Ion mobility spectrometer to mass spectrometer interface
Inventors
Assignees
US Department of Homeland Security
Publication Number
US-8536518-B2
Publication Date
2013-09-17
Expiration Date
2031-06-27
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Abstract
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.
Core Innovation
The invention provides a method and apparatus for interfacing a Commercial Off The Shelf (COTS) ion mobility spectrometer (IMS) to a mass spectrometer (MS) that utilizes collisional focusing. It addresses the incompatibility between standalone IMS instrumentation and commercially available MS due to the unsuitable environment created by the differentially pumped interface of a mass spectrometer that employs collisional focusing. The interface modifies the internal configuration of the MS to allow tandem operation with IMS instruments.
Specifically, the invention enables transfer of the ion beam from the IMS to the MS without distortion of the chemical species or temporal profile. This is achieved by increasing the electric field strength between the orifice and skimmer and decreasing the pressure in the differentially pumped interface, which reduces background gas collisions that would otherwise distort the ion beam during transit. The modified interface overcomes the broadening effect caused by collisional focusing and allows selective gating of the ion beam into the MS.
The problem being solved is that commercial standalone IMS devices cannot be combined in tandem with MS instruments that use collisional focusing due to the physics of the differentially pumped interface of the MS. This leads to ion packet broadening and an unsuitable environment for IMS measurements. Furthermore, false positives and false negatives in IMS detection arise from inability to differentiate ions of similar size or inefficiency in ionization in competitive environments. The invention provides a practical apparatus and method to integrate existing IMS and MS systems, especially for explosive trace detection applications, improving selectivity and sensitivity beyond single instrument capabilities.
Claims Coverage
The patent presents five main inventive features covering apparatus and methods for interfacing a COTS IMS to a COTS MS, focusing on modifications to the interface and gating capabilities.
Integration of COTS IMS and triple quadrupole MS with atmospheric pressure interface
An apparatus comprising a COTS IMS with specified components, an atmospheric pressure interface including interface flange, orifice electrode with pinhole, focusing ring, skimmer electrode, radio frequency quadrupole, drift gas inlet, vacuum pump, and a triple quadrupole COTS MS with electron multiplier detector fluidly coupled through the interface.
Modified faraday plate with centered hole for ion beam passage
A faraday plate detector constructed with a centered hole of approximately 6 mm diameter positioned after the IMS guard grid to allow passage and measurement of a portion of the ion beam into the MS.
Atmospheric pressure interface modification enabling tunable electric fields and reduced pressure
A method involving an interface flange used to attach the IMS to the MS, positioning a faraday plate with centered hole aligned with the orifice pinhole, introducing drift gas via the flange between the faraday plate and orifice electrode, and using a skimmer electrode electrically isolated to allow tunable voltages between orifice and skimmer and between skimmer and Q0, with reduction in hole size and length of the skimmer to lower pressure in the intermediate pumping stage.
Ion beam gating via electrically isolating and voltage modulation of orifice and skimmer electrodes
A method for gating the ion beam by applying alternating electric fields between the electrically isolated orifice and skimmer electrodes to obstruct or permit ion beam passage into the MS. Blocking is achieved by applying a negative or inverse potential field gradient, and passing by applying a positive potential field gradient with specified voltage settings.
These inventive features collectively provide a practical solution and apparatus for interfacing a COTS IMS to a COTS MS employing collisional focusing, by modifying the atmospheric pressure interface to allow effective ion transfer, reduce ion packet broadening, enable ion beam gating, and optimize operating pressures and electric fields.
Stated Advantages
The invention provides a simple, cost-efficient platform enabling tandem operation of IMS and MS instruments, enhancing selectivity and sensitivity compared to standalone devices.
The interface reduces ion packet broadening caused by collisional focusing through increased electric field strength and decreased pressure in the differentially pumped interface, resulting in improved resolving power of mobility measurements.
The modifications permit ion beam gating in the mass spectrometer interface, allowing highly selective measurements of ion populations based on mobility.
The apparatus enables the use of commercially available IMS and MS instruments in tandem, avoiding the expense and limited availability of integrated IMS/MS systems.
Documented Applications
Integration of ion mobility spectrometers and mass spectrometers for improved detection of explosives trace residue at security checkpoints, enhancing the capability of explosive trace detectors (ETDs).
Characterization of ion chemistry of commercially deployed IMS-based explosive trace detectors by combining IMS with tandem mass spectrometry using the modified interface.
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