US 5,092,155 AGranted

High speed detection of vapors of specific compounds

AssigneeThermedics Inc.

InventorsDavid P. Rounbehler, Eugenie Hainsworth

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Abstract

A highly selective, sensitive, fast detection system and method are disclosed for detecting vapors of specific compounds in air. Vapors emanating from compounds such as explosives, or stripped from surfaces using heat and suction from a hand-held sample gun, are collected on surfaces coated with gas chromatograph (GC) material which trap explosives vapors but repel nitric oxide, then are desorbed and concentrated in one or more cold spot concentrators. A high speed gas chromatograph (GC) separates the vapors, after which specific vapors are decomposed in two pyrolyzers arranged in parallel and the resulting nitric oxide is detected. A low temperature pyrolyzer with silver produces NO from nitramines or nitrite esters; a high temperature pyrolyzer decomposes all explosives vapors to permit detection of the remaining explosives. Also disclosed is a series arrangement of pyrolyzers and gas chromatographs and an NO detector to time-shift detection of certain vapors and facilitate very fast GC analyses. The use of hydrogen as a carrier gas, plus unique collectors and concentrators, high speed heaters, NO detectors, and very fast, temperature-programmable GC's enhance selectivity, sensitivity and speed of detection.

Claims18

Dependent claims

Apparatus for detecting vapors of specific nitrogen-containing compounds comprising;

means for forming a gas sample containing vapors of said sepcific compounds and a non-oxidizing carrier gas;
a first gas chromatograph for effecting timewise separation of the vapors of said gas samples;
means for directing said gas sample through said first gas chromatograph;
an NO detector operable to detect nitric oxide and to
a low temperature pyrolyzer, a second gas chromatograph, and a high temperature pyrolyzer connected in series between said first gas chromatograph and said NO detector;
said low temperature pyrolyzer operable to produce nitrogen dioxide or nitric oxide by decomposing vapors of a first set of compounds, if present in said gas sample received from said first gas chromatograph without producing nitric oxide from other substances in said gas sample;
said second gas chromatograph operable to allow very rapid passage therethrough of the nitrogen dioxide and nitric oxide produced in said low temperature pyrolyzer while retarding passage of vapors of a second set of compounds and other substances in said gas sample to effect additional timewise separation of said sample;
said high temperature pyrolyzer operable to produce nitric oxide by decomposing nitrogen dioxide and vapors of said second set of compounds present in the gas sample received from said second gas chromatograph;
and
means for detecting, based on signals produced by said NO detector, the vapors of said specific compounds present in said gas sample.

7 more elements

Dependencies are inferred from the claim text.