (DUSSS), and subsequent electrothermal atomic absorption spectrometry (ETAAS). The nanometer-sized zirconium dioxide (ZrO2) was used as the sorbent material. The optimal conditions for the proposed solid phase extraction were: 50 mg ZrO2, 20 min extraction time, pH 2.5 for Cr(VI) and pH 8.0 for Cr(III) and for the ETAAS measurement: 1500°C pyrolysis and 2300°C atomisation temperatures, 1.5 g L−1 Mg(NO3)2 as matrix modifier. The samples were sonicated directly in the autosampler cup, using an ultrasonic probe at 20% power setting for 10 seconds prior to injection into the graphite tube with Ľvov platform. In this way, all drawbacks due to the elution procedure were eliminated. The limit of detection and limit of quantification for Cr(III) obtained under optimised conditions were 0.48 μg L−1, and 1.61 μg L−1, respectively, and for Cr(VI) 0.27 μg L−1 and 0.90 μg L−1. The pre-concentration factors attained for both the species were 25. The effects of alkaline, alkaline earth and some metal ions and some anions were also examined. The relative standard deviation estimated from six replicate measurements at a concentration of 0.4 μg L−1 for both Cr(III) and Cr(VI) with a pre-concentration factor of 25 was 2.96% and 4.06%, respectively. The accuracy of the method was confirmed by analysis of the standard reference material SRM 1643e “Trace Elements in Waterˮ. The proposed technique is simple, sensitive, environmentally friendly, and the risk of contamination is low. Hence, it was successfully applied to spiked synthetic and real water samples with recoveries ranging from 91.3% to 109.2%