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.