Polarity parameters of the Symmetry C18 and Chromolith Performance RP-18 monolithic chromatographic columns.

A set of 12 compounds of different chemical nature has been established to characterise RPLC columns on the basis of a polarity retention model previously developed: log k=(log k)(0)+p(P(m)(N)-P(s)(N)). This model allows the calculation of the retention factor (k) of any non-ionized compound using one parameter which describes the polarity of the solute (p), another one for the polarity of the mobile phase (P(m)(N)) and two more parameters for the characterisation of the stationary phase ((log k)(0) and P(s)(N)). The selected set of compounds allows the determination of (log k)(0) and P(s)(N) of stationary phases and it has been used to characterise two commercial columns (Symmetry C18 from Waters and Chromolith Performance RP-18 monolithic from Merck). Column parameters, together with those of the mobile phase permit successful transfer of retention data between chromatographic systems. Prediction of retention of a variety of non-ionized analytes has been also successfully achieved using the column descriptors and p values of solutes from a previously established p data base.