Phases In Gas-liquid Chromatography Research Articles

Nematic Mesogen with 1,3,4-Oxadiazole Unit as Stationary Phase in Gas-Liquid Chromatography

This paper is the first that deals with the new synthesis of nematic liquid crystal titled bis-[5-yl-phenylbenzidine-4`-butyloxyphenly-2-yl-1,3,4-oxadiazole] and secondly discusses research on materials that can be used in stationary phase by using (GLC) as a type of chromatography. The usage of bis-[5-yl-phenylbenzidine-4`-butyloxyphenly-2-yl-1,3,4-oxadiazole]nematic phase has resulted in a lot of superb separations of a lot of poly aromatic hydrocarbons. The retention time change in an unusual way with temperature, appearance a significant increase at the normal liquid transmission point; as expected, that impact is reduced with further planar compounds. FT-IR and 1HNMR were used to characterize the synthesized chemical structure, and POM and DSC were used to investigate the liquid crystalline characteristics.

تطبيق المواد البلورية السائلة في كروماتوغرافيا الغاز- السائل

The objective goal of this research was concentrated on synthesize liquid crystalline which identified using FT-IR and the thermal crystalline characteristic were also investigated using the DSC and hot-stage polarized microscope technigues, the liquid crystalline, which showed great thermal stability over wide range of temperatures, has proposed to be applied as a stationary phase in gas liquid chromatography, some organic compounds which similar in atomic carbon number but different in geometrical stricture were sucessfully analyzed on the chromatography columns.

Ionic liquids as novel stationary phases in gas liquid chromatography: Inverse or normal isotope effect?

The separation of deuterated and non-deuterated compounds in gas liquid partitioning chromatography (GLC) on silicone type stationary phase usually results in the inverse isotope effect. With ionic liquids (ILs) as stationary phase, however, this may show a totally different nature. The inverse isotope effect, in which heavier (deuterated) isotopic compounds (isotopologues) elute earlier, is to be expected when van der Waals (London) dispersion forces play a dominant role in the solute–stationary phase interaction. Such (apolar) interactions seem to play only a minor role when ILs are the stationary phases, leading to only a marginal inverse isotope effect, e.g. for the separation of 2,4,6-trichloroanisole and its [2H5]-isotopologue on 1,12-di(tripropylphosphonium) dodecane bis(trifluoromethansulfonyl) amide (commercialized as SLB-IL59, Supelco). Indeed, with the most polar stationary phase available (commercialized as SLB-IL111; Supelco), this separation showed a normal isotope effect. Further examples are presented and the nature of the isotope effect observed is discussed.

Specific Surface of a Stationary Phase in Gas-Liquid Chromatography

A model of the surface of a stationary phase in gas-liquid chromatography based on the statistic theory of macromolecules was considered. Quantitative relationships between the capacity of a liquid adsorbent and its molecular structure were determined.

Immobilized Ionic Liquids as High-Selectivity/High-Temperature/High-Stability Gas Chromatography Stationary Phases

Ionic liquids (ILs) are a class of nonmolecular solvents in which the cation/anion combination can be easily tuned to provide desired chemical and physical properties. When used as stationary phases in gas-liquid chromatography, ionic liquids exhibit dual nature retention selectivity. That is, they are able to separate polar molecules such as a polar stationary phase and nonpolar molecules such as a nonpolar stationary phase. However, issues such as optimization of the wetting ability of the ionic liquid on fused-silica capillaries, the maximum operating temperatures of the stationary phases, and nonuniform film thickness on the wall of the capillary at high temperatures have limited their use in gas chromatography. As described in this paper, these limitations are overcome by cross-linking a new class of ionic liquid monomers by free radical reactions to provide a more durable and robust stationary phase. By lightly cross-linking the ionic liquid stationary phase using a small amount of free radical initiator, high-efficiency capillary columns were produced that are able to endure high temperatures with little column bleed. Two types of cross-linked IL stationary phases are developed. A partially cross-linked stationary phase allows for high-efficiency separations up to temperatures of approximately 280 degrees C. However, by creating a more highly cross-linked stationary phase of geminal dicationic ILs, exclusively, an increase in efficiency is observed at high temperatures allowing for its use over 350 degrees C. In addition, through the use of solvation thermodynamics and interaction parameters, it was shown that the cross-linking/immobilization of the ionic liquid does not affect the selectivity of the stationary phase thereby preserving its dual nature retention behavior.

