To establish a method for determining caffeine content in tea by ultra performance liquid chromatography-triple quadrupole mass spectrometry.

The samples were separated on a BEH C₁₈ column(2.1 mm×50 mm, 1.7 μm) via isocratic elution with a mobile phase consisting of 0.1% formic acid in water and acetonitrile (80:20, V:V). The flow rate was set at 0.3 mL/min, with an injection volume of 5 μL and a column temperature maintained at 25 ℃. Quantification was performed using the external standard method. Mass spectrometric analysis was conducted in the positive mode with the quantitative ion pair being m/z 195.0/137.9, and the qualitative ion pairs being m/z 195.0/109.9 and m/z 195.0/82.9. The capillary voltage was set at 1.00 kV, the cone voltage was set at 50 V, the desolvation gas (N₂) temperature was set at 500 ℃, the desolvation gas (N₂) flow rate was set at 1000 L/Hr, the cone gas flow rate at was set 50 L/hr, and the collision gas was high-purity argon.

The results demonstrated a limit of detection was 0.25 ng/mL for caffeine. The method exhibited excellent linearity with in the mass concentration range of 1–2000 ng/mL, with a correlation coefficient (r) of 0.9994. The spike average recovery rates ranged from 101.6% to 106.6%, with relative standard deviation (RSD) between 1.47% and 3.12%(n=3). The precision, repeatability and stability results were all satisfactory.

This method is rapid, sensitive, offers high resolution and is well-suited for the quantitative analysis of caffeine in tea.