Differential Mobility Spectrometer for Ion Flux Attenuation
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Solution Overview
Problem
Existing differential mobility spectrometry (DMS) systems face challenges in analyzing complex samples and improving the duty cycle of mass spectrometry, particularly due to space charge effects from ions with varying abundances.
Innovation Solution
A system of fluidically coupled vacuum chambers and a controller that operates a differential mobility spectrometer (DMS) in multiple modes, including modes for ion separation, attenuation based on abundance, and selective transmission, using asymmetric waveforms and modulated compensation voltages to manage ion fluxes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ions are separated using conventional DMS with fixed amplitude and ramped compensation voltage, then ion separation is achieved, but space charge effects from high abundance ions limit the dynamic range and quantitative analysis capability
Solution Approach 1:
The compensation voltage waveform is changed from a fixed ramped pattern to a dynamically modulated pattern where the compensation voltage is adjusted in real-time based on the detected ion abundance at each mobility value. This dynamic adaptation allows the system to compensate for space charge effects by modulating the voltage to maintain optimal ion transmission despite varying ion densities.
Solution Approach 2:
The system implements a feedback mechanism where ion abundance information is continuously monitored and used to adjust the compensation voltage waveform. The detected ion signal feeds back to the voltage control system, which then modulates the compensation voltage to optimize separation and minimize space charge effects, enabling improved quantitative analysis.
2Productivity
If the DMS operates in traditional survey scan mode with linearly ramped compensation voltage, then the duty cycle is limited by the time required to scan through the full compensation voltage range, but comprehensive ion mobility coverage is achieved
Solution Approach 1:
The system employs periodic modulation of the compensation voltage rather than continuous linear ramping. By using modulated waveforms that periodically adjust the compensation voltage based on ion abundance patterns, the system can rapidly cycle through compensation voltage values, significantly reducing the time required to achieve comprehensive ion mobility coverage while maintaining high duty cycle operation.
Solution Approach 2:
The system performs preliminary detection of ion abundance across the mobility range and uses this information to pre-adjust the compensation voltage waveform for subsequent scans. This preliminary action allows the system to optimize the compensation voltage pattern before full analysis, reducing the time needed to achieve complete ion mobility separation in subsequent operations.
3Illumination intensity
If high ion fluxes are transmitted to the mass spectrometer, then sufficient signal intensity is achieved, but space charge effects increase and reduce measurement precision
Solution Approach 1:
The system dynamically changes the compensation voltage parameter based on ion abundance to optimize the balance between signal intensity and measurement precision. By modulating the compensation voltage to match the detected ion flux, the system maintains optimal ion transmission that provides sufficient signal intensity while preventing excessive ion accumulation that would cause space charge effects and degrade quantitative accuracy.
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
Enhances the analysis of complex samples by reducing space charge effects, improving the duty cycle, and enabling quantitative analysis by selectively attenuating higher abundance ions, thus enhancing the dynamic range and robustness of mass spectrometry.
Implementation Method 1
Differential mobility spectrometry (DMS), also known as field asymmetric ion mobility spectrometry (FAIMS), serves as a post-ionization method for filtering ions in a controlled atmosphere, based on their respective mobilities or mobility coefficients
Implementation Method 2
ions entrained in a gas stream are oscillated by alternating field polarities, provided typically by a high frequency, periodic, asymmetric voltage waveform that alternates between a high-field and a reversed low-field
Implementation Method 3
Differences in mobility of the ions between the alternating field polarities result in a net displacement of the ions, urging ions to drift progressively off-axis and discharge on electrodes
Implementation Method 4
for ions having a specific mobility (or a range of mobilities), this displacement may be compensated by a DC voltage, termed the compensation voltage (CV). By scanning the CV at fixed amplitude and waveform frequency, the ions having the specific mobility (or the range of the mobilities) are instead transported through the DMS
Data Source
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AI summary
1. An apparatus comprising: a series of mutually fluidically coupled vacuum chambers, including a first vacuum chamber and a second vacuum chamber; and a controller; wherein the first vacuum chamber comprises: an ion inlet, for introduction of ions therethrough from an ion source; and a first ion guide, wherein the first ion guide is configured to guide the ions introduced through the ion inlet towards the second vacuum chamber, for example via a differential pressure aperture; wherein the second vacuum chamber comprises: a differential mobility spectrometer, DMS; and wherein the controller is communicatively coupled to the DMS; characterized by: wherein the controller is configured to control the DMS in a set of modes, wherein the set of modes includes: a first mode, wherein the DMS is configured to separate the ions, for example using an asymmetric waveform and/or a ramped compensation voltage; and a second mode, wherein the DMS is configured to separate the ions and to selectively attenuate respective fluxes of the separated ions according to respective abundances thereof, for example using an asymmetric waveform and/or a modulated compensation voltage.