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

Abstract

Retention indices for 79 alkyl-substituted polycyclic aromatic sulfur heterocycles (PASHs) were determined by using reversed-phase liquid chromatography (LC) on a monomeric and polymeric octadecylsilane (C18) stationary phase. Molecular shape parameters [length, breadth, thickness (T), and length-to-breadth ratio (L/B)] were calculated for all the compounds studied. Based on separations of isomeric methylated polycyclic aromatic hydrocarbons on polymeric C18 phases, alkyl-substituted PASHs are expected to elute based on increasing L/B ratios. However, the correlation coefficients had a wide range of values from r = 0.43 to r = 0.93. Several structural features besides L/B ratios were identified to play an important role in the separation mechanism of PASHs on polymeric C18 phases. First, the location of the sulfur atom in a bay-like-region results in alkylated-PASHs being more retentive than non-bay-like-region alkylated-PASHs, and they elute later than expected based on L/B value. Second, the placement of the alkyl group in the k region of the structure resulted in a later elution than predicted by L/B. Third, highly nonplanar methyl-PASHs (i.e., 1-Me and 11-MeBbN12T) elute prior to the parent PASH (BbN12T).

Retention behavior of alkyl-substituted polycyclic aromatic sulfur heterocycle isomers in gas chromatography on stationary phases of different selectivity

“…Previous studies have observed an early elution for these isomers prior to the unsubstituted parent BbN12T on a smectic liquid crystalline phase, which was attributed to the non-planarity of these two isomers ( T = 4.99 Å and T = 5.32 Å for 11-Me and 1-MeBbN12T, respectively) [13]. Similar observations have been reported for the RPLC separation of these isomers on a polymeric C 18 stationary phase [48]. However, in the present study 11-MeBbN12T does not elute prior to the unsubstituted BbN12T on the 50% LC-DMPS phase.…”

“…The regression calculations for the correlation of L/B and retention on all four stationary phases are summarized in Tables 5 and 6. Wilson et al [47, 48] have recently demonstrated the use of statistical t -test for determining the linear significance of correlation coefficients ( r ) for the retention of isomeric PASHs and MePASHs in RPLC on polymeric C 18 stationary phases and their L/B values using equation 2: $$t_{\mathrm{italicexp}}=\frac{\mid r\mid \sqrt{df}}{\sqrt{1-r^2}}$$ where df is the degrees of freedom ( n – 2) and n is the number of data points. Based on the df , a significant linear correlation does exist for the correlation coefficient if t exp > t crit [49].…”

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

“…This study provides the most comprehensive investigation of reversed-phase LC retention behavior of PASH to date. A similar study for alky-substituted PASHs is published elsewhere [38]. …”

Retention behavior of isomeric polycyclic aromatic sulfur heterocycles in gas chromatography on stationary phases of different selectivity

“…Previous studies have used correlation coefficients ( r ) as a parameter for measuring the linear correlations for PAH retention and L/B [5, 23, 24]. A statistical test can be performed to test the significance of a correlation coefficient when not close to 1 [44].…”

“…In a companion study, the same three stationary phases have been evaluated for the separation of alkyl-substituted PASHs [41]. A similar study has been published investigating the RPLC retention behavior and shape selectivity correlations for the same PASHs [23] and alkyl-substituted PASHs [24]. …”