Microwave assisted mixed-micelle cloud point extraction of Au and Tl from environmental samples without using a chelating agent prior to ICP-MS determination

Abstract

A rapid microwave assisted mixed-micelle cloud point extraction procedure is developed for the pre-concentration and separation of ultra trace levels of Au and Tl simultaneously from environmental samples prior to their determination by ICP-MS. The method is based on the formation of extractable complexes of anionic species AuCl₄⁻ and TlCl₃²⁻ with solubilizing cationic and hydrophobic sites of mixed-micelles, in the presence of HCl. The mixed-micelles consisting of cetyltrimethylammonium bromide (CTAB) and Triton X-114 are used for pre-concentration and extraction of formed extractable complexes of Au and Tl from a bulk aqueous phase into a small surfactant-rich phase, avoiding the addition of an external chelating agent. The phase separation is induced by microwave irradiation. The potential oxide interferences of Ta and Hf are eliminated effectively up to 2 and 5 μg mL⁻¹ levels, respectively, enabling interference free determination of mono isotopic ¹⁹⁷Au. The main parameters affecting the cloud point extraction process are evaluated and optimized. Under the optimized conditions, the pre-concentration factors and limits of detection are 125 and 110, and 0.12 and 0.02 pg mL⁻¹, respectively, for Au and Tl. The recoveries of analytes are in the range of 97–103% at 10–40 pg mL⁻¹ for Au and Tl with relative standard deviations of 0.5–2.2%. The accuracy of the procedure is validated by analyzing certified reference materials such as NIST SRM 1643c and 1643d (Trace elements in water), 2709 (San Joaquin soil) and 2711 (Montana soil), and NRCC NASS-5 (Open ocean seawater), as well as being applied to tap and seawater samples.