Capillary columns with previously or in situ synthesized super-crosslinked polystyrene phases are prepared. It has been shown that columns with stationary phases based on presynthesized hypercrosslinked polystyrenes, spherical monodisperse particles, or “nano-sponges,” despite their microporous structure, show insufficient kinetic efficiency and selectivity in the separation of light hydrocarbons. Higher kinetic efficiency was observed in columns where the hypercrosslinked polystyrene phase was synthesized directly in the column, although the porosity structure of this phase remains unknown. All columns with hypercrosslinked polystyrene stationary phase have good thermal stability, with no observed chemical destruction and physical aging at temperatures up to 250°C.

The possibility is verified of estimating the phase ratio of a chromatographic column chromatographically from the semi-empirical dependence of the retention time of homologs on the number of carbon atoms in their structure. The effect the nature and pressure of the carrier gas has on the phase ratio is considered. It is shown that the average value is 1190 ± 100 for the polar phase and 380 ± 50 for the non-polar phase, regardless of the nature of the carrier gas. An exception is СО2, where phase ratio β drops strongly after adjusting the initial data. At the same time, it is clear that the values of the phase ratio determined chromatographically differ strongly from those claimed by the manufacturers of columns, while system dead time tМ and energy $$\Delta {{G}_{{{\text{C}}{{{\text{H}}}_{{\text{2}}}}}}}$$ of the methylene unit sorption of a homological series can be reliably determined via extrapolation.

Polyimide PIM-1, which forms a porous polymer layer on the walls of a capillary column, exhibits high thermal stability. It is studied as a stationary phase for gas chromatography. A column with the PIM-1 stationary phase displays a drastic difference in efficiency, depending on the molecular size of the analyte: 2500–3000 theoretical plates per meter for methane and ethane and fewer than 1000 plates for larger molecules. This behavior of the column is attributed to the poor accessibility of sorption sites, as is apparent from the high loss of entropy during the sorption of light hydrocarbons and the low diffusion coefficients for these sorbates. The effect the physical aging of PIM-1 has on the separating properties of a column is studied in the accelerated thermal aging mode using the example of separation of a model C1–C4 hydrocarbon mixture. It is shown that upon heating the stationary phase to 200°C, sorbate retention and column efficiency fall monotonously. When the temperature is raised to 300°C, an unexpected increase in the analyte retention is observed, though the column’s efficiency continues to fall with respect to all sorbates except isobutane, for which this parameter increases. The causes of these unexpected effects have yet to be revealed.

Changes in retention factor k of light hydrocarbons on PIM-1 stationary phase with an increase of ageing temperature are tested. Varying the ageing temperature from 50 to 200°C causes a slight decrease in solute retention, which, however, changes to strong increase as soon as the ageing temperature exceeds 200°C. An increase of the solute retention factor k means the proportional increase of the Henry equilibrium constant K, which in turn under constant chromatographic conditions probably points out the thermodynamic changes in the structure of PIM-1 which can be caused either by a chemical decomposition or by a structural rearrangement. Due to high chemical stability of PIM-1, an increase of solute retention with thermal ageing is a consequence of structural rearrangements of polymeric chains, resulting in more adapted adsorption sites. At the same time, accessibility of the adsorption sites decreases as it is indicated by the reduction of column efficiency and diffusion coefficients.

Chromatographic determination of the thermodynamic parameters of sorption for light hydrocarbons retention on a stationary phase based on poly [trimethylsilyl (propyn-1)] (PTMSP) was performed and the effect of column preheating at temperatures up to 260°C on the retention of analytes was investigated. It was shown that heating the column to 130°C does not affect the retention of the analytes. At temperatures above 130°C, the gradual decrease of the retention of analytes on PTMSP stationary phase is observed. The process is non-selective and proceeds at the same extent for all the studied hydrocarbons, regardless of the size and geometry of the molecule. Values of enthalpy and entropy of sorption of light hydrocarbons are determined for the original column and after its aging at 200°C. The enthalpy of sorption of the analytes at the PTMSP phase is practically independent on the heating temperature of the PTMSP phase, whereas the loss of entropy increases after heating. The increase of the entropy factor after the heating of the PTMSP stationary phase is associated with its aging and is confirmed by the construction of compensation functions for treated and untreated columns.

