Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
1999-07-21
2002-12-17
Anderson, Bruce (Department: 2881)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
C250S287000, C250S288000
Reexamination Certificate
active
06495823
ABSTRACT:
FIELD OF INVENTION
This invention relates to a Field Asymmetric Ion Mobility (FAIM) filter, and more particularly, to a micromachined FAIM filter and spectrometer.
BACKGROUND OF INVENTION
The ability to detect and identify explosives, drugs, chemical and biological agents as well as air quality has become increasingly more critical given increasing terrorist and military activities and environmental concerns. Previous detection of such agents was accomplished with conventional mass spectrometers, time of flight ion mobility spectrometers and conventionally machined FAIM spectrometers.
Mass spectrometers are very sensitive, highly selective and provide a fast response time. Mass spectrometers, however, are large and require significant amounts of power to operate. They also require a powerful vacuum pump to maintain a high vacuum in order to isolate the ions from neutral molecules and permit detection of the selected ions, and are also very expensive.
Another spectrometric technique which is less complex is time of flight ion mobility spectrometry which is the method currently implemented in most portable chemical weapons and explosives detectors. The detection is based not solely on mass, but on charge and cross-section of the molecule as well. However, because of these different characteristics, molecular species identification is not as conclusive and accurate as the mass spectrometer. Time of flight ion mobility spectrometers typically have unacceptable resolution and sensitivity limitations when attempting to reduce their size, that is a drift tube length less than 2 inches. In time of flight ion mobility, the resolution is proportional to the length of the drift tube. The longer the tube the better the resolution, provided the drift tube is also wide enough to prevent all ions from being lost to the side walls due to diffusion. Thus, fundamentally, miniaturization of time of flight ion mobility systems leads to a degradation in system performance. While these devices are relatively inexpensive and reliable, they suffer from several limitations. First, the sample volume through the detector is small, so to increase spectrometer sensitivity either the detector electronics must have extremely high sensitivity, requiring expensive electronics, or a concentrator is required, adding to system complexity. In addition, a gate and gating electronics are usually needed to control the injection of ions into the drift tube.
FAIM spectrometry was developed in the former Soviet Union in the 1980's. FAIM spectrometry allows a selected ion to pass through a filter while blocking the passage of undesirable ions. Conventional FAIM spectrometers are large and expensive, e.g., the entire device is nearly a cubic foot in size and costs over $25,000. These systems are not suitable for use in applications requiring small detectors. They are also relatively slow, taking as much as one minute to produce a complete spectrum of the sample gas, are difficult to manufacture and are not mass producible.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a FAIM filter and detection system which can more quickly and accurately control the flow of selected ions to produce a sample spectrum than conventional FAIM devices.
It is a further object of this invention to provide such a filter and detection system which can detect multiple pre-selected ions without having to sweep the bias voltage.
It is a further object of this invention to provide such a filter and detection system which can even detect selected ions without a bias voltage.
It is a further object of this invention to provide such a filter and detection system which can detect ions spatially based on the ions' trajectories.
It is a further object of this invention to provide such a filter and detection system which has a very high resolution.
It is a further object of this invention to provide such a filter and detection system which can detect selected ions faster than conventional detection devices.
It is a further object of this invention to provide such a filter and detection system which has a sensitivity of parts per billion to parts per trillion.
It is a further object of this invention to provide such a filter and detection system which may be packaged in a single chip.
It is further object of this invention to provide such filter and detection system which is cost effective to implement and produce.
The invention results from the realization that an extremely small, accurate and fast FAIM filter and detection system can be achieved by defining a flow path between a sample inlet and an outlet using a pair of spaced substrates and disposing an ion filter within the flow path, the filter including a pair of spaced electrodes, one electrode associated with each substrate and a controller for selectively applying a bias voltage and an asymmetric periodic voltage across the electrodes to control the path of ions through the filter.
The invention results from the further realization that by providing an array of filters, each filter associated with a different bias voltage, the filter may be used to detect multiple selected ions without sweeping the bias voltage.
The invention results from the further realization that by varying the duty cycle of the periodic voltage, no bias voltage is required.
The invention results from the further realization that by segmenting the detector, ion detection may be achieved with greater accuracy and resolution by detecting ions spatially according to the ions' trajectories as the ions exit the filter.
This invention features a micromechanical field asymmetric ion mobility filter for a detection system. There is a pair of spaced substrates defining between them a flow path between a sample inlet and an outlet, an ion filter disposed in the path and including a pair of spaced filter electrodes, one electrode associated with each substrate and an electrical controller for applying a bias voltage and an asymmetric periodic voltage across the ion filter electrodes for controlling the paths of ions through the filter.
In a preferred embodiment there may be a detector, downstream from the ion filter, for detecting ions that exit the filter. The detector may include a plurality of segments, the segments separated along the flow path to spatially separate the ions according to their trajectories. There may be confining electrodes, responsive to the electrical controller, for concentrating selected ions as they pass through the filter. The confining electrodes may be silicon. The silicon electrodes may act as spaces for spacing the substrates. There may be a heater for heating the flow path. The heater may include the ion filter electrodes. The electrical controller may include means for selectively applying a current through the filter electrodes to heat the filter electrodes. The substrate may be glass. The glass may be Pyrex®. There may be an ionization source, upstream from the filter, for ionizing a fluid flow from the sample inlet. The ionization source may include a radioactive source. The ionization source may include an ultraviolet lamp. The ionization source may include a corona discharge device. There may be a clean air inlet for introducing purified air into the flow path. There may be a pump in communication with the flow path, for regulating a fluid flow through the flow path.
The invention also features a field asymmetric ion mobility filter and detection system. There is a housing having a flow path between a sample inlet and an outlet, an ion filter disposed in the flow path and including a pair of spaced filter electrodes, an electrical controller for applying a bias voltage and an asymmetric periodic voltage across the ion filter electrodes for controlling the path of ions through the filter, and a segmented detector, downstream from the ion filter, its segments separated along the flow path to spatially separate the ions according to their trajectories.
In a preferred embodiment there may be confining electrodes, responsive to the electrical contro
Miller Raanan A.
Nazarov Erkinjon G.
Anderson Bruce
Hamilton, Brook, Smith and Reynolds, P.C.
The Charles Stark Draper Laboratory Inc.
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