High‐energy collision‐induced dissociation of small polycyclic aromatic hydrocarbons

Abstract

High-energy collision-induced dissociation (CID) experiments on polycyclic aromatic hydrocarbons (PAHs)having 2-6 rings, naphthalene, anthracene, phenanthrene, fluoranthene, pyrene and coronene, were performed, and the relative abundances of their fragment ions were investigated as a function of collision energy. The results revealed that the PAHs except naphthalene showed a bimodal-type distribution of positive fragmentation ions, which is closely similar to the fragment-ion distribution reported for the CID of three-dimensional fullerene, C 60 Y and C 70 Y . The three-ring isomers of anthracene and phenanthrene and the four-ring isomers of fluoranthene and pyrene can be distingushable in their spectra under an electron ionization energy of 70 eV, but the high-energy CID spectra of the three-and four-ring isomers were almost identical. The fragmentation corresponding to fragment ions in the low-mass region of the bimodal CID spectra could be interpreted by the simple statistical model that fragment ions are formed by random evaporation from the molecular ions after a considerable structural rearrangement, 'phase transition', occuring at some high-energy state.

High-performance liquid chromatography/electrospray tandem mass spectrometry of polycyclic aromatic hydrocarbons

“…Increasing the collision energy leads to enhanced fragmentation, successive fragments resulting from the neutral loss by elimination of hydrocarbons and complex structural rearrangements. As observed by Arakawa et al 23, as well as with the collision induced dissociation (CID) of C 60 + and C 70 + fullerene24, the mass fragmentation distribution becomes bimodal when the collision energy reaches a certain level. This threshold varies with the PAH studied.…”

“…Arakawa et al reported recently23 some results of PAHs fragmentation obtained by electron ionisation (EI) and using a high‐energy collision cell on a magnetic electrostatic analyses (BE‐type) double focusing mass spectrometer, where they investigated the differentiation of isomers. The results presented here show that, using charge transfer from tropylium post‐column derivatisation, the comparatively soft ESI technique provides enough internal energy to the precursor ions to initiate fragmentation in the collision cell of a tandem quadrupole mass spectrometer and could therefore be used to differentiate isomers.…”

“…When the collision energy is set at the lowest value (25 eV), the [M − H] + deprotonated molecule predominates and very low levels of fragmentation are observed, mainly the loss of C 2 H 2 ( m/z 26). Slightly increasing the collision energy produces only high mass ions; however, following further increases the precursor ions carry sufficient internal energy to undergo additional fragmentation leading to fragments in the low mass region 23,. 24 Continually increasing the collision energy decreases the intensity of high mass fragment ions, while low range fragment ions increase in intensity.…”

“…[M − H] + , [M − C 1 H x ] + , [M − C 2 H x ] + ) and relative intensities of these fragments are very specific to each compound. Therefore, although it is beyond the scope of this preliminary paper, the ratio between the intensity of the peaks could be used to differentiate PAHs of identical molecular weight for example by using the calculation method proposed by Arakawa et al 23…”

“…This paper is the first report of tandem ESI‐MS to provide fragmentation patterns of PAHs, which potentially yields valuable structural information, allowing the identification of PAHs by mass spectrometry. Previous work has involved either APCI‐LC/MS/MS with a high‐pressure quadrupole collision cell13 or tandem electron impact EI‐MS23 for isomer determination or‐using HPLC/ESI‐MS to obtain only molecular ions 14,. 15 Additionally, manipulation of the collision energy is used to control the fragmentation patterns, which we propose is a valuable method for analysis of environmental extracts containing a mixture of such compounds.…”