Harmonic Trapping ICR Cells for Ultrahigh Mass Resolution
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Solution Overview
Problem
Ion cyclotron resonance mass spectrometers face a dilemma in generating an ideal harmonic potential distribution while maintaining the excitation of axially extended ion clouds in an extended dipolar field of good axial uniformity, limiting the duration and accuracy of mass spectra acquisition.
Innovation Solution
The design incorporates four rectangular sheath electrodes with resistive layers of changing resistance, combined with rotationally hyperbolic endcap electrodes, to create a harmonic trapping field that reaches up to the walls of the ICR cell, allowing for extended dipolar excitation and improved ion cloud coherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional cylindrical ICR cells with constant-width electrodes are used, then the structure is simple and easy to manufacture, but the potential distribution is not harmonic and transient duration is limited to a few seconds
Solution Approach 1:
The electrode width varies along the axial direction, with narrower width at the center and wider width at the ends. This non-uniform local geometry creates a harmonic potential distribution that extends transient duration from seconds to minutes, while maintaining a relatively simple cylindrical overall structure
Solution Approach 2:
The electrode dimensions are made dynamic along the axial direction rather than constant. The varying electrode width creates different potential gradients at different axial positions, establishing a harmonic trapping potential that significantly extends ion cloud coherence time
2Measurement precision
If the magnetic field strength is increased to improve mass resolution, then mass resolution improves, but the device complexity and cost increase due to stronger superconducting magnets
Solution Approach 1:
The invention changes the electrical parameters of the ICR cell by implementing non-uniform electrode width and varying trapping potentials along the axial direction. This creates a harmonic potential distribution that extends transient duration, allowing high mass resolution to be achieved with lower magnetic field strengths, thereby reducing magnet system complexity and cost
3Measurement precision
If longer transients are achieved through improved potential distribution, then mass resolution improves, but the electrode manufacturing precision requirements increase
Solution Approach 1:
The electrode width varies continuously or in controlled steps along the axial direction, creating a gradient structure. This local variation in geometry generates the harmonic potential distribution needed for long transients. The manufacturing complexity is localized to the electrode shaping process rather than requiring ultra-precise positioning of multiple components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enables ion clouds to maintain coherence for longer periods, resulting in transients that can last minutes, achieving high mass resolution and accuracy, with mass resolutions exceeding 22 million and improved mass accuracy compared to previous ICR mass spectrometers.
Implementation Method 1
four rectangular sheath electrodes with resistive layers of changing resistance
Implementation Method 2
create a harmonic trapping field that reaches up to the walls of the ICR cell
Implementation Method 3
The two other longitudinal longitudinal electrodes serve to measure the orbiting of the ion clouds by their image currents, which are induced in the electrodes as the ion clouds fly past
Implementation Method 4
which are positioned in a homogenous magnetic field of high field strength
Implementation Method 5
In ion cyclotron resonance mass spectrometers (ICR-MS), the charge-related masses m/z of the ions are measured by means of the frequencies of the orbital motions of clouds of coherently flying ions
Data Source
Figure 1~4
Figure 5~7
Figure 8~9
AI summary
The invention relates to devices and methods for the acquisition of mass spectra with very high mass resolution in ion cyclotron resonance mass spectrometers and methods to produce the devices. The invention presents cylindrical ICR measuring cells with special electrode geometries to generate harmonic trapping potentials for orbiting ions up to the walls of the cell. Only a single DC trapping voltage has to be applied to create the harmonic trapping potential distribution. The sheath of the cylindrical cell is divided by longitudinal gaps into a multitude of sheath electrodes, which either have to carry layers with resistance profiles able to generate parabolic voltage profiles along the sheath electrodes, or which form sheath electrodes of varying width by parabolic gaps, able to create complicated potential distributions which are harmonic on average for orbiting ions. Orbiting ions of a given mass m/z can oscillate harmonically in axial direction with exactly the same oscillation frequency, independent of the radius of their orbit and of their axial osci llation amplitude. Ideally, the cylinders are closed by endcaps with rotationally hyperbolic form, divided into partial electrodes like in infinity cells. The ions can then be excited to their cyclotron motions by dipolar excitation fields also uniformly filling the ICR cell up to the endcaps. The ion clouds orbiting on their cyclotron trajectory are kept together for much longer periods than was possible hitherto, even if they orbit near the sheath electrodes. The image currents thus give rise to minute-long transients, from which mass spectra with ultrahigh mass resolution can be obtained.