Determination of the GABAergic antidepressant drug fengabine and some of its metabolites in plasma by capillary gas chromatography with electron-capture detection

A sensitive capillary gas chromatographic method was developed for the determination of fengabine (a GABAergic antidepressant drug) and some of its metabolites in plasma samples. The method involves a single and rapid liquid-liquid extraction of the parent drug and metabolites from plasma buffered at pH 5, evaporation of the organic phase under nitrogen, derivatization to tert.-butyldimethylsilyl ethers and esters and automatic gas chromatography on a fused-silica, silicone-bonded capillary column coupled to an electron-capture detector. The detection limit for fengabine and other compounds is lower than 1 ng/ml in plasma; the method was successfully applied to pharmacokinetic and drug monitoring clinical studies and tested on more than 2000 biological samples and was found not to suffer from endogenous or exogenous interferences.     

Semi-preparative enantiomer separation of 1-chloro-2,2-dimethylaziridine by complexation gas chromatography -absolute configuration and barrier of inversion

1-Chloro-2.2-dimethyl-aziridine has been resolved into its enantiomerically pure invertomers by semi-preparative complexation gas chromatography at 25°C. The absolute configuration has been correlated with the chromatographic elution order. An inversion barrier of ΔG‡ = 115.5 kJ/mol was determined in the gas phase at 338.6 K.     

Diffusion coefficients from stopped-flow gas chromatography

Summary Mutual diffusion coefficients of two gases A and B can be determined in an empty gas chromatographic column by letting component B enter at an intermediate position of the column and continuously flow through a part only of it, as a carrier gas. The other component A is injected in a small amount instantaneously at the closed end of the column with the detector placed at the other end. By repeatedly stopping and then restoring after a short time the flow of B, narrow extra peaks are produced on the chromatographic elution curve, owing to diffusion of A into B. An equation is derived giving the area under the curve of each stop-peak as a function of time of the corresponding stop. Plotting the experimental data according to this equation permits the determination of the diffusion coefficient of A into B. Some results obtained by this method show negligible variations with changes in the experimental parameters.     

Determination of toluenesulfonic acid isomers by gas chromatography

Summary A gas chromatographic method for the determination of isomeric distribution in toluenesulfonic acid samples is described. The acids are transformed into the corresponding ethyl esters by reaction with triethyl orthoformate in toluene. The reaction mixture can be injected, without further purification, into the gas chromatograph. The separation is best performed on columns containing OV-210 or polyphenyl ether (6 rings) as the stationary phase.     

Plasma quantification of quazepam and its 2-oxo and N-desmethyl metabolites by capillary gas chromatography

The authors have developed a gas chromatographic method for the simultaneous quantification of quazepam in plasma and its two main metabolites, 2-oxoquazepam and N-desmethylquazepam. This method involves an extraction from plasma using butyl acetate, and an analysis by electron-capture detection on a CP-Sil 5 WSCOT capillary column. Intra- and inter-day precision and accuracy were better than 10% for each of these three compounds, even near their detection limit estimated at 0.2 ng/ml. Linearity proved satisfactory between 0.2 and 60-70 ng/ml. For endogenous plasma components, adequate specificity was achieved. Despite some inconveniences, a long analysis time, a progressive saturation of the column owing to a low oven temperature, and a relatively short life-span of the CP-Sil 5 columns, this method was the only one available in the literature for the quantification of quazepam and its metabolites from the same plasma sample. It was successfully applied to phase I studies in healthy volunteers.     

Detection of oxilofrine in plasma and urine by high-performance liquid chromatography with electrochemical detection and comparison with gas chromatography-mass spectrometry

A high-performance liquid chromatographic (HPLC) method with electrochemical detection for the determination of oxilofrine [1-(4-hydroxyphenyl)-2-methylaminopropanol] in human plasma and urine (before and after cleavage of the metabolic conjugates) is described. Isolation from biological fluids is performed batchwise by weak acid cation exchange. Separation of plasma and urine components is achieved on a reversed-phase C18 column as an ion pair with heptanesulphonic acid. For amperometric detection the potential of the electrode was set at 0.95 V versus an Ag/AgCl reference electrode. The detection limit for oxilofrine in plasma is 1 ng/ml and in urine 12.5 ng/ml at a signal-to-noise ratio of 2.0 using 1.0 ml of plasma and 0.02 ml of urine. The method was compared with a gas chromatographic-mass spectrometric method and showed a good concordance for plasma (r = 0.996) and urine (r = 0.994). With the HPLC method it is also possible to determine related sympathomimetic drugs, e.g., etilefrine, norefenefrine or octopamine, after a slight modification of the mobile phase.     

Determination of perphenazine and its sulphoxide metabolite in human plasma after therapeutic doses by gas chromatography.

A gas chromatographic method for the determination of perphenazine (Tri-lafon) and its main metabolite in human plasma, perphenazine sulphoxide, has been developed. The procedure involves the use of an electron capture detector and permits the determination of the drug and its metabolite at concentrations down to 0.2 mug/l. This is sufficient for analyzing plasma from patients on ordinary treatment with perphenazine. Tests for specificity revealed no interference by nortriptyline or biperidine.     

