Dependence on Composition of GC Retention on a Self-Associating Solvent/Hydrocarbon Mixture: Its Interpretation by the Computation of Available Sites for Interaction with Solutes

Abstract

Diamides, e.g., N-lauroyl-l-valine-tert-butylamide, self-associate in appropriate media through hydrogen bonding. Such selectors form with apolar solvents binary phases, for which the contribution of the polar constituent to the overall retention is the product of the retention on the pure diamide, its weight fraction (x), and a concentration dependent factor (μx). In this paper a model is presented to interpret the effect of the weight fraction on μx. The diamide in the apolar solvent forms a mixture of structures of association degree 1 to n, between which n − 1 equilibria can be written. Every associate has at its terminals a site capable of hydrogen bonding to appropriate solutes (e.g., α-amino acid derivatives). It is proposed that μx = Nx/N1, where Nx is the number of available sites for hydrogen bonding at weight fraction x and N1 is that of the pure diamide (x = 1). On the assumption that the above equilibria have closely similar constants, equations were developed to compute the number of the ava...