Retention study of inorganic and organic selenium compounds on a silica-based reversed phase column with mixed ion-pairing reagents

Separation of seven inorganic and organic selenium compounds, namely selenic acid [Se(VI)], selenous acid [Se(IV)], trimethylselenonium iodide (TMSe+), selenocystine (SeCys), selenomethionine (SeMet), selenoethionine (Seet), and selenocystamine (SeCM), has been performed on a LiChrosorb C 18 column by using mixed ion-pair reagents; 1-butanesulfonic acid and tetramethylammonium hydroxide. Flame atomic absorption spectrometry (FAAS) was used as an element-specific detector. The retention behaviors of selenium compounds in terms of several chromatographic parameters, such as pH of the mobile phase, the concentrations of ion-pair reagents, and the content of organic modifier (methanol) were investigated. It was found that the separation of both inorganic and organic selenium compounds can be achieved within 12 min with a mobile phase of 10 mM 1-butanesulfonic acid - 4 mM tetramethylammonium hydroxide - 4 mM malonic acid 0.05 % methanol adjusted to pH 4.5 at a flow rate of 1.0 mt min(-1). The results obtained in this study showed that the use of mixed ion-pair reagents is very useful to improve the separation of selenium compounds. The applicability of this technique for the speciation of selenium compounds in real samples was demonstrated by the determination of selenium compounds in a selenium nutritional supplement. The results were found to be in good agreement with those obtained by ion-exchange HPLC-ICP-MS.