HPLC SEPARATIONS OF SOME SUBSTITUTED BENZENES ON THERMALLY TREATED CLAYS

HPLC columns were packed with quasi-spherical montmorillonite particle s which were prepared by spray-drying and then thermally treated. Sepa rations of phenylureas (linuron, neburon, diuron and monuron), phospho thioate phenyl esters (parathion, methyl parathion and paraoxon) and o ther smaller substituted benzenes were performed on the columns. The r elative retention of the substituted phenyl pesticides demonstrated th e important role polar substituents play in the eluate-surface interac tions 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 int erlayer spaces due to swelling as the polarity of the liquid phase inc reased. The role of the exchangeable cation (Na+, Co2+ and Cu2+) in th e adsorption was found to be complex. The cations determine both the s trength of interaction, which increases with the valence of the cation , and the accessibility of the interlayer adsorption sites which decre ased with the valence.