Determination of anthraquinone in tea by stable isotope dilution assay-gas chromatography-tandem mass spectrometry

The aim of this study was to develop an analytical method for the accurate determination of the anthraquinone residue in tea samples (Pu'er tea, oolong tea, green tea, and black tea) by stable isotope dilution assay-gas chromatography-tandem mass spectrometry (SIDA-GC-MS/MS). Samples were purified by solid-phase extraction after extraction with n-hexane:acetone (1:1, v/v). The anthraquinone residue was then detected by selected reaction monitoring (SRM) in electron ionization mode. Anthraquinone-d8 was added in the tea sample extraction process to eliminate the matrix effect. The average recoveries were in the range of 84.2-98.1% at different spiked levels (0.02, 0.04 and 0.08 mg kg(-1)), and the relative standard deviations were below 9.7%. The limits of quantification, calculated as 10 times the standard deviation, was 0.02 mg kg(-1). The developed method is simple, rapid, and accurate to quantitate the concentration of anthraquinone residues in tea samples.