Analysis of a solute polarity parameter in reversed-phase liquid chromatography on a linear solvation relationship basis

A study was made to correlate an overall solute polarity descriptor (p) with several molecular parameters: excess molar refraction (E), dipolarity/polarizability (S), effective hydrogen-bond acidity (A) and basicity (B), and McGowan volume (V), through the linear solvation model (p=c+eE+sS+aA+bB+vV). The achieved values of p were introduced in a retention model developed previously for reversedphase liquid chromatography (RPLC), which describes the retention according to the polarity contributions of solute, mobile phase and stationary phase. The retention behaviour (log k) of a solute in a given chromatographic system (i.e. column/organic solvent) is appropriately summarised by p, which in addition is useful to transfer retention data between solvents and/or columns. The model was tested with several sets globally including more than 200 compounds of different nature, which were eluted in acetonitrile– and methanol–water mobile phases. Satisfactory correlations were always found. When octanol–water partition coefficients (log Po/w) were corrected with a term considering the solute acidity, good correlations were also observed between p and log Po/w. The study shows that the retention at any mobile phase composition may be predicted using the five solvation descriptors, once characterised the polarity of the column with a small training set. Alternatively, log Po/w and hydrogen-bond acidity data can be used for these predictions.