Abstract:

L-Theanine is a unique non-protein amino acid in tea, and shows many physiological functions. To directly extract L-theanine from tea is a lengthy and very costly process. Although the chemical synthesis of theanines is simple, the product is unfortunately a mixture of DL-enantiomers. A chiral derivatization method was developed for the separation and quantification of theanine enantiomers by reversed-phase high performance liquid chromatography （RP-HPLC）. 1-Fluoro-2,4-dinitrophenyl-5-L-alanine amide （FDAA）was used as the chiral reagent. This method showed good linearity for both L-theanine (ranging from 1.732×10-3 to 2.077 μg) and D-theanine (ranging from 1.696×10-3 to 2.044 μg). The recoveries were in the range of 97.3%-102.0% for L-theanine and 97.2%-103.2% for D-theanine. This method also showed excellent limit of detection (~5×10-4 μg) and limit of quantification (~1×10-3 μg) for both L-theanine and D-theanine. The results demonstrated that this method is precise, accurate and can be used for the determination of theanine enantiomers.

Key words: 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide （FDAA）, chiral derivatization, D-theanine enantiomers
, high performance liquid chromatography (HPLC)