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

Abstract

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 ≤ 234 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.

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

“…S1) on the structure. In a companion study [37] the LC retention behavior of the parent PASHs is reported, and this study demonstrated that the three- and four-ring unsubstituted PASHs eluted later than expected based on L/B when the sulfur atom was located in a bay-region of the structure. These observations suggest that when the sulfur atom is located in a bay -like-region, the sulfur atom is protected from from interacting with the stationary phase (C 18 ).…”

“…LC retention measurements were recorded using the same instrumentation described in a companion publication on LC separation of parent PASHs [37]. Separations were performed on monomeric (Agilent 5) and polymeric (Zorbax Eclipse PAH) C 18 columns purchased from Agilent (Avondale, PA) with the following characteristics: 25 cm length, 4.6 mm diameter, and 5 μm average particle diameters.…”

“…In past decades, PASHs have received far less attention than PAHs despite their carcinogenic and mutagenic potential [9, 10] and their presence in air particulate matter [11, 12], sediments [13–15], coal liquids [16], diesel [15], heavy oil [17–21], crude oil [15, 18, 22–31], shale oil [16, 22, 32, 33], coal tar [22, 23, 29, 34–36], mussels [13, 14,], and fish [13, 14,]. In a previous study [37], we reported LC retention indices for 70 PASHs on both monomeric and polymeric C 18 phases. In this study, LC retention indices were determined for 79 alkyl-substituted PASHs, and the correlation of retention on the polymeric C 18 phase and PASH geometry ( L/B and T ) was investigated.…”

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

“…Recently, reversed-phase liquid chromatography (RPLC) on octadecylsilane (C 18 ) stationary phases has been shown to provide unique selectivity for separating isomeric PASHs [23–25]. However, GC still provides significantly greater separation capabilities over RPLC for determining PASHs in complex samples.…”

“…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]. …”