Multipole Collision Cell Field Zoning for Ion Focusing and Clear-Out
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Tandem mass spectrometers face issues with ion focusing due to the slowing of ion velocities in collision cells, leading to ion drainage and reduced sensitivity, which necessitates pause times between measurements, increasing instrument complexity and cost.
Innovation Solution
A multipole ion guide device with a combination of RF-only and DC axial fields along different portions of its length, allowing ions to be focused radially inward during RF-only exposure and then moved axially through a DC axial field, reducing ion loss and improving transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas is used in the collision cell for collisional focusing, then ion velocity is reduced and ions become focused near the longitudinal axis, but ion drainage slows down and clear-out time increases
Solution Approach 1:
The patent applies dynamic control of ion velocity by switching between two operational modes: a first mode during ion introduction where ions are slowed for focusing, and a second mode during ion extraction where ions are accelerated for rapid drainage. This dynamic adjustment resolves the contradiction between achieving collisional focusing (requiring slow ions) and achieving rapid ion clear-out (requiring fast ions).
Solution Approach 2:
The patent implements periodic switching between different ion velocity regimes. During the measurement phase, ions are decelerated to enable collisional focusing and improved mass resolution. During the inter-measurement phase, ions are accelerated to enable rapid clear-out and prevent chromatogram tailing. This periodic alternation between opposing velocity states resolves the time-resolution contradiction.
2Speed
If DC axial field is applied throughout the collision cell, then ions are moved axially through the cell, but ions drift away from the longitudinal axis and focus is lost
Solution Approach 1:
The patent segments the collision cell into distinct functional zones: a first region where DC axial field is applied for rapid ion transport, and a second region where only RF fields are applied for ion focusing without axial drift. This spatial segmentation allows simultaneous optimization of both axial transport speed and ion focusing precision in different regions of the same device.
Solution Approach 2:
The patent applies different field characteristics to different spatial locations within the collision cell. The DC axial field is localized to specific regions where rapid ion transport is needed, while RF-only regions are provided where ion focusing is the primary objective. This local differentiation of field quality resolves the contradiction between axial transport and focusing.
3Measurement precision
If ion velocity is reduced for collisional focusing, then mass resolution improves, but productivity decreases due to required pause times
Solution Approach 1:
The patent employs periodic switching between measurement mode (low ion velocity for high resolution) and inter-measurement mode (high ion velocity for rapid clear-out). This periodic alternation eliminates the need for extended pause times between measurements, thereby maintaining high productivity while achieving high mass resolution during the measurement phase.
Solution Approach 2:
The patent ensures continuous ion flow through the system by rapidly accelerating ions during inter-measurement intervals to prevent accumulation and chromatogram tailing. This continuous action eliminates idle pause times, maintaining productivity while allowing high-resolution measurements to occur during designated measurement windows.
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 enhances ion transmission and reduces ion loss processes, leading to more consistent fragmentation spectra and improved sensitivity without the need for complex alignment and additional focusing elements, thus increasing instrument productivity and reducing costs.
Implementation Method 1
exposing the at least some of the ions to an RF-only field extending along a first portion of the length
Implementation Method 2
exposing the at least some of the ions to a DC axial field extending along a second portion of the length
Implementation Method 3
Collisions between the gas and the ions cause the velocities of the ions to be reduced and the ions become focused near the longitudinal axis
Data Source
AI summary
A multipole ion guide includes a plurality of electrodes disposed about a longitudinal axis of the device so as to define an ion transmission volume for transmitting ions along a length of the device between opposite inlet and outlet ends. An electronic controller is operably connected to an RF power source and to at least some of the electrodes and is configured to apply at least an RF potential to the electrodes. During use the electrodes generate an RF-only field along a first portion of the device and an axial DC field along a second portion of the device. Ions are focused radially inward toward the longitudinal axis of the device by the RF-only field within the first portion of the device prior to and/or subsequent to experiencing the axial DC field within the second portion of the device.