Cross-Linked Hydroxy-Al-Montmorillonite as a Stationary Phase in Liquid Chromatography

Faina Tsvetkov, U. Mingelgrin and N. Lahav
Institute of Soils and Water, Agricultural Research Organization The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
The Seagram Center for Soil and Water Sciences, The Faculty of Agriculture The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76-100, Israel

Abstract: Quasi-spherical particles (7-µm mean diameter) were prepared from cross-linked hydroxy-Al-montmorillonite (basal spacing = 15.3 and 18.6 Å) by spray-drying. These particles (SP-CLM) were used as a packing material for columns in high-pressure liquid chromatography (HPLC). Aromatic phosphate esters, chlorosubstituted phenyl-ureas, monosubstituted benzenes, and the o-, m-, and p-isomers of disubstituted benzenes were separated on the columns, using isopropanol and hexane. Alkyl and alkoxy groups in the solute molecules sterically hindered the interaction of these molecules with the solid phase. The retention of the isomers of disubstituted benzenes that possess one electronegative (or dipolar) and one nonpolar substituent increased in the order: o- < m- < p-. In contrast, for all investigated disubstituted benzenes containing two electronegative (or dipolar) substituents, the o-isomer was retained on the 18.6-Å SP-CLM more strongly than the m- and p-isomers. The chromatographic data suggest that the strength of the interaction of phenolic groups with the solid phase increased with the acidity of these groups. The o-isomers of phenols that contained an additional electronegative (or dipolar) substituent displayed an exceptionally strong adsorption. The capacity of the o-isomers of disubstituted benzenes containing two electronegative (or dipolar) substituents to form chelates with Al probably was responsible for the strong retention of such o-isomers compared with the retention of the corresponding m- and p-isomers.

Cross-linked hydroxy-Al-montmorillonite acted as a strong and selective adsorbent for many families of organic compounds. It was used successfully as the solid phase in HPLC separations with eluents ranging from nonpolar (e.g., hexane) to highly polar (e.g., water).

Key Words: Adsorption • Chelation • Cross-linked smectite • Disubstituted benzene • High-pressure liquid chromatography • Hydroxy-Al • Monosubstituted benzene • Phenyl-urea • Phosphate esters

Clays and Clay Minerals; August 1990 v. 38; no. 4; p. 380-390; DOI: 10.1346/CCMN.1990.0380407
© 1990, The Clay Minerals Society
Clay Minerals Society (www.clays.org)