Application of reversed phase liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry to the determination of polycyclic aromatic sulfur heterocycles in environmental samples

Abstract

Reversed-phase liquid chromatography (RPLC) was combined with atmospheric pressure chemical ionization mass spectrometry (APCI-MS), via a heated pneumatic nebulizer interface, for the determination of the polycyclic aromatic sulfur heterocycle (PASH) content of samples obtained by the fractionation of an extract of a pond sediment contaminated by coke-oven residues. Some of the samples produced by the fractionation procedure contained large amounts of other polycyclic aromatic compounds (PACs) which co-eluted with the compounds of interest, making it difficult to obtain mass spectra suitable for compound identification and verification. Therefore, the use of tandem mass spectrometry (MS/MS), as a selective method for the identification of target analytes in complex matrices, was investigated. Initially, PASH standards were injected into the mass spectrometric system by flow injection and their collisionally induced dissociation mass spectra recorded. From these results, it was possible to select ions suitable for selected reaction monitoring (SRM) experiments on both the PASH standards (to establish detection limits and also retention times which could be used to identify these compounds) and the fractions (to establish the possible presence of the selected PASHs in the fractions). The RPLCSRM experiments led to a tentative identification of some of the PASH standards in the fractions. However, the use of multiple reaction monitoring experiments allowed the positive identification of dibenzothiophene, phenanthrol4,5-bcdl thiophene, phenanthro [3,4-b] thiophene and benzo [ bl naphthol 2,341 thiophene in the fractions, along with several of their isomers. Quantification of the PASH standards by RPLC-SRM in the extracts found them to be present at high levels.

Isomeric identification and quantification of polycyclic aromatic hydrocarbons in environmental samples by liquid chromatography tandem mass spectrometry using a high pressure quadrupole collision cell

“…To date there has been no study, to our knowledge, that employed APCI-LC/MS/MS for PAH analysis, although Thomas et al 28 have employed APCI-LC/MS/MS for analysis of polycyclic aromatic sulfur heterocycles. Most of the MS/MS studies referred to above employed gas chromatography coupled to mass spectrometry.…”

Fragmentation pathways of some benzothiophene radical cations formed by atmospheric pressure chemical ionisation

“…For the more volatile PASHs, gas chromatography (GC) is often employed in conjunction with electron ionization (EI) or chemical ionization (CI) MS 1, 4–6. High‐performance liquid chromatography (HPLC), although in normal usage not providing the resolution of capillary GC, is employed for non‐volatile compounds 7–10. Certain PAHs have the same nominal masses as PASHs and, if unresolved chromatographically, will interfere in the determination of PASHs, unless a mass spectrometer with very high resolving power is used 11–13.…”

“…For systems with lower resolution mass spectrometric detectors, MS/MS can often be employed to differentiate PASHs from PAHs. In this regard, product‐ion scans have been employed to identify specific PASHs 7, 8, 10, 14, 15…”

“…Subsequently, most work has involved the use of atmospheric pressure chemical ionization (APCI), with one study reporting the observation of only molecular ions,9 while others reported both molecular ions and protonated molecules, with protonation becoming more important as the number of rings in the analyte increased 10. This behavior has also been observed with PAHs 22.…”

“…from the molecular ion is often observed and is more common with alkylated PASHs and PASHs with more than three rings 7, 8, 10, 21. Losses of S (32 u)8, 10, 14 and CHS . (45 u)10, 14 from the molecular ion have been noted.…”