High accuracy ion mobility spectrometry
Inventors
Hauck, Brian • Siems, William • McHugh, Vincent • Harden, Charles S. • Hill, Jr., Herbert H.
Assignees
Washington State University WSU • Government of the United States of America
Publication Number
US-10585066-B2
Publication Date
2020-03-10
Expiration Date
2038-06-11
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
Abstract
Ion mobility spectrometry (IMS) systems, devices, and associated methods of operation are disclosed herein. In one embodiment, an IMS system includes an ionization region configured to receive and ionize a sample into ionized molecules and a detector configured to detect ionized molecules. The IMS system also includes a drift region in between and directly coupled to both the ionization region and the detector. The drift tube includes a first ion gate proximate the ionization region and a second ion gate proximate the detector. The first and second ion gates are configured to alternately introduce a batch of ionized molecules toward the detector while the other is maintained open, thereby allowing accurate measurement of a drift time of the ionized molecules corresponding to a drift length that is a distance between the first and second ion gates.
Core Innovation
Ion Mobility Spectrometry (IMS) systems and associated methods are disclosed that improve the accuracy of ion mobility measurements by employing a drift tube with two ion gates spaced apart from each other. The IMS system includes an ionization region to ionize a sample into ionized molecules, a drift region between first and second ion gates, and a detector proximate to the second ion gate. The first ion gate is near the ionization region and the second is near the detector.
The invention addresses the problem of inaccuracies in ion mobility measurements stemming from assuming the drift length as the length between a single ion gate and the detector. Variations in process conditions, such as the presence of a vacuum near a mass spectrometer detector, cause ions to drift differently near the detector compared to the drift region, skewing drift time measurements and reducing accuracy. Factory calibrations are limited and cannot be performed in the field, leading to wide detection windows and increased risk of false positives.
The method involves alternately pulsing the first and second ion gates while the other is maintained open, thus introducing batches of ionized molecules toward the detector in two stages of operation. Drift time profiles are collected for each stage, and subtracting the second profile from the first yields drift time measurements corresponding accurately to the drift length between the two ion gates. This refined measurement allows for highly accurate ion mobility calculations, reducing error from about ±2% to ±0.2%. This accurate correspondence between drift time and drift length significantly improves calibration and detection accuracy in IMS systems.
Claims Coverage
The claims include three independent claims covering methods and systems implementing the dual ion gate configuration for accurate ion mobility spectrometry, detailing control of ion gates, drift time measurement, and derivation of reduced mobility values.
Two-stage ion gate operation for accurate drift time measurement
A method of ion mobility spectrometry in a drift tube having first and second ion gates, comprising ionizing a sample, pulsing the first ion gate to introduce ionized molecules while maintaining the second ion gate open for detection, then maintaining the first ion gate open while pulsing the second ion gate to introduce additional ionized molecules, and deriving a final drift time by subtracting the second drift time from the first drift time.
Use of Bradbury-Nielson or Tyndall-Powell gates for ion gate control
First and second ion gates are individually Bradbury-Nielson or Tyndall-Powell gates, with electrical control signals applied to open or maintain the gates during the two stages of ion introduction for drift time measurement.
Drift tube system with dual ion gates and controller for reduced mobility derivation
An IMS system comprising an ionization region, a detector, and a drift region between them equipped with first and second ion gates proximate to the ionization region and detector respectively, configured to alternately introduce batches of ionized molecules toward the detector. A controller operates the gates to measure first and second drift times and derive a reduced mobility value by subtracting the drift times corresponding to the distance between the ion gates.
The inventive features provide a system and method for high accuracy ion mobility measurement by controlling two ion gates within the drift tube to obtain drift times corresponding precisely to the length between the gates, improving calibration accuracy and reducing measurement error.
Stated Advantages
Reduces errors in IMS measurements, improving accuracy from approximately ±2% to about ±0.2%.
Enables precise correlation between drift time and drift length, facilitating highly accurate ion mobility calculations.
Allows for improved instrument calibration and reduced width of detection windows, potentially lowering false positive alarms.
Documented Applications
Military or security detection of drugs and explosives using ion mobility spectrometry.
Field-deployed IMS systems for chemical composition identification by measuring ion mobility values.
Interested in licensing this patent?