Dipolar and quadrupolar detection using an FT-ICR MS setup at the MPIK Heidelberg

Abstract

Dipolar and single-phase two-electrode quadrupolar detection schemes have been investigated at a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) setup built for the KATRIN experiment at the Max-Planck-Institute for Nuclear Physics (MPIK) in Heidelberg. We present first experimental results of ⁷Li⁺ signals from a cylindrical Penning trap configuration for both detection schemes. While the prominent signal of the conventional dipolar detection scheme marks the reduced cyclotron frequency, the main signal for the quadrupolar detection appears at the sum of the reduced cyclotron frequency and the magnetron frequency. For ideal trapping fields, this sum frequency equals the ion cyclotron frequency ν c = qB/(2πm). Sidebands due to the combined motions of the cyclotron mode and magnetron mode are observed by quadrupolar detection which allows the determination of the respective combinations of eigenfrequencies

Narrow Aperture Detection Electrodes ICR Cell with Quadrupolar Ion Detection for FT-ICR MS at the Cyclotron Frequency

“…However, the implemented ICR cells remained limited to serving particular questions of authors' interests in precision mass spectrometry of atomic ions. 41 Performance-wise, the reported mass (frequency) spectra demonstrated a visible contribution from the second harmonic of the reduced cyclotron frequency.…”

Ion Trap with Narrow Aperture Detection Electrodes for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Interestingly, flat (wide aperture) excitation electrodes (capacitor configuration) may be considered to provide an optimum excitation field configuration; (2) simultaneous detection of a number of transients or detection at frequency multiples when several NADEL pairs are employed, for instance leading to an optimized design of the recently implemented quadruple frequency multiple detection ICR cell [36]; (3) enabling implementation of efficient quadrature ion excitation and quadrupolar ion detection schemes when two pairs of 90°wide excite electrodes and two NADEL pairs are employed without the need for a high-frequency switch between excitation and detection modes. Quadrupolar ion detection should further benefit high mass accuracy and high dynamic range demanding applications by providing measurements of trapping potential-insensitive unperturbed ion cyclotron frequency [23,55]; (4) creation of special ion motion conditions in ICR cell even with dipolar ion excitation leading to ion detection at unperturbed cyclotron frequency [56]; (5) facilitating and improving the efficiency of fluorescence-based ion spectroscopy due to substantially increased optical access to and from the cell [57][58][59]; and, last but not least, (6) enabling high throughput high-resolution mass spectrometry by accelerating ions to high post-excitation radii when, significantly, an order of magnitude higher resolving power can be obtained in the same ion detection period. The latter regime requires the development of the matching signal processing methods, capable of efficient analysis of periodic non-sinusoidal transients with high order harmonics [60].…”

“…Quadrupolar modes of ion excitation, including the quadrature excitation, are other attractive approaches for improving the coherence of excited ion motion [20][21][22][23]. ICR cell operation in these modes also suffers from the same low flexibility of the current ICR cell design, when wide aperture detection electrodes compete with the excitation electrodes for space.…”

One- and two-pulse quadrupolar excitation schemes of the ion motion in a Penning trap investigated with FT-ICR detection

“…A detailed description can be found in Refs. [30,31]. The trap is placed in an ultra-high vacuum system, i.e.…”

“…(a) Schematic view of the FT-ICR setup[30,31]. The Penning trap is placed in a homogeneous region of the magnetic field.…”