High-Stability Ionic Liquids. A New Class of Stationary Phases for Gas Chromatography

Room-temperature ionic liquids are a class of non-molecular ionic solvents with low melting points. Their properties have the potential to be especially useful as stationary phases in gas-liquid chromatography (GLC). A series of common ionic liquids were evaluated as GLC stationary phases. It was found that many of these ionic liquids suffer from low thermal stability and possess unfavorable retention behavior for some classes of molecules. Two new ionic liquids were engineered and synthesized to overcome these drawbacks. The two new ionic liquids (1-benzyl-3-methylimidazolium trifluoromethanesulfonate and 1-(4-methoxyphenyl)-3-methylimidazolium trifluoromethanesulfonate) are based on "bulky" imidazolium cations with trifluoromethanesulfonate anions. Their solvation characteristics were evaluated using the Abraham solvation parameter model and correlations made between the structure of the cation and the degree to which the ionic liquids retain certain analytes. The new ionic liquids have good thermal stability up to 260 degrees C, provide symmetrical peak shapes, and because of their broad range of solvation-type interactions, exhibit dual-nature selectivity behavior. In addition, the ionic liquid stationary phases provided different retention behavior for many analytes compared to a commercial methylphenyl polysiloxane GLC stationary phase. This difference in selectivity is due to the unique solvation characteristics of the ionic liquids and makes them very useful as dualnature GLC stationary phases.

Optimization of separation on the basis of unifac parameters and evaluation of the composition of the stationary phase in gas-liquid chromatography

An algorithm for the optimisation of separation in gas-liquid chromatography based on varying the composition of the stationary phase and the column temperature is presented using the critical parameter Rs≥0.75 (σRs→max). The stationary phase composition, on the basis of retention parameters expressed in terms of vapour pressure and activity coefficient has been derived. Determination of the composition of the stationary liquid was carried out by defining the noture of solute-solvent interactions using group additive value contributions to the activity coefficients. Predicting values on experimentally determined parameters reduced calculation errors by a factor 2 to 3.

Dielectric and Chromatographic Characterization of Polyethylene Glycols as Stationary Phases

Three types of polyethylene glycols of different molecular weights namely, 600, 4000 and 20000, were evaluated as liquid stationary phases in gas liquid chromatography. Thus, the retention mechanism for the studied polymer stationary phases, 15% by weight on chromosorb PAW and their thermodynamic parameters have been investigated via inverse gas chromatography. The effect of polymer molecular weight on their efficiency as liquid stationary phases for the gas chromatographic separation of different types of hydrocarbons is also studied. The dielectric constant of dilute solutions for the studied polymers as dissolved in solvent chloroform was studied corresponding to their polarities. Two different modes of clusters were determined due to the solute-solute and solute-solvent interaction through hydrogen bonds. All studied polymers have higher performance for separation of cyclic and aromatic compounds. Good chromatographic separation of n-alcohols is obtained toward polyethylene glycol (PEG20000) of relatively higher molecular weight. The saturated hydrocarbons can be separated very efficiently using low molecular weight polyethylene glycol (PEG600).

Comparison of two azobenzene liquid crystal stationary phases in open tubular column gas chromatography

Comparative applications of two liquid crystals used as stationary phases in gas-liquid chromatography were investigated using different kinds of solutes. These liquid crystal molecules are: 4-(4-trans-pentylcyclohexanecarboxyloxy)-2′-methoxy-4′-(4-trans-pentylcyclohexanecarboxyloxy)-azobenzene (LC1) and 4-(4-trans-pentylcyclohexanecarboxyloxy)-2′-butoxy-3′-methyl-(4-butoxybenzoyloxy)-azobenzene (LC2). Their thermal properties were established with differential scanning calorimetry (DSC). The chromatographic separation abilities of LC1 and LC2 were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aromatic compounds and cis- and trans-isomers. Comparison between LC1 and LC2 is presented. Elution properties of LC1 and LC2 showed some differences. LC2 exhibited a higher separation efficiency especially for alkanes, light aromatics and polyaromatics, and the elution orders of some solutes were reversed compared with LC1. Then, the two liquid crystals are efficient before and after solid-solid or solid-nematic transitions. Nevertheless, they present higher plate numbers in the nematic state. Nice separations of volatile aromatic compounds are obtained by the two liquid crystals.

SILVER COMPLEXES OF POLY(METHYLPHENYLSILOXANE) FOR SEPARATION OF ALIPHATIC, OLEFINIC AND AROMATIC HYDROCARBONS BY GAS CHROMATOGRAPHY AND DETERMINATION OF THE π-COMPLEX FORMATION CONSTANTS

Abstract Silver trifluoroacetate and trifluoromethanesulfonate become highly soluble to poly(methylphenylsiloxane) because of the ion's coordination to the phenyl group: the resulting solution is highly stable. The silver trifluoroacetate or trifluoromethanesulfonate solution has been employed as the liquid phase in gas-liquid chromatography in order to study the separation of mixtures of cyclohexane, cylcohexene and benzene in the temperature range from 50 to 170°C. Use of an internal standard, such as cyclohexane, enables one to evaluate the complex formation constants as well as the salting-out effect merely by measuring the retention time in the presence or absence of Ag+. The complex formation constants of some aromatic and gaseous olefinic compounds have been determined.

