Rapid identification of acylated flavonol tetraglycosides in oolong teas using HPLC-MSn

A method was developed to separate and identify acylated flavonol tetraglycosides (AFTGs) by combining isocratic HPLC with electrospray ionisation tandem mass spectrometry. Better separation was obtained for oolong tea infusion using a manually packed Sephadex LH-20 mini-column than with an ACCUBOND ODS solid-phase column. Seven unknown and one known AFTGs were found in oolong teas prepared by various semi-fermentation processes and their structures were identified by mass spectrometry. According to the analyses of diverse oolong teas including Dongding Oolong, Tieguanyin, Wuyi Oolong, Fenghuang Oolong, Gaoshan Shibi, Laocong Shuixian and Baihao Oolong, AFTGs seemed to be universally present, and each oolong tea could be classified into one of three groups (Dongding Oolong, Tieguanyin and Wuyi Oolong) on the basis of its AFTGs profile. The results suggest that the developed method is rapid and sensitive for identifying natural compounds.