The gas-chromatographic behaviour (selectivity performance for cyclohexanebenzene and m-, p-xylenes pairs separation) of dimethyldioctadecylammonium complexes with kaolinite, fire-clay, halloysite, attapulgite, hectorite and various montmorillonites, nontronites and vermiculites has been investigated. The obtained data indicate the influence of specific surface and charge density on relative retention value (α), and of substitution location (tetrahedral versus octahedral sheet) within the clay lattice on selectivity. Hence, derivatives with nontronites and vermiculites, that is the clay minerals where the principal lattice substitutions are predominantly occurring within the tetrahedral sheet and possessing the highest surface charge density, are very effective sorbents for gas-chromatographic use. The application of gas-chromatography as investigation tool of clays surface is suggested. © 1969 Springer-Verlag.