Determination of selenium in some food matrices by electrothermal atomic absorption spectrometry after preconcentration with diethyldithiophosphate

Abstract

Selenium preconcentration for its electrothermal atomic absorption spectrometric determination in biological tissues, such as food samples, is described. The method is applicable to matrices containing 0.05–1 mg kg⁻¹ Se, like fish, meat, and flour. After a closed nitric acid digestion procedure, an aliquot of the sample is diluted with 0.2% v/v HNO₃, diethyldithiophosphate solution is added and the complex formed is loaded on a minicolumn containing 30 mg of SiO₂–C₁₈, using a peristaltic pump. The complex, eluted with ethanol, is collected into a cuvette for the determination of selenium. A calibration curve is made from selenium(IV) solutions, prepared in 0.2% v/v HNO₃. In order to minimize diethyldithiophosphate interference, a chemical modifier is used, chosen after comparison among Rh, Pd, Ir and Ni, and Rh proved to be the best. The furnace program can include a pyrolysis step at 1000 °C or, alternatively, omit it, skipping from a drying step to the atomization. A typical analytical curve goes up to 4 ng mL⁻¹ Se. An enrichment factor of 65 is possible, taking 6 min for each preconcentration step. Good results were obtained for several certified reference materials. The entire procedure, including the digestion, can proceed rapidly, because there is no need for a pre-reduction step, coprecipitation or a lengthy solvent extraction.