Resolution of seleno-amino acid optical isomers using chiral derivatization and inductively coupled plasma mass spectrometric (ICP-MS) detection

This work describes the separation of the enantiomeric forms of Se-amino ac ids by reversed phase liquid chromatography following formation of the dias tereomers using 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfey's reag ent) as the derivatizing agent. Optimization of the chromatographic conditi ons by UV absorption at 340 nm (lambda (max) for Marfey's derivatives) was possible. The final operating conditions involved the use of 50% (v/v) MeOH at pH 5.3 (acetic acid-sodium acetate), which provided a good separation o f the diastereomers of Se-methionine within 26 min. Slight modification of the sample introduction system by on-line dilution (1:4) of the chromatogra phic eluent using a PTFE tee piece was required for good performance of the ICP-MS. Final instrumental set-up involved the use of both detectors on-li ne (diode array and ICP-MS). Under these conditions, detection limits at th e ppb level (11 ppb as Se in the Se-methionine diastereomer) using ICP-MS d etection were obtained with negligible band broadening caused by the on-lin e dilution. The methodology was finally applied to the qualitative identifi cation Of D and L enantiomers in selenium nutritional Supplements (selenize d yeast and tablets) and a pharmaceutical preparation.