Abstract:
The invention relates to a direct on column non-vaporizing injector for gas chromatographic analyses and comprising an accessory device capable of allowing injection with sample vaporization and possible splitting. The accessory device is formed by a tubular element which, at one end, can be fixed to the injector body coaxially to the passage for the injection syringe needle, while its opposite end is closed by an insert provided with an axial hole in which the gas chromatographic capillary column head is pneumatically inserted, said insert being provided with at least one other hole for splitting the vaporized sample. The tubular element houses a vaporization tube which under conditions of thermal exchange with heating means, is pneumatically connected to said passage for the injection syringe needle and to said insert holes and receives the upper end of the gas chromatogaphic column. Gas is employed countercurrently to strip off undesired components while the liquid sample is held in the vaporization chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an injector for the injection of samples to be analyzed in a gas chromatographic capillary column and, more precisely, to an injector of the non vaporizing direct on-column type, comprising an accessory device applicable thereof to allow its use also to perform injections of the vaporizing type with undilutable samples or concentrated solutions requiring a splitting of the vaporized sample, as well as to eliminate the solvent before the sample is transferred to the capillary column. 
     2. Description of the Prior Art 
     In U.S. Pat. No. 4,269,608 assigned to the same assignee, there is described an injector which can perform the injection of samples to be analyzed without vaporization, directly in the gas chromatographic column. 
     Said injector comprises a duct for the introduction of the injection syringe needle which can be closed by means of a valve, the lower section of said duct housing the end of a gas chromatographic column. 
     Said gas chromatographic column end is pneumatically connected to the duct thanks to an O-ring kept in position by a small tube coaxial to the column and screwed to the injector body. This small tube, according to what is described and claimed in the aforementioned patent, forms a jacket around the column head and the hollow space between the jacket and the column is fed with a fluid at a controlled temperature. 
     From U.S. Pat. No. 4,383,839 there is also known a method for the injection with vaporization of a liquid sample in a gas chromatographic capillary column comprising the steps of 
     (a) injecting the liquid sample into the initial part of a sample vaporization tube which does not contain a stationary liquid phase (or contains an immobilized phase), the sample being kept liquid during the whole injection process; 
     (b) heating the vaporization tube and feeding it with carrier gas to entrain the vaporized sample; 
     (c) diverting part of the resulting mixture of vaporized sample and carrier gas by means of a splitter and sending the remaining part to a gas chromatographic column containing a stationary liquid phase for chromatographic separation. 
     The vaporization tube can be empty or a fiberglass sponge can be placed in it to hold the sample when it is in the liquid state and to release it when it passes to the vapour state. In fact, the fiberglass sponge is impermeable to the sample at the liquid state, while it is permeable to the sample when the letter is at the vapour state. 
     OBJECTS OF THE INVENTION 
     An object of this invention is now to provide an injector of the non-vaporizing direct on-column type, for instance such as the one described and illustrated in the aforementioned U.S. Pat. No. 4,269,608 and comprising an accessory device which allows said injector to be used to perform a method of the type described and claimed in the aforementioned U.S. Pat. No. 4,383,839. 
     Another object of the present invention is to provide an injector with an accessory device having the abovementioned features, which is capable of holding inside the vaporization tube the sample at the liquid state and of releasing it when it passes to the vapour state, even in the case of very polar samples, for which the use of said fiberglass sponges could involve drawbacks due to their high surface and the difficulty of completely de-activating them. 
     Another object of this invention is to provide an injector with an accessory device of the aforementioned type, which allows the elimination, during the injection stage and in any case before the vaporization stage, of the volatile components present in a sample to be analyzed, thus allowing it only the heavy components in the sample to be analyzed. 
     SUMMARY OF THE INVENTION 
     Said objects are achieved by an on-column type injector with accessory device which comprises a tubular element, one end of which can be fixed to the injector body coaxially to the duct for the passage of the injection syringe needle, while the opposite accessory device end is closed by an insert provided with an axial hole, in which the head of a capillary gas chromatographic column is pneumatically housed, and with a hole for controllaby splitting the vaporized sample, the tubular element housing a vaporization tube under conditions of thermal exchange with heating means and which is pneumatically connected to said passage for the injection syringe needle and to said holes of the insert. 
