Su-Hwei Chen

Simultaneous determination of memantine and amantadine in human plasma as fluorescein derivatives by micellar electrokinetic chromatography with laser‐induced fluorescence detection and its clinical application

A nonionic surfactant MEKC method with LIF detection was developed for the simultaneous determination of memantine, an anti‐Alzheimers disease agent, and amantadine, an anti‐Parkinsons disease drug, in human plasma. Before analysis, the plasma samples were pretreated by liquid–liquid extraction with ethyl acetate, and derivatized with 6‐carboxyfluorescein N‐hydroxysuccinimide ester. The chemical derivatization is performed with 6‐carboxyfluorescein N‐hydroxysuccinimide ester in ACN – 5 mM pH 9.0 borate buffer (40:60, v/v) at 35°C for 3 h. After the derivatization reaction, hydrodynamic injection (0.5 psi, 8 s) was used to introduce the derivatized solution, and the separation was performed in borate buffer (30 mM, pH 9.5) with the nonionic surfactant Brij‐35® (0.07%, w/v); the separation voltage was 6 kV. The linear ranges of the method for the determination of memantine and amantadine in human plasma were over a range of 2.0–60.0 ng/mL. The detection limit was 0.5 ng/mL (S/N=3). This method was applied successfully to monitor the concentration of memantine or amantadine in patients with Alzheimers disease or Parkinsons disease.

Head-column field-amplified sample stacking in capillary electrophoresis for the determination of cimetidine, famotidine, nizatidine, and ranitidine-HCl in plasma

In this study, low concentrations of histamine2‐receptor (H2‐)antagonists were effected across a water plug, with separation taking place in a binary buffer comprising ethylene glycol and NaH2PO4 (pH 5.0), and detection at 214 nm. Liquid‐liquid extraction with ethyl acetate – isopropanol is shown to provide extracts that are sufficiently clean. The calibration curves were linear over a concentration range of 0.1–2.00 νg/mL cimetidine, 0.2–5.0 νg/mL ranitidine‐HCl, 0.3–5.0 νg/mL nizatidine, and 0.1–3.0 νg/mL famotidine. Mean recoveries were > 82%, while the intra‐ and interday relative standard deviations (RSDs) and relative errors (REs) were all < 13%. The method is sensitive with a detection limit of 3 ng/mL cimetidine, 30 ng/mL ranitidine HCl, 50 ng/mL nizatidine and 10 ng/mL famotidine (S/N = 3, electric‐driven injection 90 s). This newly developed capillary electrophoresis (CE) method was applied for the determination of analytes extracted from plasma taken from a volunteer dosing a cimetidine, ranitidine, and nizatidine tablet simultaneously. These three H2‐antagonists can be detected in real samples by this method, excluding the low dosing of famotidine tablet.

Enantioseparation of cetirizine by sulfated-β-cyclodextrin-mediated capillary electrophoresis

A sulfated beta-cyclodextrin (sulfated beta-CD)-mediated capillary electrophoresis method is described for the enantioseparation of cetirizine using achiral cefazolin as an internal standard. The enantioseparation of the drug was performed in a borate buffer (5 mM, pH 8.7) with 1% sulfated beta-CD (w/v) as chiral selector at 10 kV. Several parameters affecting the separation were studied, including the pH and the concentration of borate buffer and chiral selector. Under optimized conditions, a baseline separation of two enantiomers was achieved in less than 7 min. Using cefazolin as an internal standard (IS), the linear range of the method for the determination of levocetirizine was over 1.0 to 50.0 microg/mL; the detection limit (signal-to-noise ratio = 3) of levocetirizine was 0.5 microg/mL. The method allowed the enantioseparation of cetirizine in bulk samples and enantiomeric purity evaluation of levocetirizine (R-enantiomer) in pharmaceutical tablets (Xyzal), and it was also found to be suitable for enantioseparation in human plasma.

A fluorimetric liquid chromatography for highly sensitive analysis of very long chain fatty acids as naphthoxyethyl derivatives.

