Mechanism of separation on cholesterol-silica stationary phase for high-performance liquid chromatography as revealed by analysis of quantitative structure-retention relationships.

The retention characteristics of a newly synthesized stationary phase were determined for reversed-phase high-performance liquid chromatography obtained by chemical immobilization of cholesterol on spherical silica gel. For a designed series of analytes the retention factors, log k, were determined at several compositions of the methanol-water mobile phase. Logarithms of retention factor corresponding to a hypothetical pure water eluent, log k(w), were calculated by extrapolation of the linear relationships of individual log k data versus volume percent of methanol. The series of 24 test analytes were characterized structurally by means of the logarithms of n-octanol-water partition coefficients, log P, by a set of the linear solvation energy relationship (LSER)-based descriptors of the polarity and bulkiness of the analytes and by structural descriptors of analyte size and polarity acquired by molecular modelling. Quantitative structure retention relationships (QSRR) were derived by multiple regression analysis using the three groups of structural descriptors of analytes and the log k(w) data determined on the new stationary phase. For the sake of comparison the corresponding QSRR equations were also derived for retention parameters determined on a standard octadecylsilica and on the so-called immobilized artificial membrane (IAM) stationary phase. The QSRR analysis clearly proved distinctive retention properties of the new cholesterol-silica stationary phase. It has been concluded that the new phase may possess valuable analytical specificity. Its application for modelling penetration of xenobiotics through biological membranes appears rather unlikely.