Kinetic‐energy‐sensitive mass spectrometry for separation of different ions with the same m/z value

Abstract

A double-focusing mass spectrometer (MS) equipped with a superconducting-tunnel-junction (STJ) detector has been applied to measure relative ionization cross-sections for the production of ions that are accompanied by different ion species with the same mass-to-charge (m/z) value. The STJ detector fabricated for this study enables kinetic energy (E) measurement of incoming individual ions at a counting rate of up to approximately 100 k ions/s and an energy resolution (DeltaE/E) of 15%. Both high counting rate and high-energy resolution are necessary to independently determine both m and z and not the m/z value only in ion-counting MS experiments. Ions such as (14)N(2) (2+) and (14)N(+) with the same m/z value can be clearly discriminated using a kinetic-energy-sensitive MS. This fine discrimination capability allows direct determination of relative ionization cross-sections of the homonuclear diatomic ions (14)N(2) (2+)/(14)N(2) (+) and (16)O(2) (2+)/(16)O(2) (+), which are difficult to measure due to the strong interference by the signals of their dissociated atomic ions with noticeably large ionization cross-sections. The new instrument requires no low-abundance heteronuclear diatomic molecules of the forms (14)N(15)N or (16)O(17)O to carry out ionization studies and thus, is expected to be useful in fields such as atmospheric science, interstellar science, or plasma physics.

Fragmentation of14,15N2by electron impact investigated using a time-delayed spectroscopic technique

“…5, where the contribution from each distribution to the m/q = 14 or 15 products, relative to 14,15 N 2 + , are shown as a function of the electron energy. The measured ratios between the cross section associated with each of the energy distributions and the cross section of the parent molecule for ions with m/q = 14 and m/q = 15 are given in Tables I and II, [27,28] and with the homoisotopic 14 N 2 measurement of Shiki et al [16] at 70 eV, with very good general agreement. To the authors' knowledge, besides Ref.…”

“…To the authors' knowledge, besides Ref. [16], which uses a cryogenic detection system, there are no other previous measurements reporting the N 2 2+ /N 2 + ratio for homoisotopic species. For a consistency verification, the sum of all ratios (total) for 14 N 2 is compared to the single-coincidence measurements of Tian and Vidal [29], also showing very good agreement.…”

“…In the case of N 2 , the part of the KED corresponding to the most energetic ions has been measured by several authors using electrons and heavy ions as impinging particles, with fairly conclusive results of the main groups that make up the distribution [10][11][12][13][14][15]. For low-energy released ions (E 1.0 eV), the scenario is much poorer as the need to combine accurate detection efficiency, good energy resolution, and separation of ions with the same mass-to-charge ratio is not easily achieved using techniques associated with mass spectrometry [14,16]. N 2 2+ falls in this case because it is a stable ion with the same mass-to-charge ratio as N + and is produced at thermal energies.…”

Determination of Iron Content and Dispersity of Intact Ferritin by Superconducting Tunnel Junction Cryodetection Mass Spectrometry

“…44 A technical description and review of STJs may be found elsewhere. [45][46][47] Use of STJ detection at 1 MTh and higher have been reported for IgM (~1 MDa) 48 and polystyrene (~2 MDa) 49 50,51 Signal responses from a more typical ionizing detector, such as a microchannel plate (MCP) detector, coupled to a typical MALDI-TOF instrument would not achieve the S/N level required to be useful for most analyses at these high m/z.…”

Superconducting Molecule Detectors Overcoming Fundamental Limits of Conventional Mass Spectrometry

“…1 that the ions of C60 + and C60 ++ are clearly separated according to the deposited energies, which ensures that charge state discrimination for individual ions is possible. After eliminating the secondary peaks, the charge state discrimination enables separation of doubly-charged homonuclear diatomic molecule ions ( 14 N ++ 2 ) from singly-charged atomic ions ( 14 N + ) for the first time [10]. Both of 14 N ++ 2 and 14 N + have the same m/z of 14, so that any conventional MS instruments are unable to distinguish these two ionic species.…”