Simultaneous determination of catechins in human saliva by high-performance liquid chromatography.

Green tea extracts have been suggested to possess a preventive effect against dental caries. A quantitative method for their anticariogenic substances, catechins, was developed to evaluate their concentrations in human saliva after mouthrinsing with green tea extract. Salivary catechins were extracted to the organic phase after forming a complex with diphenylborate and an ion-pair with tetra-n-butylammonium, and then back-extracted to the acidic aqueous phase. The extract was analyzed by high-performance liquid chromatography using diode array detection at absorption wavelengths ranging from 269 to 278 nm. In reversed-phase chromatography by a gradient elution, eight catechins originating from green tea and an internal standard were separated in 15 min without interfering peaks. All the catechins were simultaneously and selectively determined in the concentration range 0.05-25.0 microg/ml. In replicate spiking experiments with standards, the mean recovery ranged between 86 and 99%, and both intra- and inter-assay C.V.s were within 2.3%. When mouthrinsing with an aqueous solution of green tea extract (5.0 mg/ml) containing eight catechins, the quantitative results revealed that each catechin was retained at microg/ml levels in saliva for up to 60 min.