The theory of gas-liquid chromatography : The influence of the thickness of the stationary liquid film

The thermodynamic theory of gas-liquid chromatography has been developed, taking into account specific properties of thin films of the liquid phase expressed in terms of the “disjoining pressure”. Equations were derived to describe the dependence of the retention volume on the thickness of the stationary phase over the whole range of thickness. The results are in good agreement with experimental values.A chromatographic method for determining the constants of disjoining pressure is suggested.     

Retention characteristics in gas chromatography as function of molecular mass of the stationary phase

The thermodynamic characteristics of the selectivity of stationary phases in gas-liquid chromatography have been used to study the change in selectivity of a stationary phase with its increasing molecular mass within the limits of the same class of compounds. It is shown that the entropy of disssolution is the dominant thermodynamic factor of selectivity in the case of paraffinic stationary phases; a linear relatinship exists between the logarithm of relative retention of different sorbates and the reciprocal molecular mass of the stationary phase. In the case of solutions where hydrogen bonds can be formed, the enthalpy of dissolution serves as the dominant factor; in this case a linear relationship exists between the relative retention of alcohols and the reciprocal molecular mass of the stationary phase (polyethylene glycol). For the other classes of sorbates and stationary phases, the entropy as well as the enthalpy of dissolution contribute to the relative retention when the molecular phase varies within a single class of substances. The theoretical postulations have been confirmed by experimental data for paraffinic stationary phases, polyethylene glycols, and phthalic acid esters.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 81–90, January–February, 1988.     

碳数规律中A/(1/r)、B''''/(1/r)值与固定液极性的关系

采用n-烷烃在不同极性的固定液中,在不同色谱柱温下试验的大量数据表明,碳数规律中A、B'值与柱温倒数(1/T)的关系中,(?)/(?)(1/T)值随固定液极性增加而增大;(?)B'/(?)(1/T)值随固定液极性增加而减小,即(?)A/(?)(1/T)值与Mertynolder常数成正比;(?)B'/(?)(1/T)值与Mertynolder常数成反比。     

The correlation between molecular polarizability of PAHs and their retention data on various stationary phases in reversed-phase HPLC

Summary The equation for the potential energy of interactions established for gas-liquid chromatography has been confirmed in reversed phase liquid chromatography. Equations derived for molecular polarizabilities of PAHs and their retention data have very high correlation coefficients. The results indicate that the inductive effect between solute and stationary phase is the main one and the dispersive effect is very small compared with the inductive effect but its contribution increases with the carbon chain length of the stationary phase.     

Analysis of the products of synthesis of the pheromone of the bollworm by gas-liquid chromatography

The possibility has been shown of the effective separation and identification of the main component of the pheromone of the bollworm, hexadec-cis-ll-enal, and accompanying impurities by gas-liquid chromatography on the nonpolar stationary liquid phase E-301 deposited on Chromaton N-AW-HMDS.     

The thermodynamic characteristics of retention of tricyclo[5.2.1.0<Superscript>2,6</Superscript>]decane isomer molecules on different sorbents in gas chromatography

The thermodynamic characteristics of sorption of the isomeric tricyclo[5.2.1.0^2.6]decane (tetrahydrodicyclopentadiene, TDCPD) molecules were for the first time determined experimentally and by molecular statistical methods under the conditions of gas-adsorption chromatography on graphitized thermal carbon black and gas-liquid chromatography on stationary liquid phases of different polarities (Apiezon L and Carbowax 20M). The effects of the chemical nature of sorbents on the retention of the TDCPD isomers are considered. A procedure for calculating the thermodynamic characteristics of adsorption of molecules with a complex structure is suggested within the framework of the atom-atom approximation of the semiempirical molecular statistical theory of adsorption for the example of isostructural norbornane molecules. The procedure involves simultaneous variation of geometric parameters and refinement of the parameters that determine the special features of the electronic structure. This method was used to determine several geometric parameters of the TDCPD molecules for the first time. The results were in close agreement with the quantum-chemical data.     

