A Validated RP-HPLC-DAD Method for the Determination of L-Theanine in Tea

L-Theanine, an amino acid occurring in the leaves of the tea plant (Camellia sinensis) possesses several beneficial pharmacologic effects. Its effects on the central nervous system are most widely studied, in addition, other activities (potential anticancer, cardiovascular) also stress the significance of this compound. However, analytical methods for the quantification of l-theanine in tea based on the application of HPLC are scarce in the literature. Considering the chemical characteristics of the molecule (high polarity, lack of chromophore group), derivatization and the application of special stationary phases have been preferred for reliable analysis. Here, we report the development and validation of an eligible RP-HPLC-DAD method without the need of pre- or post-column derivatization and using a buffer-free mobile phase (chromatographic separation of l-theanine with water, eluting other compounds with water-acetonitrile gradient) for the determination of l-theanine. The elaborated method provides quick (analysis time 15 mins) and reliable (mean intraday precision 0.94 RSD%, interday precision 0.48 %, recovery > 96.1 %, LOQ = 0.38 mg theanine/g dry tea leaf weight) quantification of this amino acid in aqueous tea extracts.