Photodissociation Dynamics of <i>n</i>-Butylbenzene Molecular Ion

Oh, Seong Tae; Choe, Joong Chul; Kim, Myoung Soo

doi:10.1021/jp9605818

Cited by 36 publications

(90 citation statements)

References 35 publications

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“…In order to obtain better insight into the energetics of CID during mass acquisition the n‐butylbenzene molecular ion at 134 Th was used as a precursor ‘thermometer’ ion. The fragmentation behavior of n‐butylbenzene has been extensively studied and the fragmentation pathways and thermodynamics are well known 10, 11, 15, 16, 21, 22, 27, 31, 46–53. By observing the ratios of product ions at 91 and 92 Th the new fragmentation method is shown to provide comparable information to on‐resonance excitation with several noteworthy benefits: (1) on‐resonance conditions are guaranteed without any prior tuning or calibration and (2) significant time savings are possible in the new approach because no extra scan events are required other than ionization, isolation and mass acquisition periods.…”

mentioning

confidence: 99%

Energetics and efficiencies of collision‐induced dissociation achieved during the mass acquisition scan in a quadrupole ion trap

Jackson

Hyland

Laskay

2005

Rapid Comm Mass Spectrometry

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Using n-butylbenzene as a test molecule, evidence is provided that fast, efficient or highly energetic collision-induced dissociation (CID) can be achieved during the mass acquisition ramp of a commercially available quadrupole ion trap (QIT) mass spectrometer. The method of excitation is very similar to axial modulation for mass range extension except that lower amplitude waveforms are used to excite the precursor ions within the trap instead of ejecting them from the trap. ITSIM simulations verify that fast kinetic excitation followed by kinetic-to-internal energy transfer occurs on the rapid time-scale required for the recapture and mass analysis of product ions during the mass acquisition ramp. CID efficiencies larger than 50% can be obtained using this new approach and ratios of Th 91/92 of n-butylbenzene fragment ions as large as 9 are possible, albeit at significantly reduced efficiencies. These very large ratios indicate an internal energy above 7 eV for the precursor ions indicating that fragmentation of larger ions could also be possible using this new approach. The main benefits of the new method are that no extra time is required for fragmentation or cooling and that on-resonance conditions are guaranteed because the ions' secular frequencies are swept through the fixed frequency of excitation. Also presented are the effects of experimental variables such as excitation frequency, excitation amplitude and scan rate on the CID efficiencies and energetics. Copyright # 2005 John Wiley & Sons, Ltd.Quadrupole ion traps (QITs) are widely recognized for their flexibility and sensitivity in accomplishing tandem mass spectrometry (MS/MS), which is an invaluable tool for the quantitative, qualitative and mechanistic interrogation of gas-phase ions.1,2 The ability to perform MS/MS is important because it is a central technology for proteomics 3,4 and applications such as drug/metabolite monitoring and forensic sciences. 1,5,6 Most applications of MS/MS rely on the ability to obtain reproducible and reliable fragmentation spectra from selected precursor ions in order to match database entries or to make other dependable conclusions based on the fragmentation spectra. However, faster and more complex separation technologies are being developed that demand MS/MS spectra to be obtained more quickly and on smaller sample sizes than is favorable for reliable on-resonance excitation to be performed. These new demands require fresh approaches for achieving MS/MS while, if possible, not adding to the complexity or cost of the instrumentation.On-resonance excitation using supplemental alternating current (ac)-waveforms applied to the end-cap electrodes has been the most widely used approach for achieving collisional activation of selected precursor ions. This method of fragmentation is available on almost all modern commercially available instruments and has been extremely well characterized. For example, the performance of on-resonance excitation has been found to be dependent on a number of experimental variables includi...

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confidence: 99%

Energetics and efficiencies of collision‐induced dissociation achieved during the mass acquisition scan in a quadrupole ion trap

Jackson

Hyland

Laskay

2005

Rapid Comm Mass Spectrometry

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“… The study of the major MS fragmentations of these carbonyl derivatives, however, has not received due attention. For example, although the McLafferty rearrangement of carbonyl compounds has been the focus of extensive and continuous research , studies on oximes and silyl oxime ethers have been limited. Surprisingly, to date, only one article has reported the McLafferty rearrangement for ketoximes.…”

Section: Introductionmentioning

confidence: 99%

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

et al. 2012

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The McLafferty rearrangement is an extensively studied fragmentation reaction for the odd-electron positive ions from a diverse range of functional groups and molecules. Here, we present experimental and theoretical results of 12 model compounds that were synthesized and investigated by GC-TOF MS and density functional theory calculations. These compounds consisted of three main groups: carbonyls, oximes and silyl oxime ethers. In all electron ionization mass spectra, the fragment ions that could be attributed to the occurrence of a McLafferty rearrangement were observed. For t-butyldimethylsilyl oxime ethers with oxygen in a β-position, the McLafferty rearrangement was accompanied by loss of the t-butyl radical. The various mass spectra showed that the McLafferty rearrangement is relatively enhanced compared with other primary fragmentation reactions by the following factors: oxime versus carbonyl, oxygen versus methylene at the β-position and ketone versus aldehyde. Calculations predict that the stepwise mechanism is favored over the concerted mechanism for all but one compound. For carbonyl compounds, C–C bond breaking was the rate-determining step. However, for both the oximes and t-butyldimethylsilyl oxime ethers with oxygen at the β-position, the hydrogen transfer step was rate limiting, whereas with a CH2 group at the β-position, the C–C bond breaking was again rate determining. n-Propoxy-acetaldehyde, bearing an oxygen atom at the β-position, is the only case that was predicted to proceed through a concerted mechanism. The synthesized oximes exist as both the (E)- and (Z)-isomers, and these were separable by GC. In the mass spectra of the two isomers, fragment ions that were generated by the McLafferty rearrangement were observed. Finally, fragment ions corresponding to the McLafferty reverse charge rearrangement were observed for all compounds at varying relative ion intensities compared with the conventional McLafferty rearrangement.

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“…In general the following trend appears to apply. Toluene ion fragmentation leads to a mixture of Trop + and Bz + ions, with the ratio depending on the internal energy of the toluene ions, whereas larger alkyl benzenes (ethyl- [1,9], propyl- [10,11] and butyl-benzene [12]) predominantly lead to Bz + ions (>80%).…”

Section: Introductionmentioning

confidence: 99%

Formation of C7H7+ ions from ethylbenzene and o-xylene ions: Fragmentation versus isomerization

Schulze

Paul

Weitzel

2006

International Journal of Mass Spectrometry

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Photodissociation Dynamics of n-Butylbenzene Molecular Ion

Cited by 36 publications

References 35 publications

Energetics and efficiencies of collision‐induced dissociation achieved during the mass acquisition scan in a quadrupole ion trap

Energetics and efficiencies of collision‐induced dissociation achieved during the mass acquisition scan in a quadrupole ion trap

Fragmentation of oxime and silyl oxime ether odd‐electron positive ions by the McLafferty rearrangement: new insights on structural factors that promote α,β fragmentation

Formation of C7H7+ ions from ethylbenzene and o-xylene ions: Fragmentation versus isomerization

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