Simultaneous determination of twelve tea catechins by high-performance liquid chromatography with electrochemical detection
A high-performance liquid chromatographic method with electrochemical detection 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 at the C-2 position, C, GC, CG and GCG; and four methylated catechin derivatives, epigallocatechin-3-O-(3-O-methyl)gallate, gallocatechin-3-O-(3-O-methyl)gallate, epigallocatechin-3-O-(4-O-methyl)gallate and epicatechin-3-O-(3-O-methyl)gallate. These catechins were separated on an ODS C18 reversed-phase column by isocratic elution with 0.1 M NaH2PO4 buffer (pH 2.5)–acetonitrile (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–acetonitrile (1∶1) at 30 °C for 40 min inhibited the epimerization at C-2 significantly from these epicatechins compared to extraction with hot water at 90 °C. This analytical method is sensitive to and appropriate for the simultaneous determination of various biologically active catechins in green tea.