Thermodynamic Characteristics Of Sorption Research Articles

Chromatographic behavior of benzimidazole derivatives on hypercrosslinked polystyrene by reverse-phase HPLC

An important part in the research of separation of various compound classes is the study of relationship between structure and property by describing the effect of structure on compounds’ chromatographic retention. The aim of this work was to study the chromatographic retention of the firstly synthesized benzimidazoles from water-acetonitrile and water-methanol solutions on hypercrosslinked polystyrene (HCP) by high-performance liquid chromatography (HPLC). The effect of water-methanol and water-acetonitrile solutions’ composition on the benzimidazole derivative retention factors on HCP was studied. The thermodynamic characteristics of sorption of benzimidazoles’ transition from water-organic solutions onto the surface of HCP phase were obtained. The thermodynamic compensation effects were studied. It has been shown that the benzimidazole nitro derivative realizes additional specific interactions with the aromatic network of HCP. The slope ratio of the Soczewiński–Wachtmeister equation was calculated. It was shown that 1-hydroxymethylbenzimidazole and 2-aminobenzimidazole characterized by small volumes and containing hydrophilic substituents do not subordinate Soczewiński–Wachtmeister model under ranging from 75 to 85% concentrations of acetonitrile.

Retention Characteristics and Sorption Enthalpies of Esters of Natural Hydroxycarboxylic Acids on DB-1 Stationary Phase

Sorption characteristics and retention of esters of glycolic, lactic, malic, and tartaric acids with C1‒C8 alcohols of linear structure are studied by gas-liquid chromatography in the temperature range of 90‒260°C on DB-1 nonpolar phase. The values of the retention indices of the compounds studied are obtained. On the basis of experimentally determined retention times, the thermodynamic characteristics of sorption under the conditions of limiting dilution are estimated. The dependences of the change in sorption enthalpies on the length of the linear alkyl substituent and on the value of the logarithmic retention index are found. The possibility of estimating the energy of intermolecular interactions of lactic acid esters in the liquid phase is shown on the basis of the obtained values of sorption enthalpies and vaporization enthalpies.

Sorption, thermodynamic, and selective properties of camphor-substituted copper(II) tetrapyrazinoporphyrazine as a stationary phase for gas chromatography

The surface of a Chromaton N-AW diatomite adsorbent was modified with copper(II) tetra(1',7',7'-trimethylbicyclo[2.2.1]heptano-[2',3'-b]-pyrazino)porphyrazine. Adsorption of vapors of 20 organic compounds on the surface of the modified adsorbent was studied by inverse gas chromatography. Electron-donor isomers of methylpyridine and dimethylpyridine, isomers of weakly polar xylenes and cresols, aliphatic alcohols, and other hydrocarbons capable of showing various types of intermolecular interactions with the complex of camphor-substituted tetrapyrazinoporphyrazine with copper(II) were chosen as adsorbates. Specific retention volumes of adsorbates, heat and adsorption entropy, and Gibbs adsorption energy were calculated. The effects of temperature and chemical nature of the adsorbates on the thermodynamic characteristics of sorption are discussed. Factors of separation of closely-boiling hydrocarbons are calculated. It has been found experimentally that the macroheterocycle-based adsorbent shows high selectivity to closely-boiling compounds of various types, unattainable for the unmodified adsorbent.

Characteristics of retention and enthalpies of sorption from the gas phase of esters of trimethylolpropane and С2–С5 acids on DB-1 stationary phase

Characteristics of retention and their temperature dependences, along with the thermodynamic characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220–280°C for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of structures containing from 2 to 6 carbon atoms.

Thermodynamics of the sorption of organic compounds on polyethylene glycol 400–permethylated β-cyclodextrin stationary phase and its enantioselectivity in gas chromatography

The thermodynamic characteristics of sorption of 24 organic compounds of various classes from the gas phase on the binary stationary phase based on polyethylene glycol 400 and permethylated β-cyclodextrin were determined. The influence of geometrical structure and optical activity of organic compounds on the possibility of forming sorbate–macrocycle complexes was examined. It was found that the studied stationary phase shows the enantioselectivity towards low-polar terpenes under the conditions of gas chromatography.

Термодинамические характеристики сорбции металлов-ионов ионитами

Термодинамические характеристики сорбции металлов-ионов ионитами

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.

Thermodynamic characteristics of the sorption of glycerol ethers on stationary phase OV-101

Retention characteristics, temperature dependences of the retention characteristics, and thermodynamic characteristics of sorption on the nonpolar OV-101 phase are determined for 33 glycerol mono-, di-, and triethers with linear and branched monobasic alcohols containing one to five carbon atoms in the temperature range of 100–180°C.

Sorption of adamantanes on polyethylene glycol-modified graphitized thermal soot

The thermodynamic characteristics of sorption of adamantane and its functional derivatives on graphitized thermal soot (GTS) modified with polyethylene glycol Carbowax 20M were determined by equilibrium gas chromatography. The resulting thermodynamic characteristics were analyzed and compared with the data measured for adamantanes on the surface of nonmodified GTS and polyethylene glycol deposited on an inert substrate. The solid carbon substrate was shown to affect the character of intermolecular interactions in the GTS-modifier system and the retention of framework compounds under the conditions of gas, liquid, and solid-state chromatography.

Gas-chromatographic studies of the sorption thermodynamics of adamantanes on a carbon adsorbent modified with polyethylene glycol with β-cyclodextrin additives

The thermodynamic characteristics of sorption of adamantane and its derivatives on a mixed stationary phase consisting of a graphite-like solid substrate, polyethylene glycol, and β-cyclodextrin (βCD) were determined by gas chromatography. The introduction of β-CD additives to a polar polymer matrix was shown to considerably decrease the chromatographic retention of the sorbates, which is evidence of the macrocyclic effect. The presence of β-CD molecules was found to increase the selective properties of the mixed sorbent with respect to the structural isomers of adamantanes.

