Analysis of green tea extract dietary supplements by micellar electrokinetic chromatography

Dietary supplements are growing in popularity as a source of catechins such as epigallocatechin gallate (EGCG). The first determination of five catechins in green tea extract dietary supplements using an extraction followed by micellar electrokinetic chromatography (MEKC) with UV detection is presented here. The optimum run buffer is 5 mM borate–60 mM phosphate with 50 mM SDS at pH 7.00 with detection at 210 nm. The limit of detection is 2–3 μg/mL (S/N = 3) and the limit of quantitation is 6–8 μg/mL (S/N = 10). Results indicate that the amount of catechins varies greatly among manufacturers, between capsules of the same manufacturers, and between batches.