DETERMINATION OF SELENOCYST(E)AMINE, SELENOCYST(E)INE AND SELENOMETHIONINE BY GAS-CHROMATOGRAPHY WITH FLAME PHOTOMETRIC DETECTION

A selective and sensitive method for the determination of selenocyst(e)amine, selenocyst(e)ine and selenomethionine (Se-Met) by gas chromatography (GC) was developed. Selenocystamine and selenocystine were reduced to selenocysteamine (Se-CYE) and selenocysteine (Se-Cys), respectively, by adding sodium tetrahydroborate prior to derivatization. Se-CYE, Se-Cys and Se-Met were converted into N,Se-isopropoxycarbonyl (isoPOC), N,Se-isoPOC methyl ester and N-isoPOC methyl ester derivatives, respectively, and determined by GC with flame photometric detection (FPD) using a DB-17 capillary column. These derivatives were sufficiently volatile and stable, giving single and symmetrical peaks, and provided an excellent FPD response. The detection limits of Se-CYE, Se-Cys and Se-Met were ca. 1.4, 1.0 and 1.4 pmol injected, respectively. The calibration graphs for these selenium compounds were linear in the range 1-20 nmol and sufficiently reproducible for quantification.