Laser Ionization Detection (LID) and Photoemissive (PE) Ion Mobility Spectrometry (IMS) Development

Significant advances are reported in the detection of trace analytes in ambient air by laser ionization detection and photoemissive ion mobility spectrometry. A numerical model was developed that describes the behavior of laser-produced ions in an applied electric field and the subsequent induced cu...

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Bibliographic Details
Main Author: Swenson, Orven F
Format: Report
Language:English
Subjects:
ANALYTES
AQ U02-09-1985
Atomic and Molecular Physics and Spectroscopy
DETECTION
Electrical and Electronic Equipment
ELECTRODES
ELECTRON CAPTURE
INDENES
ION MOLECULE INTERACTIONS
IONIZATION
LASER APPLICATIONS
Lasers and Masers
PE62202F
PHOTOELECTRIC EMISSION
SPECTROMETRY
WUAFRL1900E28A
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Summary:Significant advances are reported in the detection of trace analytes in ambient air by laser ionization detection and photoemissive ion mobility spectrometry. A numerical model was developed that describes the behavior of laser-produced ions in an applied electric field and the subsequent induced current flow in an external detection circuit between the biased electrodes. The modeling and extensive measurements on parallel-plate and cylindrical electrodes resulted in a novel hemishperical cell geometry in which the cathode is a wire on a ceramic base (actually the wire will be positioned in a small depression in the base) and the anode is a half-cylinder of metal wire. This design minimizes noise generated by scattered ultraviolet light, allows a very small detection volume, is readily flash heated to eliminate memory effects, provides a peak in the induced current that makes it easier to extract temporal data, and is easily manufactured. Very narrow features were demonstrated in a laser ionization spectral study for molecules as large as indene even at room temperature under ambient pressure conditions. The narrowness of these features means that on-and-off-resonance measurements to separate out background LID signals are very feasible. A combined LI-IMS was demonstrated as an effective approach for speciation in ambient pressure air. An alternative ionization approach of photoemissive electron capture combined with IMS was demonstrated as a promising technique for detecting electronegative species such as explosives molecules. Original contains color plates: All DTIC reproductions will be in black and white.