S. Yu. Kudryashov

Averaging the pressure and flow rate of the carrier gas in a gas chromatographic column

SummaryA systematic derivation of corresponding equations shows that averaging the pressure and the flow rate of the mobile phase in a gas chromatographic column over the column length and over the time that an unretained component resides in the column, requires the use of three different compressibility correction factors,j21,j32, andj43. When multiplied by the adjusted retention volume,VR-VM, the Martin and James mobile phase compressibility correction factorj32, only, produces the value of specific retention volume,VgT, which is connected unambiguously with the thermodynamic phase distribution coefficient,K, of the sorbate.

The Thermodynamic Parameters of Sorption and Selectivity of Chiral Nematic Liquid Crystals of Terephthalidene-bis-2-methylbutyl para-Aminobenzoate

The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and isomeric forms of butanediol-2,3 by chiral nematic liquid crystals, terephthalidene-bis-2-methylbutyl para-aminobenzoate, were studied over the temperature range of the existence of the meso- and isotropic phases. The contributions of dipole—dipole and specific interactions to the enthalpy of sorption were estimated. Sorbate—liquid crystal systems were characterized by positive deviations from ideality caused by the enthalpy factor. The mesophase of the liquid crystal studied was found to possess selectivity with respect to the optical isomers of butanediol-2,3 (αR/S = 1.03 over the temperature range 140–150°C). It was shown that diol–liquid crystal molecular H-complexes formed played an important role in the mechanism of chiral recognition of butanediol-2,3 optical isomers under gas-liquid chromatography conditions.

Adsorption of volatile organic compounds on Carbopack Y adsorbent modified by β-cyclodextrins

The thermodynamic study on the adsorption of vapor-phase organic compounds on surface of the Carbopack Y carbon-based sorbent modified by monolayer of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin or heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin was performed. The dependence of the thermodynamics of absorption on the structure of the adsorbate and modifier molecules was studied.

Adsorption of organic vapors on the Carbopack Y carbon adsorbent modified with heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin

The adsorption of organic vapors on the Carbopack Y carbon adsorbent modified with a mono-molecular layer of heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin was studied by gas chromatography. The deposition of the macrocyclic modifier on the carbon substrate substantially strengthened the adsorbate—adsorbent intermolecular interactions and led to localization of adsorption due to the inclusion of adsorbate molecules, irrespectively of their polarity, in the macrocyclic voids of the modifier molecules. As a consequence, the thermodynamic characteristics of adsorption were greatly affected by the sizes and spatial structure of adsorbate molecules.

Using reverse gas-liquid chromatography to determine the thermodynamic functions of sorption in a system of constant volume

A static “ideal gas phase-nonvolatile liquid” system of constant volume in which the volatile component (sorbate) is redistributed is compared to a chromatographic system under conditions corresponding to equilibrium gas-liquid chromatography. The basis for calculating the thermodynamic characteristics of sorption using chromatographic data is described. The standard conditions and way of expressing the constant of interphase sorbate distribution are specified.

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.

Thermodynamics of the adsorption of organic compounds from the gas phase over a monolayer of liquid crystal formed on the surface of a carbon adsorbent

Inverse gas-solid chromatography is used to study the adsorption of vapors of organic compounds with different structures and polarities on a carbon adsorbent modified with a monolayer of 4-(3-hydroxypropyloxy)-4′-formylazobenzene (HPOFAB) polar LIQUID crystal. The resulting thermodynamic characteristics of adsorption on the original and modified adsorbents are compared. The effect the nature and structure of adsorbate molecules and the liquid crystal modifier have on the thermodynamic characteristics of adsorption is considered.

Sorption properties of perbenzoylated β-cyclodextrin deposited onto a carbon support

Thermodynamic parameters are determined for the adsorption of vapors of hydrocarbons and polar compounds of different structure on carbon adsorbent modified by a monomolecular layer of heptakis(2,3,6-tri-O-benzoyl)-β-cyclodextrin. The effect of the structure and polarity of organic compounds on adsorption onto an adsorbent support with a chiral macrocyclic modifier are considered.

Interrelation between the Spatial Structure of Unsaturated Hydrocarbon Molecules and Heats of Their Adsorption

The total area (sm) of Voronoi-Dirichlet polyhedron faces corresponding to all intermolecular contacts of one molecule in the structure of crystals and the total volume of pyramids (Vm) built on such faces and containing the nuclei of atoms participating in intermolecular contacts in their vertices were determined for 19 unsaturated hydrocarbons. The differential molar heat of adsorption of the hydrocarbons on graphitized thermal carbon black was found to be linearly related to the sm or Vm integral parameters of their Voronoi-Dirichlet polyhedra. Aromatic hydrocarbons on the one hand and saturated hydrocarbons, olefins, and acetylene on the other are characterized by different dependences because of the special shapes of their molecular Voronoi-Dirichlet polyhedra.

Generating gas flows with a constant trace concentration of hydrogen sulfide

The dynamic gas extraction of hydrogen sulfide from aqueous solutions of sodium sulfide was studied theoretically and experimentally. The effects of the number of bubblers, the concentration of sodium sulfide, and the pH of solution on the concentration of hydrogen sulfide in the generated gas flow were found. The proposed method for generating gas flows with a constant trace concentration of hydrogen sulfide can be used for calibrating the verifying instruments for gas analysis.