HPLC SEPARATIONS OF SOME SUBSTITUTED BENZENES ON THERMALLY TREATED CLAYS

HPLC columns were packed with quasi-spherical montmorillonite particles which were prepared by spray-drying and then thermally treated. Separations of phenylureas (linuron, neburon, diuron and monuron), phosphothioate phenyl esters (parathion, methyl parathion and paraoxon) and other smaller substituted benzenes were performed on the columns. The relative retention of the substituted phenyl pesticides demonstrated the important role polar substituents play in the eluate-surface interactions and the strong influence of steric factors on these interactions. The retention of the pesticides decreased sharply as the polarity of the mobile phase increased. The retention of the smaller substituted benzenes showed a similar trend, but for these smaller molecules this trend was partially counteracted by the increased accessibility of interlayer spaces due to swelling as the polarity of the liquid phase increased. The role of the exchangeable cation (Na+, Co2+ and Cu2+) in the adsorption was found to be complex. The cations determine both the strength of interaction, which increases with the valence of the cation, and the accessibility of the interlayer adsorption sites which decreased with the valence.