Retention behaviour of model solutes on mixed silica-magnesia adsorbents by TLC. Comparison with the adsorption properties of alumina and silica

The retention behaviour of positional isomers (phenols, aniline derivatives, quinoline bases) on mixed silica-magnesia adsorbent has been compared with the retention behaviour of the solutes on alumina and on silica. The results are presented as R(M Alumina) vs R(M mix) and R(M) (Silica) vs R(M mix) relationships. The analysis of the structural effects of the solutes and the position on R(M I) vs. R(M II) diagrams allows the comparison of the active centers on the surface of the investigated adsorbents. The influence of the polar modifier on the retention of model compounds is also discussed. The selectivity of silica-magnesia and silica-magnesium carbonate mixed adsorbents and also Florisil, silica and alumina in three eluent systems (ethyl acetate, 2-propanol and dioxane in n-heptane) is presented as Delta R(M) values of pairs of positional isomers.