AC-Only Mass Filter Staging to Reduce Quadrupole Contamination
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Solution Overview
Problem
Existing mass filters, particularly quadrupole mass filters, suffer from rapid contamination and degradation due to ions impacting and charging up on the electrodes, leading to reduced performance and mass resolution.
Innovation Solution
Implementing an AC-only mass filter upstream of a resolving mass filter to radially confine and excite ions, using multiple AC voltages to spread contamination over a larger area and reduce the rate of electrode contamination, while selectively transmitting ions based on mass-to-charge ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a quadrupole mass filter is used to selectively transmit ions, then mass filtering capability is improved, but electrode contamination and charge build-up increase over time
Solution Approach 1:
The system is divided into two separate mass filter stages: a first mass filter (Q1) that performs initial ion filtering, and a second mass filter (Q2) that performs final mass analysis. By segmenting the filtering process, the first filter captures the majority of contaminating ions before they reach the second filter, thereby protecting the second filter's electrodes from rapid contamination while maintaining overall mass filtering capability
Solution Approach 2:
The first mass filter acts as an intermediary component between the ion source and the second mass filter. It serves as a protective barrier that attenuates the ion flux reaching the second filter, reducing the rate of contamination on the second filter's electrodes while allowing desired ions to pass through for analysis
2Object-affected harmful factors
If a low resolution quadrupole mass filter is placed upstream of the main analytical quadrupole, then contamination of the main analytical quadrupole is reduced, but the upstream filter itself becomes contaminated quickly
Solution Approach 1:
Different operational modes are applied to different stages: the first mass filter operates in a scanning mode with varying RF and DC voltages to filter different mass ranges, while the second mass filter operates in a fixed mode optimized for high-resolution analysis. This local differentiation allows the first filter to handle diverse ion populations, spreading contamination across its electrodes, while the second filter maintains optimal performance
3Adaptability or versatility
If multiple AC voltages are applied to radially excite ions in the first mass filter, then ion transmission control is improved, but device complexity increases
Solution Approach 1:
The system applies periodic AC voltages at specific frequencies (including the secular frequency of ion motion) to radially excite selected ions in the first mass filter. This periodic excitation causes unwanted ions to be ejected from the stable region, providing precise control over which ions are transmitted to the second filter while using well-established frequency modulation techniques
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
The AC-only mass filter significantly reduces the rate of contamination on the downstream resolving mass filter by distributing ion impacts over a larger area, maintaining filter performance and resolution over time.
Implementation Method 1
applying a first AC voltage to electrodes of the first mass filter so as to radially confine ions between the electrodes
Implementation Method 2
applying at least one second AC voltage between electrodes of the first mass filter so as to radially excite some of said ions
Data Source
Figure 1~2
Figure 3A~3D
Figure 4~5
AI summary
A method of mass filtering ions is disclosed comprising: providing a first, AC-only, mass filter (2); providing a second mass filter (4) downstream of the first mass filter; applying a first AC voltage (8) to electrodes of the first mass filter so as to radially confine ions between the electrodes, and applying a second AC voltage (10) between electrodes of the first mass filter (2) so as to radially excite some of said ions such that these ions are not transmitted; and using the second mass filter (4) to mass filter ions; wherein at any given time the second mass filter (4) only transmits ions having a first range of mass to charge ratios and filters out all other ions; and wherein the step of applying the at least one second AC voltage (10) to electrodes of the first mass filter (2) radially excites ions such that at least some ions having mass to charge ratios above said first range are not transmitted into the second mass filter.