The thermodynamic characteristics of retention of tricyclo[5.2.1.02,6]decane isomer molecules on different sorbents in gas chromatography

The thermodynamic characteristics of sorption of the isomeric tricyclo[5.2.1.02.6]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.

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 of water vapors by high-strength para-aramid fibres

The water vapor sorption isotherms were measured for different types of high-strength fibres based on carbocyclic and heterocyclic para-aramids: Rusar (copolymers of amidobenzimidazole and p-phenylene terephthalamide), Twaron and Kevlar (poly-p-phenylene terephthalamide), and for comparison, capron (polycaproamide). The parameters of the thermal sorption equation and the thermodynamic characteristics of sorption of water vapor were calculated with previously obtained sorption data with the previously developed theoretical-probability model of sorption. A correlation was found between the integral heat of sorption in amorphous regions of para-aramid fibres and the specific cohesive energy.

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.

Influence of the chemical nature of siloxanes on the thermodynamic characteristics of sorption for a series of linear and cyclic saturated hydrocarbons

The thermodynamic characteristics of sorption (Henry’s constants of sorption equilibrium K sorp, heats of sorption q, and standard entropies of sorption ΔS°) were studied by gas chromatography to describe the behavior of linear and cyclic saturated hydrocarbons on phenylmethylsiloxane HP-5, fluoromethylsiloxane OV-210, and methylsiloxane OV-1. The K sorp and q values and, correspondingly, the energy of dispersion interactions decrease in the series HP-5 > OV-1 > OV-210. The difference in structures of adamantane, trans-decalin, and decane molecules has almost no effect on the heats of sorption. Henry’s constants increase on going from decane to trans-decalin and, further, to adamantane. This effect becomes more pronounced with an increase in the sorbent polarity (OV-1 < HP-5 < OV-210). The entropy factor can play a key role in sorption processes on siloxanes.

Thermodynamic Study of Iron(III) Sorption on Clay

Sorption of Fe(III) cations on Cambrian blue clay is discussed in term of the Langmuir isotherm. The thermodynamic characteristics of sorption were determined. The Gibbs energies of formation of sorbed Fe(III) aqua and hydroxo cations were calculated. The role of hydroxo complexes in sorption was considered.

Gas chromatographic and IR spectroscopic characteristics of tri- and tetramethylcyclohexenyl butenyl ketones

Infrared spectroscopic characteristics and gas chromatographic retention indices of tri- and tetramethylcyclohexenyl butenyl ketones were determined at different temperatures of analysis. Thermodynamic characteristics of sorption on the apolar stationary phase were calculated. The sorption characteristics of tri- and tetramethylcyclohexenyl butenyl ketones show that under conditions of capillary gas chromatography these compounds are retained due to the dispersive energy. It was shown by FTIR spectroscopy that the formation of conjugation systems of double bonds is responsible for the higher retention of the β-isomers compared with that of the α-isomers. The shortening of the distance between the carbonyl and trimethylcyclohexenyl groups was found to be accompanied by a decrease in the retention of the isomeric compounds.

The influence of molecular conformation ofN-alkylsubstituted six-membered cyclic amines and alkylcyclohexanes on the thermodynamic characteristics of sorption in gas chromatography

The standard partial molar free energies, enthalpies, and entropies of sorption of the methylene units in the homologous series of alkylcyclohexanes andN-alkylsubstituted sixmembered heterocycles (piperidines, morpholines, and thiomorpholines) were determined on a capillary column with the methylsiloxane OV-101 stationary phase at 70–150°C. A characteristic feature of all series under study is an abnormally high increase in the values of thermodynamic parameters of sorption on going from the methyl to the ethyl homolog. This peculiarity is believed to be associated with the presence of thegauche butane orgauche methylethylamine fragments in the ethyl homolog. Thesegauche fragments have an increased sorption activity under conditions of gas chromatography in comparison with the correspondingtrans form.

Thermodynamic characteristics of sorption of heterocyclic compounds m capillary gas chromatography

Dependences of sorption energies of sulfur-, oxygen-, and nitrogen-containing heterocyclic compounds on the nature of heteroatoms, structure of substituents and their position in the ring were studied. The contributions of heteroatoms, functional and alkyl groups to the energy of dispersive interaction of position isomers with nonpolar stationary phases were determined for imidazoles, piperidines, morpholines, thiomorpholines, dioxalanes, oxathiolanes, dithiolanes, thiophenes, and furans. The nonequivalence of contributions of the same substituents to the sorption energy of each of the heterocyclic compounds, depending on the nature of the heteroatom and position of the substituent, was shown. The obtained values of contributions of heteroatoms and substituents can be used for apriori calculation of retention indices of position isomers of five- and six-membered heterocycles containing one or two heteroatoms in the ring.

Calculation of thermodynamic characteristics of thiazole sorption from retention indices taking into consideration the nonadditivity of the energetic contributions of identical alkyl groups

1. The dependence of the energy of the dispersion interaction of substituted thiazoles with a nonpolar stationary phase, Apiezon, on the position of the alkyl substituent in the ring has been demonstrated. 2. The greatest contribution to the energy of the dispersion interaction is made by alkyl substituents in position 5, and the smallest by those in position 2 of the thiazole ring. 3. The possibility has been demonstrated of calculating the thermodynamic characteristics of the sorption of substituted thiazols, and of predicting retention indices by incorporating the deficit of the energy contributions of alkyl groups in positions 2 and 4.