Comparative study of the instrumental couplings of high performance liquid chromatography with microwave-assisted digestion hydride generation atomic fluorescence spectrometry and inductively coupled plasma mass spectrometry for chiral speciation of selen

A comparison of chiral separation and analysis of selenomethionine in breast and formula milk, using high performance liquid chromatography (HPLC) on a glycopeptide teicoplanin-based chiral stationary phase (Chirobiotic T), coupled to atomic fluorescence spectrometry (AFS) and inductively coupled plasma (ICP) MS detectors has been performed. The coupling HPLC-microwave-assisted digestion hydride generation requires on-line post-column analytes treatment, and a severe sample clean-up for fat and proteins elimination using centrifugation and ultrafiltration. Underivatized dl-selenomethionine enantiomers were completely resolved in 10 min using unbuffered water mobile phase at 1 ml min−1 flow. Good selectivity and sensitivities (detection limits 3.1 and 3.5 ng ml−1 as Se for l- and d-selenomethionine, respectively) were obtained, and method robustness and simplicity, together to the low cost of AFS detector, makes it suitable for infant milk routine analysis. HPLC–ICP-MS coupling exhibits very low detection limits (0.9 ng ml−1, as Se) for each dl-selenomethionine enantiomers, but the method suffers from matrix influence, that produces a poor S/N ratio and low reliability. The methods were applied to breast and formula milk samples with recoveries of 80% of the total selenium presence, which is attributable to the existence of other unknown species. l-Selenomethionine was the only isomer present in breast milk, but a 30% of d-selenomethionine was also detected in formula milk.