Abstract:
The invention relates to a vaporization injector for a gas chromatograph, said injector comprising a structure ( 11 ) mounted in a detachable manner on the gas chromatograph body and including the sample introduction means, the vaporization chamber and pneumatic connections for feeding the carrier gas to the vaporization chamber and to the septum purge means, as well as pneumatic connections for evacuating the splitted sample and carrier gases.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 371 of PCT/IT2010/000030, filed Feb. 1, 2010, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns a vaporisation injector suitable for operating in a gas chromatography instrument. 
     The injector is a device which allows the transfer of a sample, consisting of the substance to be analysed and a solvent, for example from a syringe to the gas chromatography column by means of a carrier gas. The injectors can be on-column injectors, when the sample is injected into the column in a liquid form and vaporises at the beginning of the column, or they can be vaporisation injectors, in which case the sample is heated and vaporised inside the injector. 
     The subject of the present invention is a vaporisation injector, generally consisting of a heated vaporisation chamber into which the sample is fed for example via the needle of a syringe which crosses an insulation septum. 
     From the vaporisation chamber, the vaporised sample is transferred to the column by the action of the carrier gas, said transfer being performed on the whole sample injected (splitless), or only on a fraction of the sample injected (split). In the latter case the main part of the sample is diverted and discharged together with a fraction of the carrier gas. Furthermore, a current of the carrier gas is diverted before it meets the sample, in order to purge the septum. 
     DESCRIPTION OF THE PRIOR ART 
     Therefore, a vaporisation injector with splitting of the sample must also have, in addition to the means for heating the vaporisation chamber, suitable pneumatic connections to subdivide the carrier between the inlet into the vaporisation chamber and a duct for purging of the septum, and to subdivide the flow of the carrier and the sample between the part sent to the column and the part which is diverted or splitted. 
     In the evolution of these injectors the three different lines described above are controlled by proportional valves, preferably acting on one single manifold, the septum is mounted so that it can be replaced and the inside surface of the vaporisation chamber is covered by a liner which can also be removed for cleaning or replacement. 
     Non-vaporisable parts of the sample and fragments of septum can accumulate in the injector in the long term, negatively affecting the subsequent analyses, also in the event of replacement of the liner and/or septum. Although the majority of the contaminants remain on the liner, part of them tend to accumulate on the bottom, inside the injector body. The splitting line is also subject to contamination by the sample which can even clog it, and for this reason a carbon filter is provided. Said filter, however, cannot treat the line between the injector and the filter, which thus becomes a trap for the heaviest compounds. 
     The injectors produced so far, with relative pneumatic system, are fixedly mounted on the body of the gas chromatograph and hence maintenance can be performed only at the level of the septum, the liner and the carbon filter which can be installed on the carrier, purging and/or splitting lines. Therefore, the contamination of the other parts of the injector, injector body and pneumatic system cannot be removed unless the injector is entirely replaced. 
     OBJECTS OF THE INVENTION 
     The object of the invention is to provide a vaporisation injector which can be easily and rapidly disassembled, like the liner, to allow cleaning, for example by sonication or other known processes, or replacement of parts. 
     A further object of the invention is to provide a pneumatic system which allows disassembly of the injector and furthermore permits the installation of filters in particularly convenient and accessible positions for maintenance or replacement, while maintaining total system efficiency. 
     SUMMARY OF THE INVENTION 
     In order to achieve these and other objects, the invention concerns a vaporisation injector having the characteristics and construction features as described in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be illustrated with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates in perspective the injector body, disassembled from the relative block of a gas chromatograph, housing the heating means, the electronics and the manifold of the pneumatic system. 
         FIGS. 2 and 3  illustrate in perspective the conformation and modes of removal of the injector body from the above-mentioned block. 
         FIGS. 4 ,  5  and  6  illustrate, again in perspective, the arrangement of the apertures for inlet and outlet of the gases and the arrangement of the seals in the injector body. 
         FIGS. 7 to 10  illustrate, in different perspective views, the arrangement of the gas channels inside the injector body. 
         FIGS. 11 and 12  are axial sections of the septum supporting head in two versions which can be replaced or modified. 
