Simultaneous preconcentration, identification, and quantitation of selenoamino acids in oils by enantioselective high performance liquid chromatography and mass spectrometry

Selenium is an essential micronutrient for humans. In food, selenium can be present in both inorganic and organic forms, the latter mainly being selenomethionine, Se-methyl-selenocysteine, and selenocystine. Selenoamino acid speciation rarely involves the chirality of selenoamino acids. In this work, a 5 cm long CHIROBIOTIC TAG chromatographic column was used for enantioresolution of selenoamino acids (d- and l-selenomethionine, Se-methyl-l-selenocysteine, d-, l- and meso-selenocystine); in the optimized conditions, the complete resolution of the analytes was achieved within 15 min by using a very polar aqueous mobile phase (gradient elution by methanol/acetonitrile/H2O, 45:45:10 (v/v/v) with 10 mmol L-1of ammonium formate and 0.5% formic acid as the mobile phase A and acetonitrile/H2O, 20:80 (v/v) with 20 mmol L-1of ammonium formate at apparent pH 4 as the mobile phase B). The affinity of the teicoplanin aglycone was further exploited to devise a preconcentration method for selenoamino acids in oils. In particular, the CHIROBIOTIC TAG precolumn was used to directly concentrate the selenoamino acids after simple dilution of oil samples with dichloromethane. An optimized procedure for selenoamino acid trapping and preconcentration under normal phase conditions was developed. The enrichment procedure also ensured band focusing during the subsequent separation. The target analytes were finally identified and quantified by triple quadrupole selected reaction monitoring. The method allowed obtainment of recovery values up to 73%, with limits of detection between 280 and 750 ng and limits of quantification between 375 and 960 ng for the different selenoamino acids. The method was applied to commercial oil samples, and only l-selenomethionine was detected.