Relation between adsorption energy and Kovats’ index following from theory of generalized charges

Abstract

Developed by our scientific group, the theory of generalized charges (TGC) has shown its simplicity
and performance for description of intermolecular interactions and adsorption [1-10]. It is well-known that
chromatographic behavior of substances depends on adsorption energy. This relation is very complex,
demanding, on the one hand, statistic integrals considering, in which the multiformity of adsorbed molecule
states, their dependence on angles and coordinates, shape of molecule etc., are included. On the other hand,
determination of adsorption energy is usually realized using sufficiently rough principle of atom-atomic
potentials that makes the procedure of binding energy with molecular structure very complicated and devoid
of prognosis capacity, because it demands many empirical nontransferable parameters. However, surprisingly
it may seem, between those complex terms of chromatography and thermodynamics one can establish very
simple and sufficiently precise relations. This is possible due to TGC – its new view on the adsorption
theory. TGC deduces a set of very convenient nonlinear relations without empirical parameters.
During present investigation the relation between Kovats’ index and enthalpy of adsorption process
in the Henry law area is defined. This binding reaches by mean of value ( )
43 Q = 06.0 I + 2 I
, that has
meaning of the generalized charge for the case of non-polar interaction on the smooth surface and for large
Kovats’ indices (greater than 400).
With precision to experimental standard deviation of 3-4%, the reference data [14,15] allows us to
obtain values of the standard adsorbent energy for the graphitized thermal black (U0 A = − 40.2 kJ/mol) and
chromatographic phase OV-1 ( 70.1 U0A = − kJ/mol).
However, the main exclusion is that the regularity based on deduced relations works for various
molecules including cyclic and aromatic molecules. Universality of this regularity view allows us to spread it
to more complex interactions: for example, to polar molecules and adsorbents. This very convenient
regularity has been used for development of new polarity determination method for chromatographic phases
in our previous work [17].