Simultaneous determination of twelve tea catechins by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method with electrochemical detec tion was developed for the determination of twelve tea catechins including four major catechins: epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG); four of their epimers a t the C-2 position, C, GC, CG and GCG; and four methylated catechin derivat ives, epigallocatechin-3-O-(3-O-methyl)gallate, gallocatechin-3-O-(3-O-meth yl)gallate, epigallocatechin-3-O-(4-O-methyl)gallate and epicatechin-3-O-(3 -O-methyl)gallate. These catechins were separated on an ODS C-18 reversed-p hase column by isocratic elution with 0.1 M NaH2PO4 buffer (pH 2.5)-acetoni trile (87:13) containing 0.1 mM EDTA.2Na. The detection limits (S/N = 3) of these catechins were approximately 10-40 pmol ml(-1) at an applied voltage of 600 mV. Extracting these catechins from tea leaf powder with H2O-aceton itrile (1:1) at 30 degreesC for 40 min inhibited the epimerization at C-2 s ignificantly from these epicatechins compared to extraction with hot water at 90 degreesC. This analytical method is sensitive to and appropriate for the simultaneous determination of various biologically active catechins in green tea.