Determination of catechins in green tea infusions by reduced flow micellar electrokinetic chromatography.

A sulfated-β-cyclodextrin (s-β-CD) modified reduced flow micellar electrokinetic chromatography (RF-MEKC) method was developed and validated for the determination of catechins in green tea. The optimal electrolyte consisted of 0.2% triethylamine, 50mmol/L SDS and 0.8% s-β-CD (pH=2.9), allowing baseline separation of five catechins in 4min. The samples and standards were injected at 0.6psi for 5s under constant voltage of -30kV. Sample preparation simply involved extraction of 2g of tea with 200mL water at 95°C under constant stirring for 5min. The method demonstrated excellent performance, with limits of detection (LOD) and quantification (LOQ) of 0.02-0.1 and 0.1-0.5μg/mL, respectively, and recovery percentages of 94-101%. The method was applied to six samples of Brazilian green tea infusions. Epigallocatechin gallate (23.4-112.4μg/mL) was the major component, followed by epigallocatechin (18.4-78.9μg/mL), epicatechin gallate (5.6-29.6μg/mL), epicatechin (4.6-14.5μg/mL) and catechin (3.2-8.2μg/mL).