In this study, online sample concentration method, which coupled field‐amplified sample injection (FASI) and sweeping technology with micellar electrokinetic chromatography (MEKC), was used to detect and analyze acidic and basic components in a single run. In order to concentrate the acidic and basic components simultaneously in a single run sweeping step, a combination of successive anion‐ and cation‐selective injections were used. Before sample loading, a rinse buffer containing 50 mM Tris buffer (pH 3) with 41% MeOH and 0.1% polyethylene oxide (PEO) was injected in order to suppress the electroosmotic flow (EOF). Sample loading of anionic components was achieved by electrokinetic injection at a negative voltage of −2.5 kV for 80 s, and then the cationic components were injected at a positive voltage of +5 kV for 120 s. Finally, sweeping with SDS micelles from the separation buffer (25 mM Tris buffer with 60 mM SDS, pH 3) was performed at a negative voltage of −20 kV. This capillary electrophoretic methodology was applied to the quantification of acidic and basic drugs in commercial tablets and in plasma samples. The precision and accuracy of the proposed method at different concentrations ranging from high, medium, to low were evaluated on spiked plasma samples. The intra and interday precision and accuracy values at three concentrations were all below 6.1%. The method was also successfully applied to monitor the tested drugs in the plasma of nine elderly cardiovascular and/or Alzheimer's disease patients after oral administration of the commercial products.

We developed a simple and selective CE with UV detection at 233 nm for the analysis of metformin in plasma based on direct sample injection without any pretreatment. The sample was employed with an electrokinetic injection of 10 kV for 100 s. CE separation of metformin from biological matrix was performed at 25 degrees C using a BGE consisting of 25 mM Tris buffer at pH 4.0. The linear range of the CE method for the determination of metformin in plasma was over the range of 0.1-2.0 mug/mL; the LOD of the drug in plasma (S/N = 3; injection 10 kV, 100 s) was 30 ng/mL. Data by CE were compared with the results obtained by a validated HPLC method. CE assay of metformin exhibited a very good correlation (r(2 )= 1) with respect to HPLC. CE determination of metformin is a robust, sensitive, and reproducible method with the advantage over HPLC of being fast, without prior extraction, or precipitation of proteins, also enabling quick assessment of metformin for pharmacokinetic and clinical studies.

A sensitive high-performance CZE combining on-column field-amplified sample injection (FASI) has been developed for simultaneous determination of aripiprazole and its active metabolite, dehydroaripiprazole, in human plasma. A sample pretreatment by means of liquid-liquid extraction (LLE) (diethyl ether) with subsequent quantitation by FASI-CZE was used. The separation of aripiprazole and dehydroaripiprazole was performed using a BGE containing 150 mM phosphate buffer (pH 3.5) with 40% methanol and 0.02% PVA as a dynamic coating to reduce interaction of analytes with the capillary wall. Before sample loading, a methanol plug (0.3 psi, 6 s) was injected to permit FASI for stacking. The samples were injected electrokinetically (10 kV, 30 s) to introduce sample cations and the applied voltage was 20 kV with on-column detection at 214 nm. Several parameters affecting the separation and sensitivity of the drug and its active metabolite were studied, including reconstitution solvent, organic modifier, pH and concentration of phosphate buffer. The linear ranges of the method for test drug and its active metabolite, in plasma using amlodipine as an internal standard, were over the range 5.0-100.0 ng/mL. One female volunteer (25 years old) was orally administered a single dose of 10 mg aripiprazole (Abilify, Otsuka) and blood samples were drawn over a 60 h period for pharmacokinetic study. The method was also applied to monitor the concentration of aripiprazole and dehydroaripiprazole in plasma collected after oral administration of 20 or 30 mg aripiprazole (Abilify, Otsuka) daily at steady state in one schizophrenic patient.