Particle preconcentrator

Abstract

An apparatus and method for preconcentrating particles and vapors. The preconcentrator apparatus permits detection of highly diluted amounts of particles in a main gas stream, such as a stream of ambient air. A main gas stream having airborne particles entrained therein is passed through a pervious screen. The particles accumulate upon the screen, as the screen acts as a sort of selective particle filter. The flow of the main gas stream is then interrupted by diaphragm shutter valves, whereupon a cross-flow of carrier gas stream is blown parallel past the faces of the screen to dislodge the accumulated particles and carry them to a particle or vapor detector, such as an ion mobility spectrometer. The screen may be heated, such as by passing an electrical current there through, to promote desorption of particles therefrom during the flow of the carrier gas. Various types of screens are disclosed. The apparatus and method of the invention may find particular utility in the fields of narcotics, explosives detection and chemical agents.

1. An apparatus for concentrating vapor or particles entrained in a moving air stream said apparatus comprising:
 at least one pervious screen disposed substantially perpendicularly to the air stream, whereby the air stream passes through said screen and at least some of the particles or vapor are caught upon said screen;  
 means for interrupting the passage of the air stream through said at least one screen;  
 means for heating said at least one screen; and  
 means for generating a carrier gas stream cross-flow past said at least one screen, whereby particles or vapor caught upon said screen are entrained into the carrier gas stream.  
 
     
     
       2. An apparatus according to  claim 1 , further comprising a fan for inducing the movement in the air stream. 
     
     
       3. An apparatus according to  claim 1  wherein said means for interrupting the passage of the air stream comprises at least one diaphragm shutter. 
     
     
       4. An apparatus according to  claim 1  wherein said means for generating a crossflow of a carrier gas stream comprises a carrier gas outlet valve comprising, a diaphragm shutter. 
     
     
       5. An apparatus according to  claim 4  wherein said at least one pervious screen comprises a plurality of substantially parallel screens. 
     
     
       6. An apparatus according to  claim 4  further comprising means for heating the at least one screen. 
     
     
       7. An apparatus according to  claim 6  wherein said at least one screen comprises an electrically conductive screen and said means for heating comprises means for supplying electric current in said screen. 
     
     
       8. An apparatus according to  claim 5  wherein said screens comprise woven wire mesh. 
     
     
       9. An apparatus according to  claim 7  wherein said screen comprises at least one sheet of metallic felt. 
     
     
       10. An apparatus according to  claim 9  further comprising a means for detecting vapor particles entrained in said carrier gas stream. 
     
     
       11. An apparatus according to  claim 10  wherein said means for detecting comprises an ion mobility spectrometer. 
     
     
       12. An apparatus for detecting particles or vapor comprising a metallic felt screen in communication with a detector, wherein the detector can detect trace amounts of contraband. 
     
     
       13. An apparatus for detecting particles or vapor comprising:
 ( a )  a metallic felt screen in communication with a detector and in communication with a main gas stream generator to generate a main gas stream, wherein the metallic felt screen is disposed such that it is substantially perpendicular to the main gas stream; and      ( b )  a carrier gas stream generator in communication with the metallic felt screen to present a carrier gas stream to the metallic felt screen, which carrier gas stream then continues to the detector.     
     
     
       14. The apparatus of  claim 13 , wherein the carrier gas stream generator, the metallic felt screen, and the detector communicate with one another by way of a gas flow path. 
     
     
       15. The apparatus of  claim 14 , wherein the gas flow path comprises a structure to contain and direct the carrier gas stream. 
     
     
       16. The apparatus of  claim 14 , wherein the gas flow path comprises a duct. 
     
     
       17. The apparatus of  claim 13 , wherein the carrier gas stream generator comprises a suction generator. 
     
     
       18. The apparatus of  claim 13 , wherein the carrier gas stream generator presents the carrier gas stream to the metallic felt screen in a cross flow. 
     
     
       19. The apparatus of  claim 18 , wherein the cross flow is parallel to the metallic felt screen. 
     
     
       20. The apparatus of claims  12  or  13 , further comprising a heater to heat the metallic felt screen. 
     
     
       21. The apparatus of claims  12  or  13 , further comprising an intake duct in communication with the metallic felt screen to intake and direct the main gas stream to the metallic felt screen. 
     
     
       22. The apparatus of  claim 21 , comprising an exhaust duct in communication with the intake duct to exhaust the main gas stream after it has been directed to the metallic felt screen. 
     
     
       23. The apparatus of claims  12  or  13 , wherein the detector comprises an ion mobility spectrometer, an electron capture device, a gas chromatograph, a chemiluminescence device, a mass spectrometer, an ion trap mobility spectrometer, or a thermo redox device. 
     
     
       24. An apparatus for detecting particles or vapor comprising:
 ( a )  an intake duct;      ( b )  a main gas stream generator;      ( c )  a metallic felt screen;      ( d )  an exhaust duct;      ( e )  a carrier gas stream generator; and      ( f )  a detector,        wherein the intake duct communicates with the metallic felt screen and with the exhaust duct to intake and direct a main gas stream to the metallic felt screen where the metallic felt screen is disposed such that it is substantially perpendicular to the main gas stream whereby the main gas stream passes through the metallic felt screen and at least some of the particles or vapor are caught upon the screen, whereafter the main gas stream is exhausted by the exhaust duct, and wherein the carrier gas stream generator communicates with the metallic felt screen and with the detector to present a carrier gas stream to the metallic felt screen, whereafter the carrier gas stream is directed to the detector.     
     
     
       25. A method of detecting particles or vapor on an item comprising:
 ( a )  dislodging the particles or vapor from the item;      ( b )  adsorbing the dislodged particles or vapor to a metallic felt screen;      ( c )  desorbing the adsorbed particles or vapor;      ( d )  directing the desorbed particles or vapor to a detector; and      ( e )  detecting the desorbed particles or vapor.     
     
     
       26. The method of  claim 25 , wherein dislodging the particles or vapor from the item and adsorbing the dislodged particles or vapor to the metallic felt screen comprises:
 ( a )  disposing the metallic felt screen such that it is substantially perpendicular to a main gas stream, wherein the main gas stream is induced past the item to dislodge the particles or vapor from the item;      ( b )  entraining the dislodged particles or vapor in the main gas stream; and      ( c )  directing the main gas stream having the entrained particles or vapor through the metallic felt screen, whereby the particles or vapor are adsorbed.     
     
     
       27. The method of  claim 26 , wherein the main gas stream is induced by a fan. 
     
     
       28. The method of  claim 26 , wherein desorbing the particles or vapor comprises generating a carrier gas stream and directing it to the metallic felt screen. 
     
     
       29. The method of  claim 28 , wherein the carrier gas stream is generated by suction. 
     
     
       30. The method of  claim 28 , wherein the carrier gas stream is directed to the metallic felt screen in a cross flow. 
     
     
       31. The method of  claim 30 , wherein the cross flow is parallel to the metallic felt screen. 
     
     
       32. The method of  claim 26 , wherein desorbing the particles or vapor comprises heating the metallic felt screen. 
     
     
       33. The method of  claim 26 , wherein the particles or vapor are detected by an ion mobility spectrometer, electron capture device, a gas chromatograph, a chemiluminescence device, a mass spectrometer, an ion trap mobility spectrometer, or a thermo redox device.