Quantitative analysis with thermal conductivity detection in gas-liquid chromatography

The form of detector now most generally used in gas-liquid chromatography is the katharometer (thermal conductivity cell). This detector, in common with certain other “differential” types that have been employed, requires calibration for a quantitative interpretation of the clution curve, since the signal recorded is not dependent on some simple molecular parameter of the clutcd component and also is not a linear function of its concentration. The present paper mentions several causes of this non-linearity. It further illustrates, with the aid of practical examples (the analysis of narrow hydrocarbon distillates) how the katharomcter can be calibrated by analysing mixtures of the pure components in question, and how the calibration factors are applied in the quantitative interpretation of analyses,     

Rapid micro-method for the measurement of diazepam and desmethyldiazepam in blood plasma by gas-liquid chromatography.

A rapid gas-liquid chromatographic technique has been developed for use in the simultaneous measurement of both diazepam and its major metabolite, desmethyldiazepam, in blood plasma. Neither solvent transfer nor evaporation steps are required in this procedure. Extremely small plasma volumes (20 to 100 microleter) are used and this has proved advantageous, especially when analysing samples from neonates. A linear response to amounts from 1-10(-12) to 1-10(-9) g/sec of both diazepam and desmethyldiazepam has been obtained and thus the direct analyses of these compounds both during therapy and after overdosage has been possible. Interference from either endogenous or exogenous sources has been found to be minimal.     

Trace analysis of vinclozoline by gas chromatography with electrolytic conductivity detection and solid-phase extraction

A procedure for the analysis of vinclozoline in tap and surface water by GC and Hall detector has been developed. Each step — the analysis of vinclozoline in acetone standard solution, in deionized water and in tap water after solid-phase extraction — was checked by statistical tests (variance homogeneity, linearity test, residue analysis, runaway tests, F-test, t-test). The detection limits and determination limits were calculated from the calibration curve and its prediction interval (according to the DFG). The detection limit for vinclozoline in tap water was found to be 0.03 g/l and the determination limit is 0.06 g/l by a recovery rate of 89%.     

Method for the measurement of plasma dehydroepiandrosterone by gas-liquid chromatography with electron capture detection.

A method is described for the measurement of plasma dehydroepiandrosterone, as the iodomethyldimethylsilyl ether derivative, by gas-liquid chromatography and electron capture detection using the relatively new and highly stable stationary phase Dexsil 300. Preliminary purification of the plasma extract was required and alumina column chromatography was utilised, both before and after derivatization of the steroid extract. Specificity, precision, sensitivity and accuracy were all satisfactory. The method was used to study the relationship between age and the level of plasma dehydroepiandrosterone in a group of normal women. A significant negative correlation was observed.     

Determination of isosorbide dinitrate and its two mononitrate metabolites in human plasma and saliva through gas-liquid chromatography with electron-capture detection

Summary Two sustained-release formulations of isosorbide dinitrate (ISDN) were administered to eight healthy male subjects and plasma and saliva samples were analysed. The determination of ISDN and its two metabolites 2-isosorbide mononitrate (2ISMN) and 5-isosorbide mononitrate (5ISMN) was carried out after extraction through gas chromatography with an electron-capture detector. Different packed and capillary columns were tested and optimal Chromatographic and extraction parameters for the measurement were worked out. A dose of 120 mg ISDN sustained-release preparation results in a plasma concentration of 1–42 ng/ml ISDN, 1–76 ng/ml 2ISMN and 12–475 ng/ml 5ISMN, respectively, during 48 h after drug administration. Good saliva-plasma correlation was obtained only for 5ISMN. Plasma samples should not come into contact with plastic materials in order to avoid losses of ISDN and mononitrates due to adsorption. The relative standard deviation for ISDN and 2ISMN was found to be ± 3–7% and for 5ISMN ± 2–5%.

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Bestimmung von Isosorbiddinitrat und seinen beiden Mononitrat-Metaboliten in menschlichem Plasma und Speichel durch Gas-Flüssig-Chromatographie mit Electron-Capture Detektor

Zusammenfassung Zwei Retard-Präparate von Isosorbiddinitrat (ISDN) wurden acht gesunden männlichen Probanden verabreicht. Die Bestimmung von ISDN und den beiden Metaboliten 2-Isosorbidmononitrat (2ISMN) und 5-Isosorbidmononitrat (5ISMN) in Plasma- und Speichelproben erfolgte nach Extraktion durch Gas-Chromatographie mit einem Electron-Capture Detektor. Verschiedene gepackte Säulen und Capillarsäulen wurden getestet und optimale chromatographische Bedingungen sowie günstige Extraktionsparameter ausgearbeitet. Nach Verabreichung einer Dosis von 120 mg in Form der ISDN Retard-Präparate betrugen die Plasmakonzentrationen während 48 h für ISDN zwischen 1 und 42 ng/ml, für 2ISMN zwischen 1 und 76 ng/ml sowie für 5ISMN zwischen 12 und 475 ng/ml. Bei den Speichelproben konnte nur für das 5ISMN gute Korrelation mit den Plasmaproben erreicht werden. Kontakte von Plasmaproben mit Plastikgefäßen sollten vermieden werden, da evtl. niedrigere Ergebnisse für ISDN und die Mononitrate durch Adsorption erhalten werden. Die relative Standardabweichung beträgt für ISDN und 2ISMN ± 3–7% und für 5ISMN ± 2–5%.

