Dispersive liquid liquid microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic selenium in environmental water samples.

A novel method based on dispersive liquid liquid microextraction (DLLME) followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) determination was proposed for the speciation of inorganic selenium by using 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (Bismuthiol II) as both chelating reagent and chemical modifier. In this method, 500 μL ethanol (as disperser solvent) containing 70 μL chloroform (as extraction solvent) and 0.2 g L(-1) Bismuthiol II (as chelating reagent) was rapidly injected into a sample solution to form cloudy solution. The complex of Se(IV) with Bismuthiol II was rapidly extracted into the extraction solvent at pH 2.0, while Se(VI) was remained in the aqueous solutions. Thus, the separation of Se(IV) and Se(VI) could be realized. After centrifugation, the complex of Se(IV) and Bismuthiol II concentrated in the extraction solvent was introduced into the ETV-ICP-MS for determination of Se(IV). Se(VI) was reduced to Se(IV) prior to determination of total selenium, and its assay was based on subtracting Se(IV) from total selenium. The main factors influencing the DLLME and the vaporization behavior of selenium in ETV were investigated systematically. Under the optimal conditions, the limit of detection (LOD) for Se(IV) was 0.047 ng mL(-1). The relative standard deviation (RSD) was 7.2% (CSe(IV)=1.0 ng mL(-1), n=8) with an enhancement factor of 64.8-fold from only 5 mL of water sample. The proposed method was successfully applied to the speciation of inorganic selenium in different environmental water samples with recoveries ranging from 94.8 to 108% for the spiking samples. In order to validate the proposed method, a Certified Reference Material of Environment Water (GBW(E)080395) was analyzed, and the determined value obtained was in good agreement with the certified value.