Ion Source Mass Filter for TOFMS Saturation
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Solution Overview
Problem
Time-of-flight mass spectrometers (TOFMS) face saturation issues when used with high current ion sources, leading to interference from major compounds that overwhelm minor species, limiting analysis capabilities and detection limits due to the inability to filter out unwanted ions effectively.
Innovation Solution
A mass filter is designed to segment ions into narrow m/q bands, preventing saturation by selectively transmitting only desired ions to the TOFMS, while rejecting ions belonging to these bands, using a RF quadrupole ion guide and additional RF fields to resonate and eject unwanted ions, thus maintaining broad-band analysis capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high current ion source is used to increase ion flux, then productivity is improved, but saturation effects occur in the TOFMS detection system
Solution Approach 1:
The mass spectrum is segmented into multiple windows, each covering a specific mass range. The detector is read out in multiple steps, with each step capturing ions within a particular mass window. This segmentation allows the system to handle high ion flux by distributing the detection load across multiple time steps and mass ranges, preventing saturation in any single detection channel.
2Speed
If TOFMS accepts the whole mass range simultaneously, then analysis speed is improved, but saturation effects from major compounds occur
Solution Approach 1:
The detector readout is performed periodically in multiple steps, with each step focused on a specific mass window. The system cycles through different mass ranges in a periodic manner, allowing high ion flux to be handled by distributing detections across multiple time periods. This maintains fast analysis by avoiding the need to sequentially scan the entire mass range, while preventing saturation by focusing each periodic step on a limited mass range.
3Reliability
If ADC DAQ systems are used to increase dynamic range, then saturation resistance is improved, but device complexity increases
Solution Approach 1:
The detection process is segmented into multiple readout steps, each handling a specific portion of the mass spectrum. This segmentation allows the use of simpler ADC systems for each individual step, as each step deals with a limited dynamic range corresponding to its specific mass window. The overall high dynamic range is achieved through the combination of multiple simpler detection steps rather than requiring a single complex high-capacity ADC system.
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 solution allows for precise detection of minor species without saturation, enhancing measurement statistics and reducing background noise, enabling accurate analysis of minor compounds in the presence of major components across various applications.
Implementation Method 1
a filter for segmenting incoming ions according to their m/q ratio into a first group of ions and into a second group of ions
Implementation Method 2
a time-of-flight mass spectrometer for analysis of transmitted ions
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~6
AI summary
An apparatus for mass analysis of ions comprises a high current ion source (10), in particular an ion source providing at least 5 million ions/s, preferably at least 50 million ions/s, at an output of the ion source, a time-of-flight mass spectrometer (40) for analysis of ions transmitted from the ion source (10) and a filter (20) for segmenting incoming ions according to their m/q ratio into a first group of ions and into a second group of ions. The filter (20) is coupled to the ion source (10) and the filter (20) and the time-of-flight mass spectrometer are arranged in such a way that the ions of the first group are transmitted to the mass spectrometer (40) and that the ions of the second group are not transmitted to the mass spectrometer (40). Furthermore, the filter (20) is designed in such a way that the second group consists of ions belonging to one or several narrow bands of m/q. The apparatus allows for analyzing minor compound ions generated by the high current ion source (10) with good selectivity, undisturbed by major compounds.