Direct speciation of Cr in drinking water by in situ thermal separation ETAAS

Abstract

In situ speciation of Cr(VI) and Cr(III) based on thermal separation and electrothermal atomic absorption spectrometry (ETAAS) detection has been developed. The complexant 2-thenoyltrifluoracetone (TTA) was used to selectively react with Cr(III); the product of the Cr(III)–TTA complex vaporized at 400 °C, while Cr(VI) quantitatively remains up to a temperature of 1200 °C and was subsequently detected by AAS. The complexation reaction products of the volatile Cr–TTA complex were verified using electro-spray ionization high resolution quadrupole-Orbitrap-mass spectrometry (ESI-HR-MS). The Cr(III) concentration was established by calculating the difference between the total Cr (Cr(T)) and Cr(VI) concentrations. Under optimum experimental conditions, the detection limits for Cr(VI) and Cr(T) are 0.046 μg L⁻¹ and 0.039 μg L⁻¹, with RSDs for 1.0 μg L⁻¹ of Cr(VI) and 1.0 μg L⁻¹ of Cr(T) of 3.1% and 2.8% (n = 5), respectively. The accuracy of this method was validated by testing two water standard reference materials (SRMs) for total chromium. The proposed method was employed for analysis of drinking water. The Cr(VI) concentrations for tap water, bottled water, and well water were found to be 1.41, 0.53 and 0.68 μg L⁻¹, respectively, which is in good agreement with the reference values measured by ion chromatographic ICP-MS. This high throughput method has great potential for screening of Cr species at ultra-trace levels in drinking water.