Determination of L-theanine in bottled green-tea drinks by HPLC using an aminopropyl bonded silica gel column

Abstract

This paper describes a simple analytical method for the determination of L-theanine, a major free amino acid in green tea, by high-performance liquid chromatography (HPLC) with ultraviolet detection (UV). This method provides high linearity of the working curve for calibration as well as repeatability. The correlation coefficient of the working curve for calibration was estimated to be to 0.9991 for L-theanine in the concentration range from 1 mg L-1 to 100 mg L-1. The limit of detection (LOD) was calculated on 3σ at 1 mg L-1 as 0.210 mg L-1 using a standard solution for L-theanine. The limit of quantification (LOQ) was calculated on 10σ at 1 mg L-1 as 0.704 mg L-1 using a standard solution for L-theanine. In addition, the recoveries of spiked the bottled green-tea drinks at concentration levels from 10 to 75 mg L-1 were estimated to be 91.1-99.3 %, and the relative standard deviations were 1.04-2.51 %. This method could be successfully applied to the determination of the L-theanine in bottled green-tea drinks.