Influences of support,stationary phase polarity and loading in gas-liquid chromatographic retention

Summary Support effects for a range of diatomite supports have been determined from variations in both retention volume and retention index data for four solute probes as a function of stationary phase loading. The phases examined were Silicone 702, Silicone QF 1 and Carbowax 600. It was found that when polar phases were used, the main cause of retention data variation was gasliquid interfacial adsorption, support activity being eliminated if the surface of the support was effectively covered by such phases. For non-polar phases, support effects may still be apparent with loadings over 5%. With liquid loadings less than this value, unreal retention volumes may result from solute-support adsorption. Retention data, as a function of stationary phase loading, for highly fluorinated and non-fluorinated compounds reveals that the Retention Indices of the former are as significant as the latter class. In both cases high stationary phase loadings are recommended for the reporting of retention data.     

Gas chromatographic resolution of carbohydrate enantiomers. A new chiral phase for pentoses

New chiral polymers have been prepared by conversion of cyano groups of polysiloxanes XE-60 and OV-225 into carboxylic groups and subsequent coupling to give the respective S-valine-R-α-phenyl-ethyl amide. In contrast to the corresponding stationary phases with S-α-phenylethyl amide groups, which have been used for the resoultion of trifluoroacetylated hexose derivatives, the new phase show high enantioselectivity for pentose and 6-deoxyhexose derivatives.     

A gas-liquid chromatographic method for the analysis of diphenoxylic acid in urine

Summary A gas-liquid chromatographic method has been developed and evaluated for the measurement of diphenoxylic acid in urine. This method uses base hydrolysis to liberate diphenoxylic acid from compounds conjugated in urine, followed by removal of interfering substances in urine by column chromatography on alumina. Quantitation was carried out using p-chlorodiphenoxylic acid as an internal standard.     

Mobile phase effects on retention on a new butylimidazolium-based high-performance liquid chromatographic stationary phase

A new HPLC stationary phase based on n-butylimidazolium bromide has been characterized by a linear solvation energy relationship (LSER) approach in the binary acetonitrile/water mobile phases. The retention properties of the stationary phase were systematically evaluated in terms of intermolecular interactions between 28 test solutes and the stationary phase. The results and further comparisons with conventional reversed phase system confirm that retention properties are similar to phenyl phases in acetonitrile/water mixtures. The results obtained with acetonitrile/water mixtures are also compared with results obtained using methanol/water mixtures.     

Ionic liquid-modified silica as a new stationary phase for chromatographic separation

A new stationary phase based on silica modified with 1-methyl-3-propylimidazolium chloride was synthesized and characterized in this paper. A derivative of 1-methyl-3-propylimidazolium chloride was used to chemically modify the surface of silica particles to act as the stationary phase for HPLC. The modified particles were characterized by Fourier Transform Infrared (FT-IR), ¹³C NMR spectroscopy and thermogravimetric analysis (TGA). The surface modification procedure rendered particles with a surface coverage of 0.89 μmol/m² of alkylimidazolium chloride. Columns packed with the modified silica and blank silica particles were tested under HPLC conditions. Preliminary evaluation of the stationary phase for HPLC was performed using aromatic compounds as model compounds. The separation mechanism appears to involve multiple interactions including ion exchange, hydrophobic and electrostatic interactions.     

Considerations on the temperature dependence of the gas-liquid chromatographic retention

A discussion on the temperature dependence of the partition coefficient K is developed. This discussion embraces topics such as the limitations of conventional thermodynamic approaches followed in the chromatographic literature, qualitative theoretical notions arising from molecular thermodynamics and the experimental information that is accessible through modern capillary gas chromatography. It is shown that the heat capacity difference of solute transfer for flexible molecules has at least one maximum in the chromatographic range of temperature. As a consequence, a great amount of experimental data is required for a correct thermodynamic interpretation of the chromatographic retention.     

Formation constants and enthalpies of reaction from gas-liquid chromatographic measurements

Summary The determination of the formation constants and enthalpies of reaction for four C₈ diene-silver ion complexes using gas-liquid chromatography is described.     

Revision of a theoretical expression for gas-liquid chromatographic retention.

In this communication, we revise some aspects of the [ideal gas/Van der Waals fluid] partition, derived in an earlier publication. The general character of the conclusions concerning the dependence of the partial molar free energy of solution, deltaGs(n), on the chain length, n, of linear solute molecules is shown through the relationship with more general partition formulations. Simultaneously, the correction of an error in the expression of the retention time dependence on the phase ratio of the chromatographic column, beta, is carried out. The misleading source of this error was redundant accounting in the solute translational contribution to deltaGs(n).     

A quantitative gas-liquid chromatographic method for the determination of neostigmine and pyridostigmine in human plasma

A sensitive and selective analytical method was used to measure the concentration of neostigmine and pyridostigmine in human plasma. The procedure involved preliminary ion-pair extraction of the drugs into dichloromethane, followed by concentration and analysis of the ion-pair complex using a gas-liquid chromatographic system fitted with a nitrogen detector. Using the peak area ratio technique, pyri-dostigmine bromide was used as the internal standard for the quantitation of neo-stigmine in plasma; neostigmine bromide was the internal marker for the determination of pyridostigmine. The method depends on the thermal dequaternisation of the quaternary amines, and can be used to detect 5 ng/ml in a 3-ml plasma sample. Accurate measurement can be made at levels of 50–1000 ng/ml. This assay procedure has been applied to the separate determination of the plasma concentration of neostigmine and pyridostigmine after single administration of intravenous doses in aneasthetised patients.