Analysis of catechins and caffeine contents in commercial tea drinks

In this study, several commercial tea drinks of different manufacture and fermentation were analyzed by an isocratic HPLC for their catechins and caffeine contents. By using a short RP-18 column (4×125 mm, 0.45 μm), four major catechins (namely EGC, EGCG, EC and ECG) and caffeine were totally separated within 20 minutes at a flow rate of 0.75 ml/min, when water/MeOH/HOAc (77-78/20/2-3,V/V/V) was used as the mobile phase. Caffeine (60-300ppm) content was always higher than the concentration of total catechins (19-146 ppm). The catechin contents in samples decreased after prolonged storage. Changing the monitoring wavelength from 280 nm to 245 nm improved the detection accuracy of EGC; its molar extinction coefficient is higher at A245. Chloroform treatment of tea samples can also prevent the interference that results from the presence of relatively large amounts of caffeine. On the other hand, the vanillin method was proven to be unsuitable for the analysis of catechins in processed tea drinks.