Three-parameter model of intermolecular interactions as a basis for classification and selection of gas-chromatographic stationary phases

Abstract

The present article proposes a mathematical model based on the representation of the intermolecular
interaction energy as the sum of three terms: non-polar, polar and hydrogen bond energies, which depend on
the parameters of each of the interacting objects - the generalized charge, dipole moment and the probability
of hydrogen bond formation. The work is a continuation of the method developed by the authors for describing
gas-chromatography stationary phases. The proposed method of stationary phases classification (Three-
Parameter Characterization method) differs from existing, mainly theoretical justification, the lack of adjustable
parameters and good predictive power; this method does not require special experiments or complex
computer calculations, it is very economical to use experimental data.
Selectivity of stationary phase is described by two relative characteristics - polarity and hydrophilic;
polarity is the ratio of the square of the dipole moment of the stationary phase to its generalized charge and
hydrophilicity, in turn, the probability of formation of a hydrogen bond. Quantitative concepts of polarity and hydrophilicity are introduced, they can be found from experimental data on chromatographic retention indices.
Also, these characteristics for objects of intermolecular interaction can be calculated a priori from the
molecular structure. The characteristics found are to be plotted on so-called selectivity map with coordinates
of polarity and hydrophilicity. Developed method agrees well with the corresponding characteristics of the
Rorschneider – McReynolds method. The selectivity map allows choosing the most suitable stationary phase
for separation of the target analytes according to the principle “similia similibus solvuntur". This method has
a good predictive ability and can be used to predict the behavior of analytes in gas chromatography.