Normal-phase liquid chromatography retention behavior of polycyclic aromatic hydrocarbon and their methyl-substituted derivatives on an aminopropyl stationary phase

Abstract

Retention indices for 124 polycyclic aromatic hydrocarbons (PAHs) and 62 methyl-substituted (Me-) PAHs were determined using normal-phase liquid chromatography (NPLC) on a aminopropyl (NH2) stationary phase. PAH retention behavior on the NH2 phase is correlated to the total number of aromatic carbons in the PAH structure. Within an isomer group, non-planar isomers generally elute earlier than planar isomers. MePAHs generally elute slightly later but in the same region as the parent PAHs. Correlations between PAH retention behavior on the NH2 phase and PAH thickness (T) values were investigated to determine the influence of non-planarity for isomeric PAHs with four to seven aromatic rings. Correlation coefficients ranged from r = 0.19 (five-ring peri-condensed molecular mass (MM) 252 Da) to r = −0.99 (five-ring cata-condensed MM 278 Da). In the case of the smaller PAHs (MM ≤ 252 Da), most of the PAHs had a planar structure and provided a low correlation. In the case of larger PAHs (MM ≥ 278 Da), nonplanarity had a significant influence on the retention behavior and good correlation between retention and T was obtained for the MM 278 Da, MM 302 Da, MM 328 Da, and MM 378 Da isomer sets.

Qualitative characterization of SRM 1597a coal tar for polycyclic aromatic hydrocarbons and methyl-substituted derivatives via normal-phase liquid chromatography and gas chromatography/mass spectrometry

“…11-MeBaA is the one planar isomer to elute in F6, an expected behavior that confirms previously reported retention index ( log I ) data [26]. The largest number of MM 242 Da isomers were identified in F7 (13 total), which included the non-planar 4-Me and 5-MeChr isomers ( T = 5.01 Å and 5.28 Å, respectively).…”

“…S5b). Based on the retention behavior reported by Wilson et al [26], BcPhe and Nap elute in the NPLC fraction before BaA, TriPhe and Chr. The GC/MS chromatograms obtained for the cata -condensed MM 242 Da MePAH isomers in SRM 1597a, F6, F7, and F8 are shown in Fig.…”

“…For detailed characterization of specific PAH isomer groups, the coal tar sample has been fractionated by NPLC using a semi-preparative NH 2 column to isolate isomeric fractions of PAHs in previous studies [4, 5, 16]. A similar approach, based on extensive NPLC PAH retention data [26], was implemented in the present study prior to PAH determination by GC/MS using a recently developed 50% phenyl phase GC column (SLB-PAHms).…”

“…The largest number of MM 242 Da isomers were identified in F7 (13 total), which included the non-planar 4-Me and 5-MeChr isomers ( T = 5.01 Å and 5.28 Å, respectively). For no apparent reason, these two isomers are retained on the NH 2 phase slightly longer than the non-planar isomers in F6 [26]. The only three isomers for which no reference standards were available are 1-Me, 2-Me, and 12-MeNap.…”

“…In the current study, a NPLC fractionation procedure coupled with UV detection was developed based on retention data reported elsewhere for over 180 PAHs and MePAHs [26] and applied to a coal tar sample (SRM 1597a). The NPLC fractionation of SRM 1597a allowed for the identification of 72 PAHs and 56 MePAHs through comparison of GC retention data with pure reference standards.…”