Sample extraction detector for the liquid chromatographic determination of secoverine in biological samples

A simple detection system for liquid chromatography based on post-column ion-pair extraction in a solvent-segmented stream is described. The fluorescent ion-pairing reagent 9,10-dimethoxyanthracene-2-sulphonate is added to the aqueous mobile phase prior to the column. An organic solvent, used for extraction of the ion pairs and for segmentation purposes, is added to the column effluent by gravity; about 70% of this phase is drawn through the detector cell using the siphon principle. The noise is significantly less than that of system with a pulsating peristaltic pump. The system has been used for the detection of the prospective drug secoverine. Under optimized conditions, band broadening due to the extraction detection system is sigma t = 7 sec. The detection limit of secoverine is ca. 20 pg, the repeatability in the nanogram range is 2% (relative standard deviation) (n = 6) and the linear range is at least 4 decades. The use of pre-column containing a 1--2-mm layer of stationary phase for clean-up and trace enrichment allows the direct injection of 200--1000 microliters of plasma or serum. In this way, secoverine can be determined in the parts per 10(12) range.