     In particular, the vaporization tube can have a series of inner protrusions, turned towards the axis of the tube itself and reciprocally offset and opposed in such a way as to hold the sample when it is at the liquid state. 
     Moreover, the end of said tubular element in which the gas chromatographic column head in inserted, can have, besides the hole necessary to perform the vaporized sample splitting, a second hole communicating with a duct connected, through a valve, to a carrier gas line. Said duct can moreover be connected, downstream of said valve and by means of a fitting provided with an adjustable neck, to the duct for the introduction of the sample carrier gas, while the valve can be a three-way valve, allowing a selective connection of the carrier gas line to the duct for carrier gas introduction into the on-column injector or to the duct leading to the tubular element. 
     Thanks to the aforementioned second hole in the tubular element, during the injection of the sample to be analyzed and in any case before the vaporization stage of the sample portion to be transferred to the capillary column, it is possible to introduce carrier gas into the tubular element through said second hole and in such a way to contact strike the sample with a gas current flowing in the opposite direction to that of the sample introduction in the gas chromatographic column, said gas current carrying the sample volatile substances out of the on-column injector by means of a suitable discharge duct provided in the injector body and equipped with cut off and control valves. 
     The invention will be now described more in detail with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an on-column injector equipped with a vaporization accessory device and provided with a system for the elimination of the volatile components present in the sample to be analyzed. 
     FIG. 2 is a cross-sectional view of a modified embodiment of the vaporization accessory device according to the invention. 
     FIG. 3 is a section taken along the line III--III of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the injector 1, for example such as the one described and illustrated in the aforementioned U.S. Pat. No. 4,269,608 comprises a duct 2, which can be closed by a valve, capable of allowing the passage of the injection syringe needle, and a duct 1&#39; for the introduction of carrier gas. The lower part of the injector comprises a protruding body 3 coaxial to the duct 2 allowing the injector to be fixed to the walls 4 of an oven which houses a gas chromatographic capillary column 5, in particular preferably made of fused silica. 
     The protruding body 3 has a threaded cavity 6 coaxial to the duct 2 and into which said duct 2 and a duct 6&#39; open, the latter duct communicating with a fluid source at controlled temperature, for example, even if not exclusively, air, possibly controlled by a valve 6&#34;. 
     In the known embodiment, a small tube coaxial to the initial part of the column is screwed in the threaded cavity 6, forming a collecting chamber for the fluid at controlled temperature coming from the duct 6&#39;. 
     According to the invention, in said threaded cavity 6, an accessory device 8 formed by a tubular element 7 is screwed instead of said small tube; in the lower end of said tubular element 7 is screwed an insert 9 provided with two radial holes 10 and 10&#39; and with an axial hole 11, wherein the gas chromatographic column head 5 is inserted and pneumatically sealed and mechanically locked by a gasket 9&#39; and a locking nut 9&#34;. 
     Inside the tubular element 7, a vaporization tube 12 is positioned, the upper end of which is inserted in the duct 2 of the injector and pneumatically sealed by means of an O-ring 13 pressed against the injector body by the tubular element itself. The lower end of tube 12 is inserted in the axial hole 11 of insert 9 and pneumatically sealed by means of a gasket 14. In particular, the lower end of tubular element 7 has a threaded cavity 21 provided with a shoulder 22 capable of holding a washer 23 made of insulating material, for instance Vespel (registered trade mark), against which the gasket 14 is pushed by the insert 9. 
     The first of the two radial holes 10 and 10&#39; of insert 9 communicates with a duct 10&#34; and is designed to allow splitting of the vaporized sample, while the second hole 10&#39; communicates with a duct 10&#34; connected, through a three-way valve 29 to which the duct 1&#39; is also connected, to a source of carrier gas. Moreover, the ducts 1&#39; and 10&#34;&#39; can be connected to one another, downstream via the valve 29, by a duct 30 provided with an adjustable neck 31. 
