Abstract:
A sample feeding device for a trace detector is disclosed. The sample feeding device comprises: a sample feeding chamber disposed in the sample feeding device to desorb a sample from a sample feeding member; and a valve assembly configured to fluidly communicate the sample feeding chamber with a drift tube of the trace detector during feeding sample. With the above configuration of the present invention, for example, the sensitivity of the detector can be increased by improving the permeation ratio of the sample. In addition, interior environment of the drift tube is isolated from exterior environment to avoid a drift region of the drift tube from being polluted. The important parameters, such as sensitivity, a position of a peak of a substance, a resolution, of the detector can be kept constant. As a result, operation reliability and consistency of the detector can be achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Chinese Patent Application No. 201010619932.6 filed on Dec. 31, 2010 in the State Intellectual Property Office of China, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a sample feeding device for a trace detector and a trace detector with the sample feeding device. 
         [0004]    2. Description of the Related Art 
         [0005]    Currently commercially available detectors for safety inspection mainly detect harmful substances such as explosives and narcotics by ion mobility spectrometry. Such detectors comprise a sample feeding device. The sample feeding device can gasify and desorb solid particles or gas entering into the device. The gasified sample molecules are then introduced into an ionization region by air flow. After that, the ionized sample molecules enter into a drift region. The molecules are identified based on their drift time in the drift region. Most of commercially available detectors employ a semi-permeable membrane. The semi-permeable membrane can isolate an interior of a drift tube from the outside environment to prevent dust and foreign substance molecules from entering into the drift tube so as to ensure the cleanness of the interior of the drift. Only molecules (generally large molecules) having certain property can permeate the semi-permeable membrane to enter into the drift tube. The semi-permeable membrane exhibits a certain permeation ratio. A general permeation ratio is only around 10%. Therefore, most of the sample molecules are lost outside the semi-permeable membrane and few sample molecules enter into the drift tube, which results in considerable reduction in sensitivity of the detectors. In addition, the semi-permeable membrane generally operates at a high temperature, which requires a system to provide the semi-permeable membrane with an additional operation environment and heat. As a result, the operation power of the system is increased. If the detector is portable, power sustaining time of a battery will reduce. A detector without a semi-permeable membrane will produce a complex background peak since the drift region is in direct communication with the atmosphere environment and thus the interior environment in the detector tends to be polluted. In addition, a peak of a substance greatly varies and a position of the peak is unstable with the change of the exterior environment so that stability of detection operation is seriously degraded. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the present invention to provide a sample feeding device for a trace detector, such as an ion mobility spectrometer (IMS), and a trace detector, such as an ion mobility spectrometer (IMS), having the sample feeding device, which can increase sensitivity of the trace detector, such as an ion mobility spectrometer (IMS). 
         [0007]    According to an aspect of the present invention, there is provided a sample feeding device for a trace detector. The sample feeding device comprises a sample feeding chamber disposed in the sample feeding device to desorb a sample from a sample feeding member; and a valve assembly configured to fluidly communicate the sample feeding chamber with a drift tube of the trace detector during feeding sample. 
         [0008]    According to another aspect of the present invention, the valve assembly comprises a sealing member; and a flange disposed on an inner wall of the sample feeding chamber, wherein the sample feeding chamber fluidly communicates with the drift tube of the trace detector by separating the sealing member from the flange and the sample feeding chamber is isolated from the drift tube of the trace detector by bringing the sealing member into contact with the flange. 
         [0009]    According to a further aspect of the present invention, the flange divides the sample feeding chamber into a first sample feeding chamber and a second sample feeding chamber. The first sample feeding chamber is configured to be in fluid communication with the trace detector and the second sample feeding chamber is configured to desorb the sample from the sample feeding member, the first sample feeding chamber fluidly communicates with the second sample feeding chamber by separating the sealing member from the flange and the first sample feeding chamber is isolated from the second sample feeding chamber by bringing the sealing member into contact with the flange. 
         [0010]    According to a further aspect of the present invention, the sample feeding device further comprises a sample feeding port in communication with the second sample feeding chamber. 
         [0011]    According to a still further aspect of the present invention, the second sample feeding chamber is isolated from the sample feeding port while the first sample feeding chamber fluidly communicates with the second sample feeding chamber by separating the sealing member from the flange, and thereby the first sample feeding chamber and the second sample feeding chamber are isolated from an outside of the sample feeding device. 
         [0012]    According to a further aspect of the present invention, the sealing member comprises a cylindrical part; a head connected with the cylindrical part, the head having an annular groove; and a seal ring disposed in the annular groove which is configured to contact with the flange to isolate the first sample feeding chamber from the second sample feeding chamber. 
         [0013]    According to a further aspect of the present invention, the sample feeding device further comprises an actuating member configured to move the sealing member to fluidly communicate the first sample feeding chamber with the second sample feeding chamber or to isolate the first sample feeding chamber from the second sample feeding chamber. 
         [0014]    According to a further aspect of the present invention, the actuating member comprises a carriage having opposite outer walls substantially parallel to each other; and slide rods disposed on the outer walls, the carriage being connected with the cylindrical part of the sealing member; and an actuating frame having grooves in which the slide rods are slideably disposed, and thereby when the actuating frame moves, the carriage is actuated to move by cooperation of the slide rods and the grooves so as to move the sealing member. 
         [0015]    According to another aspect of the present invention, there is provided a trace detector. The trace detector comprises the sample feeding device; a drift tube for ionizing and charging the sample from the sample feeding device and drifting the ionized sample; and a Faraday plate configured to collect the ionized sample. 
         [0016]    With the above configuration of the present invention, the sensitivity of the detector can be increased by improving a permeation ratio of the sample. In addition, interior environment of the drift tube is isolated from exterior environment to avoid a drift region of the drift tube from being polluted. The important parameters, such as sensitivity, a position of a peak of a substance, a resolution, of the detector can be kept constant. As a result, stableness and consistency of the detector can be achieved. 
         [0017]    According to another aspect of the present invention, a sample feeding device comprises a linkage, a single sample feeding chamber (airtight chamber), a is sample molecule desorption device and a sample feeding port. The airtight sample feeding chamber is in directly communication with a gas path located within a drift tube. The device can control the sample feeding chamber to communicate with an outside atmosphere or not to communicate with the outside atmosphere. When the detector does not operate, that is, no sample is fed, the linkage enables the airtight sample feeding chamber to be isolated from the outside atmosphere so that the gas path within the drift tube is in a sealed state and is isolated from the outside environment. The linkage is activated by an outside signal, that is, by a triggering signal in response to feeding sample. After the linkage is activated, the airtight sample feeding chamber communicates with the outside atmosphere so that the sample molecules can be directly entrained into the drift tube from outside of the drift tube. After the sample molecules enter into the drift tube, they are firstly ionized. The charged sample molecules pass through a drift region and then are collected by a Faraday plate. The sample is identified based on drift time. 
         [0018]    Since the sample feeding device does not comprise a semi-permeable membrane or a device having a particular permeation ratio, desorbed or gaseous sample molecules can freely enter into the drift tube. The sample feeding efficiency is greatly improved so that sensitivity is radically increased. In addition, the airtight sample feeding chamber enables an interior of the drift tube to be in a sealed state, that is, in a non-sample feeding state for a long time. Foreign substance is prevented from entering into the drift tube and thus the drift tube can be kept in a clean state to ensure substance differentiating ability of the drift tube and to still keep the substance differentiating ability uniform in different environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic perspective view of a sample feeding device according to an embodiment of the present invention. 
           [0020]      FIG. 2  is a schematic perspective cut-away view of the sample feeding device of  FIG. 1 . 
           [0021]      FIG. 3  is a schematic perspective view of an airtight sample feeding chamber assembly of the sample feeding device of  FIG. 1 . 
           [0022]      FIG. 4  is a schematic perspective cut-away view of the airtight sample feeding chamber assembly of  FIG. 3 . 
           [0023]      FIG. 5  is a schematic perspective cut-away view of the sample feeding device of  FIG. 1  in a non-sample feeding state. 
           [0024]      FIG. 6  is a schematic perspective view of a sealing member of the sample feeding device of  FIG. 1 . 
           [0025]      FIG. 7  is a schematic perspective view of a base of the sample feeding device of  FIG. 1 . 
           [0026]      FIG. 8  is a schematic perspective view of a sealing member support of the sample feeding device of  FIG. 1 . 
           [0027]      FIG. 9  is a schematic perspective view of a carriage of the sample feeding device of  FIG. 1 . 
           [0028]      FIG. 10  is a schematic perspective view of the sealing member, the sealing member support, and the carriage in an assembled state. 
           [0029]      FIG. 11  is a schematic perspective view of an actuating frame of the sample feeding device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0030]    The embodiments are described below in order to further explain the present invention by referring to the figures. 
         [0031]    Referring to  FIGS. 1-11 , a trace detector such as an ion mobility spectrometer, according to the present invention comprises a sample feeding device  100 ; a drift tube for ionizing and charging a sample from the sample feeding device  100  and drifting the ionized and charged sample; and a Faraday plate configured to collect the ionized and charged sample. 
         [0032]    As illustrated in  FIGS. 1-11 , the sample feeding device  100  comprises a sample feeding chamber  10  disposed in the sample feeding device  100  to desorb a sample from a sample feeding member; and a valve assembly  20  configured to fluidly communicate the sample feeding chamber  10  with the drift tube of the trace detector during feeding sample. As illustrated in  FIGS. 3-4 , the sample feeding chamber  10  is formed by a sample feeding chamber assembly  12  and a sample feeding port  14  is formed in the sample feeding chamber assembly  12 . In addition, a gas path  16  is formed in the sample feeding chamber assembly  12  to communicate with the drift tube and the sample feeding chamber  10 . 
         [0033]    As illustrated in  FIGS. 1-11 , the sample feeding device  100  further comprises an actuating frame  30 , a heating assembly  40 , and a base  50 . As illustrated in  FIGS. 1-2 , a gas path located within the drift tube communicates with the sample feeding port through the airtight sample feeding chamber  10 . 
         [0034]    The valve assembly  20  comprises a sealing member  22 ; and a flange  24  disposed on an inner wall of the sample feeding chamber  10 . The sample feeding chamber  10  fluidly communicates with the drift tube of the trace detector by separating the sealing member  22  from the flange  24  and the sample feeding chamber  10  is isolated from the drift tube of the trace detector by bringing the sealing member  22  into contact with the flange  24 . The flange  24  divides the sample feeding chamber  10  into a first sample feeding chamber  101  and a second sample feeding chamber  102 . The first sample feeding chamber  101  is configured to be in fluid communication with the trace detector, that is, to be in fluid communication with the gas path  16 . The second sample feeding chamber  102  is configured to desorb the sample from the sample feeding member. The first sample feeding chamber  101  fluidly communicates with the second sample feeding chamber  102  by separating the sealing member  22  from the flange  24  and the first sample feeding chamber  101  is isolated from the second sample feeding chamber  102  by bringing the sealing member  22  into contact with the flange  24 . The sample feeding port  14  is in communication with the second sample feeding chamber  102 . 
         [0035]    As illustrated in  FIG. 6 , the sealing member  22  comprises a cylindrical part  221 ; a head  222  connected with the cylindrical part, the head having an annular groove  223 ; and a seal ring  224  (referring to  FIG. 4 ) disposed in the annular groove  223 . The seal ring  224  is configured to contact with the flange  24  to isolate the first sample feeding chamber  101  from the second sample feeding chamber  102 . 
         [0036]    The sample feeding chamber assembly  12  comprises a housing  17  and a top cover  18 . The first sample feeding chamber  101  is formed by a seal ring  19 , the sealing member  22 , the flange  24 , the top cover  18  and the housing  17 . 
         [0037]    The seal ring is a circular ring formed of rubber such as medical silicone rubber and fluororubber, or polytetrafluoroethylene. The sealing member  22  is illustrated in  FIG. 6 . The head  222  has a shape of a pot. A groove  223  is formed at an intermediate portion of the head having the shape of a pot. The seal ring  224  is placed in the groove  223 . The top cover  18  is a disk-shaped element. A groove is formed on a bottom of the disk-shaped element, and the seal ring  19  is placed in the groove. The top cover  18  is sealed against the housing  17  through the rubber seal ring  19  to enclose a space of the first sample feeding chamber  101 . 
         [0038]    The housing  17  is hollow and has multiple functions. The housing  17  acts as a support for the entire sample feeding device, and comprises the sample feeding port  14 , and the sample feeding chamber  10  formed by a hollow portion of the housing. A protrusion or the flange  24  is disposed at an intermediate portion of the sample feeding chamber. As illustrated in  FIG. 4 , the portion of the sample feeding chamber above the protrusion  24  is referred to as the first sample feeding chamber  101 , and the portion of the sample feeding chamber below the protrusion  24  is referred to as the second sample feeding chamber  102 . The first sample feeding chamber  101  is in communication with the interior of the drift tube through a hole. The second sample feeding chamber  102  is directly connected with the sample feeding port  14 . The sample feeding port  14  is composed of a cuboid space of which an upper portion is in direct communication with the second sample feeding chamber  102 . When the sample feeding device does not operate, a downward force, i.e. gravity, is applied to the sealing member  22  so that the seal ring  224  is pressed against the projection  24  within the housing. The first sample feeding chamber  101  and the second sample feeding chamber  102  are then isolated from each other and no gas flows between the first sample feeding chamber  101  and the second sample feeding chamber  102 . In this case, the state of the sample feeding device is in a sate as illustrated in  FIG. 5 . 
         [0039]    As illustrated in  FIG. 7 , the housing  17  is secured to a side of the base  50  by means of screws located on a side of the housing to constitute an integral housing. The cylindrical part  221  of the sealing member  22  is fastened to a sealing member support  20  (by means of screws). As illustrated in  FIG. 9 , the sealing member support  70  (referring to  FIG. 8 ) is mounted to the carriage  60  (referring to  FIG. 9 ) through two screw holes  63  located at a center of the carriage  60 . The carriage  60  is fastened to the heating assembly  40  through four screw holes  62  located at four corners of the carriage  60 . The heating assembly  40  is provided with a case and a heating element disposed in the case. The case may be polytetrafluoroethylene heater sheath. 
         [0040]    With the above configuration, the sealing member  22 , the sealing member support  70 , the carriage  60 , and the heating assembly  40  are integrated, and move upwards or downwards integrally. Four slide rods  61  are disposed on sides of the carriage  60  and placed in grooves  31  of the actuating frame  30  (referring to  FIG. 11 ). When the actuating frame  30  slides in a same horizontal plane, the carriage  60  moves upwards or downwards with the slide of the actuating frame to move the sealing member  22  upwards or downwards. The actuating frame  30  is exteriorly connected with a power source such as a motor. The actuating frame  30  moves horizontally under the action of an external force. 
         [0041]    The heater may be located within the heater sheath. The heater may be heating means such as an electric heater or laser. When no sample is fed, the heater is at a normal atmospheric temperature, or in a semi-heating state, that is, at a temperature lower than a thermal desorption temperature and greater than an ambient temperature. When a sample is fed, the sample feeding device begins to operate. The sample feeding device heats the fed sample test paper to a high temperature quickly to thermally desorb the sample from the test paper into gas rapidly. 
         [0042]    When the sample feeding device does not operates, that is, no sample is fed, the first sample feeding chamber  101  is isolated from the exterior environment and the system is in a state as shown in  FIG. 5 . In this case, the interior of the drift tube is isolated from the outside, in a clean and high-temperature environment, and is not affected by gases from the exterior environment. When the sample feeding device operates, a sample feeding test paper with sample is inserted into the sample feeding device from the sample feeding port  14 , and placed onto a top surface of the carriage  60 . A sensor located under a lower end of the carriage  60  at a position  90  outputs a triggering signal to the system. The system sends the signal to the power source such as a motor. 
         [0043]    The power source such as a motor translates the actuating frame  30  so that the carriage  60  carrying the sample test paper lifts by a height measured upwards from a low groove part  311  of the actuating frame  30  to a high groove part  312  of the actuating frame  30 . In this case, the sealing member  22  ascends from a bottom end to a top end within the airtight sample feeding chamber  10 . As a result, the first sample feeding chamber  101  is in communication with the outside of the first sample feeding chamber so that the drift tube is in communication with the outside of the drift tube, and the top surface of the carriage  60  is brought into contact with a bottom surface of the housing  17  so that the second sample feeding chamber  102  is isolated from the sample feeding port  14 , that is, the sample feeding chamber  10  is isolated from the outside of the sample feeding chamber. While receiving the triggering signal or after a delay from receiving the triggering signal, the heating assembly located at the bottom of the sample feeding device begins to operate in a manner such as thermal radiation or convection to gasify and desorb the sample from the sample feeding test paper quickly. Under the action of gas flow, gas entraining the sample enters into the first sample feeding chamber  101  across both sides of the sealing member support  70 , and then flows into the ionization region within the drift tube through the hole for gas. The sample molecules are ionized in the ionization region, and then the charged sample particles enter into the drift region under the effect of an electric field. Different molecules are identified based on their different drift times. 
         [0044]    According to the above embodiment, the second sample feeding chamber is isolated from the sample feeding port while the first sample feeding chamber fluidly communicates with the second sample feeding chamber by separating the sealing member from the flange, and thereby the first sample feeding chamber and the second sample feeding chamber are isolated from the outside of the sample feeding device. Apparently, the solution can be achieved in other manners. For example, a second valve assembly may be provided to fluidly communicate the second sample feeding chamber with the sample feeding port or to isolate the second sample feeding chamber from the sample feeding port. By operating the second valve assembly in cooperation with the valve assembly  20  simultaneously, the second sample feeding chamber is isolated from the sample feeding port while the first sample feeding chamber and the second sample feeding chamber communicates with each other. Therefore, the present invention is not limited to the above embodiment. 
         [0045]    In addition, the carriage  60  and the like move upwards or downwards as illustrated in the figures. However, this is only for the purpose of convenience in description. The carriage  60  and the like may move in any direction. 
         [0046]    Furthermore, the sample feeding test paper may not be placed on the top surface of the carriage  60 , but may be placed in a sample feeding test paper fixing part disposed on the carriage  60 . Therefore, although the carriage  60  moves for example in a right-left direction rather than upwards or downwards, the sample feeding test paper will not fall from the carriage  60 . 
         [0047]    In the above embodiment, the top surface of the carriage  60  is brought into contact with the bottom surface of the housing  17  so that the second sample feeding chamber  102  is isolated from the sample feeding port  14  (in this case, the carriage  60  has no center hole. However, the carriage  60  may have the center hole as shown in the figures. After the test paper is inserted into the sample feeding port, the first sample feeding chamber  101  is in communication with the second sample feeding chamber  102 , the first sample feeding chamber  101  and the second sample feeding chamber  102  is separated from the exterior environment through the test paper, and gas exchanges between the first and second sample feeding chambers  101  and  102  and the exterior environment.