Correlation of solute retention in isothermal gas chromatography (GC) with chromatographic parameters is necessary for identifying unknown compounds, predicting analyte retention times, calculating chromatographic and thermodynamic parameters, etc. and therefore has been widely studied in the literature [[1], [2], [3]]. One of the long-used correlations is the linear correlation of the net retention time t’R of n-alkanes with the number of methylene moieties in their structure. This number is often called the carbon number of n-alkanes (ZS) [[1], [2], [3], [4]]:logt’R=log(tR−tM)=bZS + c

This empirical linear relationship is used to estimate GC parameters such as dead time (tM), corrected retention time, Kovats indices, etc. [2,4]. The disadvantage of the relationship is that the dead time is hidden in the total retention time (tR) and cannot be directly estimated from the graphical relationships. But the problem was solved and various models were proposed, including linear [[5], [6], [7], [8]] or nonlinear [[9], [10], [11]], which made it possible to find the required parameters by calculation.

Linear correlations are widely used in inverse gas chromatography (IGC), which allows the thermodynamic parameters of compounds to be estimated from chromatographic experimental data [12,13]. The most well-known correlation in IGC is the correlation of the logarithm of the solute retention k with the reciprocal column temperature 1/Tc, based on the known thermodynamic relationship [4]:ΔG=-RTCLnkβ=ΔH-TCΔSwhere K is the distribution constant of the solute between the mobile and stationary phases; ΔG, ΔH and ΔS are the free energy, enthalpy and entropy of solute adsorption, respectively; R represents the gas constant and β represents the phase ratio of the column, i.e. the ratio of the volume of the mobile phase VM in the column to the volume of the stationary phase VS.

Important application of IGC is characterization of dispersive properties of solid surfaces. Series of homologous n-alkanes is used as a test solute to create a linear correlation of energetic parameters with alkane carbon number [14]. Evaluated parameters can be used for evaluation of surface properties of numerous solid materials [14,15]. Nevertheless, the most common use of IGC is investigation of polymers [16].

The study of the properties of polymer stationary phases in GC was initiated by the work of Smidsrød and Guillet [17] on poly(N-isopropylacrylamide). The authors examined the traditional correlation of the logarithm of solute retention with the reciprocal column temperature 1/TC and observed a strong influence of the nature of the analyte on the shape of the correlation diagram. The observed features of the correlations were explained by phase transitions of the polymer stationary phase [18]. It is interesting to note that linear diagrams without any features were also observed for polymers with a large free volume and a large specific surface area [19,20]. Chemically, this group of polymers is important for the chemistry of membrane materials, and, at the same time, these polymers are considered as promising microporous adsorbents for GC [21,22].

Recently, a new series of polymers containing an n-alkyl substituent in the side chain was synthesized by addition polymerization of 5-alkyl-2-norbornene (PAN) [23,24]. The length of the polymer side chain varied from methyl to tetradecyl, providing a change in the number of methylene units in the polymer side chain (polymer carbon number, Zp) from 1 to 14. The structure of the new polymers allows not only the traditional correlation of analyte retention with the number of methylene units in the analyte molecule ZS, but also to correlate the analyte retention with the carbon number of the polymer stationary phase Zp. The change in the phase state of the stationary phase with a change in the carbon number of the polymer can be considered as an isothermal phase transition process [18], and its effect on the chromatographic properties of the stationary phase will be considered in the proposed publication.