Application of open-tubular column/gas-liquid chromatography to the analysis of complex mixtures of branched-chain fatty acids.

Methyl and butyl esters of branched-chain fatty acids of subcutaneous triacylgycerols from barley-fed lambs were subjected to urea-adduction and the resulting fractions were analyzed as methyl esters by gas-liquid chromatography on wall-coated open-tubular columns. The chromatogram of each fraction was less complex than that of the original and there was evidence to suggest that, in the original mixture of branched-chain acids, components resistant to urea-adduction were present, but their occurrence was obscured in chromatograms by the presence of monomethyl-substituted acids.     

Improved resolution of natural diacylglycerols by gas-liquid chromatography on polar siloxanes.

A new cyanoalkylphenylsiloxane (SILAR 5CP) liquid phase is shown to possess sufficient polarity to permit improved GC separations of natural diacylglycerols based on unsaturation and positional placement of fatty acids as well as on molecular weight, which was previously possible only on ethylene glycol succinate polyesters. Unlike the polyesters, the polar siloxane polymer has moderate thermal stability and provides GC columns which can be used for several months without replacing the packing. The GC analyses were made with conventional columns containing 3% SILAR 5CP on Gas Chrom Q at 270 degrees C isothermally. The diacylglycerols were chromatographed as the TMS ethers. Excellent seperations were obtained for the 1,2(2,3)- and 1,3-diacyglycerols derived from corn, linseed, peanut and cod liver oils and for the 1,2-diacyl-sn-glycerols from hepatic glycerophospholipids.     

Evaluation of a rapid method for preparation of fatty acid methyl esters for analysis by gas-liquid chromatography

The major limitation to fatty acid analysis by gas-liquid chromatography is associated with preparation of fatty acid methyl esters (FAME). In the present study, FAME preparations were made from plant oils (corn, olive, sunflower), sunflower oil margarine, lard and various animal tissue fats by a rapid transesterification involving tetramethylammonium hydroxide in methanol, and also by a longer conventional saponification-esterification method. Fats from animal (beef, mutton, pork) adipose tissues were extracted by a simpler modified procedure and also by the Folch method prior to the rapid and the conventional FAME preparations, respectively. FAME analysis on a gas-liquid chromatograph equipped with a Silar 10C glass capillary column indicated similar fatty acid composition of a given fat or oil, whether FAME was prepared by the rapid or the longer conventional method. The data obtained by both methods were very highly correlated for all the fats (r = 0.9895 - 0.9999). However, the rapid method showed a tendency for enhanced recoveries of lower chain fatty acids (e.g. 14:0), and also of unsaturated C18 isomers. Possibly, losses of fatty acids that occurred during the lengthy fat extraction, fatty acid esterification or ether-evaporation FAME concentration steps (conventional method) were minimised by the single transesterification step (rapid method). This rapid transesterification method appears to be an attractive alternative to FAME preparation from a wide variety of different fats for gas-liquid chromatographic analysis.     

Determination of valproic acid (dipropylacetic acid) in plasma by gas-liquid chromatography.

A specific and sensitive procedure for the determination of valproic acid at therapeutic concentrations in human plasma has been developed. The method involves a microscale extraction of the drug from acidified plasma into chloroform. Caproic acid is added as internal standard. The extract is subsequently analysed on a gas chromatography fitted with a flame ionisation detector, and quantitation achieved by the relative-peak-height technique.     

Fast analysis by gas chromatography

Summary The efficiency of fast GC columns depends largely on the quality of the chromatograph. A theoretical and experimental study shows the relative importance of the various phenomena involved and permits the optimization of a GC System. Extremely good performances, exceeding 2,500 plates per second have been routinely obtained.Ezzel a tanulmánnyal Halász István Professzor Urat köszöntjük 60. születésnapja alkalmából.     

On the quantitative analysis of multicomponent mixtures by gas-liquid chromatography

Summary The thermal conductivity cell response to some heterocyclic and hydrocarbon compounds was determined relatively to pyridine and was used to calculate with accuracy the molar as well as the weight concentration of analysed multicomponent mixtures from peak area values. From these and other results obtained by correcting data that have been previously reported in literature it was shown that by applying the appropriate factor it was possible to obtain the composition of the unknown mixture either as the mole or the weight per cent with accuracy.

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Zusammenfassung Das Ansprechen der Wärmeleitfähigkeitszelle auf einige heterocyclische Verbindungen und Kohlenwasserstoffe wurde gemessen (bezogen auf Pyridin) und zur Berechnung der Zusammensetzung von Mischungen mehrerer Komponenten aus den Peak-Flächenwerten benutzt. Es wurde gezeigt, daß man bei Verwendung eines geeigneten Faktors die Zusammensetzung einer unbekannten Mischung in Mol-% oder Gew.-% genau errechnen kann.

     

Determination of trimethylsilyl methylated nucleic acid bases in urine by gas-liquid chromatography.

A method for the determination of the urinary excretion level of methylated nucleic acid bases by gas-liquid chromatography (GLC) has been developed. A clean-up procedure prior to GLC analysis consisted of hydrolysis, filtration, charcoal adsorption, and anion exchange. Studies to determine optimum derivatization conditions for conversion of the methylated bases to their trimethylsilyl derivatives and to evaluate GLC parameters and columns to obtain the best separation were conducted. Application of the method was shown by determining the excretion levels of methylated bases in urine of normal controls and of patients with various types of malignancy.     

Some aspects of the analysis of Validol tablets by gas-liquid chromatography

The possibility of using the pharmaceutical substance Validol as a reference sample instead of a model mixture of components was theoretically considered for the analysis of Validol tablets. It was shown that the maximum relative error appeared because the difference in the compositions of the reference sample and the substance used in production should not exceed 2.5%. A procedure was developed for the analysis of Validol tablets. The performance characteristics of the procedure and the accuracy of the results were determined in an analysis of model mixtures and commercial tablets.     

Predicting retention data in gas-liquid chromatography by multivariate analysis

Satisfactory reproduction of the retention data matrix in the case of a series of mono-substituted benzenes and a series of aliphatic substances proves the general character of the prediction equation

where x_Qi, φ_j are the retention data x of unknown solute Q_i on phase φ_j; a_Qi, b_Qi, c_Qi and d_Qi are regression coefficients which to some extent account for forces of orientation, charge transfer and association; and x_STi, φ_j are independent variables representing the retention data of the four compounds of the standard set of substances on a given phase φ_j. These four compounds are selected by diverse methods of multivariate analysis. The predicted values show very satisfactory agreement with the observed values.     

Trace analysis of complex organic mixtures using capillary gas-liquid chromatography and the dynamic solvent effect

A sampling system for high resolution gas-liquid chromatography, based on the dynamic solvent effect, is described. Volatiles are accumulated off-line in a concentrator/injector and delivered to the column using an on-line inlet. Volatiles may be accumulated from gaseous or liquid matrices; they may be transferred to these by gas sparging or solvent extraction of any type of sample. The sampling technique is quantitatively precise; e.g. coefficients of variation of peak percentage areas better than 5% for a range of solutes at a concentration of 2:10⁷. Examples of the application of the sampling system are presented.