Shou-Mei Wu

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.

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.

Enantiomeric analysis of methotrexate in pharmaceuticals by cyclodextrin-modified capillary electrophoresis

A capillary electrophoresis for the chiral separation of racemic methotrexate (rac-MTX) was developed and validated. The two enantiomers were separated by using fused-silica capillary and a running buffer containing phosphate and hydroxypropyl-β-cyclodextrin (HP-β-CD). Several parameters were studied, including concentration and pH of phosphate buffer, separation voltage, and type and concentration of CD. The quantitative ranges were 12.5–200.0 μM for each enantiomer. The intra- and inter-day relative standard deviations (R.S.D.) and relative errors (R.E.) (n=5) were all <5%. The detection limits were found to be about 4 μM (S/N=3, injection 5 s) at 280 nm. All recoveries were greater than 93%. This method was applied to the assay of l-MTX in pharmaceuticals.

Trace Analysis of Very Long Chain Free Fatty Acids in Plasma by Fluorogenic Derivatization and Liquid Chromatography

Abstract A simple and sensitive liquid chromatographic method is described for the simultaneous determination of docosanoic, tetracosanoic and hexacosanoic acids as fluorogenic derivatives. These acids, spiked in plasma, were extracted with n-heptane and the resulting extract was derivatized with 4-bromomethyl-7-methoxycoumarin (BrMmC) in dichloromethane using potassium carbonate and 18-crown-6 as catalysts. The derivatives obtained were chromatographed on a reversed-phase C8 column with acetonitrile: water (91: 9, v/v) as a mobile phase and 7-methoxy-4-(tricosanoyloxymethyl)-coumarin as an internal standard. The linear ranges for the determination of docosanoic, tetracosanoic, and hexacosanoic acids were over 31-500, 36-580 and 36-580 pmol, respectively. The limit of detection for each acid was about 0.3 pmol per 10 μL injection (S/N=3). This work was presented in part at the annual symposium of the Pharmaceutical Society of the R.O.C., Taichung, Dec. 22th, 1996.

Determination of Ethosuximide in Plasma By Derivatization and High Performance Liquid Chromatography

Abstract A simple and sensitive liquid chromatographic method is described for the determination of ethosuximide in plasma as a highly sensitive derivative. Ethosuximide in plasma, after separation with isopropanol extraction, was derivatized with strong chromophore reagent, 4-bromomethyl-7-methoxy-coumarin. The resulting derivatives were separated on a Nova-Pak C18 column with water-acetonitrile-methanol(60:20:20, v/v) as the mobile phase. The linear range for the determination of ethosuximide in spiked plasma was over 2-40 nmol. The limit of detection for ethosuximide was about 7.0 ± 1.2 pmol per 20 μL injection (S/N= 5). The intraday relative standard deviation (n = 6) and the interday relative standard deviation (n = 12) were all less than 2.5% for ethosuximide. The recovery for ethosuximide in plasma was greater than 96%.

SIMULTANEOUS DETERMINATION OF DIGOXIN AND DIGITOXIN BY DERIVATIZATION AND HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

A simple and sensitive liquid chromatographic method has been developed for the determination of digoxin and digitoxin by derivatization. The method is based on the derivatization of digoxin and/or digitoxin with derivatizing agent, 1-naphthoyl chloride, in pyridine at 50?C. Under the mild condition, the digoxin and digitoxin were derivatized into their highly sensitive derivatives. After the derivatization reaction, a dimethylamine- acetonitrile solution was added to the reaction mixture to eliminate the interference from the excess derivatizing agent. The derivatives obtained were performed on a reversed-phase C8 column with 88% acetonitrile as the mobile phase. The parameters affecting the derivatization of digoxin and digitoxin, including reaction temperature, reaction time, and the amount of derivatizing agent, were investigated. The linear ranges of the method for the determination of digoxin and digitoxin were over 1–50 nmol/mL and 5–50 nmol/mL; the detection limit (signal to noise ratio = 5; injec...

Derivatization-High Performance Liquid Chromatographic Determination of Methanol in Human Plasma

Abstract A simple and sensitive high performance liquid chromatographic method is described for the determination of methanol in human plasma, as a highly sensitive derivative. The methanol, spiked in plasma, after simple ultrafiltration treatment, was derivatized with 3-bromomethyl-7-methoxy-1,4-benzoxazin-2-one in a heterogeneous system, using benzalkonium chloride as phase transfer catalyst. The resulting derivative was chromatographed on a LiChrospher diol column with n-hexane:dichloromethane (9:1, v/v) as the mobile phase and 1-nitronaphthalene as the internal standard. The HPLC system showed good selectivity for methanol determination. Several parameters affecting the derivatization of methanol extracted from spiked plasma were investigated. The linear range for the determination of methanol in spiked human plasma was over 1–10 μmol/mL; the detection limit (signal to noise = 5, sample size 10 μL) of methanol was about 0.06 ± 0.02 μmol/mL. The intraday relative standard deviation (n = 6) and the inte...

MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY OF CYCLOSPORIN A IN A COMMERCIAL PREPARATION

A simple micellar electrokinetic capillary chromatography is described for the determination of cyclosporin A in commercial preparation. The analysis of cyclosporin A was performed in a Tris buffer (10 mM; pH 7.1) with sodium dodecyl sulfate (SDS) (30 mM) as an anionic surfactant. Applied voltage was 20 kV and temperature was 25°C. Cefaclor was used as an internal standard and detection set at 200 nm. Several parameters affecting the separation of the drug were investigated, including the pH of the buffer, the concentrations of the buffer and SDS. The linear range of the method for the determination of cyclosporin A was over 30–500 μM. Application of the method to the determination of cyclosporin A in capsules from a commercial source proved to be satisfactory.

Chemically Removable Derivatization Reagent for Chromatography. II. 2-(1-Naphthyl)Ethyl 2-[1-(4-Benzyl)-Piperazyl]Ethanesulfonate Dihydrochloride

Abstract A sulfonate reagent, 2-(1-naphthyl)ethyl 2-[1-(4-benzyl)piperazyl]ethanesulfonate dihydrochloride, was synthesized for analytical derivatization in liquid chromatography. The reagent has two main functions, one with a chromophore (naphthyl) for detection and the other with a substituted piperazine moiety for being removable after derivatization. The reagent was preliminarily applied to the derivatization of iodide anion. The results indicated that the reagent can be readily removed by acid after derivatization; this favorably avoids the interference of the excess reagent with the resulting iodide derivative for analysis.