Determination of fendiline in human plasma by means of capillary gas chromatography and nitrogen-phosphorus selective detection.

A sensitive and specific method for the determination of fendiline in human plasma is presented. Fendiline was extracted from human plasma after the addition of phosphate buffer two times with 4 ml of n-hexane. The organic phase was separated and evaporated to dryness at 40 degrees C under a stream of nitrogen. The residue was dissolved and an aliquot was injected into the gas chromatograph. Chromatographic separation was performed with a DB-1 column with helium as carrier gas. Nitrogen-selective detection was performed. Quantification was performed with the signal output. The limit of detection was 1 ng/ml of plasma.     

Determination of plasma amino acids by gas chromatography

A complete methodology, incorporating a novel clean-up technique, for quantitative determination of amino acids in plasma by gas chromatography is described. Glucose, a component causing major analytical interference, is removed by an enzymic reaction included in the pre-chromatographic clean-up. The procedure for derivatisation of amino acid standards is shown to be reproducible down to a level of 2.5 micrograms for each amino acid, relative standard deviations for all amino acids except arginine and histidine being 3% or lower. For the entire procedure applied to plasma, relative standard deviations for most amino acids are below 5% with recoveries ranging from 90 to 120%. Normal values, obtained using eighteen plasma samples, are in reasonable agreement with published data. Plasma amino acid values were determined simultaneously by gas chromatographic and ion-exchange chromatographic techniques. Statistical evaluation shows there to be no significant difference between corresponding values for eleven amino acids. Values for tyrosine, histidine and particularly phenylalanine show significant differences (p less than 0.001).     

Determination of bencyclane in human plasma by means of capillary gas chromatography and nitrogen-phosphorus selective detection

A sensitive and specific method for the determination of bencyclane in human plasma is presented. Bencyclane was extracted from human plasma with two 3-ml volumes of isooctane and was shaken for 10 min. The organic phase was separated and evaporated to dryness at 40 degrees C under a nitrogen stream. The residue was dissolved and an aliquot was injected into the gas chromatograph. The separation was performed with a DB-17 column with helium as the carrier gas. Nitrogen-selective detection was performed. The quantification was performed with the signal output. The limit of detection was 1 ng/ml.     

Determination of a new blood glucose-lowering agent in biological fluids by capillary gas chromatography using electron-capture detection

A gas chromatographic method for the determination of 5-(4-chlorophenyl)-2-[(4-methylphenyl)sulphonyl]-4-pentynoic acid (I) in plasma (serum) and urine has been developed. After an extraction process, the cleaned-up organic extract was derivatized with diazomethane at ambient temperature. Results are evaluated from peak-height ratios with respect to the appropriate internal standard. The detection limit following extraction of a 1-ml plasma sample is about 20 ng/ml.     

Evaporation of the liquid stationary phase in gas chromatography

Summary The theory of the evaporation of the liquid stationary phase is elaborated and experimentally verified. On the basis of this theory the role played by the losses in the amount of liquid phase present is quantitatively determined. General techniques are examined which minimize the losses; these techniques are based on saturating the incoming carrier gas with liquid phase vapours and raising the pressure of the carrier gas in the column, e.g. by connecting a capillary to the column outlet in order to offer resistance to the gas flow. The application of these techniques ensures stable performance of the gas chromatographic columns using a volatile liquid phase.     

Simultaneous determination of codeine and chlorpheniramine in human plasma by capillary column gas chromatography

A specific and highly sensitive capillary column gas chromatographic method was developed for the simultaneous determination of codeine and chlorpheniramine in human plasma. The method involves a solvent extraction and analysis by capillary column gas chromatography on a cross-linked 50% phenylmethyl silicone fused-silica capillary column with flame thermionic detection. A 10% solution of n-butanol in toluene was used as extraction medium and pyrilamine was used as internal standard. Reproducibility, linearity of calibration curves and specificity were all satisfactory with both drugs. The plasma concentration of codeine and chlorpheniramine could be measured at levels down to 0.9 ng/ml as codeine phosphate and 0.4 ng/ml as chlorpheniramine maleate, respectively. The method was applied to plasma samples from normal volunteers, and was confirmed to be adequate for biopharmaceutical and pharmacokinetic studies.     

Quantitation of hexaprazol in human plasma and urine by capillary gas chromatography with nitrogen-sensitive detection

A selective and sensitive gas chromatographic assay for hexaprazol, a new antiulcer drug, in human plasma and urine has been developed. The method involves liquid-liquid extraction and capillary gas chromatography with nitrogen-sensitive detection. The limit of quantitation of plasma hexaprazol is ca. 25 ng/ml. The assay procedure permits the measurement of the levels of the unchanged drug following its clinical administration to humans.     

