Ultra-trace speciation analysis of thallium in environmental water samples by inductively coupled plasma mass spectrometry after a novel sequential mixed-micelle cloud point extraction

Abstract

A simple and novel sequential mixed-micelle cloud point extraction procedure has been developed for ultra-trace speciation analysis of thallium in environmental water samples by inductively coupled plasma mass spectrometry (ICP-MS). A mixed micelle consisting of sodium dodecyl sulfate (SDS) and Triton X-114 is used as a chelating as well as an extracting agent. Tl(III)–DTPA (diethylenetriaminepentaacetic acid) complex in an HCl medium is extracted into a surfactant-rich phase in the presence of Tl(I). The Tl(I) in the supernatant is subjected to a similar extraction procedure after bromine oxidation. Ultrasonically assisted back-extraction is used to extract the Tl(III) species from the surfactant-rich phase into a small volume of aqueous L-cysteine. The pre-concentration factor and detection limit are 125 and 0.02 pg mL⁻¹, respectively. The recoveries are in the range 98–103% at 10–20 pg mL⁻¹Tl(III) with relative standard deviation (RSD) of 1–3%. The procedure is validated by comparing the sum of the concentrations of individual Tl species with total thallium concentration in certified reference materials such as Trace elements in water NIST SRM 1643c and Open ocean seawater NASS-4 and NASS-5, and also by applying it to various samples collected locally.