SummaryA simple and sensitive liquid chromatographic method is described for the simultaneous determination of biologically important very long chain fatty acids (docosanoic, tetracosanoic and hexacosanoic acids) as fluorogenic derivatives. The method is based on the derivatization of the fatty acids with 2-(2-naphtoxy)ethyl 2-(piperidino)ethanesulfonate (NOEPES) in toluene in the presence of potassium carbonate and 18-crown-6. Several parameters affecting the derivatization were studied, including reaction temperature, reaction time, reaction solvent, base catalyst and the amount of the reagent. The resulting derivatives were analyzed by HPLC with fluorimetric detection (λex=235 nm; λem=366 nm). The linear range for the determination of docosanoic, tetracosanoic and hexacosanoic acids was 0.028–1.4 μM with a detection limit of about 5.6 nM (S/N=3) (56 fmol per 10 μL injection). Application of the method to the analysis the non-esterified (free) very long chain fatty acids spiked in plasma proved feasible.

Simultaneous determination of cimetidine, famotidine, nizatidine, and ranitidine in tablets by capillary zone electrophoresis

A simple capillary zone electrophoresis (CZE) method is described for the simultaneous determination of cimetidine (CIM), famotidine (FAM), nizatidine (NIZ), and ranitidine (RAN). The analysis of these drugs was performed in a 100 mM phosphate buffer, pH 3.5. Several parameters were studied, including wavelength for detection, concentration and pH of phosphate buffer, and separation voltage. The quantitative ranges were 100–1000 νM for each analyte. The intra‐ and interday relative standard deviations (n = 5) were all less than 4%. The detection limits were found to be about 10 νM for CIM, 20 νM for RAN, 20 νM for NIZ, and 10 νM for FAM (S/N = 3, injection 1 s) at 214 nm. All recoveries were greater than 92%. Applications of the method to the assay of these drugs in tablets proved to be feasible.

Trace analysis of haloperidol and its chiral metabolite in plasma by capillary electrophoresis

Capillary zone electrophoresis was developed for the simultaneous determination of haloperidol (HP) and its chiral metabolites [(+)- and (-)- reduced haloperidol, (+)- and (-)-RHP] in human plasma. The method involved the presence of an internal standard and liquid-liquid extraction from plasma. After concentration, the residue from the organic extract was dissolved in aqueous acid for capillary electrophoretic analysis. The background electrolyte was Tris-phosphate buffer with dimethyl-beta-cyclodextrin and PEG 6000. In spiked plasma the quantitative ranges were 40-400 nM for HP and 50-500 nM for (+)-RHP or (-)-RHP. The intra-day and inter-day relative standard deviations (n = 3) were all < 20% for each substance. The detection limits were found to be 15 ng/ml for HP and 30 ng/ml for both enantiomers of RHP (S/N = 3, injection 20 s). All recoveries were > 70%. We investigated the in vivo metabolism of HP in Chinese schizophrenia patients. The results show that (-)-RHP seems to be the only chiral metabolite from these two HP-dosed patients.

Stereochemical analysis of betamethasone and dexamethasone by derivatization and high-performance liquid chromatography

A simple and economical high-performance liquid chromatographic method has been developed for the simultaneous determination of betamethasone and dexamethasone. The method is based on the derivatization of the structural epimers of betamethasone and dexamethasone with a homochiral reagent, N-carbobenzoxy-L-phenylalanine. The derivatives obtained were easily recognized by a non-chiral silica column with n-hexane-dichloromethane-isopropanol (100:100:4, v/v/v) as a mobile phase and a good separation was obtained for quantitation. The method was satisfactorily applied to the determination of betamethasone and dexamethasone in tablets.

Sample stacking by field-amplified sample injection and sweeping for simultaneous analysis of acidic and basic components in clinic application

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 Alzheimers disease patients after oral administration of the commercial products.

CE with direct sample injection for the determination of metformin in plasma for type 2 diabetic mellitus: An adequate alternative to HPLC.

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.

Micellar electrokinetic chromatography of scopolamine-related anticholinergics.

A simple micellar electrokinetic chromatography (MEKC) method is described for the separation of scopolamine N-oxide hydrobromide (SO), scopolamine hydrobromide (SH), scopolamine N-methylbromide (SM) and scopolamine N-butylbromide (SB), and for the quantitation of SH, SM and SB (using SO as an internal standard). The analysis of these drugs was performed in a phosphate buffer (30 mM; pH 7.00) with sodium dodecyl sulfate (SDS) (30 mM) as an anionic surfactant. Several parameters affecting the separation of the drugs were studied, including the concentrations of the buffer and SDS. The stability of the drugs in the phosphate buffer (pH 7.00) was also examined. Partial application of the method to the determination of scopolamine N-butylbromide in tablets proved to be feasible.