Mass spectrometry of polyaromatic sulfur compounds in the presence of palladium(II)

Abstract

Electrospray ionization mass spectrometry (ESI-MS) and tandem MS in an ion trap were used to explore the reduction of a PdCl(2) solution and the role of the metal in the formation of organosulfur radical cations. For tandem MS experiments, a 32 Da neutral loss (M - S), was observed for dibenzothiophene, thianthrene and benzonaphthothiophene, whereas both 32 and 33 Da neutral losses were observed for 2-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. The effects of several variables on the formation of molecular ions or molecular fragments were studied to optimize radical cation formation, including the concentration ratio between PdCl(2) and sulfur and the collision energy. Electrochemical and chromatographic data were used to provide an explanation for the relative sensitivity observed for a mixture of polyaromatic sulfur heterocycles.

Post‐source decay of alkylated and functionalized polycyclic aromatic compounds

“…4). Rudzinski et al 18. also demonstrated that sulfur appears to be more difficult to remove by collision‐induced dissociation (CID) in alkylated PASHs than in non‐alkylated PASHs.…”

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…”

“…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.…”

“…Wood et al reduced PASHs with calcium metal to thiols and used negative ion CI with isobutane to yield deprotonated molecules, [M–H] − 24. Others have added Pd(II) to solutions of PASHs and obtained molecular ions, rather than protonated molecules, using electrospray ionization (ESI) 8, 15. A novel approach to the ionization of PASHs involved their conversion into S‐methyl sulfonium salts using CH 3 I and AgBF 4 ,11, 13 which permitted direct analyses using ESI‐MS.…”