Ion Mobility Spectrometer Charge Control
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Solution Overview
Problem
Ion mobility spectrometers face challenges in achieving reproducible drift times and peak widths due to ions repelling each other during separation, leading to space-charge effects that affect separation efficiency and accuracy.
Innovation Solution
The method involves controlling the charge density entering the ion mobility separator by adjusting the accumulation time and ion fill rate in the ion trap, ensuring that each packet of ions released has a predetermined maximum charge, thereby minimizing space-charge interactions and improving separation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large number of ions are released into the IMS drift tube to maximize signal intensity, then the sensitivity is improved, but the ions repel each other causing space-charge effects that broaden IMS peaks and reduce resolution
Solution Approach 1:
The patent applies preliminary action by pre-cooling ions in an ion trap before they enter the drift tube. This cooling process reduces the kinetic energy and spatial spread of ions before injection, allowing more ions to be introduced without excessive repulsion effects. The ion trap serves as a preparation stage where ions are accumulated and cooled to a controlled temperature, thereby reducing space-charge effects during subsequent drift while maintaining high ion numbers for sensitive detection.
2Productivity
If ions are accumulated in an upstream ion trap during intervals between pulses to maximize duty cycle, then the ion transmission efficiency is improved, but the accumulated ions experience space-charge effects that affect separation accuracy
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the accumulation time in the ion trap based on the charge already accumulated. The control system monitors the ion population in the trap and modulates the accumulation duration to maintain optimal charge density. This prevents excessive space-charge effects while maximizing the duty cycle, as the accumulation period is extended or reduced according to real-time charge measurements, ensuring consistent drift time reproducibility across different operating conditions.
Solution Approach 2:
The patent implements feedback control where the charge accumulated in the ion trap is continuously monitored and used to adjust subsequent accumulation parameters. The control system receives information about the current ion population and modifies the accumulation time or gate voltages accordingly. This closed-loop feedback mechanism ensures that the ion trap operates at optimal charge density, preventing space-charge effects from degrading drift time precision while maintaining high productivity through efficient ion accumulation.
3Manufacturing precision
If the ion packet charge is not controlled and ions repel each other during passage through the separation region, then the separation efficiency deteriorates, but controlling the charge reduces the number of ions that can be analyzed
Solution Approach 1:
The patent applies preliminary action by pre-cooling ions in an ion trap before they enter the drift tube. This cooling process reduces the kinetic energy and spatial spread of ions before injection, allowing more ions to be introduced without excessive repulsion effects. The ion trap serves as a preparation stage where ions are accumulated and cooled to a controlled temperature, thereby reducing space-charge effects during subsequent drift while maintaining high ion numbers for sensitive detection.
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 the resolution and reproducibility of ion mobility spectrometers by reducing space-charge effects, leading to narrower IMS peaks and more consistent drift times, thus improving the overall analytical performance.
Implementation Method 1
AC voltages that oscillate at RF frequencies are applied to the electrodes so as to create a pseudo-potential force that confines the ions
Implementation Method 2
An electric field or travelling DC wave is applied along the drift tube so as to urge ions from an ion entrance to an ion exit of the drift tube. As the ions traverse the drift tube they separate according to their mobility through the buffer or drift gas.
Implementation Method 3
detecting the charge of ions in the first packet of ions using a detector
Data Source
AI summary
A method of analyzing ions by ion mobility separation is disclosed. The method comprises controlling the amount of charge within an ion trap and then pulsing the ions from the ion trap into an ion mobility separator. This enables the charge injected into the ion mobility separator to be controlled and hence prevents space-charge interactions between the ions from distorting the ion mobility peaks detected by the detector.