Determination of underivatized amino acids in microsamples of a yeast nutritional supplement by LC-MS following microwave assisted acid hydrolysis
In this paper we describe a rapid method for microscale microwave assisted acid hydrolysis followed by quantitative amino acid analysis, using liquid chromatography mass spectrometry UPLC-ESI-MS (QTOF) without derivatization. Such an approach allows substantial decrease in the amount of yeast sample (less than 1 mg) required for effective analysis. The vapor phase hydrolysis approach was compared to condensed phase hydrolysis and all the microwave parameters were optimized for 16 amino acids. Separation was achieved on a BEH C-18 column. Limits of detection and quantitation (LODs/LOQs), using standard solutions, were in the sub-ppb range. The method was successfully applied to the determination and quantitation of methionine and selenomethionine by isotope dilution and standard addition methods in yeast on a yeast certified reference material sample.