Identification and determination of polyphenols in tea by liquid chromatography with multichannel electrochemical detection

A liquid chromatography method with multi-channel electrochemical detection is reported for the identification and determination of polyphenols in gre en tea, black tea, and extracted green tea powder. Following a simple aqueo us extraction, (-)-epigallocatechin (EGC), (+)-catechin (C), (-)-epicatechi n (EC), (-)-epigallocatechin gallate (EGCG), (-)-gallocatechin gallate (GCG ), (-)-gallocatechin (GC), (-)-epicatechin gallate (ECG), and (-)catechin g allate (CG) were successfully separated by reversed phase liquid chromatogr aphy within 25 min. The detection limits (S/N=3) of the polyphenols studied were 0.1-1.5 ng/mL at a potential of +900mV. The calibration curve was linear over the range o f 1-1000 ng/mL for EGG, C, EC, EGCG, GCG, and GC, 5-1000 ng/mL for ECG and CG. Using this method, the concentration of these eight polyphenols in five different brands of green tea, one brand of black tea, and extracted green tea powder were determined.