Measurement of theanine using reverse-phase ion-pair liquid chromatography with photodiode array detection

There is increasing demand for theanine as a taste-enhancing additive and as a supplement for improving and maintaining human health. We describe the development of an ion-pair reversed-phase liquid chromatographic method for the analysis of theanine in tea. Samples may be directly analysed after sonication for 10 min. The mobile phase consists of an aqueous 2 mM solution of pentadecafluorooctanoic acid (ion pair reagent) and acetonitrile (82:18, v/v). The theanine peak is detected using a UV detector at 200 nm. The limit of detection is 5.1 ng and the limit of quantitation is 15.6 ng. The method is accurate with recoveries higher than 97%.