Ion Mobility Spectrometer Gate Control for Ion Admission Resolution
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Solution Overview
Problem
Ion mobility spectrometers using pulsed ionization sources face a trade-off between admitting a wide range of ion mobilities and maintaining resolution, as longer gate openings reduce the apparatus' resolution.
Innovation Solution
The corona discharge source is operated at least twice for every gate opening, with the gate configured to allow faster ions from one discharge and slower ions from a preceding discharge to pass through, and three discharges occur during each gate opening period, utilizing a corona needle and grid voltage control to manage ion admission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the gate is held open for longer periods to admit a wider range of ion mobilities from the discharge, then the range of ion mobilities admitted is improved, but the resolution of the apparatus is substantially reduced
Solution Approach 1:
The corona discharge source is pulsed at least twice during each gate opening period, creating periodic ionization events. The gate remains open continuously while the discharge occurs periodically, allowing ions of different mobilities to be admitted in a structured sequence that maintains both wide acceptance and high resolution
Solution Approach 2:
The corona discharge source produces ions in advance during the gate opening period. By pulsing the discharge multiple times while the gate is open, ions are prepared and made available for admission in a controlled manner before detection, enabling the system to capture a broad mobility range without compromising the temporal resolution needed for accurate measurement
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 allows for improved resolution in ion mobility spectrometers by ensuring a wide range of ion mobilities are admitted while maintaining acceptable resolution, as the rapid switching of the corona discharge and gate operation effectively manages ion passage.
Implementation Method 1
A corona drive circuit 25 is connected between the needle 20 and the tube 24 to apply a high voltage of around 5 kV between them sufficient to produce a corona discharge effective to ionize chemicals and vapours admitted through the inlet 1
Implementation Method 2
A gate 3 admits the ions to the left-hand end of a drift chamber 4 where they are caused to flow to the right-hand end by a voltage field applied to electrodes 5
Data Source
AI summary
An IMS or other analytical instrument has a corona discharge needle (20) to ionize sample gases or vapours. A gate (3) is opened or closed to admit or prevent entry of the ions produced by the corona discharge to a drift chamber (4). The operation of the corona discharge needle (20) and the gate (3) are controlled such that the gate is open during at least two discharges, to admit faster ions produced by the most recent discharge together with slower ions produced by an earlier discharge.