Gas--liquid chromatographic determination of carbamazepine and phenylethylmalonamide in plasma after reaction with dimethylformamide dimethylacetal

A previously published procedure for the gas chromatographic analysis of carbamazepine has been modified and expanded to allow simultaneous determination of phenylethylmalonamide, a metabolite of primidone. Internal standards that closely resemble each compound are used, and derivatives are made by reaction with dimethylformamide dimethylacetal. This change of internal standard for carbamazepine and the use of a commercial, pretested column-packing material eliminate the major pitfalls of the original method.     

Gas chromatographic determination of gallopamil and norgallopamil in human plasma

A highly sensitive gas chromatographic assay is described for the simultaneous determination of gallopamil, a calcium channel blocking agent, and its major metabolite, norgallopamil. A multi-step extraction procedure is employed followed by on-column capillary gas chromatographic analysis using nitrogen-selective detection. Acetylation of norgallopamil is performed to enable accurate quantification of the metabolite. Linearity was achieved over the range 1-50 ng/ml for both analytes. Assay specificity, precision and accuracy were investigated.     

Gas chromatographic analysis of fosfomycin in plasma for pharmacokinetic analysis.

An efficient method for gas chromatographic analysis of fosfomycin in plasma was developed for preliminary investigations of the bioavailability in poultry of 3 commercial complexes of fosfomycin: a levorotatory Ca(-) salt, a racemic Ca(+/-) salt, and a tromethamine (THAM) salt. The method was used to determine whether the less expensive racemic mixture would provide equivalent levels of fosfomycin in blood as the pure Ca(-) form and the THAM salt. The THAM salt, a more expensive product to market, was thought to have the greatest bioavailability. The assay is selective, sensitive, and applicable to pharmacokinetic analysis.     

Gas chromatographic analysis of isomeric organic mononitrates in plasma.

A specific, sensitive and precise capillary gas chromatographic method using electron-capture detection was developed for the determination of four isomeric vasodilating organic mononitrates, viz. L-isoidide mononitrate (L-IIMN), isosorbide-2-mononitrate (IS-2-MN), isomannide mononitrate (IMMN) and isosorbide-5-mononitrate (IS-5-MN), in rat plasma. With a sample size of 100 microliters of rat plasma, the detection limits were found to be between 0.5 and 2 ng/ml for these mononitrates, and the absolute recovery was found to range from 83 to 90%. The within-day coefficients of variation for the assay of the four isomers were less than 5%, while the between-day coefficients of variation were less than 10%. Because of the short retention times of these isomers in this assay, routine analyses of about sixty plasma samples per day can be carried out. The possibility of in vivo interconversion among these four isomers in rats was investigated after individual administration of each isomer. No interconversion was found based on examination of plasma samples. The gas chromatographic method was applied to the pharmacokinetic studies of these four isomers in rats; at an intravenous dose of 2 mg/kg, the biological half-lives of L-IIMN, IMMN, IS-2-MN and IS-5-MN were found to be 13.2, 25.2, 54.6 and 112 min, respectively.     

Liquid chromatographic analysis of propafenone enantiomers in human plasma

A convenient and sensitive high-performance liquid chromatographic method for analysis of the enantiomers of propafenone (PPF) in human plasma was developed. Racemic propafenone and (-)-ephedrine (internal standard) were first extracted from plasma samples into a mixture of hexane-2-propanol-heptafluorobutanol (95:5:1.25, v/v). After evaporation of the organic layer, the samples were derivatized with R(-)-naphthylethyl isocyanate. The derivatization reached its maximum within 30 s at room temperature with an efficiency of 93.9 +/- 2.8% (mean +/- S.D.). The formed diastereomers were subsequently separated on a silica column with a mobile phase of hexane-2-propanol-isobutanol (96:2:2, v/v) at a flow-rate of 1.5 ml/min. The ultraviolet detection wavelength was set at 220 nm. Using 1 ml plasma, the detection limit was 6.25 ng/ml for the propafenone enantiomers. The assay was successfully employed to measure propafenone enantiomers in plasma samples of a healthy subject after oral administration of a single 150-mg dose of the racemate.     

Gas chromatographic method for the determination of nomifensine in human plasma.