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Herrn Prof. Dr. Rudolf Bock zum 70. Geburtstag gewidmet     

Determination of unchanged hydralazine in plasma by gas-liquid chromatography using nitrogen-specific detection

A gas chromatographic method is described for the specific determination of unchanged hydralazine in plasma. On treatment with 2,4-pentanedione, hydralazine is converted into 1-(3,5-dimethyl-1-pyrazolyl)phthalazine, a stable compound which is easily extracted from biological material and determined quantitatively by gas chromatography with nitrogen-specific detection. 4-Methylhydralazine is used as an internal standard. The sensitivity of the method is ca. 10 ng/ml. Hydrazones of hydralazine do not interfere with the assay.     

Quantitation of l-alpha-acetylmethadol and its metabolites in human serum by capillary gas-liquid chromatography and nitrogen detection

A procedure is described for the simultaneous measurement of l-alpha-acetylmethadol and its two pharmacologically active metabolites: noracetylmethadol and dinoracetylmethadol. In the method an intramolecular conversion reaction of the two metabolites to their amide configuration is utilized. The reaction is performed while the metabolites are still in the serum. Following solvent extraction the samples are analyzed by capillary gas-liquid chromatography coupled with nitrogen detection. Quantitation is achieved by internal standardization. The lower limit of sensitivity is 5 ng/ml in serum. Absolute sensitivity is 0.1 ng for all three compounds. The advantages over other procedures are: speed due to the single extraction step; increased recovery of noracetylmethadol and dinoracetylmethadol due to decreased polarity of the amides; greater stability of the metabolites in the amide configuration; better chromatographic quantitation and separation because detector response for the amides is greater than it is for the original configuration of the metabolites and the area of the chromatographic tracing is free of interfering substances.     

New membrane-based electrolytic suppressor device for suppressed conductivity detection in ion chromatography

This paper discusses the newest advancement in chemical suppression preceding conductivity detection. The new suppressor uses electrolysis of deionized water to generate the required acid or base for the suppression neutralization reaction and utilizes the electrical field to enhance, through electrodialysis, the suppressor's capacity for neutralization. The suppressor is able to accommodate eluents as high as 150 mM NaOH, without the need for a separate regenerant solution, by recycling the conductivity detector cell waste to the regenerant and electrolysing the water in the waste stream to the required acid or base. The device is able to use deionized water as regenerant and neutralize the eluent stream to deionized water without the expected increase in resistance by employing ion exchange material in intimate contact with the electrodes and the membranes. The current is carried with low resistance through the ion-exchange material via ion transport from one ion-exchange site to another.     

Quantitative analysis of disulfiram and its metabolites in human blood by gas-liquid chromatography.

A simple method is described that permits the direct quantitative determination of carbon disulphide, free diethyldithiocarbamate and disulphides derived from disulfiram in 1 ml of a patient's blood. It is based on a gas chromatographic determination of carbon disulphide produced from diethyldithiocarbamate and disulfiram using the head-space technique and a flame-photometric detector. The method is compared with a recently described spectrophotometric method.     

Determination of diazepam and its metabolites by high-performance liquid chromatography and thin-layer chromatography

A sensitive, simple high-performance liquid chromatographic assay, capable of simultaneously measuring diazepam, its active metabolites oxazepam, temazepam and N-desmethyldiazepam and two phenyl hydroxylated metabolites, 4'-hydroxy-N-desmethyldiazepam and 4'-hydroxydiazepam, is described. The assay is easily modified to include separation of additional metabolite(s), e.g. oxazepam glucuronide(s). A thin-layer chromatographic assay, which resolves diazepam, the active metabolites and the two phenyl hydroxylated derivatives in one solvent system, is also reported. Application of these procedures to the quantitation of diazepam and its metabolites was shown, after delivery of diazepam (5 micrograms/ml or 16 microM) at a constant flow-rate (10 ml/min per liver) through the single-pass perfused rat liver preparation. Blood perfusion medium and bile were analysed for parent drug and metabolites before and after enzyme hydrolysis. These assay methods are found to be particularly pertinent and useful in providing a more comprehensive metabolic profile of diazepam metabolism, especially when aromatic hydroxylation pathways predominate.