Ion Mobility Spectrometer Using Gas Jet and Electric Field Barrier
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Solution Overview
Problem
Current ion mobility spectrometers are limited by low mobility resolution, requiring long drift regions and large instrument dimensions, which hinder the separation of ions with similar mobilities and complicate the measurement of ion mobility spectra.
Innovation Solution
A method utilizing a gas jet formed by adiabatic expansion through a nozzle, combined with an electric field barrier, to sort ions based on their mobilities, allowing for high-resolution mobility spectra acquisition without the need for extensive ion guides or long drift regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long drift regions are used to achieve high mobility resolution, then the separation of ions with similar mobilities is improved, but the instrument dimensions and device complexity increase significantly
Solution Approach 1:
The invention changes the fundamental operating parameters by transitioning from continuous ion drift in long regions to pulsed ion injection over potential barriers. By using short pulses (nanosecond to microsecond range) and adjusting barrier heights dynamically, the system achieves high mobility resolution in compact dimensions through parameter optimization rather than spatial extension.
Solution Approach 2:
The continuous drift region is segmented into multiple discrete potential barriers that ions must sequentially overcome. This segmentation allows the use of short drift regions with multiple measurement stages, achieving cumulative resolution equivalent to much longer continuous drift paths while maintaining compact instrument size.
2Measurement precision
If large diameters are chosen for drift regions to reduce radial diffusion, then diffusion broadening is reduced, but the device complexity and instrument size increase
Solution Approach 1:
Ions are pre-cooled and pre-focused into tight bundles before entering the drift region through capillary channels. This preliminary confinement reduces initial radial spread, allowing the use of narrow drift regions without suffering from significant diffusion broadening, thereby simplifying the overall device configuration.
Solution Approach 2:
The invention uses gas flow dynamics to confine and guide ions through narrow channels. By controlling gas pressure and flow patterns, ions are kept centered in narrow drift regions, achieving effective diffusion control through fluid dynamic means rather than requiring large physical dimensions.
3Speed
If high electric field strengths are applied to increase drift velocity, then the measurement speed is improved, but the mobility resolution decreases due to reduced collision frequency
Solution Approach 1:
The system applies periodic pulsed electric fields rather than continuous high fields. During each pulse, ions are accelerated to achieve fast transit, then the field is reduced to allow thermalization and collision-based mobility sorting. This periodic modulation combines the benefits of high speed with adequate collision frequency for resolution.
Solution Approach 2:
The electric field strength is dynamically adjusted during the measurement process - high fields are applied initially to accelerate ions quickly, then progressively reduced to allow for collision-based separation. This dynamic field modulation optimizes both speed and resolution at different stages of the measurement cycle.
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 achieves unexpectedly high mobility resolutions, exceeding Rmob=35, and allows for compact, efficient ion mobility spectrometers that can be easily integrated into mass spectrometers, with minimal diffusion broadening and precise mobility determination.
Implementation Method 1
A jet of ion-containing gas is formed by adiabatic expansion of the gas through a nozzle
Implementation Method 2
combined with an electric field barrier, to sort ions based on their mobilities
Data Source
AI summary
Ion mobilities are measured by entraining the ions in a gas and adiabatically expanding the ion-containing gas through a nozzle to form a gas jet. An electrical field barrier with variable height is located at the nozzle exit. The field barrier may be located adjacent to the nozzle exit or an ion guide may be located between the nozzle and the field barrier. If a continuous ion current is supplied, the height of the barrier is varied and the ion current of the ions passing over the barrier is measured, the ion current can be differentiated to generate a mobility spectrum. Alternatively, the ions can be temporarily stored in the ion guide so that measurement of the ion current of the ions passing over the barrier results in a direct measurement of the mobility spectrum.