采用超高压液相色谱-四级杆飞行时间质谱法鉴别和定量测定5种单丛乌龙茶中的游离氨基酸,探讨色谱分离条件和质谱参数对氨基酸测定的影响。样品经热水提取,采用HILIC柱分离,以20 mmol/L甲酸铵(含体积分数0.1%的甲酸)和乙腈(含体积分数0.1%甲酸)为流动相梯度洗脱,电喷雾正离子化检测、数据采集方法为全信息质谱数据采集模式,基质匹配标准曲线法定量。结果表明,不同采集模式对准分子离子峰和碎片离子峰的丰度及数量的影响较大,22种氨基酸标准溶液的质量浓度和检测响应的线性关系良好,其相关系数均大于0.99;检出限在1.3～95.7 μg/L,超高压液相色谱-高分辨质谱法的准确度高、精密度和重复性均可满足要求。单丛乌龙茶中总游离氨基酸的总量为485.12～575.95 mg/100 g,乌叶、鸭屎香、玉兰香、白叶、水仙等5种单丛乌龙茶中含有多种常见氨基酸,各氨基酸在不同单丛乌龙成茶中的含量差异较大(P<0.05),其中茶氨酸、谷氨酸、精氨酸、丝氨酸、天冬氨酸等的含量较高。
The free amino acids in five Dancong Oolong tea were identified and quantitatively determined by ultra-high pressure liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF MS), and the effects of chromatographic separation conditions and mass spectrometry parameters on the determination of amino acids in Dancong Oolong tea were investigated. The samples were extracted with hot water, separated by a HILIC column, and gradient elution was performed with 20 mmol/L ammonium formate (containing 0.1% formic acid) and acetonitrile (containing 0.1% formic acid) as mobile phase. Full information mass spectrometry elevated (MSE) with electrospray positive ion mode (ESI+) was used to detect the amino acids and data collection, and quantitative analysis was performed by matrix matching standard curve method. Results showed that the acquisition mode of mass spectrometry significantly influenced the abundance and quantity of the precursor ion and fragment ion peak, and there was a good linear relationship between the concentration of 22 amino acid standards and detection response, and the correlation coefficients were greater than 0.99. The detection limit (LOD) for analysts was in the range of 1.3-95.7 μg/L, and the optimized UHPLC-HRMS method was successfully applied to the analysis of amino acids in Oolong tea samples due to the high accuracy, precision and repeatability. And the total amount of free amino acids in Dancong Oolong tea was in the range of 485.12-575.95 mg/100 g. The five Dancong Oolong tea, such as Wuye, Yashixiang, Yulanxiang, Baiye, Shuixian, contained a variety of common amino acids, while the contents of different amino acids showed significant difference (P<0.05), in which the contents of theanine, glutamate, arginine, serine and aspartic acid were higher compared with control.
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