Development of chiral HPLC for selenoamino acids with ICP-MS detection: application to selenium nutritional supplements

The enantiomeric separation of three underivatized selenoamino acids, D,L-selenocystine, D,L-selenomethionine and D,L-selenoethionine, with UV and ICP-MS detection is described. An HPLC column with a chiral crown ether stationary phase and a mobile phase of 0.10 M HClO4 was used. Absolute detection limits obtained with UV detection ranged from 34.5 to 47.1 ng whereas those obtained with the plasma detector were ca. 40-400 times better. The separations with either detector were good, with little detector effect on the resolution. Ten commercially available dietary selenium supplements were analyzed using the chiral column to identify and quantify the selenium species present with both detection modes. Selenium species were easily identified using ICP-MS detection, whereas UV detection was not viable because of interferences from the sample matrix and inadequate sensitivity. Selenium species that were unretained using the chiral column were identified using anion exchange chromatography. Total amounts of selenium in the samples were also measured using a conventional digestion and an enzymatic digestion with ICP-MS detection.