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Determination of 21 free amino acids in 5 types of tea by ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC–MS/MS) using a modified 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) method

Zhou, Peng, Zhao, Feng, Chen, Mingjie, Ye, Naixing, Lin, Qin, Ouyang, Liqun, Cai, Xiaoming, Meng, Peng, Gong, Xuedong, Wang, Ying
Subtropical plant science 2019 v.81 pp. 46-54
arginine, aspartic acid, derivatization, detection limit, diodes, fermentation, free amino acids, glutamic acid, green tea, high performance liquid chromatography, principal component analysis, reversed-phase liquid chromatography, spectrometers, tandem mass spectrometry, theanine, ultra-performance liquid chromatography, white tea
6-Aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) pre-column derivatization coupled with reversed-phase liquid chromatography and diode array detection (RPLC–DAD) is one of the conventional methods for analysis of free amino acids in tea. In this article, we improved method detection sensitivity and resolution by replacing the optical detector with a mass spectrometer (MS). We also optimized the extraction process and mobile phases. Application of mass spectrometry makes co-eluting compounds easier to separate. The improved method was then successfully applied in the analysis of twenty-eight commercial tea samples with various degrees of fermentation. Umami-tasting AAs were higher in green tea than in white tea, while sweet-tasting AAs were more elevated in white tea. Principal component analysis indicated that theanine, arginine, aspartic acid and glutamic acid could be potent discriminators for tea fermentation degree.