Abstract:
A system and method for improving operation of a needle trap by changing a flow path through a needle trap to enable a needle to draw a fluid sample into a working end of the needle and out through the side hole, wherein drawing the sample through the side hole eliminates the possibility of a leak through the side hole while drawing a fluid sample into the working end.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a needle trap for field sampling that can be used to deliver a sample to a gas chromatography/mass spectrometry (GC/MS) system. More specifically, a needle trap that has a side hole may leak when drawing a sample in through the needle. An improved flow path through the needle is obtained when plugging the non-working end of a needle and using the side hole to draw in a fluid sample through the working end of the needle using a vacuum pump, and forcing the sample back out through the working end by applying a pressure to the side hole when delivering a sample to an analyzer. 
         [0003]    2. Description of Related Art 
         [0004]    There are many devices designed for chemical analysis. One such useful device is a gas chromatography/mass spectrometry (GC/MS) system. The GC/MS system and other similar devices are used in analyzing and identifying compounds. Samples can be delivered to such systems using a needle trap. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In a first embodiment of the present invention, a system and method for improving operation of a needle trap by changing a flow path through a needle trap to enable a needle to draw a fluid sample into a working end of the needle and out through the side hole, wherein drawing the sample through the side hole eliminates the possibility of a leak through the side hole while drawing a fluid sample into the working end. 
         [0006]    These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0007]      FIG. 1  is a profile cut-away view of a prior art needle trap. 
           [0008]      FIG. 2  is a profile cut-away view of a first embodiment of the present invention. 
           [0009]      FIG. 3  is a profile cut-away view of the first embodiment of the needle trap in a gas chromatography injector. 
           [0010]      FIG. 4  is a profile cut-away view of the first embodiment of the needle trap prepared to take a fluid sample by applying a suction force to the side hole. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow. 
         [0012]    Stainless steel needles, sized similarly to gas chromatographic injection needles and packed with a sorbent bed, are used for extraction of gaseous samples, followed by thermal desorption into GC systems. All analytes, both freely dissolved in the gas and associated with particulate matter entrained in the sample, are extracted by the devices. 
         [0013]      FIG. 1  is a cut-away profile view of a needle trap  10  from the prior art.  FIG. 2  is a cut-away profile view of a needle trap  50  of the first embodiment of the present invention. 
         [0014]      FIG. 1  shows a needle trap  10  having a needle  12  with a rounded tip  14  at a working end, with glass wool  16  in the rounded tip. A first packing bed  18  is disposed in the needle  12  and adjacent to the glass wool  16 . A second packing bed  20  is disposed in the needle  12  and adjacent to the first packing bed  18 . Glass wool  22  is disposed in the needle  12  and adjacent to the second bed material  20 . The needle  12  then contains an empty volume or dead space  28  until reaching a side hole  24 . The needle  12  then continues with the empty volume  28  from the side hole  24  until reaching the end of the needle and a Teflon plug  26 . 
         [0015]    In contrast, the present invention provides a different needle trap  50  construction in  FIG. 2 . The needle trap  50  includes a needle  52  with a rounded tip  54  at a working end, with a first loose fitting piece of wire  56  inserted into the rounded tip. The first loose-fitting wire  56  may be cut at an angle. The function of the loose-fitting wire  56  may be to keep the packing beds  58 ,  60  from falling out of the needle  52 . 
         [0016]    A first packing bed  58  is disposed in the needle  52  and adjacent to the first loose-fitting wire  56 . A second packing bed  60  is disposed in the needle  52  and adjacent to the first packing bed  58 . A second loose-fitting wire  62  is disposed in the needle  52  and adjacent to the second packing bed  60  until reaching and then passing a side hole  64 . A tight-fitting wire  66  is then disposed adjacent to the loose-fitting wire  62  until passing out of the needle  52  opposite the working end. The function of the tight-fitting wire is to act as a plug that prevents the flow of fluid past the side hole and out of the non-working end of the needle. 
         [0017]    It should be understood that the length of the loose-fitting wire  62  and the tight-fitting wire  66  may vary in relation to the side hole  64 . However, it should also be apparent that the first embodiment of  FIG. 2  eliminates the dead space  28  of the prior art using the loose-fitting wire  62  and the tight-fitting wire  66 . 
         [0018]    Differences between the needle traps  10 ,  50  include the following aspects. First, the dead space  28  may be defined as the space between the glass wool  22  and the end of the needle at the non-working end in the prior art. This dead space is filled by the loose-fitting wire  62  and the tight-fitting wire  66  in the present invention. 
         [0019]    The needle trap  10  may use a plunger-like device to draw a sample into the needle  12 . The side hole  24  is supposed to be sealed by the Teflon sleeve  30 , but it may leak. 
         [0020]    While the tight-fitting wire  66  does not allow the flow of a gas through the needle  52 , the loose-fitting wire  62  does allow a limited flow of gas. The loose-fitting wire  62  substantially reduces the volume of the dead space in the first embodiment. It has been observed that when an injection from the needle  52  into an analyzer injection port  80  (shown in  FIG. 3 ) is made, the lack of dead space in the first embodiment of  FIG. 2  may cause the GC peaks to come out sharper and cleaner. 