Application of substituted liquid crystals as stationary phases in gas-liquid chromatography for the separation of mono-and dimethyl naphthalenes

Thirteen mono- and dilaterally substituted liquid crystalline compounds were investigated for their gas chromatographic behaviour as stationary phases for the separation of mono- and dimethylnaphthalenes. A normal packed column system was used. These compounds offered a good separation for some pairs of methylnaphthalenes.

P-Alkoxy- andp-alkylbenzoates of α, a'-bi-p-hydroxytoluene. New series of liquid-crystalline compounds

Abstract Six p-alkoxy and eight p-alkylbenzoates of 1,2-(p-hydroxyphenyl)ethane were synthesized for potential use as stationary phases in gas-liquid chromatography. All the p-alkoxy derivatives were nematic. The first five members of the alkyl series were nematic and the rest exhibited both smectic and nematic character. Most possess the desired combination of a wide liquid-crystalline temperature range and a high mesomorphic-isotropic transition temperature. The nematic-isotropic transition temperatures and entropies show the usual alternations characteristic of a high-melting series.

Characterization of solvent properties of gas chromatographic liquid phases

Characterization of solvent properties of gas chromatographic liquid phases

Proposed substitution of apolane-87 for squalane as a nonpolar reference phase in gas chromatography

Squalane is the standard, nonpolar reference phase used in schemes to characterize the solvent strength and selectivity of stationary phases in gas-liquid chromatography. A commentary, supported by additional experimental evidence, is provided to indicate a lack of suitability for this purpose. Primary objections to its use as a reference phase are its high volatility, compositional variations due to the presence of impurities, susceptibility to oxidative degradation, poor film forming and stabilizing properties, and retention properties that are strongly influenced by the character and treatment of the support used to prepare column packings. Because similar problems were not observed, or were much less significant, for the synthetic hydrocarbon Apolane-87, its use as a reference phase is to be preferred. Reference values for retention indexes, gas—liquid partition coefficients, and partial molal Gibbs free energies of solution for a series of solvent-selectivity test solutes are provided for both phases.

Dispersive force parameters as a measure of the polarity of surfactants used as stationary phases in gas-liquid chromatography

The possibility of describing the polarities of compounds by the use of dispersive force parameters is examined. Relationships between the structures of the compounds examined and these parameters are derived. The increments in the parameters for selected structural fragments are also presented.

Characterization of gas chromatographic liquid phases using McReynolds constants: An experiment for instrumental analysis laboratory.

This paper describes an experiment that is designed to aid in the development of an understanding of the fundamental processes involved in gas chromatographic separations by introducing the student to the Kovats retention index system.

Responses of Diabrotica lemniscata and D. longicornis (Coleoptera: Chrysomelidae) to Stereoisomers of 8-methyl-2-decyl-propanoate and Studies on the Pheromone of D. longicornis1

The four stereoisomers of 8-methyl-2-decyl-propanoate (MDP) were tested in the field for attractiveness to Diabrotica longicornis (Say) and D. lemniscata LeConte. Males of both species were attracted to the (2S,8R) isomer, and D. lemniscata was weakly attracted to the (2R,8R) isomer. Tests of the response of D. longicornis to combinations of isomers revealed that the (2R,8R) isomer significantly reduced catch at traps baited with (2S,8R); the other two isomers were without detectable effect. Sex pheromones were collected from virgin female D. virgifera virgifera LeConte and D. longicornis. When used as bait in traps in the presence of males of D. v. virgifera and D. longicornis, the material from D. v. virgifera attracted only conspecific males; that from D. longicornis attracted males of both species. According to electroantennographic monitoring of gas chromatographic effluent with D. longicornis males, a substance obtained from the extracts of filter papers that had been contaminated with secretions from virgin female D. longicornis had retention times coincident with MDP on four gas chromatographic liquid phases.

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

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.

Prediction of retention data by using parameters of intermolecular interaction : I. A model for calculation of non-polar and polar interaction parameters

Two interaction energy parameters, D and ϕ, characterizing the interaction between solute and stationary phase in gas-liquid chromatography have been suggested. In the calculation of these parameters, molecular values like atomic group refractions, dipole moments and Van der Waals radii have been used. Moreover, it has been attempted to consider mutual orientations of the interacting molecules.

Gas-liquid chromatography system with α-cyclodextrin as an analytical tool for the studies of stereoselective hydrogenation of α-pinene

α-Cyclodextrin dissolved in formamide solution was applied as the stationary phase in gas-liquid chromatography for the enantio- and diastereoselective separation of α-pinene and pinanes. It was found that the stereoselectivity arising from inclusion of these compounds in α-cyclodextrin cavities is considerable. The method developed was used to monitor the stereochemical cource of α-pinene hydrogenation.