L. A. Onuchak

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.

Analysis of Flavonoids in Silybum marianum Fruit by HPLC

Flavonoids of spotted milkweed (Silybum marianumL. Gaerth.) were optimally separated using reverse-phase HPLC with isocratic elution by CH3CN-H2O over Separon SGX C18. The flavolignans silybin, silydianin, silychristin, and the flavonoid taxifolin were identified in the chromatograms of extracts from this plant

The thermodynamic parameters of sorption and enantioselectivity of the chiral smectic liquid crystal 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid

The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and optical isomers of camphene and butanediol-2,3 by a chiral smectic liquid crystal, 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid, from the gas phase were studied over the temperature range including the S*C and S*A mesophases and isotropic phase. The standard and excess thermodynamic functions of sorption were determined for 26 sorbates of the classes of substances specified. The S*C and S*A mesophases exhibited selectivity with respect to the separation of para and meta xylenes (αp/m = 1.06–1.07, 90–108°C) and pronounced enantioselectivity (αR/S = 1.05–1.09, 87–108°C). The helically twisted structure of the smectic liquid crystal was shown to play an important role in the mechanism of the chiral recognition of optical isomers of polar and low-polarity compounds under gas-liquid chromatography conditions.

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.

Sorption and selective properties of binary liquid-crystalline sorbent based on 4-Methoxy-4′-ethoxyazoxybenzene and a cetylated β-Cyclodextrin

The mesomorphous, sorption, and selective properties of a binary sorbent based on achiral liquid crystal 4-methoxy-4′-ethoxyazoxybenzene and macrocyclic heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin (10.25 wt %) are investigated. Macrocyclic additive was found to induce the formation of a helically twisted nematic phase (N*). The standard and excess thermodynamic functions of sorption by binary sorbent from gaseous phase are determined for 29 organic compounds (n-alkanes, cycloalkanes, arenes, monoatomic alcohols, heterocycles, optical isomers of camphene, limonene, and butanediol-2,3). The investigated sorbent is found to have high structural selectivity over the wide temperature range of the N* mesophase (αp/m = 1.11–1.06, 95–120°C) and moderately expressed enantioselectivity within the narrow region of transition from the solid crystalline state to the N* mesophase (α+/− = 1.024–1.088, 91–100°C).

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.

Determination of Triandrin and Salicin in Salix viminalis L. by Reversed-Phase High-Performance Liquid Chromatography

The optimal separation of phenolic components of the bark of basket willow Salix viminalis L. was attained using reversed-phase high-performance liquid chromatography with isocratic elution. Triandrin (1-O-β-D-glucopyranoside of p-coumaryl alcohol) and salicin (1-O-β-D-glucopyranoside of salicyl alcohol) were identified. Regularities in the retention of triandrin and salicin in the Separon SGX C18–binary mobile phase (acetonitrile–water) system were considered. A procedure was developed for the quantitative determination of triandrin in raw basket-willow bark and its extract.

Features of the sorption redistribution of hydrocarbons and alcohols in a gas-supramolecular liquid crystal system

Thermodynamic characteristics of the sorption redistribution of hydrocarbons (C8–C12n-alkanes, C10H16 terpenes, xylene isomers) and alcohols (C3–C5 alkanols, butanediol-2,3, menthol) in a gas-4-(3-hydroxypropyloxy)-4′-formylazobenzene (HPOFAB) supramolecular smectic-nematic liquid crystal system are studied via inverse gas chromatography. The sorption capacity of HPOFAB with respect to nonmesogene sorbates is found to be strongly diminished due to its associated structure, especially in the smectic A phase. Great positive deviations from the Raoult law in the studied nonmesogene-HPOFAB systems are observed not only in mesophases, but also in the isotropic HPOFAB phase, which has a high selectivity to para- and meta-xylenes, in contrast to the isotropic phases of classic (non-associated) liquid crystals.

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.