Determination of sterically hindered phenols by gas-liquid chromatography

Conclusions The possibility has been shown and the optimum conditions have been found for the identification of various 4-alkyl-2,6-di-tert-butylphenols by gas-liquid chromatography on the stationary liquid phases poly(ethylene glycol adipate) and Apiezon-L deposited on Celite C22.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1618–1622, July, 1970.     

On the influence of sorbent activity,mobile phase polarity,and structure of the investigated substances on thermodynamic characteristics of the chromatographic system

Advantages of the thermodynamic characteristics of Chromatographic systems are discussed with respect to previous experimental results. It seems that the principles of the thermodynamic approach can be successfully applied not only to paper and thin-layer chromatography, but also to gas-liquid and high-performance chromatography.     

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     

Influence of flow parameters of the mobile phase on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography

The influence of the flow parameters of the mobile phase (flow rate and mean pressure in the column) on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography is studied experimentally. Conditions are formulated under which the chromatographic process can be described in terms of the theory of equilibrium gas-liquid chromatography with an ideal gas as the mobile phase and the distribution of the sorbate between phases is not affected by the presence of a weakly sorbed carrier gas.     

Measurement of thermodynamic equilibria by chromatography

Summary After a brief recall of the chromatographic principles, the different applications of gas chromatographic measurements of thermodynamic equilibria were reviewed. Gas and liquid chromatographies are now well known and elegant methods for measuring the physicochemical properties and phase equilibrium thermodynamic constants. Although fundamentally a dynamical method and mostly known as a powerful separation technique, chromatography can be schematized by a sucession of equilbria of a chemical species partitioning between a mobile phase and a fixed liquid or solid stationary phase. It can be operated in either infinite dilution or finite concentration conditions and permits to collect a large number of data for calculating molecular interactions for solutes which are either rare or available at the trace level. Gas chromatography permits the measurement of gas adsorption isotherm, gas-liquid equilibria, molecular diffusion and interaction virials. The modelization of successive partition equuilibria occuring in the chromatographic column leads to rather simple expression of differential enthalpy, entropy, free energy of adsorption or solution, variation of heat capacity, complexation constant, second virial coefficients, gas-solid and gasliquid isotherm and also binary or ternary equilibria. The possibilities of High Performance-Liquid Chromatography to investigate adsorption from solutions and chemical equilibria are also discussed.     

Analysis of the products of synthesis of the pheromone of the bollworm by gas-liquid chromatography

The possibility has been shown of the effective separation and identification of the main component of the pheromone of the bollworm, hexadec-cis-ll-enal, and accompanying impurities by gas-liquid chromatography on the nonpolar stationary liquid phase E-301 deposited on Chromaton N-AW-HMDS.A. S. Sadykov Institute of Bioorganic Chemistry, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 576–579, July–August, 1989.     

Gas chromatographic characteristics and application studies of the stationary phase of CH-B-15-C-5

In this paper, separations of organic compounds, such as, n-alkanes, alcohols, ethyl asters of C(1)-C(8) carboxylic acid, halogen derivatives, position-isomers of the replacement aromatic hydrocarbon, optical isomers of ethyl lactate and isoamyl alcohol, etc. were studied using 4'-cholestenoxycarbonyl-benzo-15-crown-5 liquid crystal crown ether (CH-B-15-C-5) as stationary phase in gas-solid chromatography (GSC), general gas-liquid chromatography (GLC) and crown ether liquid crystal gas-liquid chromatography (CL-GLC). Also, the chromatographic characteristics, such as the chemical stability, thermal stability, selectivity, polarity and operating temperature range, of the CH-B-15-C-5 as stationary phase for GSC, GLC and CL-GLC systems were studied. The results showed that the polarity of this chromatographic column is mean-weak; the chemical and thermal stabilities and the selectivity are good and the operating temperature range is wide. The results of separations of organic compounds are satisfactory.     

