Estimation of tea catechin levels using micellar electrokinetic chromatography: A quantitative approach

A simple, inexpensive micellar electrokinetic chromatography (MEKC) method with UV detection was used to determine seven catechins and one xanthine (caffeine) in tea. All the compounds were successfully separated (15 kV) within a 15-min migration period with a high number of theoretical plates (>8.0 × 104) in a running buffer (pH 7) containing 10 mmol l−1 sodium tetraborate, 4 mmol l−1 sodium phosphate, and 25 mmol l−1 SDS. The regression lines of all standard catechins were linear within the range of 0.03–4 μg ml−1. Green tea infused at 95 °C for 10 min showed higher levels of catechins (especially epigallocatechin galate, epicatechin gallate, and epicatechin) than tea infused at 80 °C. In addition, major differences were observed in the levels of catechins in the first and second infusions (both brewed at 95 °C for 10 min). Finally, green tea leaves were infused separately with tap water, deionised water, spring water, reverse osmosis water, and distilled water at 95 °C, and the catechin content of the infusions was investigated by the proposed method. In the infusion brewed with tap water, catechins appeared to be epimerisation from the epistructure to the nonepistructure. This epimerisation may take place more readily in tap water than in distilled water owing to the complexity of the ions present in tap water.