Comparative study of hydrocarbon, fluorocarbon, and aromatic bonded RP-HPLC stationary phases by linear solvation energy relationships

The retention properties of eight alkyl, aromatic, and fluorinated reversed -phase high-performance liquid chromatography bonded phases were characteri zed through the use of linear solvation energy relationships (LSERs), The s tationary phases were investigated in a series of methanol/water mobile pha ses. LSER results show that solute molecular size and hydrogen bond accepto r basicity under all conditions are the two dominant retention controlling factors and that these two factors are linearly correlated when either diff erent stationary phases ai:a fixed mobile-phase composition or different mo bile-phase compositions at a fixed stationary phase are considered. The lar ge variation in the dependence of retention on solute molecular volume as o nly the stationary phase is changed indicates that the dispersive interacti ons between nonpolar solutes and the stationary phase are quite significant relative to the energy of the mobile-phase cavity formation process. PCA r esults indicate that one PCA factor is required to explain the data when st ationary phases of the same chemical nature (alkyl, aromatic, and fluoroalk yl phases) are individually considered. However, three PCA factors are not quite sufficient to explain the whole data set for the three classes of sta tionary phases. Despite this, the average standard deviation obtained by th e use of these principal component factors are significantly smaller than t he average standard deviation obtained by the LSER approach, In addition, s electivities predicted through the LSER equation are not in complete agreem ent with experimental results. These results show that the LSER model does not properly account for all molecular interactions involved in RP-HPLC. Th e failure could reside in the Vt solute parameter used to account for both dispersive and cohesive interactions since "shape selectivity" predictions for a pair of structural isomers are very bad.