Determination of Tl(III) and Tl(I) in food samples with two-step direct immersion single-drop microextraction followed by graphite furnace atomic absorption spectrometry

Abstract

In this study, a new procedure of two-step direct immersion single-drop microextraction (TS-DI-SDME) was firstly developed for the sequential separation and enrichment of Tl(III) and Tl(I) before graphite furnace atomic absorption spectrometry detection. At pH 6.0, Tl(III) selectively reacts with 1-(2-Pyridylazo)− 2-naphthol to form the complexes which can be extracted into one organic drop, while Tl(I) remained in the solution. Then, another organic drop containing dicyclohexano-18-crown-6 was immersed in the sample solution after the extraction of Tl(III) for the enrichment of Tl(I) at the same pH value. Main parameters affecting the separation and enrichment of Tl species were investigated. Under optimized conditions, limits of quantification (LODs) were 6.3 ng L−1 and 8.3 ng L−1 for Tl(III) and Tl(I), respectively. Repeatability and reproducibility were assessed by calculating relative standard deviations (RSDs), which were less than 5.1% and 6.7% for Tl(III) and Tl(I), respectively. Preconcentration factors of 300-fold were achieved for Tl species. This method was used successfully for the determination of Tl(III) and Tl(I) in food samples. To validate this procedure, a certified reference material of milk powder was analyzed with the satisfactory results. This method may avoid the problems of tedious operations, sample contamination and analysis errors in redox speciation strategies.