On-line deoxygenation for reductive electrochemical detection of artemisinin and dihydroartemisinin in liquid chromatography
A straightforward method for the deoxygenation of mobile phases and samples required for reductive detection in liquid chromatography is described. The method, which is based on the use of a commercially available on-line deoxygenator placed between the column and the detector, eliminates 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 artemisinin and its main metabolite, dihydroartemisinin, and also artelinate, in liquid samples. With the deoxygenator, efficiencies of the order of 4000–10 000 theoretical plates were obtained for artemisinin using 3.0, 4.0 and 4.6 mm diameter columns. The extra-column band broadening due to the deoxygenator was not found to be a limiting factor. Amperometric detection with a gold electrode gave rise to lower background currents and better peak current reproducibilities than that with glassy carbon and gold amalgam electrodes. The relative standard deviations 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 artemisinin and dihydroartemisinin were calculated to be 2 and 3 pmol, respectively.