ONLINE DEOXYGENATION FOR REDUCTIVE ELECTROCHEMICAL DETECTION OF ARTEMISININ AND DIHYDROARTEMISININ IN LIQUID-CHROMATOGRAPHY

A straightforward method for the deoxygenation of mobile phases and sa mples required for reductive detection in liquid chromatography is des cribed, The method, which is based on the use of a commercially availa ble on-line deoxygenator placed between the column and the detector, e liminates the problems associated with separate deoxygenations of the mobile phase and samples and restrictions imposed by work in an oxygen -free environment, The method is compatible with determinations of art emisinin and its main metabolite, dihydroartemisinin, and also artelin ate, in liquid samples, With the deoxygenator, efficiencies of the ord er of 4000-10 000 theoretical plates mere obtained for artemisinin usi ng 3.0, 4.0 and 4.6 mm diameter columns, The extra-column band broaden ing due to the deoxygenator was not found to be a limiting factor, Amp erometric detection with a gold electrode gave rise to lower backgroun d currents and better peak current reproducibilities than that with gl assy carbon and gold amalgam electrodes, The relative standard deviati ons in the peak current for 10 injections of 100 pmol of artemisinin, dihydroartemisinin and artelinate were 3.0, 1.4 and 3.3%, respectively , The peak currents for the compounds depended linearly on the amount injected in the range 10-200 pmol and the detection limits for artemis inin and dihydroartemisinin were calculated to be 2 and 3 pmol, respec tively.