Micro Faraday-Element Array Detector for Ion Mobility Spectroscopy

University of Arizona
posted on 08/11/2010

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Background: Ion mobility spectrometry (IMS) is an analytical technique used to separate and identify ionized molecules in the gas phase based on their ion mobility in a carrier buffer gas. Though heavily employed for military or security purposes, such as detecting drugs and explosives, the technique also has many laboratory analytical applications, recently being coupled with mass spectrometry and high performance liquid chromatography.

Advances in IMS application to explosive detection might be proposed for a new generation of analyzers and could include: (1) improve detection limits by limiting fragmentation of ions; (2) improve selectivity through the addition of a reliable and fast GC inlet; (3) improve speed or economy through small, mass produced analyzers; (4) improve deployability through the use of a non-radioactive source; (5) improve interlaboratory comparisons through standardized libraries; and (6) enhance instrument performance through advances in sampling. Some of these improvements are specific for explosives, while others would be found true for all IMS applications, thus representing a technology wide challenge (Ewing, et al., Talanta, Vol. 54, Issue 3, May 2001, p. 515-529).

 

Market:  Explosives trace detection (ETD) portals are walk-through inspection systems for detecting trace levels of narcotics and explosives on individuals. Global sales for installed ETD portals totaled around $20 million in 2005, but are expected to increase by as much as 300% in 2006 due largely to TSA orders (Instrument Business Outlook, 2006).

 

Invention:  This invention provides advances to the field through a novel ion collection/detection system for an IMS. The novel IMS includes a drift tube having a collecting surface covering a collecting area at one end of the tube. The surface comprises a plurality of closely spaced conductive elements on a non-conductive substrate, each conductive element being electrically insulated from each other element. A plurality of capacitive transimpedance amplifiers (CTIA) adjacent the collecting surface are electrically connected to the plurality of elements, so charge from an ion striking an element is transferred to the capacitor of the connected CTIA. A controller counts the charge on the capacitors over a period of time.

 

Advantages:  The current state-of-the-art detection limit using a Faraday cup is around six thousand ions per second in the most expensive isotope ratio mass spectrometers. This corresponds to one femtoamp of current. It takes very sophisticated electronics to measure this small current with any certainty. The direct current measuring devices used in prior art ion mobility spectrometers are able to only measure currents in the picoamp range. This new IMS detector technique raises the detection limit of the device three orders of magnitude to over six million ions per second. This limitation requires high ion fluxes that cause poor linear dynamic range, false positive responses, and numerous other problems.

 

Status:  Issued US Utility Patent No. 6,809,313 on Oct. 26, 2004. We seek development partners and industrial manufactures of IMS equipment that are interested in improving their product lines.

 

UA ID:  UA10-126

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The current state-of-the-art detection limit using a Faraday cup is around six thousand ions per second in the most expensive isotope ratio mass spectrometers. This corresponds to one femtoamp of current. It takes very sophisticated electronics to measure this small current with any certainty. The direct current measuring devices used in prior art ion mobility spectrometers are able to only measure currents in the picoamp range. This new IMS detector technique raises the detection limit of the device three orders of magnitude to over six million ions per second. This limitation requires high ion fluxes that cause poor linear dynamic range, false positive responses, and numerous other problems.