         FIG. 13  shows, in an axial section, an embodiment form of the injector adapted for introduction of gaseous samples. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The injector shown in  FIGS. 1 to 3  is essentially composed of a fixed part, the components of which can nevertheless be disassembled, here called “block” and indicated in general by reference number  10 , and a removable part  11 , which constitutes the injector body. 
     The block  10  comprises the control electronics  12 , the control valves  13  of the pneumatic system; the filters  14  and a manifold  15  for distribution of the incoming carrier gas and the outgoing splitting and purge gases, in addition to the means  16  for controlled heating of the injector body, the structure of these components being essentially known in the field. 
     The body  10  furthermore defines a surface  17  designed to support the body  11  of the injector and having two threaded apertures  18  for housing screws  19  for fastening the injector body. 
     The injector body  11  consists of a cylindrical element  20  designed to be inserted in the heating element  16  and terminating at the top in a wider area  21  comprising a counter-surface resting on the surface  17  of the block, with apertures  22  for the screws  19 , in addition to the gas distribution means which will be described below. 
     At the top, the injector body  11  has an upper closing nut  23  to permit access to the vaporisation chamber where a liner  24  can be housed and removed for replacement or cleaning. However, due to the possibility to remove the injector body, a liner is not strictly required. A further nut  23 ′ is also provided for removing the upper cover, containing the injection hole, in order to allow access to the support  41  of the septum so that it can be removed for cleaning or replacement. 
       FIGS. 4 to 10  illustrate details of the injector pneumatic system. The carrier gas is fed to the manifold  15 , which feeds it to the aperture  25  provided on the fixed surface  17  connected to a corresponding aperture  26  presented by the counter-surface  27  of the injector body. The surface  17  also has two further apertures  28  and  29  which connect to corresponding apertures  30  and  31  on the injector body. The apertures  28 ,  31  and  29 ,  30  are provided respectively for outlet of the splitting gas and for outlet of the purge gas, which are conveyed to the outside, via the mouths  32  and  33 . The apertures  25 ,  28  and  29  are provided with seals, for example in the form of O-rings. 
     Inside the injector body, passages are provided for the transit gases and O-rings for separation of the flows, as can be seen in  FIGS. 7 to 10  in particular. More specifically, the carrier gas which enters the injector body is sent, via the channels indicated by  34  in  FIGS. 7-10 , to the cover of the liner  24 , from where it is fed to the inside of the liner  24  and, partly, to the injector head to purge the septum. 
     The carrier gas and sample flow which is not sent to the column (splitting flow) is conveyed back towards the head of the injector on the outside of the liner  24  and fed to a discharge channel  35  and to the apertures  31  and  28 . 
     The separation between the carrier gas and the splitting gas is obtained by means of a first toroidal gasket (O-ring)  36 . The gas coming from cleaning of the septum (purge flow) is sent to the apertures  30  and  29  through the channels indicated by  38  and said flow is separated from the carrier flow by means of a second toroidal gasket (O-ring)  39  in the injector head. Lastly, a third toroidal gasket  40  separates the purge gas from the external atmosphere. 
     The flows are controlled, according to known methods, by pressure sensors and proportional valves, installed on the block  10 . 
     With reference to  FIGS. 11 and 12 , the head  41  supporting the septum can be provided and applied in two different versions. More specifically,  FIG. 11  illustrates a supporting head in which the injection needle does not come into contact with the hot inner surface of the injector, i.e. to carry out the so-called cold needle injection technique. 
     In  FIG. 12  the supporting head  41 ′ of the septum, which can be similar to that of  FIG. 11  and therefore replaces it, or is different from that of  FIG. 11  with some modifications, has an insert  42 , applied previously or which can be inserted, to reduce the diameter of the needle passage, permitting local heating of the latter, in order to carry out the so-called hot needle injection technique. Alternatively, again for hot needle injections, it is possible to simply replace the supporting head  41  of  FIG. 11  with the same type of supporting head but having a narrower channel for passage of the needle. 
       FIG. 13  shows an embodiment of the injector which is able to allow the introduction of gas samples, for instance as obtained from a purge and trap sampler or a thermal desorber. The injector body comprises a gas connector  43  for the introduction of the carrier and a second gas connector  44  for the introduction of the gaseous sample. The purge line  45  and split line  46  are also shown. Of course in case of a gas sampling the upper aperture  47  for the introduction of a syringe needle should be closed, for instance by a septum.