A new technique for decomposition of selected ions in molecule ion reactor coupled with ortho-time-of-flight mass spectrometry

Abstract

A molecule ion reactor (MIR), i.e. a gas filled radio-frequency only quadrupole with a longitudinal electrical field (RFQLEF), is used as an atmospheric pressure ionization interface for an orthogonal time-of-flight mass spectrometer (O-TOFMS). A new phenomenon of selective ion 'heating' in a MIR near Mathieu's instability threshold was found and confirmed by computer simulation. The 'heating' in collisions with buffer gas molecules leads to ion decomposition. In the case of multicharged ions, fragments with an m/z value higher than that of the parent ion have a stable motion and can be analysed by an O-TOFMS. Fragmentation of bradykinin and beta-endorphin molecular ions having a selected charge state is demonstrated. The spectra show clear 'ladder' structure. The phenomenon may be used as an alternative to tandem mass spectrometry (MS/MS) for molecule structure analysis.

Ion trap mass analysis at high pressure: A theoretical view

“…The cooling of the ions to the center of the trap also helps to improve mass resolution and mass accuracy by minimizing the effects due to difference in initial conditions for the mass selective instability scan [8,25,26]. The fragmentation of the ions for tandem mass spectrometry also relies on their collisions with the buffer gas molecules, which can cause increased ion internal energies and lead to subsequent fragmentation [27][28][29][30][31]. For each of these steps, dedicated experimental conditions are used to reach a balance between providing adequate collision energies and minimally interfering with intentionally stable ion trajectories.…”

Characteristics of a rf-only hexapole ion-guide interface for plasma-source time-of-flight mass spectrometry

“…2 Szabo reports that higher q values (up to 1.7) can be used to define stability in a hexapole; 24 however, under these v conditions ion motion can couple with the rf field and increase its energy. 38 In the rf-only mode, the Mathieu stability parameter a is ordinarily set to zero and the ion motion is dependent only upon q. Higher-order n-poles have diffuse stability regions in contrast to the well-defined zones of the quadrupole, 4,24,25 which challenges their understanding and use. Theoretical treatment of ion motion in these devices is beyond the scope of this paper but is addressed elsewhere.…”

Radial stratification of ions as a function of mass to charge ratio in collisional cooling radio frequency multipoles used as ion guides or ion traps

“…Another example involves the use of collisional cooling RF multipole ion guides to transmit ions from an intermediate pressure region of an ion source (e.g., an electrospray ionization interface) into a higher vacuum region of a mass analyzer. In this case, a considerable space charge can possibly be realized since the space charge is the major force driving the ions axially (unless an axial DC field is created by some means6–9). A special case of ion guides possessing significant pressure gradients and gas flows along the axis, which might create additional force for the axial motion of ions, was not considered; such gas flows may also prevent the collisional cooling from reaching completion, thus disturbing the stratified radial structure.…”