Speciation of selenium compounds with ion-pair reversed-phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection

For selenium speciation analysis, the hyphenation of chromatographic separa tion with element-specific detection has proved a useful technique. A power ful separation system, which is capable of resolving several biologically a nd environmentally important selenium compounds in a single column, is grea tly needed. However, that has been difficult to achieve. In this paper eigh t selenium compounds, namely, selenite [Se(IV)], selenate [Se(VI)], selenoc ystine (SeCys), selenourea (SeUr), selenomethionine (SeMet), selenoethionin e (SeEt), selenocystamine (SeCM) and trimethylselenonium ion (TMSe+), were separated by using mixed ion-pair reagents containing 2.5 mM sodium 1-butan esulfonate and 8 mM tetramethylammonium hydroxide as a mobile phase. The se paration of these anionic, cationic and neutral organic selenium compounds on a LiChrosorb RP18 reversed-phase column took only 18 min at a flow-rate of 1.0 ml/min with isocratic elution, and baseline Separation among the six organic Se compounds was achieved. Inductively coupled plasma mass spectro metry (ICP-MS) was employed as element-specific detection. A comparison of ICP-MS signal intensity obtained with a Barbington-type nebulizer and with an ultrasonic nebulizer (USN) was made. Different signal enhancement factor s were observed for the various selenium compounds when a USN was used. The speciation technique was successfully applied to the study on chemical for ms of selenium in a selenium nutritional supplement. Selenomethionine was f ound to be the predominant constituent of selenium in the supplement. (C) 2 000 Elsevier Science B.V. All rights reserved.