The separation of green tea catechins by micellar electrokinetic chromatography

A micellar electrokinetic chromatographic (MEKC) separation system was developed for the efficient separation of biologically and clinically important green tea catechins. Six structurally isomeric tea catechins, e.g., (-)epigallocatechin-3-gallate (EGCG), (-)epicatechin gallate (ECG), (-)gallocatechin gallate (GCG), (-)epigallocatechin (EGC), (-)epicatechin (EC), and (+)catechin (C), were effectively separated using a tetraborate/sodium dodecyl sulfate (SDS)/β-cyclodextrin micellar buffer system. The effects of several critical separation parameters (micelle charge type, surfactant type, organic solvent buffer modifier, micelle concentration, buffer pH, and cyclodextrin buffer modifier) were evaluated for enhanced isomer separation and resolution. The pH was shown to be a strong factor influencing the separation of the isomers, but baseline resolution of all six structural isomers was only effected when a micellar buffer system contained β-cyclodextrin buffer modifier. The proficiency of the developed method was tested by determining the analytical levels (mg/g) of crude catechins in aqueous extractions of three varieties of green tea (Camellia sinesis).