Correlation between reversed-phase retention and solute molecular surface type and area : II. Retention of low polarity non-hydrocarbonaceous surfaces

Abstract

On octadecylsilica (ODS) systems and pure methanol as eluent, the retention of homonuclear proton-free solutes like P 4, As 4, S 9, Se 8 and sulphur homocycles S n with n > 9 appears to depend only on their respective total molecular surface area (TSA). When plotted versus TSA, their ln k′ values lie on one straight line. The retention of these solutes is distinctly higher than that of n-alkanes having equal TSA. In terms of retention index, I K, the difference is about +500 units. It is proposed that the lower alkane retention is due to an additional interaction with the eluent methanol. The retention increments produced by chalcogen atoms in RS n R, RSe n R and RTe n R chains are also proportional to their respective surface areas, and are influenced to a certain degree by the length of the terminal alkyl groups R. The retention of proton-free heteronuclear solutes like S n Se 8− n , hexachlorobenzene, hexabropmobenzene and carbon disulphide is lower than with homonuclear proton-free solutes, but higher than with alkanes if normalized to equal TSA. This is explained by the existence of stronger bond dipoles and an increased polarizability.