Abstract
Tochu tea products generated from the leaves of Eucommia ulmoides OLIVER are habitually consumed as a health beverage in Japan, China and Korea. Therefore, quality control of these products is important for safety and validity evaluation. A method using high-performance liquid chromatography-diode array detector/electrospray ionization mass spectrometry (HPLC-DAD/ESI-MS) was established to simultaneously determine ten bioactive constituents including 2 iridoids, 2 phenolic acids and 6 flavonoids in E. ulmoides leaves and Tochu tea products. Peaks were unequivocally identified by comparing retention times, on-line electrospray ionization mass (ESI-MS) spectra and UV data with those of reference compounds isolated from E. ulmoides leaves and Tochu tea products. All calibration curves of the ten compounds showed good linear regression (R > 0.9994) within test ranges. The new method provided satisfactory precision and accuracy with overall intra-day and inter-day variations of 1.8 - 3.0% and 3.5 - 5.9%, respectively, and overall recovery ranging from 95.4 - 106.1% with relative standard deviations (RSDs) within 3.6% (n = 3) for the ten compounds analyzed. The exclusive selectivity and excellent sensitivity of HPLC-DAD/ESI-MS provided comprehensive chemical information about the constituents of Tochu tea products and E. ulmoides leaves.
