An improved method for the determination of green and black tea polyphenols in biomatrices by high-performance liquid chromatography with coulometricarray detection

Tea polyphenols are strong antioxidants and are believed to have beneficial health effects, However, the blood and tissue levels of these compounds ar e not well characterized because of a lack of suitable analytical methods f or the biological resolution of these compounds. Previously, we developed m ethods for the analysis of three green tea catechins. Now we report an impr oved method for the measurement of the levels of the different catechins an d theaflavins in biological fluids and tissues. The method includes digesti on of the plasma, urine, or tissue samples with beta-D-glucuronidase and su lfatase, followed by extraction with ethyl acetate and subsequent separatio n by reversed-phase high-performance liquid chromatography (HPLC). The poly phenols are identified on the basis of their retention times, spectral anal ysis, and electrochemical behavior across an array of electrodes. In a sing le HPLC run, it is possible to determine the major catechins and theaflavin s as well as some of the catechin metabolites. The detection limits for cat echins and theaflavins are from 5 to 10 ng/ml of saliva, plasma, or urine. (C) 2000 Academic Press.