Senior Scientist

Roger Sperline

Sensitive Ion Detection Device and Method for Analysis of Compounds as Vapors in Gases

Micro Faraday-Element Array Detector for Ion Mobility SpectroscopyThe novel ion mobility spectrometry (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.
 
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. 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.
 
Advantages:
This new IMS detector technique raises the detection limit of the device three orders of magnitude to over six million ions per second
Advance selectivity through the addition of a reliable and fast GC inlet
Enhance instrument performance through advances in sampling
Improve detection limits by limiting fragmentation of ions
Applications:
Some of these improvements are specific for explosives
Increase speed or economy through small, mass produced analyzers
Heavily employed for military or security purposes, such as detecting drugs and explosives
Many laboratory analytical applications, recently being coupled with mass spectrometry and high performance liquid chromatography

Micro Faraday-Element Array Detector for Ion Mobility Spectroscopy

Differential Transimpedance Amplifier Circuit for Correlated Differential Amplification

Compressing Ion-Beam ShutterThe compressing ion-beam ion shutter developed at The University of Arizona is composed of a series of electrically charged screens. By varying the relative voltages on the screens, the flow of ions into the detector chamber is blocked or opened. When the shutter is first opened, ions accumulate between the screens. When the shutter voltage is changed, the accumulated ions are compressed in space and the ion beam approaching the shutter is simultaneously closed. By controlling, (i) the relative voltages and the timing for changing voltage on each screen in the ion shutter, and (ii) the electrical gradient in the detector chamber, The University of Arizona researcher has achieved an increase in sensitivity with ion mobility spectrometers.
 
Background:
With the increase in attention to security concerns over past few years, ion mobility spectrometers have become popular devices for rapid detection and identification of airborne toxins, volatile organics, explosives, and other materials. However, a drawback to these devices is the sensitivity with which they can measure these compounds. The lack of sensitivity of ion mobility spectrometers can be attributed in part to the current shutter designs. An increase in the sensitivity can be realized through the use of the compressing ion-beam shutters described in this invention.

Advantages:
These compressing ion-beam shutters can provide an increase in the concentration of ions available in the spectrometers.
Increased signal to noise ratio.
Increased effective sensitivity to the material being detected.

Applications:
Ion mobility spectrometers
Material detection and identification
Security and defense
Industrial hygiene
Air quality monitoring
Status: issued U.S. patent #7,538,320

KMap

Chemistry & Biochemistry - Science