Inorganic polymers as novel chromatographic stationary phase media

Aluminosilicate inorganic polymers (geopolymers) can be cheaply and readily prepared from dehydroxylated kaolinite clay and have been successfully demonstrated as a new type of stationary phase in the chromatographic separation of a mixture of three model aromatic compounds (a trisubstituted benzene, an ester and a pyrrole). Grinding and sieving to 105 μm produced powders with a similar particle size distribution and morphology to standard chromatographic silica, although smaller particle sizes and other morphologies can readily be produced. Three compositions of geopolymers were studied here and their performance was compared with conventional chromatography column packing media typically used for simple open-column and flash separations (silica and aluminas). Although the geopolymers were prepared under highly alkaline conditions, washing with acid to bring them to neutral pH before use was found to be unnecessary. The results obtained with the as-prepared geopolymer of standard composition showed it to possess a significantly greater number of plates/meter than any of the other column materials, including acidic and neutral aluminas and silica, and although more of the ester adsorbed to this column than on silica, in all other important respects the behavior of the geopolymer was comparable to silica and alumina. All the geopolymers were shown to be chemically stable to strong solvents such as ethanol, by comparison with conventional media such as silica and alumina, which were decomposed by ethanol; this suggests that unlike conventional silica, the geopolymer media may be cleaned with a strong solvent between runs without being degraded, and re-used. These results indicate that geopolymers represent a promising substitute for the commonly-used silica or alumina chromatography stationary phases, being simpler and cheaper to produce, more stable to strong solvents and showing comparable or better separation characteristics.