Ion Detector Grid for Mass Spectrometer Dynamic Range
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Solution Overview
Problem
Current ion detectors in mass spectrometers face limitations in linear dynamic range, particularly at high ion current intensities, due to saturation issues in secondary electron multipliers, amplifiers, and digitizers, which restrict the ability to accurately measure ion currents across a wide range of intensities, especially in high-resolution time-of-flight mass spectrometers.
Innovation Solution
The implementation of a grid-like detection element with high transmission, placed between or after microchannel plate stages, generates two signals with different amplifications, allowing for the measurement of image currents to extend the linear dynamic range by maintaining linearity even at high ion currents, without consuming electrons and reducing the overall multiplication factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary electron multipliers (SEM) with high amplification are used to detect low ion currents, then sensitivity is improved, but saturation occurs at high ion current intensities limiting the linear dynamic range
Solution Approach 1:
The detection process is segmented into multiple stages: a first SEM stage provides high amplification for sensitive detection of low ion currents, while a second SEM stage with lower amplification handles higher ion current intensities. This segmentation allows each stage to operate within its optimal linear range, collectively extending the overall linear dynamic range from 1:10^3 to 1:10^6 while maintaining detection sensitivity.
2Power
If a single high-gain amplifier is used to amplify ion current signals, then signal strength is improved, but the amplifier saturates at high ion currents reducing measurement accuracy
Solution Approach 1:
The amplification process is divided into two cascaded amplifier stages. The first amplifier stage provides high gain for weak signals from low ion currents, while the second amplifier stage provides additional gain for signals from higher ion currents. This segmented amplification approach extends the linear dynamic range of the detection system while maintaining measurement accuracy across different ion current intensities.
3Speed
If a single high-resolution digitizer is used to capture ion current transients, then temporal resolution is improved, but the linear dynamic range of the digitizer limits the ability to measure both low and high ion currents
Solution Approach 1:
The signal acquisition is segmented into two parallel paths: one path captures high-amplitude signals from high ion currents with appropriate gain settings, while the other path captures low-amplitude signals from low ion currents with higher gain settings. Both paths use the same high-temporal-resolution digitizer, ensuring that temporal resolution is maintained while the segmented gain structure extends the linear dynamic range to 1:10^6.
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 effectively increases the linear dynamic range of ion current measurement, preventing saturation and ensuring linearity, thereby enhancing the ability to detect and quantify ions across a broader range of intensities, particularly in high-resolution time-of-flight mass spectrometry.
Implementation Method 1
measuring, at least at one location, the image current induced on a grid-like detection element of high transmission by the penetration of the avalanche of secondary electrons
Implementation Method 2
The secondary electrons are accelerated inside the SEM and generate an avalanche of secondary electrons, typically ending up in about one million secondary electrons per ion
Data Source
AI summary
The invention relates to the linear dynamic range of ion abundance measurement devices in mass spectrometers, such as time-of-flight mass spectrometers. The invention solves the problem of ion current peak saturation by producing a second ion measurement signal at an intermediate stage of amplification in a secondary electron multiplier, e.g. a signal generated between the two multichannel plates in chevron arrangement. Because saturation effects are observed only in later stages of amplification, the signal from the intermediate stage of amplification will remain linear even at high ion intensities and will remain outside saturation. In the case of a discrete dynode detector this could encompass, for example, placement of a detection grid between two dynodes near the middle of the amplification chain. The invention uses detection of the image current generated by the passing electrons.