Highly selective and sensitive determination of free and total amino acids in Apocynum venetum L. (Luobuma tea) by a developed HPLC-FLD method coupled with pre-column fluorescent labelling.

Amino acids (AA) are important chemical constituents of tea leaves remarkably influencing the quality of tea. In this study, free AA and total AA in Apocynum venetum L. (Luobuma tea) were estimated by HPLC equipped with fluorescent detector using 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy] ethyl chloroformate (DBCEEC) as a fluorescent labelling reagent. Different parameters for derivatization and separation were optimized. AA were rapidly derivatized within 3 min at room temperature with DBCEEC. In conjunction with a gradient elution, a baseline resolution of 20 analytes was achieved on a reversed-phase Hypersil BDS C18 column. LC separation for the derivatized AA showed good reproducibility. Twenty AA were detected and showed significant linear responses with correlation coefficients (>0.9992). This developed method offered the low detection limit of 2.88-23.4 fmol.