Linear solvation energy relationships in normal phase liquid chromatography based on retention data on silica in 2-propanol/hexane eluents

We have examined the linear solvation energy relationships (LSER) based on the Kamlet/Taft solvatochromic polarity scales for normal phase liquid chromatography (NPLC), using retention data of 58 solutes in the system composed of 2-propanol/hexane as the eluent and silica particles as the stationary phase. Correlation coefficients of the LSER regressions for NPLC have been proven to be lower than those obtained for reversed phase liquid chromatography (RPLC). Furthermore, we observed inconsistency in LSER correlations among different solute subgroups. Nevertheless, the sign of each regression coefficient is in agreement with chemical senses, and polarities of the stationary phase are greater than those of the mobile phase. The polarity difference between the stationary and mobile phases clearly decreases with increase in mobile phase polarity, at least for hydrogen bond related polarities. We interpreted the LSER results in view of the retention process in NPLC to account for the general LSER trends and anomalies. We conclude that the LSER methods are inappropriate in predicting solute retention in NPLC where silica particles are used as the stationary phase, although the LSER correlations are roughly in agreement with chemical senses.