         [0021]    Putting a sample into the needle  52  takes place with flow entering through the pointed working end  54  of the needle  52  and out through the side hole  64 . In contrast, a needle in the prior art teaches flow in through the pointed end of the needle and out through the other end with the side hole being covered. However, by allowing the side hole  64  to not be covered when taking in the sample, this action eliminates the possibility of a leak through the side hole while pulling sample from the working end. 
         [0022]    During sampling there is no way to know if there is a leak from the side hole  64 . A leak would result in less or even no sample being drawn into the packing beds  58 ,  60 . Therefore, the present invention uses the side hole  64  as a port. A pump is connected to the side hole  64  while the sample is drawn into the needle  52  from the working end  54 . The pump is typically a gas pump that applies a suction force to the side hole  64  in order to draw in a fluid sample through the working end  54  of the needle  52 . A Teflon sleeve  70  slides over the side hole  64  when it needs to be covered. The Teflon sleeve is slidingly engaged over the side hole  64  to make it easy to move aside when access to the side-hole is needed. 
         [0023]    It is noted that the packing material used in the packing beds  58 ,  60  is known to those skilled in the art and is not considered to be a novel element of the first embodiment of the present invention. 
         [0024]    It should also be understood that there may be more than two packing beds in the needle trap  50 . Furthermore, the material in the packing beds may be different form each other. 
         [0025]    In the present invention shown in  FIG. 3 , the inside diameter of the injection liner  82  fits the outside diameter of the needle  52  leaving a gap of 0.001″ or less. This tight fit may cause greater than 95% of the flow of the sample from the needle  52  to go through the needle  52  and not around the needle. 
         [0026]    In contrast, the prior art solution to this problem is to have the rounded end of the needle fit tight against an indentation in the liner. The first embodiment is an improvement because it is more robust; little bits of grit or dirt won&#39;t cause the delivery system to fail. If the needle  52  is inserted all the way into the injection liner  82 , there may be more confidence that the flow is through the needle. 
         [0027]    In addition needles of slightly different lengths will still work with the design of the present invention. In contrast, the prior art solution does not allow for automation or using the stop  68  of the needle  52  on top of the injection port to start a run as can be done with the present invention. 
         [0028]    The needle trap  50  of the present invention may be a hand-held device for taking a sample that is inserted into an analytical device such as a gas chromatography (GC) system or a gas chromatograph/mass spectrometry (GC/MS) system. The needle trap  50  may also be part of an automated device. 
         [0029]    The needle  52  that is used to take the sample may be of varying widths. It is preferred that the needle  52  have a diameter that will allow the necessary clearance into an injection port on the desired analytical device. 
         [0030]    It is an aspect of the present invention that the needle trap  50  is not part of a syringe-like device having a plunger for drawing a fluid into and out of the needle  52  through both ends. Instead, the end opposite the working end  54  is sealed, and therefore the side-hole  64  becomes a port which is coupled to a pump for drawing the sample to be drawn into the needle  52  and the packing beds  58 ,  60 . As the fluid is drawn into the needle trap  50 , particulate matter in the fluid may be trapped in the packing beds  58 ,  60 , and later desorbed in an analytical device. 
         [0031]    When it is time to deliver the sample to the analytical device, the present invention avoids the problems associated with a side hole leak. Instead, a gas is delivered to the needle trap  50  through the side hole  64 , forcing the sample from the packing beds  58 ,  60  and into the analytical device. As the needle trap  50  is inserted into the injection liner  82  (see  FIG. 3 ), the Teflon sleeve  70  is pushed back to uncover the side hole  64  so that a fluid can be inserted in order to push the sample into the injector  80 . The analytical device is sealed against the stop  68  of the needle trap  50 . 
         [0032]    It should be understood that fluid may flow around the loose-fitting wire  62 , but not past the tight-fitting wire  66 . Thus, when it is time to inject the sample into the analytical device, a gas such as helium is now injected into the side hole  64 . It is also noted that the non-working end of the needle trap  50  may be sealed with a drop of glue  84  or any other appropriate seal. 
         [0033]    The fluid drawn into the needle trap  50  may be any fluid that is typically delivered to a GC, a GC/MS or any other fluid analyzer. 
         [0034]    It is noted that a certain volume of sample is drawn through the packing beds  58 ,  60  and may be referred to as the breakthrough volume. After a certain volume of a sample is adsorbed into the packing beds  58 ,  60 , the packing beds won&#39;t trap anymore and it should start coming out the other end. Calculations performed before experimental data was obtained indicated that the breakthrough volume would be about 100 mL. However, experimental results show that the breakthrough volume obtained was approximately 2 Liters, or 20 times greater than expected. Likewise, calculations showed that a flow rate should be about 10 mL/min, but experimentally, the needle trap  50  has a flow rate of 50 mL/min, or five times greater than expected. 
         [0035]      FIG. 4  is provided as a profile cut-away view of the needle trap  50  as it is being prepared to take a fluid sample. As shown, the side hole  64  is exposed on the needle trap  50  by sliding the Teflon sleeve out of the way. The side hole  64  is placed within a chamber  102  in which a vacuum pump  100  can be attached in order to apply a suction force. The chamber  102  includes seals  104  to prevent any leaks. 
         [0036]    It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements.