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Abstract Reversed‐phase liquid chromatography (LC) on C 18 stationary phases provides excellent selectivity for the separation of polycyclic aromatic hydrocarbons (PAH). Recent studies have shown that several factors affect selectivity for the LC separation of PAH including phase type (monomeric or polymeric), pore diameter and surface area of the silica substrate, and surface density of the C 18 ligands. In this paper the separation of eleven PAH isomers of molecular weight 278 is used to further illustrate the effect of stationary phase characteristics and shape of the solute (length‐to‐breadth ratio, L/B) on retention and selectivity. Only polymeric C 18 phases with a high C 18 surface coverage provided separation of all eleven isomers and the elution order of these isomers generally followed increasing L/B values. The effect of solute nonplanarity on reversed‐phase LC retention was investigated on both monomeric and polymeric phases using a series of planar and nonplanar PAH pairs. For each solute pair, the nonplanar solute eluted earlier than the planar solute, the largest selectivity factors being observed on the C 18 phase with the highest percent carbon load. Based on these studies, a model is proposed to describe the retention of PAH on polymeric C 18 phases.
Wise et al. (Wed,) studied this question.