Abstract:
Analysis of solid chemical and biological particles is achieved by a miniature mass spectrometer and apparatus attached thereto for vaporizing or ablating a stream of chemical and biological particles by a pulsed laser and/or pyrolysis heater sub-assembly at atmospheric pressure or, when desirable, in a vacuum. The mass spectrometer includes a collimation chamber, a repeller assembly, an internal ionization chamber, a mass filter and ion separation chamber, a drift space region, and a multi-channel ion detection array so as to permit the collection and analysis of ions formed over a wide mass range simultaneously. The apparatus for vaporizing or ablating includes an output port adjacent the input to the collimation and vaporization chamber so as to maximize the amount of vaporized material being fed into the mass spectrometer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention is related to the invention shown and described in U.S. Ser. No. 11/802,183 (Northrop Grumman Case No. 001631-078) entitled “Miniature Mass Spectrometer For The Analysis Of Biological Small Molecules”, filed in the name of Carl B. Freidhoff, the present inventor on May 21, 2007. This application is assigned to Northrop Grumman Corporation, the present assignee. 
     This invention is also related to the invention shown and described in U.S. Ser. No. 11/260,106 (Northrop Grumman case No. 000810-078) entitled “A MEMs Mass Spectrometer”, filed in the name of Carl B. Freidhoff on Oct. 28, 2005. This application is also assigned to Northrop Grumman Corporation. 
     The teachings of the above cross-referenced patent applications are intended to be incorporated herein by reference for any and all purposes. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to solid state miniature mass spectrometers, and more particularly to a miniature mass spectrometer test system for the analysis of chemical and solid particles of either low vapor pressure chemicals or biological materials, such as toxins or spores. 
     2. Description of Related Art 
     A mass spectrometer is a device that permits rapid analysis of an unknown sample of material to be analyzed. A small amount of the sample is introduced into the mass spectrometer where it is ionized, focused and accelerated by means of magnetic and/or electric fields toward a detector array. Different ionized constituents of the sample travel along different paths to the detector array in accordance with their mass to charge ratios. The outputs from the individual detector elements of the array provide an indication of the sample&#39;s constituents. 
     Industrial mass spectrometers are generally large, heavy and expensive, and therefore, a need exists for a miniature, relatively inexpensive light-weight solid state mass spectrometer for use by the military, homeland security personnel, hazmat crews, industrial concerns and the like to test for the presence of dangerous substances in the immediate environment. 
     A typical miniature mass spectrometer is shown and described in the present assignee&#39;s U.S. Pat. No. 5,386,115 entitled “Solid State Micro-Machined Mass Spectrograph Universal Gas Detection Sensor”, issued to Carl B. Freidhoff et al. on Jan. 31, 1995. Basically the miniature mass spectrometer disclosed in U.S. Pat. No. 5,386,115 is comprised of two semiconductor substrates joined together by an epoxy seal. Each half includes intricate cavities formed by a lithograph process for mounting and housing the components of the mass spectrometer. 
     In the above cross referenced related application U.S. Ser. No. 11/260,106, there is disclosed an improved MEMs mass spectrometer for analyzing a gas sample and comprises apparatus having metal walls connected between an elongated lid and base member fabricated on a semiconductor chip, similar to the mass spectrometer disclosed in U.S. Pat. No. 5,386,115, with the walls defining a plurality of interior chambers including sample gas input chambers, an ionizer chamber, a plurality of ion optics chambers and an ion separation chamber. A detector array at the end of the ion separation chamber includes a plurality of detector elements positioned along two parallel lines and arranged to intercept all of the ionized beams produced in the device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to the analysis of solid chemical and biological particles by a mass spectrometer test system which is adapted to operate with a minimum of support equipment and includes a vaporization chamber attached to miniature mass spectrometer apparatus for vaporizing chemical and biological particles by laser pulses, thermal pyrolysis or other energy means at pressures as high as ambient pressure or in a vacuum. The mass spectrometer apparatus includes an input collimation chamber, an internal ionization source, a mass filter and ionization chamber, drift space region, and a multi-channel array so as to permit the collection of ions formed over a wide mass range simultaneously. The particles, when desirable, can be preselected for vaporization to minimize environmental background by use of a laser induced fluorescence (LIF) detector located between the inlet nozzle and particle deflection plates. Preselection is achieved by LIF through excitation with a high energy photon, such as blue or ultraviolet, which is absorbed by the particle and partially remitted at a lower energy, such as green or red portion of the electromagnetic spectrum. Different biological and non-biological particles will have characteristic emissions. The vaporization chamber is affixed to the front end of the mass spectrometer apparatus and includes an output port adjacent an input port to the collimation and vaporization chambers so as to maximize the amount of vaporized material being fed into the mass spectrometer. 
     In a preferred aspect of the present invention there is provided a mass imaging spectrometer test system for analyzing solid particles of an input sample of chemical or biological material comprising: apparatus for converting solid particles of an input sample of chemical or biological materials into a vapor; miniature mass spectrometer apparatus connected to an output port of the converting apparatus for receiving vaporized samples therefrom, and wherein the spectrometer device includes a collimation chamber located adjacent the output port and having at least one vacuum pumping inlet for evacuating and drawing vapor of the sample into the collimation chamber; a vacuum pump assembly for drawing and conveying the vapor into and through the spectrometer; a repeller assembly located adjacent the collimator chamber; an ionization chamber located adjacent the repeller member for ionizing the ionized vapor input from the collimator chamber; an ion optics chamber located adjacent the collimation chamber; at least one evacuated mass filter and ion separation chamber located adjacent the ion optics chamber; an adjoining drift space region; means located in close proximity to the ion separation chamber and drift space region for generating an electromagnetic field for separating ions therein by their respective mass/charge ratio; and, a detector array for detecting ions separated in the mass filter and an ion separation chamber. 
     Further scope of applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and the specific example, while indicating the preferred embodiment of the invention is provided by way of illustration only, since changes and modifications coming within this scope the spirit of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description provided hereinafter and the accompanying drawings which are provided by way of illustration only, and thus are not meant to be considered in a limiting sense, and wherein: 
         FIG. 1  is a block diagram broadly illustrative of the preferred embodiment of the subject invention; 
         FIG. 2  is an exploded view of two halves of the preferred embodiment of the subject invention including an ablation and pyrolysis chamber; 
         FIG. 3  is a perspective plan view illustrative of the base member of the embodiment shown in  FIG. 2  adjoining a support member and substrate in accordance with the subject invention; 
         FIG. 4  is a fragmented top planar view further illustrative of the support member of the subject invention shown in  FIG. 3 ; and, 
         FIG. 5  is a partial perspective view illustrative of an enlarged portion of the front end portion of the subject invention including the ablation and pyrolysis chamber shown in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now collectively to drawing  FIGS. 1-5  wherein like reference characters refer to like parts throughout, the block diagram of  FIG. 1  is illustrative of miniature mass spectrometer apparatus  10  in accordance with the subject invention for the analysis of samples of solid chemical and biological particles by means of a mass spectrometer fabricated on a chip (BioMiSOC) and having solid particle vapor conversion apparatus  12  consisting of an ablation and pyrolysis chamber attached to the front end thereof for converting solid particles of an input sample to vapor. The mass spectrometer apparatus  10  of the invention is comprised of top and bottom lid and base members  16   1  and  16   2  of a semiconductor chip  16  which supports and houses a collimator chamber  18 , an ionization chamber  20 , first and second adjoining ion optics chambers  22  and  24 , a mass filter and ion separation chamber  26 , a drift space region  27 , electromagnetic field generating means  28 , an array  30  of detector elements, and a readout chip  32  which is coupled to a digital signal microprocessor (μP)  36  via a digital signal bus  34 . Lastly, display apparatus  36  for providing a visual display of the mass spectrometer output is connected to the microprocessor  36 . 
     Further, as shown in  FIG. 1 , a vacuum pump  33  is connected to the chip  16  of the mass spectrometer  16  for drawing in vapor into the collimator chamber  18  and for propagating ions formed in the ionization chamber  20  through the remaining portions of the mass spectrometer  10  to the detector array  30 . 
     Considering now the invention in greater detail, an input sample of an air stream including solid particles of low vapor pressure chemicals or biological materials, for example, toxins or spores is fed into the vaporization-ablation chamber  12  where they are vaporized. The vapor is then fed into the collimator  18  which is differentially pumped by a pumping arrangement shown in  FIG. 4 . As noted above, the mass spectrometer portion  10  of the invention disclosed herein is comprised of top and bottom members  16   1  and  16   2  of a chip  16 . The bottom portion  16   2 , moreover, forms part of a base member  35  shown in  FIG. 3 , located on a substrate member  37 . Both top and bottom members  16   1  and  16   2  each include an interior space or recess for the elements of opposing collimator chamber portions  18   1  and  18   2 , repeller member portions  19   1  and  19   2 , ionizer chamber portions  20   1  and  20   2 , first and second optics portions  22   1 ,  22   2  and  24   1 ,  24   2 , upper and lower mass filter and ion separation chamber portions  26   1  and  26   2 , and the elements of opposing drift space regions  27   1  and  27   2 . 
     Electric and magnetic field generation circuitry  28  is located adjacent the opposing mass filter and ion separation chamber portions  26   1 ,  26   2 , and the drift space region portions  27   1 ,  27   2  and operates to generate orthogonal magnetic and electric fields for separating ions passing through of the mass filter and ionization separation chamber  26  and the drift space region  27  which then impinge on the multiple detector elements  31  of the detector array  30 . A readout chip  32  then converts detected analog signals from the detector array  30  to digital signals which is then fed via a set of signal leads  34  to the microprocessor  36 . The microprocessor  36  generates spectrometer output signals whereupon a visual readout is provided by the display apparatus  38 . 
     Referring now to  FIGS. 3 and 4 , shown thereat is the bottom member  16   2  of the mass spectrometer portion  10  of the subject invention and corresponds substantially to the structure shown in  FIG. 2 . However, there is now additionally shown in  FIG. 3  two sets of electrical signal leads  40  and  42  along with eight sets of solder elements  44   1 ,  44   2  . . .  44   8  surrounding a set of eight apertures  46   1 ,  46   2  . . .  46   8  which are respectively connected to eight sets of individual evacuation pumps  48   1 ,  48   2  . . .  48   8  shown in  FIG. 4 . The pumps  48   1  . . .  48   8  are connected to apertures  46   1  . . .  46   8  via pneumatic pipe members  50   1 ,  50   2  . . .  50   8  and  52   1 ,  52   2  . . .  52   8  and act to generate a vacuum environment for the propagation of ions through the length of the mass spectrometer  10  to the detector array  30 . Electrical power is provided to the individual pumps  48   1 ,  48   2  . . .  48   8  by way of contact elements  54   1 ,  54   2  . . .  54   8 . Also shown in  FIG. 3  are three outer sets of electrical signal leads  56 ,  58  and  60  which are located on the base support member  35  for connecting the mass spectrometer  10  to external apparatus, not shown. 
     Turning attention now to  FIG. 5 , shown thereat are the structural details of the front end portion of the bottom member  16   2  of the mass spectrometer portion  10 .  FIG. 5  is intended to further illustrate the details of the ablation and pyrolysis chamber  12  and the collimator chamber portion  18   2 . In  FIG. 5 , reference numeral  13  denotes an input nozzle  13  for feeding an input sample of air including a concentrated particle stream solid material into the chamber  12 . The ablation and pyrolysis chamber  12  includes, among other things, a wall  15  having an output port  17  which mates with the front wall  21  of the collimator chamber  18 . 
     The collimator chamber portion  18   2  includes three mutually aligned outwardly diverging pairs of collimator elements  23   1 ,  23   2 , and  23   3  each having an open channel therebetween and terminating in a tip pointing to the output port  17  of the ablation chamber  12 . The foremost pair of collimator elements  23   1 , moreover, project into the output port  17  of the ablation chamber  12  so as to allow ions and vapors formed therein to be drawn into the collimator chamber  18 . 
     In addition to the input nozzle  13  which is shown located in the side wall  19 , located thereat is an ablation laser member  62  which is directed to the particle collection surface  76  downstream of the nozzle  13 . In front of the nozzle  13  and in line with the particle stream  64  are two sets of deflection plate electrodes  66  and  68  which are mutually orthogonal and are adapted to deflect an ionized particle stream  65  generated by the nozzle  13  from the ablation particle collection surface  76  so that it can be selectively deflected in mutually orthogonal directions through a plasma cleaning ring  72  in front of the deflector plate electrodes  66  and  68 . This permits elimination of particles of non-interest determined by a laser induced fluorescence (LIF) detector consisting of a laser member  78  and detector  80  monitoring the stream  65  in front of nozzle  13 . The plasma cleaning ring  72  is ignited to form an air plasma to clean the angular collection surface  76  between samples. 
     This is followed by a collection rod and pyrolysis heater assembly  74  which includes an angular collection surface  76 . Ablation laser member  62  is pulsed with sufficient energy to remove a portion of the deposited particles from the angular collection surface  76 , or the pyrolysis heater assembly is pulsed to vaporize a portion of the deposited particles from the angular collection surface  76 . The ions or vapor formed by the ablation or pyrolysis is preferentially directed through the output port  17  where it is fed into and through the collimator chamber  18  and then into the ionizer chamber  20 , followed by the ion optics chambers  22  and  24  and then into the mass filter and ion separation chamber  26 . 
     A differential vacuum pumping scheme is provided in the lower portion  18   2  of the collimator chamber  18  and includes four small circular openings  35   1 ,  35   2 ,  35   3  and  35   4  which are respectively coupled, for example, to pumps  48   1 ,  48   2 ,  48   5  and  48   6  as shown in  FIG. 4 . Additional stages of vacuum pumping are also provided by the pumps  48   3 ,  48   4 ,  48   7  and  48   8  so as to provide proper vacuum levels in the ablation and mass separation regions of the apparatus for producing ion movement through the spectrometer portion  10 . The differentially pumped front end allows the apparatus to sample at a higher pressure regime and analyze ions formed at a lower pressure, for example, atmospheric pressure. 
     Thus what has been shown described is a system including a miniature mass spectrometer for analyzing solid particles of either low pressure chemicals or biological materials and allows a vapor collection region to be close to a vaporization site so as to maximize the amount of the vaporized material that enters the mass spectrometer. This allows higher pressures to be utilized, allowing the system to be potentially smaller. The miniature mass spectrometer operates at higher pressures than laboratory units due to its small length of its mass separation region (centimeters versus 10s of cm to 1 meter in lab units). This will also reduce system power and therefore size. Moreover, sensitivity can be maximized while the timing issues can be substantially eliminated. It should be noted that, when desirable, two or more mass separation channels can be utilized if additional mass range is required. 
     The foregoing detailed description merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope.