Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in reversed-phase liquid chromatography

Retention indices for 70 polycyclic aromatic sulfur heterocycles (PASHs) were determined using reversed-phase liquid chromatography (LC) on a monomeric and a polymeric C18 stationary phase. Molecular shape parameters [length, breadth, thickness (T), and length-to-breadth ratio (L/B)] were calculated for all the compounds studied. Correlations between the retention on the polymeric C18 phase and PASH geometry (L/B and T) were investigated for six specific PASH isomer groups with molecular mass (MM) 184 Da, 234 Da, 258 Da, 284 Da, 334 Da, and 384 Da. Similar to previous studies for polycyclic aromatic hydrocarbons (PAHs), PASH elution order on the polymeric C18 phase was generally found to follow increasing L/B values. Correlation coefficients for retention vs L/B ranged from r = 0.45 (MM 184 Da) to r = 0.89 (MM 284 Da). In the case of smaller PASHs (MM ≤ 258 Da), the location of the sulfur atom in the bay-region of the structure resulted in later than expected elution of these isomers based on L/B. In the case of the larger PASHs (MM ≥ 284 Da), nonplanarity had a significant influence on earlier than predicted elution based on L/B values.