IMS to MS Interface Using Modified Skimmer for Ion Focusing
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Solution Overview
Problem
Current explosive trace detectors (ETDs) face challenges with false positive and false negative responses due to the inability to differentiate analyte molecules from interferents of similar size and inefficient ionization in competitive environments, necessitating improved selectivity and sensitivity, particularly in the context of evolving threats like improvised explosive devices (IEDs).
Innovation Solution
A method and apparatus are developed to interface a commercial off-the-shelf (COTS) ion mobility spectrometer (IMS) with a COTS mass spectrometer using a modified skimmer to create a combined IMS/MS system, allowing for enhanced selectivity and sensitivity by altering the differentially pumped interface to accommodate collisional focusing, thereby improving ion chemistry characterization and reducing false response rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard configuration IMS is interfaced with a mass spectrometer utilizing collisional focusing, then the resolving power and selectivity of explosive residue detection are improved, but the device complexity increases due to the need for modified skimmer and differentially pumped interface
Solution Approach 1:
The patent combines IMS and MS instruments into a tandem configuration, merging their analytical capabilities to achieve both ion mobility separation and mass spectrometric detection. This integration allows the system to utilize both the resolving power of IMS and the selectivity of MS, thereby improving overall measurement precision for explosive residue detection despite the increased device complexity
Solution Approach 2:
The patent modifies specific local components of the MS instrument, particularly the skimmer and differentially pumped interface, to accommodate IMS ion packets. By applying local quality changes to these specific regions rather than redesigning the entire system, the patent achieves compatibility between IMS and MS while minimizing overall device complexity
2Reliability
If IMS operating parameters are modified to increase selectivity, then false positive and false negative rates are reduced, but the difficulty of detecting and measuring ion species increases due to the need for detailed gas phase ion chemistry understanding
Solution Approach 1:
The patent introduces mass spectrometry as an intermediary diagnostic tool to characterize the ion packets produced by IMS. By using MS to identify ion species based on their mass-to-charge ratios, the system gains detailed understanding of gas phase ion chemistry without requiring complex modifications to the IMS operating parameters. This intermediary approach enables reliable differentiation of analyte molecules from interferents while simplifying the detection and measurement process
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
The modified IMS/MS interface provides a cost-effective platform for obtaining ion mobility-tandem mass spectrometry data, significantly reducing false positives and negatives by enhancing the resolving power and selectivity of explosive residue detection, effectively addressing the limitations of standalone IMS systems.
Implementation Method 1
a standard configuration mass spectrometer (MS) that utilizes collisional focusing in its differentially pumped interface
Implementation Method 2
Ion mobility spectrometry (IMS) is the analytical method most commonly implemented in ETD equipment. In IMS, the velocity of an ion though a buffer gas in the presence of an electric field is measured
Implementation Method 3
the ion is formed by efficient atmospheric pressure chemical ionization (APCI) processes
Data Source
AI summary
A method and apparatus are described herein for the interface of an ion mobility spectrometer (IMS) to a mass spectrometer (MS) that utilizes collisional focusing, through internal modification. Commercial standalone IMS instrumentation cannot be combined in tandem with a commercially available MS that utilizes collisional focusing due to the physics of the differentially pumped interface of the MS being an unsuitable environment for an IMS measurement. The invention provides for transfer of the ion beam from the IMS to the MS without distortion of the chemical species or temporal profile due to large scale collisions in the differentially pumped interface, by increasing the electric field strength between the orifice and skimmer, and decreasing the pressure in the differentially pumped interface, thereby reducing the number of background gas collisions encountered by the ion beam during transit from the IMS to the MS.