Automated in-tube solid phase microextraction coupled with HPLC-ES-MS for the determination of catechins and caffeine in tea

A polypyrrole (PPY) coated capillary and several commercially available cap illaries (capillary GC columns) were used to evaluate their extraction effi ciencies for catechins and caffeine. Compared with commercial capillaries t hat were currently used for in-tube solid phase microextraction (SPME), the PPY coated capillary showed better extraction efficiency for all of the co mpounds studied. Electrospray mass spectrometric (ES-MS) detection conditio ns were also investigated. After optimization of the extraction and detecti on conditions, a method for the sensitive and selective determination of ca techins and caffeine was developed by coupling the PPY coated capillary in- tube SPME with HPLC-ES-MS. Catechins could be determined in both positive a nd negative ion detection modes. The detection limit (S/N = 3) for each of the studied catechins was <0.5 ng mL(-1). Caffeine could only be determined under positive ES-MS detection conditions and its detection limit was 0.01 ng mL(-1). Caffeine and the five catechins in several tea samples were det ermined using the developed method. Small amounts of catechins were also de tected in grape juice and wine samples.