Determination of theanine in tea by high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

HPLC coupled online with atmospheric pressure chemical ionization MS technique was developed for the qualitative and quantitative determination of theanine in tea. The theanine and other compounds in the tea extract were separated on an Alltima C8 column with methanol and water (10:90 v/v) as mobile phase, with flow rate of 0.6 ml/min and APCI-MS SIM m/z 175.1 detection. In the positive APCI mode, sensitive and stable MS signal could be obtained by APCI-MS (SIM m/z 175.1) detection, and the APCI-MS conditions were also optimized by orthogonal design. The results indicated that HPLC-APCI-MS method was simple, sensitive and reliable for the determination of theanine in tea. It was important that the detection sensitivity was improved greatly by APCI-MS than UV. Eight tea samples from Fujian province were analysed using the established methods.