Simultaneous quantification of five DL-amino acids in beer by UHPLC-MS/MS using a novel chiral mass spectrometry probe

A novel UHPLC-MS/MS method with high sensitivity and selectivity for simultaneous detection and chiral resolution of DL-amino acids in beer was established using the newly developed mass spectrometry probe (S)-(3-(4-carboxythiazolidin-3-yl)-3-oxopropyl) diphenylsulfonium (CTOD). The gradient analysis of five chiral amino acids (DL-Asp, DL-Glu, DL-Ala, DL-Pro, and DL-Phe) was carried out on a BEH C18 (2.1 x 150 mm, 1.7 mu m) for 30 min with a mobile phase of 0.1% formic acid aqueous solution and 0.1% formic acid methanol/acetonitrile (7:3) solution. The resolutions of DL-amino acids ranged from 1.71 to 5.42. The correlation coefficients were >= 0.9994 in the range of 0.25 to 1200 pmol. Meanwhile, limits of detection (LOD) and limits of quantitative (LOQ) analysis were 0.05-0.25 pmol and 0.13-0.50 pmol, respectively. Furthermore, the intra-day and inter-day precision ranged from 0.34% to 6.31%, and the average recoveries ranged from 97.50% to 107.50%. The method was applied to the quantitative analysis and comparison of DL-amino acids in beer samples from 10 different manufacturers, and it was found that the beers were rich in D-amino acids. Four D-AAs including D-Ala, D-Pro, D-Glu, D-Phe (1.9-29.8 mu mol L-1) and five L-AAs including L-Pro, L-Ala, L-Phe, L-Glu, L-Asp (5.3-2315.9 mu mol L-1) were detected in the beer samples. The average content of L-AAs in the 10 beer samples was significantly higher than that of D-AAs. This study provides a new method for detecting chiral amino acids in beer and reliable data for evaluating the nutritional value of beer.