Experimental investigation of the molecular ions of the xylenes

Abstract

A m a s spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findings that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies than for methyl expulsion. These ditterences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadruple instrument). Though statistically significant, these Werences were small.The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.

Studying the fragmentation mechanism of selected components present in crude oil by collision‐induced dissociation mass spectrometry

“…This fragmentation seems to be enabled by the presence of a methyl group on the same ring and will be related to the loss of a methyl radical from xylene radical cations. 35 The formation of the fragment involves a proton-shift after ring-expansion, followed by expulsion of the propylphenyl radical, as depicted in Additionally, in both cases the complete removal of the side chain is observed as above. As this fragmentation is supposed to be related to xylene-type fragmentations (see above), we consider the fragment ion at m/z 309 as originating from isomer 8a, while the fragment at m/z 253 originates from isomer 8b.…”

“…4,6‐Dimethyl‐2‐(3‐phenylpropyl) DBT ( 6 , M = 330 Da) essentially behaves as the previous example but with an additional fragment peak for the complete removal of the phenylpropyl substituent ( m/z 211/212, see Figure S3, supporting information). This fragmentation seems to be enabled by the presence of a methyl group on the same ring and will be related to the loss of a methyl radical from xylene radical cations . The formation of the fragment involves a proton‐shift after ring‐expansion, followed by expulsion of the propylphenyl radical, as depicted in Scheme .…”

Distinguishing by Principal Component Analysis o-Xylene, m-Xylene, p-Xylene and Ethylbenzene Using Electron Ionization Mass Spectrometry

“…Some attempts were made in a number of studies to distinguish xylene isomers using only mass spectral data. [4][5][6][7][8][9][10][11] Different mass spectral techniques were used in these works (for example, self-ion molecule reactions in an ion trap mass spectrometer, 4,5 gas-phase reactions with metal ions in a Fourier transform mass spectrometer, 6,7 negative ion chemical ionization mass spectrometry, recording both single-stage and tandem mass spectra 8 and others). However, as far as we know, the possibility of distinguishing between o-, m-, p-xylene and ethylbenzene using only EI mass spectra is not mentioned in any publication.…”

From physical chemistry to mass spectrometry to government lab manager in half a century

“…The next graduate student who entrusted me with his future was Jonathan Curtis. Our first effort (Curtis et al, ) was a collaboration, with the Swansea group and with Bori at Sciex, that investigated mass spectrometric distinction among the xylene isomers using both high (keV) and low (tens of eV) collisional activation. But Jonathan's major contribution was to one of my obsessions that arose when I discovered a paper by Linus Pauling in the first issue of the Journal of Chemical Physics in 1933.…”