Determination of Squalene in Tea by Gas Chromatography-Triple Quadrupole Mass Spectrometry after Purification with Solid Phase Extraction Column

An aliquot (50 μL) of 100 mg·L^-1 squalane internal standard solution together with 50 mL of petroleum ether was mixed with 5.000 g of the tea sample, and the mixture was vortexed for 3 min, ultrasonicated for 30 min, and centrifuged for 3 min. The supernatant was passed through qualitative filter paper, and the filtrate was placed into a 100 mL-chicken heart bottle. The above extraction process was repeated once, and the extract was combined, and rorated and concentrated to 1-2 mL at 40℃. After 3 mL of acetonitrile-toluene mixed solution at volume ratio of 3:1 was added into the above solution, and the solution obtained was passed through the Cleanert GCB-NH₂ cartridge activated beforehand. The chicken heart bottle was washed twice with 6 mL of acetonitrile-toluene mixed solution at volume ratio of 3:1, and the washing was passed through the cartridge. Acetonitrile-toluene mixed solution at volume ratio of 3:1 of 25 mL was taken and used for eluting the cartridge. The eluent was collected, rorated and concentrated to near dryness at 40℃, blown to dry by nitrogen, mixed with 5.00 mL of n-hexane, ultrasonicated for 30 s, and passed through 0.22 μm organic filter membrane. The filtrate was separated by temperature-programmed on the HP-5MS column in the gas chromatograph. The target obtained was detected by multiple reaction monitoring mode of triple quadrupole mass spectrometer, and quantified by internal standard method. As found by the results that the linear range of squalene was in the range of 0.030 0-2.00 mg·L^-1, with detection limit (3S/N) of 0.010 0 mg ·kg^-1. The results of recovery obtained by standard addition method were in the range of 77.6%-95.6%, giving RSDs (n=6) of the determined values in the range of 4.5%-8.3%. The proposed method was applied to the analysis of the 48 batches of tea samples prepared by different fermentation processes from different producing regions, with the detected amounts in the range of 0.10-29.5 mg·kg^-1.