Multipole Ion Guide With Radially Varying Axial Force
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Solution Overview
Problem
Mass spectrometers face challenges in controlling the axial location of ions and achieving efficient mass-selective axial ejection, particularly in systems where the axial force generated by quadrupolar DC increases quadratically with radial position, leading to compromised mass resolution and ion dispersion.
Innovation Solution
A method and apparatus that utilize a rod set with a varying RF field along its length to provide a positive axial force that increases with radial displacement, counterbalanced by a secondary axial force, allowing for precise axial positioning and ejection of ions by varying the RF amplitude and using segmented or tapered electrodes to control ion motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a quadrupolar DC field is used to provide axial force in a mass spectrometer, then axial force is generated to move ions, but the axial force increases quadratically with radial position causing ion dispersion and compromised mass resolution
Solution Approach 1:
The patent applies local quality by making the axial force field radially dependent, where ions at different radial positions experience different axial force strengths. This is achieved through specifically designed electrode geometries (tapered or curved surfaces) that create a non-uniform electric field, allowing selective axial ejection of ions based on their radial position while maintaining mass resolution through controlled force gradients
2Productivity
If ions are radially displaced to enable axial ejection, then axial ejection efficiency is improved, but ion dispersion increases and mass resolution is compromised
Solution Approach 1:
The patent employs dynamics by using time-varying RF fields in combination with the static axial field to dynamically control ion motion. The RF field provides radial confinement while the axially varying field enables selective axial ejection, allowing ions to be manipulated in a controlled manner that maintains both ejection efficiency and mass resolution through dynamic field modulation
3Force
If a uniform RF field is used for radial ion confinement, then radial confinement is achieved, but axial positioning control is limited
Solution Approach 1:
The patent applies segmentation by dividing the rod set into multiple segments along the axial direction, with each segment capable of independent voltage control. This segmentation allows creation of axially varying electric fields that provide both radial confinement and controlled axial positioning, enabling precise manipulation of ion locations along the axial direction while maintaining radial confinement
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 efficient axial ejection of ions with improved mass resolution and reduced ion dispersion, allowing for the concentration of thermalized ions at the entrance end and the ejection of ions with higher radial amplitudes towards the exit, while maintaining high mass resolution.
Implementation Method 1
producing an RF field between the plurality of rods to radially confine the ions in the rod set
Implementation Method 2
The axial force generated by quadrupolar DC increases quadratically with radial position
Implementation Method 3
providing an axial electric field whose strength increases with radial position
Implementation Method 4
provide, for each of the ions, a corresponding first axial force acting on the ion to push the ion in a first axial direction
Data Source
AI summary
A mass spectrometer having an elongated rod set, the rod set having a first end, a second end, a plurality of rods and a central longitudinal axis is described as is a method operating same. Embodiments involve a) admitting ions into the rod set; b) producing an RF field between the plurality of rods to radially confine the ions in the rod set, wherein the RF field varies along at least a portion of a length of the rod set to provide, for each of the ions, a corresponding first axial force acting on the ion to push the ion in a first axial direction; and, c) for each of the ions, providing a corresponding second axial force to push the ion in a second axial direction opposite to the first axial direction; wherein the corresponding first axial force increases relative to the corresponding second axial force with radial displacement of the ion from the central longitudinal axis in any direction orthogonal to the central longitudinal axis such that the first corresponding axial force is less than the corresponding second axial force when the ion is less than a threshold radial distance from the central longitudinal axis and the corresponding first axial force exceeds the corresponding second axial force when the ion is radially displaced from the central longitudinal axis by more than the threshold radial distance in any direction orthogonal to the central longitudinal axis.