Determination of selenocystine, selenomethionine, selenite and selenate by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry

An analytical method has been developed for the determination of selenocystine, selenomethionine, selenite and selenate. Separation of the four Se species was achieved by HPLC on a Spherisorb 5 ODS-AMINO column using a concentration gradient from 3.5 to 7.0 mmol l(-1) phosphate buffer of pH 6.0 as the mobile phase at a pow rate of 1.0 ml min(-1). Detection was carried out using an on-line inductively coupled plasma mass spectrometer, The chromatographic parameters and the chemical factors affecting the separation of the Se species were optimized. The detection limits, using a 100 mu l sample loop volume and expressed as Se, were found to be 2.0, 1.0, 1.6 and 1.2 mu g l(-1) for selenocystine, selenomethionine, selenite and selenate, respectively. The precision was better than 5% in all instances. The method was successfully applied to the determination of the four Se species in water samples certified for selenite and selenate, to which selenocystine and selenomethionine had been added.