Cloud Point Extraction-Inductively Coupled Plasma Mass Spectrometry for Separation/Analysis of Aqueous-Exchangeable and Unaqueous-Exchangeable Selenium in Tea Samples

A simple method based on cloud point extraction (CPE) separation and inductively coupled plasma mass spectrometry (ICP-MS) detection was proposed for the determination of species of aqueous-exchangeable selenium and unaqueous-exchangeable selenium. When the system temperature is higher than the cloud point extraction temperature (CPT) of the surfactant of p-octyl polyethyleneglycolphenyl ether (Triton X-100), the complex of selenium(IV)-diethyl-dithiocarbamate (DDTC) (total selenium and aqueous-exchangeable selenium) could be extracted into the surfactant-rich phase, an in situ separation of selenium(IV) could be realized. Unaqueous-exchangeable selenium concentration was obtained by respectively subtracting aqueous-exchangeable selenium from the total selenium. The chemical variables affecting the CPE were optimized. Under the optimized conditions, the limit of detection (LOD) and the relative standard deviations (RSD) was 0.10 ng/mL and 3.2% (c = 10.0 ng/mL, n = 11), respectively, for Se(IV). The proposed method was applied to the speciation of aqueous-exchangeable and unaqueous-exchangeable selenium in tea samples with satisfactory results.