Determination of noscapine in plasma by liquid chromatography

A liquid chromatographic method has been developed for the determination of noscapine in plasma. Noscapine and the internal standard, papaverine, were extracted into methylene chloride by column extraction. The separation was performed on a straight-phase liquid chromatographic system using a mobile phase of hexane--methanol--chloroform--diethylamine. A high detection selectivity was obtained by UV detection at 310 nm. The precision of the method was 3.8% (standard deviation) at a level of 89 ng/ml and 9.5% (standard deviation) at 5.9 ng/ml. The selectivity of the analytical method was evaluated by comparing analytical results after isolation of extracts of plasma samples on reversed- and straight-phase liquid chromatographic systems.     

Simultaneous determination of midazolam and its three hydroxy metabolites in human plasma by electron-capture gas chromatography without derivatization

Electron-capture gas chromatography was carried out to determine midazolam and its three hydroxy metabolites (1-hydroxymethylmidazolam, 4-hydroxymidazolam and 1-hydroxymethyl-4-hydroxymidazolam) in human plasma. The assay involves extraction from plasma, buffered to pH 9.3, into cyclohexane-dichloromethane (6:4) and analysis by gas chromatography. The use of an HP-17 cross-linked, capillary column makes derivatization unnecessary. The sensitivity of the method was 2-3 ng/ml for midazolam, 1-hydroxymethylmidazolam and 4-hydroxymidazolam, and 20 ng/ml for 1-hydroxymethyl-4-hydroxymidazolam. The extraction recovery of midazolam, 1-hydroxymethylmidazolam, 4-hydroxymidazolam and 1-hydroxymethyl-4-hydroxymidazolam was 99.3 +/- 2.4, 67.0 +/- 4.6, 92.7 +/- 4.7 and 28.7 +/- 6.3%, respectively. This gas chromatographic assay was used to assess the concentration-time profiles of midazolam and its metabolites in human plasma after rectal and intravenous administration of midazolam.     

Determination of busulfan in human plasma by gas chromatography with electron-capture detection

A simple and highly sensitive gas chromatographic method has been developed for the determination of busulfan in human plasma. After extraction of plasma specimens (clinical or spiked) with ethyl acetate, busulfan and the internal standard [1,8-bis(methanesulfonyloxy)octane] were derivatized with 2,3,5,6-tetrafluorothiophenol to yield compounds monitored by a 63Ni electron-capture detector. Sample recoveries from extraction and derivatization were greater than 78 and 91%, respectively. The limit of quantitation was 0.01 microgram/ml (0.04 microM) in 1 ml of plasma with a linear relationship over the 0.01-1.0 micrograms/ml (0.04-4 microM) concentration range. The method has been applied to analyze the plasma versus time profile of busulfan in human subjects following administration of an oral dose of 4 mg/kg per day as a marrow ablative chemotherapy for bone marrow transplantation.     

Hold-up time in gas chromatography. V. Dependence of the retention of n-alkanes on the chromatographic variables in isothermal gas chromatography

The chromatographic behaviour of n-alkanes and other homologous series in isothermal gas chromatography has been shown to depart from the "linear" representation of the logarithms of the adjusted retention times vs. carbon number. One of the expressions proposed to describe this behaviour is tR(z)=A+exp(B+CzD). In this paper, a regression analysis shows that three of the parameters of the equation depend on different chromatographic variables such as hold-up time, average linear gas velocity, volume and polarity of the stationary phase and temperature of the column. The fourth parameter (D), responsible for the departure from the "linearity", does not depend on any chromatographic variable, and represents a gradual decrease of the contribution of the methylene groups to the general properties of n-alkanes, with no relation to the chromatographic phenomenon.     

Phosgene as a derivatizing reagent prior to gas and liquid chromatography

The use of phosgene as a derivatizing agent for bifunctional compounds prior to gas and liquid chromatographic analysis is reviewed. Applications include gas chromatographic determinations of metoprolol and its metabolites in biological fluids, enantiomeric separations of beta-blocking drugs and sympathomimetic agents on a chiral stationary phase and liquid chromatographic enantiomer separations.     

Determination of 1,2-benzisoxazole-3-acetamidoxime hydrochloride (PE-257) in plasma using electron-capture gas chromatography

A gas chromatographic method has been developed that permits the accurate and specific determination of a new psychotropic agent, PF-257, in plasma. PF-257 is extracted with ethyl acetate from alkaline plasma and, after a clean-up procedure, derivatized with heptafluorobutyric anhydride to form 3-[(5-n-heptafluoropropyl-1,2, 4-oxadiazol-3-yl)methyl]-1,2-benzisoxazole (HOMB). The HOMB is assayed on a gas chromatograph equipped with an electron-capture detector. Accurate determinations of PF-257 are possible in the concentration range from 1-40 ng/ml with a relative standard deviation of 6.8%. The minimum detectable concentration in plasma is 0.1 ng/ml. Plasma levels of PF-257 in rats receiving intravenous or oral dosing (10 mg/kg) were determined.