Highly sensitive method for speciation of inorganic selenium in environmental water by using mercapto-silica-Fe3O4nanoparticles and ICP-MS

Abstract

A new method for speciation of inorganic selenium (Se) in environmental water has been developed by using mercapto-silica-Fe₃O₄ nanoparticles and ICP-MS. Compared with the traditional methods, the current method had higher preconcentration factor and selectivity for speciation of inorganic Se. The parameters affecting the separation, such as pH, eluent type and sample volume, were investigated systematically. Within the pH range of 1–10, Se(IV) could be quantitatively adsorbed on the magnetic nanoparticles (MNPs), while the Se(VI) was not retained in the studied pH range and remained in solution. Without filtration or centrifugation, these Se(IV)-loaded MNPs could be separated easily from the aqueous solution by simply applying an external magnetic field. The Se(IV) adsorbed on the MNPs could be recovered quantitatively using a solution containing 2 mol L⁻¹ HCl and 0.02 mol L⁻¹ K₂Cr₂O₇. Total inorganic Se was extracted after reducing of Se(VI) to Se(IV) with L-cysteine, and the assay of Se(VI) was calculated as the difference between the total Se content and Se(IV) content. Under the optimized conditions, the method detection limit obtained for Se(IV) was 0.094 ng L⁻¹, while the precision was 8.1% (C = 10 ng L⁻¹, n = 7). The proposed method based on the MNPs was successfully applied to the speciation of inorganic Se species in environmental water from a tobacco growing area yielding a 282-fold preconcentration factor.