Solid-phase extraction for the determination of caffeine in traditional Chinese medicinal prescriptions containing Theae folium by high performance liquid chromatography

A high performance liquid chromatographic method in combination with C-18 reverse phase solid-phase extraction (SPE) was developed for determination of caffeine (CA) in traditional Chinese medicinal prescriptions which contain Theae folium. The frequently used prescriptions include Shin-Yi-San, Chuan-Chyong-Char-Tyau-San, Tsang-Eel-San, San-Hwang-Shyr-Gau-Tang, Tzy-Shenn-Ming-Mu-Tang and Shiang-Chyong-San. The present HPLC system uses a Merck RP-select B column by isocratic elution with methanol and 1% (v/v) acetic acid (1:4) as the mobile phase and detected at UV 270 nm. 8-Chlorotheophylline was used as an internal standard. The extracts of prescriptions were treated by Supelclean LC-18 SPE tube for eliminating interferences. Blank decoctions of each prescription were also examined as a test for interferences. The recoveries of caffeine from the Chinese medicinal prescriptions ranged from 88.5 to 92.3%. The relative standard deviations of caffeine ranged between 0.86 and 1.97% (intraday) and 1.04 and 3.90% (interday). The contents of caffeine in standard decoctions ranged from 13.98 to 19.62 mg g(-1). (C) 1999 Elsevier Science B.V. All rights reserved.