Determination of trimethylselenonium iodide, selenomethionine, selenious acid, and selenic acid using high-performance liquid chromatography with on-line detection by inductively coupled plasma mass spectrometry or flame atomic absorption spectrometry

An analytical method has been developed for the determination of selenious acid, selenic acid, trimethylselenonium ion, and selenomethionine. The four selenium compounds were separated by HPLC on a column (25 cmX4 mm I.D.) of the anion-exchanger ESA Anion III with a mobile phase (1.5 ml/min) of 0.00 55 M ammonium citrate (pH 5.5). Detection was carried out using an on-line inductively coupled plasma mass spectrometer (ICP-MS) or a flame atomic abs orption spectrometer (FAAS) as the selenium-specific detector. The chromato graphic parameters and the chemical factors affecting the separation of the selenium species were optimized. The four selenium compounds could be sepa rated within 8 minutes. The detection limits of the coupled HPLC-FAAS syste m were approximately 1 mg Se/l for each compound (100 mu l injection), esti mated as three times the base-line noise of the chromatograms. More powerfu l selenium detection was achieved with an ICP-MS. Selenium was measured at m/z 78. To increase the nebulization efficiency, the Meinhard concentric gl ass nebulizer was replaced by an ultrasonic nebulizer. The ICP-MS signal in tensity was increased with the ultrasonic nebulization by a factor of 7 tim es for selenious acid and 24 to 31 times for trimethylselenonium ion, selen omethionine, and selenic acid compared to that with the Meinhard nebulizati on. The detection limits achieved by the HPLC-ICP-MS with the ultrasonic ne bulization were 0.08 mu g Se/l for trimethylselenonium ion, 0.34 mu g Se/l for selenious acid, 0.18 mu g Se/l for selenomethionine, and 0.07 mu g Se/l for selenic acid, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.