On-line preconcentration and speciation analysis of Se(iv) and Se(vi) using l-methionine immobilised on controlled pore glass

Abstract

A study was undertaken to evaluate the analytical capabilities of the aminoacid L-methionine as a possible substrate for the selective sorption of selenium inorganic species for the determination of Se(IV) and Se(VI) in aqueous solution. Methionine was covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. Se was determined by flow injection hydride generation-inductively coupled plasma optical emission spectrometry (FI-HG-ICP OES). Chemical and physical variables affecting the sorption process were tested in order to select the optimal analytical conditions for the Se retention by methionine. Se(VI) was selectively retained by methionine at pH 3.0, while Se(IV) was not retained. Se(VI) was subsequently removed from the conical minicolumn with 10% HCl and on-line reduced with 12 mol l⁻¹ HCl in a water bath (100 °C). A preconcentration factor of 90 was achieved when 30 mL of sample were processed reaching a detection limit of 11 ng l⁻¹, with a sample throughput of 17 samples h⁻¹ for total selenium determination and 8 samples h⁻¹ for speciation [Se(IV) and Se(VI)]. The speciation analysis of inorganic Se in drinking water was performed following the proposed method and the recoveries were in all cases between 98 and 100%.