Multipole Ion Ejection via RF Phase Gradient
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Solution Overview
Problem
Existing multipole devices in mass spectrometers face challenges in controlling ion movement and storage, especially with large numbers of ions or those having a wide range of m/z ratios, due to poor homogeneity of DC potential and adverse effects from space charge, which complicates selective axial ejection.
Innovation Solution
A mechanism involving a multipole device with main and auxiliary rod electrodes, where RF and DC voltages are applied to create a balanced axial DC field, allowing for mass-selective excitation and axial ejection of ions by increasing their radial extents and moving them along the multipole length, decoupling them from initial mass distribution and reducing space charge effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If auxiliary rods are implemented in RF-only multipoles to generate axial DC field, then ion propulsion along the longitudinal axis is improved, but device complexity and operation complexity increase
Solution Approach 1:
The patent removes auxiliary rods from the multipole structure, extracting the complicating element while preserving the essential function of ion propulsion through simplified RF voltage application to standard multipole rods
Solution Approach 2:
The multipole rods serve dual functions: generating the RF field for radial ion confinement and creating the axial DC field gradient for ion propulsion, eliminating the need for separate auxiliary rods
2Ease of operation
If auxiliary rods are used to create axial DC potential gradient, then ion movement control is improved, but DC potential homogeneity deteriorates
Solution Approach 1:
The patent eliminates auxiliary rods that created non-uniform DC potential distributions, removing the source of potential inhomogeneity while maintaining ion movement control through RF-driven mechanisms
Solution Approach 2:
The patent changes the operational parameters by applying RF voltages with different phases to adjacent rod pairs, dynamically creating axial field gradients without the structural complexity and potential non-uniformity of auxiliary rod configurations
3Quantity of substance
If large numbers of ions with wide m/z range are stored, then ion storage capacity increases, but space charge effects and separation efficiency worsen
Solution Approach 1:
The patent employs dynamic RF voltage modulation to actively manage ion distributions, allowing large ion populations to be stored and manipulated without the static field limitations that cause space charge degradation of separation precision
Solution Approach 2:
The patent applies different RF voltage phases to adjacent rod pairs, creating segmented control regions along the multipole axis that enable independent manipulation of ion populations with different m/z ratios, thereby maintaining separation precision despite high ion densities
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 approach enables greater ion selectivity and storage capacity while maintaining effective m/z separation, allowing for controlled axial ejection and movement of ions along the entire multipole length, reducing space charge interference and increasing the charge capacity of the mass analyzer.
Implementation Method 1
A radio-frequency (RF) voltage is applied to opposed rod pairs to generate an RF field which confines the ions radially and prevents ion loss arising from collision with the rods
Implementation Method 2
Generation of the axial DC field is commonly achieved by using segmented RF-only multipoles with variable DC offset voltages between segments; an axial DC potential gradient is created by applying a first voltage to corresponding first ends of the auxiliary rods and a second voltage to corresponding second (opposite) rod ends
Implementation Method 3
The excitation voltage source is for applying an excitation voltage to mass-selectively excite ions in the multipole interior such that radial extents of trajectories of the excited ions are increased
Implementation Method 4
A mechanism is provided that overcomes the negative space charge effects and enables resonance excitation of preselected ions. Resonance excitation of preselected ions of a desired m/z is achieved by a combination of fields for manipulating the ions
Data Source
AI summary
A mass spectrometer includes a multipole having a main RF field for radially containing ions generally on a central axis. The multipole has first and second axial DC fields in opposite first and second direction along a length of the multipole. The first and second axial DC fields approach or add substantially to zero on the central axis. The multipole has an excitation voltage applied thereto for selectively exciting the ions of desired m/z ratios off the central axis. The excitation voltage thus causes excursion of the ions into a region where either the first or second axial DC field is strong. Thus, excitation of the ions and the DC fields cause ion drift toward a front end or a back end of the multipole. Further excitation moves the ions into regions of the DC fields that overcome barriers and causes axial ejection of the ions from the multipole.