An analytical method based on solvent extraction, formation of a fluorinated derivative and quantitation by gas-liquid chromatography using an electron capture detector has been developed for the determination of nomifensine in biological fluids. The specificity (controlled by mass spectrometry) and the sensitivity appear to be satisfactory for drug level measurements in human body fluids. Its relative simplicity in fact permits its use in serial analysis.     

Gas chromatographic determination of propyphenazone in plasma

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Combined immunological and thin-layer chromatographic method of the determination of morphine

     

Gas chromatographic determination of xanthinol in plasma

The determination of xanthinol in plasma is described. After extraction of the drug, together with the internal standard (papaverine hydrochloride), the extract is evaporated to dryness and the drug is derivatized with acetic anhydride for chromatography. The method is linear for 2–100μg ml^-1 ; the coefficient of variation is 3% and the recovery 80%. The resulting stable solution allows large numbers of samples to be processed with an automatic injector.     

Gas chromatographic determination of mefloquine in human and dog plasma using electron-capture detection

A sensitive and selective gas-liquid chromatographic method for the determination of plasma levels of mefloquine in human and dog plasma is described. The drug and internal standard were extracted from plasma at pH 9.0 into isopropyl acetate. After evaporation of the solvent, the residue was taken up in toluene and derivatised with heptafluorobutyrylimidazole. The derivative was quantified by gas-liquid chromatography on a 3% GC GE-SE30 column with electron-capture detection. The limit of detection for mefloquine in plasma was 10 ng/ml. The mean overall recovery from plasma was 102.7 +/- 3.3%. The method was shown to be specific for mefloquine without any interference from endogenous compounds in plasma or from the drugs pyrimethamine and sulfadoxine (compounds often administered in combination with mefloquine). The assay described was successfully applied to the determination of plasma levels of mefloquine in man and dog following oral and intravenous administration, respectively.     

High-performance liquid chromatographic analysis of isoxicam in human plasma and urine

A sensitive, selective, and rapid high-performance liquid chromatographic procedure was developed for the determination of isoxicam in human plasma and urine. Acidified plasma or urine were extracted with toluene. Portions of the organic extract were evaporated to dryness, the residue dissolved in tetrahydrofuran (plasma) or acetonitrile (urine) and chromatographed on a mu Bondapak C18 column preceded by a 4-5 cm X 2 mm I.D. column packed with Corasil C18. Quantitation was obtained by UV spectrometry at 320 nm. Linearity in plasma ranged from 0.2 to 10 micrograms/ml. Recoveries from plasma samples seeded with 1.8, 4 and 8 micrograms/ml isoxicam were 1.86 +/- 0.077, 4.10 +/- 0.107 and 8.43 +/- 0.154 micrograms/ml with relative standard deviations of 3.3%, 2.5% and 5.4%, respectively. The linearity in urine ranged from 0.125 to 2 micrograms/ml. The precision of the method was 3.3-9.0% relative standard deviation over the linear range.     

High-performance liquid chromatographic analysis of hippuric acid in human blood plasma

A method has been developed for the isocratic high-performance liquid chromatographic analysis of hippuric acid in human blood plasma. After the addition of an internal standard (3-methoxysalicylic acid), plasma samples (1 ml) were made alkaline and extracted stepwise with methylene chloride and ethyl acetate. The detection limit was 50 pmol of hippuric acid per ml of plasma. The concentrations of hippuric acid in plasma from house painters (n = 8), with long-term exposure to solvent vapours from alkyd paints, were in the range 1-21 nmol/mol (median 11 nmol/ml). These values were statistically significantly higher than those for controls (n = 9): 2-8 nmol/ml (median 3 nmol/ml).     

Gas chromatographic analysis of methyldemeton

Summary A gas chromatographic method is described for the analysis of methyldemeton present in the form of two isomers,O,O-dimethyl O-2-(ethylthio)ethylphosphorothioate andO,O-dimethyl S-2(ethylthio)ethylphosphorothioate in mixtures containg benzene, xylene, 3-thiapentanol-1, andO,O,O-trimethylthiophosphate. Such mixtures are obtained when methyldemeton is synthesized fromO,O-dimethylchlorothiophosphate and 3-thiapentanol-1 [1]. The best results are obtained using a short stainless steel column packed with 5% (w/w) OV-17 on Chromosorb G AW-DMCS 100–120 mesh.