Thermodynamic properties at infinite dilution of several solutes in ethers by gas-liquid chromatography

Summary The thermodynamic properties of different solutes at infinite dilution have been determined at 323.15 K. Deviations from ideality are discussed in terms of different contributions. The activity coefficients are compared with the calculated values by the one group contribution method.     

Solubility of some carrier gases in stationary liquid phases used in gas-liquid chromatography

A simple gas chromatographic technique for the determination of the solubility of gases in low-volatile liquids was proposed. The procedure is based on the introduction of a certain volume of the liquid saturated with the gas at atmospheric pressure into a gas chromatograph. The solubility of carrier gases (helium, hydrogen, nitrogen, methane, and carbon dioxide) in various stationary liquid phases (SLP), such as pentadecane, polydimethylsiloxane PMS-100, and polyethylene glycol PEG-600, was studied. The carrier gases studied can be arranged in the following series by solubility in SLP: He<H₂<N₂<CH₄<CO₂. This order coincides with the series reflecting change in the retention values in GLC for different carrier gases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 923–925, May, 1999.     

Nucleosides as stationary phases for the separation of xylenol isomers by gas-liquid chromatography

Summary Adenosine, guanosine and inosine used as liquid phases in gas chromatography permits the separation of all six xylenol isomers.     

The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography

Four poly(methyl 3,3,3-trifluoropropyl siloxanes) with trifluoro-propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases–a polydimethylsiloxane and a poly(methyl 3,3,3-trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution). Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron-donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.     

Preparation and chromatographic characteristics of calix[4]arene polysiloxane as stationary phases for capillary gas chromatography

Summary Two new kinds of calix[4]arene derivatives, 5, 11, 17, 23-tetra-tert-butyl-25,27-bis(isopropylcarbamoyl-methoxy)-26,28-diundecenyloxy calix[4]arene (C[4]A) and 25,27-dibutoxy-5, 11, 17, 23-tetra-tert-butyl-26,28-diundecenyloxy calix[4]arene (C[4]B0, are prepared and then are polymized by two different processes. Three calix[4]arene polysiloxane stationary phases for capillary gas chromatography are obtained. Their chromatographic characteristics, including column efficiency, polarity, selectivity, glass-transition temperature and thermal stability are studied. Retention mechanisms are also discussed.     

Use of crosslinked polysiloxane stationary phases in open-tubular capillary liquid chromatography

Crosslinked polysiloxane stationary phases were prepared on soda-lime glass capillaries and applied to the separation of polynuclear aromatic hydrocarbons and of phthalates in reversedphase liquid chromatography. Preparation procedures and chromatographic performance of these columns are described.     

Spectroscopy and the classification of liquid stationary phases in gas-liquid chromatography

Summary A table of data for acidity, basicity, polarity and London potential for stationary phases is given. These provide guidance in choosing a stationary phase for a given task from the 26 substances listed. The indices are calculated from infra-red shifts of 1-chlorobutane and the visible wavelength shifts of l₂ when they are dissolved in the stationary phases, from NMR estimates of acidity and basicity and from relative retention data. They replace the less reliable data of Burns and Hawkes. Methods of determining the indices are suggested that require only a gas chromatograph and can be applied by technicians with no specialized understanding of solution parameters. An attempt to add electron donoracceptor indices to the table was unsuccessful. A further table is given of the slopes of the log plots d(logt)/dC for use in extrapolating from one homologue to another on these stationary phases.     

Retention of cyanoalkanes and cyanoalkylbenzenes by bonded stationary phases in supercritical fluid chromatography

Summary The retention of cyanoalkanes and cyano-alkylbenzenes during SFC was investigated on alkyl and cyanoalkyl-bonded stationary phases and compared to alkane retention. The particular behaviour of short chain homologues was attributed to a silanophilic interaction with surface-OH groups on the silica and inhibition of specific interactions between solutes and C₁₀CN bonded groups.     

Synthesis and characterization of new organometallic complexes bonded stationary phases for high-performance liquid chromatography

Summary The preparation, characterization and potential liquid chromatographic applications of various organometallic iron complexes silica stationary phases are presented. These new supports are synthesized by covalently linking ferrocene, as well as some of its cationic derivatives, to appropriately derivatized silica support matrices. These columns exhibit moderate to high selectivity towards the separation of polycyclic aromatic hydrocarbons (PAHs). A charge transfer retention mechanism has been proposed. A comparison with a reference stationary phase, 3,5-dinitrobenzamide (DNB), to quantify the acceptor power of the new stationary bonded phases, is also reported. Finally, the effect of varying the derivatives of the bonded metallocene on PAHs retention is discussed.     

Synthesis of siloxane stationary phases for capillary gas chromatography and supercritical fluid chromatography

A comparison is made between dichlorosilanes and cyclic siloxanes as starting materials in the synthesis of stationary phases for capillary gas chromatography (CGC) and supercritical fluid chromatography (SFC). Siloxanes containing one or more of the side groups methyl, vinyl, phenyl, and cyanoethyl in various ratios were synthesized and compared. These phases were characterized by chromatographic (gel permeation, GPC), spectroscopic (IR, ¹H NMR, ²⁹Si NMR), and thermal (DSC) methods. Coated fused silica columns were evaluated with respect to polarity, crosslinkability with several free-radical initiators, and thermal stability. A new liquid phase, 7% cyanoethyl, 7% phenyl, 1% vinyl methyl polysiloxane is shown to be more polar than OV-1701, more temperature stable, easily crosslinked and suitable for use in supercritical fluid chromatography.     