环丁砜与某些碳八芳烃分子络合作用的研究

本文用气液色谱法及混合过程体积的变化研究C₈芳烃与环丁砜的分子络合作用,用参考柱法和混合柱法测定了五种C₈芳烃与环丁砜的络合常数,研究了C₈芳烃与环丁砜和丙二醇-1,2-碳酸酯的二元系超额体积,环丁砜与五种C₈芳烃构成的体系均有强烈的体积收缩效应,苯乙烯与环丁砜体系尤其明显,芳烃与丙二醇-1,2-碳酸酯构成的体系收缩程度远远低于前者。     

Calculation of the heats of solutions of alkylbenzenes in a nonpolar stationary phase

The heats of solution of 32 alkylbenzenes in nonpolar stationary phases (pentadecane, squalane, and Apiezon L) have been determined by gas-liquid chromatography. It is shown that the heats of solution of these substances may be calculated a priori as the sum of three quantities: a) the calculated dispersion force taking into account intramolecular screening; b) the energy of vacancy formation; and c) the interaction of the solvent molecules and the methyl groups of the solute. The presence of a double bond in the alkyl substituent increases the heat of solution of an alkylbenzene in the nonpolar stationary phase.     

Chain conformation and solvent partitioning in reversed-phase liquid chromatography: Monte Carlo simulations for various water/methanol concentrations

Many structural models for the stationary phase in reversed-phase liquid chromatography (RPLC) systems have been suggested from thermodynamic and spectroscopic measurements and theoretical considerations. To provide a molecular picture of chain conformation and solvent partitioning in a typical RPLC system, a particle-based Monte Carlo simulation study is undertaken for a dimethyl octadecyl (C(18)) bonded stationary phase on a model siliceous substrate in contact with mobile phases having different methanol/water concentrations. Following upon previous simulations for gas-liquid chromatography and liquid-liquid phase equilibria, the simulations are conducted using the configurational-bias Monte Carlo method in the Gibbs ensemble and the transferable potentials for phase equilibria force field. The simulations are performed for a chain surface density of 2.9 micromol/m(2), which is a typical bonded-phase coverage for mono-functional alkyl silanes. The solvent concentrations used here are pure water, approximately 33 and 67% mole fraction of methanol and pure methanol. The simulations show that the chain conformation depends only weakly on the solvent composition. Most chains are conformationally disordered and tilt away from the substrate normal. The interfacial width increases with increasing methanol content and, for mixtures, the solvent shows an enhancement of the methanol concentration in a 10 Angstrom region outside the Gibbs dividing surface. Residual surface silanol groups are found to provide hydrogen bonding sites that lead to the formation of substrate bound water and methanol clusters, including bridging clusters that penetrate from the solvent/chain interfacial region all the way to the silica surface.     

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.     

Comments on column characterization: A sulfur column

Summary The McReynolds' constants for liquid sulfur as a stationary phase in gas-liquid chromatography (GLC) are presented. A simple graphical method of pattern analysis is used to indicate the uniqueness of the sulfur column as compared with other stationary liquid phases characterized by McReynolds. The limitations of using a single factor (as polarity) for the basis for the selection of GLC columns is discussed.     

Chromatographic behavior of some furan derivatives

Sulfides of the furan series and derivatives of furylthienylmethane are separated by gas-liquid chromatography. Heats of solution in polyethylene glycol adipate supported on alkali-treated diatomaceous brick are calculated. Interaction with the stationary phase is considered.     

Superheated water chromatography of phenols using poly(styrene-divinylbenzene) packings as a stationary phase.

A method for the superheated water chromatography of phenols was developed using a poly(styrene-divinylbenzene) (PSDVB) stationary phase. The stationary phase of superheated water chromatography must be stable against the attack of water. A durability test for PSDVB packings and octadecylsilyl (ODS)-silica gels indicated that PSDVB packings were stable in superheated water in the temperature range of 100-150 degrees C, whereas octadecylsilyl groups of ODS-silica gels cleaved even at 100 degrees C. The retention of phenols on the PSDVB stationary phase decreased with an elevation of the column temperature. The retention mechanism was characterized using a thermodynamic theory that has been used for describing retention in conventional RP-HPLC. The application of the present method to an environmental analysis was also demonstrated, in which a suitable separation with good peak shape was obtained for p-chlorophenol in river-water samples.