Different ways of estimating the hold-up time of a system in gas chromatography are considered. It is shown that the hold-up time found from aerodynamic dependences proves to be minimal, but does not allow for the contribution from extracolumnar effects. The hold-up time, determined experimentally from the retention time of an unretainable sorbate (methane), proves to be maximal and depends on the intensity of sorbate–stationary phase interaction. The hold-up time found from the purely empiric correlation between the logarithm of the net retention time of homologs and the number of carbon atoms is intermediate between the theoretical and experimental values. It is shown that the correlation between the number of carbon atoms in a homological series and the relative retention time of sorbates (rather than their net retention time) is grounded thermodynamically. Corresponding correlations are proposed that allow estimates not only of the hold-up time of a system but also of such parameters as the phase ratio and the change in the free energy of a methylene unit during sorption on the stationary phase.

The thermodynamic parameters of sorption of a test mixture of hydrocarbons on a new type of PEG-like stationary phases are determined from the temperature dependence of sorbate retention in the temperature range of 35–110°C. The determined entropy and enthalpy of sorption are close for all the studied stationary phases, despite the different ratios of ethylene glycol and acrylate moieties in the polymer’s phase structure. At the same time, the studied phases exhibit greatly different separation abilities, due apparently to the kinetic properties of the phases, as is indicated by differences in the efficiency of the columns with these phases and in the diffusion coefficients of sorbates on these phases.

Термодинамические параметры сорбции тестовой смеси углеводородов на новом типе ПЭГ-подобных стационарных фаз определены из температурной зависимости удерживания сорбатов в диапазоне температур от 35 до 110?°С. Найденные величины энтропии и энтальпии сорбции оказались близкими для всех стационарных фаз, изученных в этой работе, несмотря на различное соотношение этиленгликольных и акрилатных фрагментов в структуре полимерной фазы. В то же время изученные фазы заметно отличаются по их разделяющей способности, что, вероятно, связано с кинетическими свойствами фаз, на что указывают различия в эффективности колонок с этими фазами и в коэффициентах диффузии сорбатов на этих фазах.

Changes in the properties of the poly[(trimethylsilyl)prop-1-yne] (PTMSP) film deposited on the walls of a quartz capillary under the action of high temperatures were studied by chromatographic methods. The change in the thermodynamic parameters of sorption of light hydrocarbons related to both physical aging of the PTMSP film and, possibly, its chemical destruction was examined.

The thermal stability of poly[1-(trimethylsilyl)-1-propyne] is investigated by heating the capillary column with this polymer as the stationary phase with the subsequent separation of the test mixture of light hydrocarbons. It is shown that heating of the column up to 130°C does not cause a decrease in efficiency or in the retention time of solutes. A further increase in temperature results in both decrease in column efficiency and sorbate retention. However, a decrease in column retentivity goes in one way for all the tested hydrocarbons. At the same time, the efficiency of the column is changed to a lesser degree for methane and ethane up to the temperature of polymer degradation, while for propane, butane, and iso-butane the difference is rather sharp. The most expressed decrease in efficiency was found for iso-butane: the column efficiency for this sorbate versus temperature of heating had two stages. The diffusion coefficients for sorbates in the polymeric phase were also evaluated and the sharp decrease in their values was found after the column heating.

Enthalpy and entropy of adsorption of polar and non-polar solutes were measured by chromatographic technique for new stationary phases prepared from membrane polymers based on tricyclonones. Data obtained within temperature interval from 40 to 150 degrees C were used to create extrathermodynamic dependences (compensation plots, dependences of enthalpy and entropy changes on solute carbon number). Compensation plots were very similar for all the stationary phases indicating similar adsorption mechanisms. The difference between the stationary phases was elucidated using dependences of enthalpy and entropy changes on solute carbon number. Higher retentivity of the stationary phase based on polymer 1 was explained by higher both enthalpy and entropy of solute adsorption on the stationary phase. (C) 2017 Elsevier B.V. All rights reserved.

Five equations for kinetic curves which connect the number of theoretical plates N and time of analysis t 0 for five different versions of optimization, depending on the parameters being varied (e.g., mobile phase flow rate, pressure drop, sorbent grain size), are obtained by means of mathematical modeling. It is found that a method based on the optimization of a sorbent grain size at fixed pressure is most suitable for the optimization of rapid separations. It is noted that the advantages of the method are limited by an area of relatively low efficiency, and the advantage of optimization is transferred to a method based on the optimization of both the sorbent grain size and the drop in pressure across a column in the area of high efficiency.