Solid phase extraction using functionalized magnetic multi-walled carbon nanotubes combined with electrothermal atomic absorption spectrometry for the determination of selenium species in water and food samples

Selenium is both an essential and toxic element. This non-metal chemical element is present in many chemical forms. Se(IV) (selenite) and Se(VI) (selenate) forms are predominant in environmental matrices. It has been reported that the inorganic form of Se(IV) is 500 times more toxic than organic forms of selenium and its toxicity is also higher than Se(VI) [1]. High concentrations of selenium can produce chronic toxicity symptoms such as loss of teeth, hair, nails, liver carcinoma, paralysis, cirrhosis, and irritation of the eyes [2]. Therefore, development of selective, sensitive, simple, and fast analytical methods for determination of selenium species in biological and environmental samples is very important. In the present study, a novel solid phase extraction method using magnetic multi-walled carbon nanotubes modified with 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (Bismuthiol II) for the separation and preconcentration of selenium (IV) prior to its determination by electrothermal atomic absorption spectrometry has been developed. The main factors influencing the extraction of selenium (IV) were investigated and optimized. Se(VI) was reduced to Se(IV) by the addition of hydrochloric acid (4.0 mol L-1) and heating the solution in a boiling water bath prior to determination of total selenium. Se(VI) concentration was determined from the difference between total selenium and Se(IV) concentrations. Under the optimal experimental conditions, the limit of detection (based on 3Sb/m) and enhancement factor were 4.4 ng L-1 and 195, respectively. The relative standard deviation at 10 µg L-1 concentration level of Se(IV) (n = 6) was found to be 3.2%. The method was successfully applied to the determination of inorganic selenium species in water and total selenium in food samples.