A comparative study of the gas chromatographic behavior of liquid crystals and polyester stationary phases using paraffinic hydrocarbons as standards

Two new categories of stationary phase have been studied: liquid crystals and polyesters. The liquid crystals were p,p′-azoxyphenetol, p(n-hexyloxy)phenyl-p′-methoxy benzoate, and p-pentyloxy-p′-ethoxyazoxybenzene; and the polyester phases 1,4-butanediol succinate (LAC-860), ethylene glycol succinate (LAC-886), diethylene glycol succinate (LAC-738), diethylene glycol adipate (LAC-296), and neopentyl glycol adipate (LAC-769). Abnormal chromatographic behavior, has been observed: an increase in specific retention volumes and an improvement in the separation of normal, branched, and cycloparaffins, depending on their structures, at high temperatures within a specified range. This phenomenon is the opposite of the behavior of traditional stationary phases. From the chromatograms obtained, plots of log v against 1/T, and differential thermal analysis it is concluded that this abnormal behavior may be attributed to the penetration of solutes through the ordered structure of the mesophase and the rod-like molecules of the polyesters. Furthermore, the chromatographic behavior of some of the polyester (LAC-series) stationary phases in respect of temperature changes is similar to that of the nematic mesophases.     

Interactions between 33 solutes and four cyano-containing stationary phases: gas chromatographic activity coefficients and the solvation parameter model

Infinite-dilution gas–liquid chromatographic activity coefficients at 393.15 K (with their thermal and athermal components) and derived excess partial molar Gibbs energies, enthalpies, and entropies have been determined for each of 33 solutes of different polarity on four stationary phases with cyano groups, using retention data taken from the literature. The strongest interactions predicted by the solvation model are the dipolarity/polarizability, the acidic solute–basic stationary phase interaction, and nonpolar cavity formation and dispersion. These interactions were compared with those evaluated from the solute activity coefficients; the effect of the solute connectivity index and dipole moment on nonpolar and polar interactions, respectively, is discussed. The dependence of the thermal activity coefficient on nonpolar interactions, and the influence of stationary phase polarity on the four solute–stationary phase interactions, were evaluated. The nonpolar interaction increases with increasing connectivity and with increasing athermal activity coefficient. The dipolarity/polarizability interaction increases with increasing solute dipole moment. Finally, polar interactions increase with increasing stationary phase polarity whereas the nonpolar interaction is independent of stationary phase polarity.     

Determination of volatiles in spirits using combined stationary phases in capillary GC

Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1:1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.     

Enantiomer separation of side-chain fluorinated alkylbenzenes by capillary gas chromatography on cyclodextrin phases

Summary The separation of racemic side-chain fluorinated alkylbenzenes and bromofluorinated analogues by capillary gas chromatography using permethylated , and -cyclodextrins dissolved in polysiloxanes of different polarity as stationary phases is described. The influence of the achiral polysiloxane matrices on the separation of enantiomers is discussed in the light of the results obtained with the different phases. For a part of the tested compounds thermodynamic data are determined which describe the interaction of enantiomers with the stationary phase. The mechanism of separation is discussed on this basis and by comparison with data for structurally similar compounds.     

Retention behavior of aromatic hydrocarbons and dansylamino acids in reversed-phase liquid chromatography with cation-exchange-induced stationary phases

The retention behavior of aromatic hydrocarbons and dansylamino acids on cation-exchangers modified with alkylammonium ions has been examined by microcolumn liquid chromatography. Several parameters affected the retention of analytes, involving concentration of the modifier in the mobile phase, its alkyl chain length and mobile phase composition. Stationary phases modified with a reagent having longer alkyl chains achieved better column efficiency.     

Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography

Novel monomeric and polymeric liquid crystalline compounds were synthesized as stationary phases for gas chromatography (GC) and supercritical fluid chromatography (SFC). Monomeric liquid crystalline compounds were used in packed column gas chromatography for the separation of isomeric aromatic compounds and insect sex pheromones. Liquid crystalline polymers possess long nematic ranges and a uniform coating was easily achieved in glass and fused silica capillaries, which could stand temperatures up to 250°C in GC and pressures of 200 MPa at 160°C in SFC. The columns provide excellent selectivity and resolution for fused ring aromatic compounds such as the isomers anthracene and phenanthrene or triphenylene and chrysene.     

Crystal hydrates: an investigation of the use of crystal hydrates as stationary phases in gas chromatography

Summary The use of crystallohydrates, crystallohydrate solutions and melts as stationary phases in gas chromatography has been proposed. Crystallohydrates have been shown to display high selectivity in the separation of polar organic compounds when use is made of water vapours as the mobile phase. Some aspects of gas-liquid chromatography in water vapours and with the stationary phase comprising crystallohydrates have been studied, and the preliminary results obtained point to the desirability of further progress in this field.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Modifications of poly(methyl-3-propylthiol)siloxane to give stationary phases for open tubular supercritical fluid chromatography

Summary Poly(methyl-3-propylthiol)siloxane has been evaluated for use as stationary phase in open tubular columns for gas and supercritical fluid chromatography. Immobilization of the stationary phase was achieved by crosslinking with 2,4,6-trichloro-1,3,5-triazine. The poly(methyl-3-propylthiol)siloxane stationary phase film was in situ oxidized to the disulphide and sulphonic acid forms and both have been evaluated for use in supercritical fluid chromatography. Good selectivity towards polar polycyclic aromatic compounds has been shown. All the modified forms of the stationary phase were loaded with silver ions and were evaluated with regard to ligand exchange chromatography using supercritical fluid carbon dioxide as a mobile phase. The utility of the stationary phase, having sulphonic acid groups loaded with silver ions, has been demonstrated by separation of fatty acid methyl esters according to their unsaturation.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.