Quantitative bioanalysis of quinine by atmospheric pressure-matrix assisted laser desorption/ionization mass spectrometry combined with dynamic drop-to-drop solvent microextraction

Dynamic drop-to-drop solvent microextraction (DDSME) combined with atmospheric pressure-matrix assisted laser desorption/ionization mass spectrometry (AP-MALDI/MS) has been successfully applied on the bioanalysis of quinine using micro liter volume (30 μL) of human urine and plasma samples. The method is based on the movement of aqueous phase (AP) in and out of the microsyringe, which increases the transfer and diffusion rate of the quinine drug from aqueous phase to organic phase (OP). The optimization parameters including the effect of solvent selection, number of samplings, sampling volume, volume of aqueous phase, volume of organic phase, addition of salt and pH were investigated for obtaining higher extraction efficiency of the analyte. The limits of detections (LODs) of quinine, using the dynamic DDSME/AP-MALDI/MS in urine and plasma samples were 0.18 and 0.24 μM, respectively. The superiority of dynamic DDSME over static DDSME and liquid–liquid extraction (LLE) was also demonstrated for the determination of quinine in aqueous solution. This method is promising in clinical application and pharmacokinetic studies, in which the availability of sample amount is extremely small.