     The inner part of the vaporization tube 12 can house a fiberglass sponge, or it can be provided, in an intermediate section between a point A downstream of the injection point and a point B upstream of the open end of column 5, with a series of protrusions 20 turned towards the axis of the tube itself and reciprocally offset and opposed, in a way as to create a zigzag passage for the injected sample. The protrusion 20 hold the sample inside the tube 12 when the sample is in the liquid state so as to prevent it from penetrating into the gas chromatographic column before it is vaporized. 
     Between the inner side walls of tubular element 7 and the vaporization tube 12 there is an hollow space 15 communicating through one or more holes 16, with said cavity 6 and therefore with duct 6&#39; leading to the cavity itself and, through one or more holes 17, with the oven chamber, in a way as to submit the vaporization tube 12 to the controlled thermal action of the fluid introduced in 6&#39; and discharged in 17. Said fluid is generally intended for cooling the tube 12, but it is also possible to introduce hot fluid for sample vaporization. However, for the latter purpose, it is more advisable, as illustrated, to use an electric resistor 18, wound around the tube 12 and having an end soldered to a small metal cylinder 24, soldered on its turn in the upper axial passage of element 7. The other end of resistor 18 is soldered to a small metal cylinder 25 fixed between the ring 23 and a shaped insulating gasket 26. Said cylinder 25 is connected to a first electrode 19 passing through body 7 by means of an insulating gasket 27, while the other electrode 28 is grounded in a point whatever. 
     Finally the injector body 1 has a third duct 32 for discharge, which is inserted in the duct 2 upstream the vaporization tube 12 and has a first valve 32&#39; for controlling the discharge flow rate and a second valve 32&#34; to control the duct opening and closure. 
     The tubular element 7 is fixed to the injector 1 and the gas chromatographic column head is connected, through insert 9, to the vaporization tube 12, in particular it is inserted with its free end straight into the lower part of the vaporization tube 12. 
     FIGS. 2 and 3 show another embodiment of the invention, wherein the vaporization tube 12 is housed in a tubular element 40 in a material adapted for heat transfer, for instance in a metallic material. This tubular element is heated by a plurality of resistors 44 housed in tubular insulating sheats 42. To heat the splitting point, which is a very important feature, a liner 46 made of aluminum, or any other direct or indirect heating means can be provided for. 
     To perform an injection with or without elimination of the volatile components (back-flush), the following operations must be accomplished. 
     The valve (not illustrated) to open and close duct 2 of the injector is opened and the upper part of the vaporization tube 12 receives through the duct 2 the injection syringe needle containing a sample to be analyzed which is at the liquid state. 
     The sample is injected into the tube 12, the syringe needle is removed and the valve controlling the duct 12, is closed. The fiberglass sponge inserted in the tube 12 or the protrusions 20 on the tube wall prevent the sample at the liquid state from penetrating into the column 5. On the other hand, during injection the temperature of tube 12 is kept at such a value as to prevent sample vaporization by means of cooling fluid introduced in 6&#39; and discharged in 17. If required, the tube 12 may be heated to a controlled temperature to eliminate by the back flush or splitting line well defined light sample components not interesting for the analysis. 
     At this point, after eventual interruption or communication of cooling, the vaporization tube 12 is heated at a chosen temperature, for instance by the electric resistor 18, until the sample is completely vaporized. The carrier gas which flows into the injector duct 2, coming from duct 1, enters the vaporization tube 20 and sweeps the vaporized sample towards the chromatographic column. Part of the mixture formed by the vaporized sample and the carrier gas can be deviated outside the column 5 and discharged through the duct 10 of insert 9 so that the column receives only a certain amount of vaporized sample. In particular, the ratio between the amount of mixture deviated by the duct 10 (splitting ratio) is determined by controlling the flow rate in said duct and the opening or closing of same through the control valve 33 and cut off valve 33&#39; connected to the duct 10, according to the temperature of tube 12. Of course, a splitless injection can be made by closing valve 33&#39;. 
     At the end of the analysis, in order to rapidly cool the tube 12, a cooling gas, for example ambient air, is introduced into the hollow space 15 of the tubular element. Said gas, after heat exchange contact with the tube 12, flows into the oven chamber through holes 17 provided in the lower part of the tubular element. 
     In case the sample to be analyzed contains volatile substances which must not enter the gas chromatographic column, during the sample injection stage and before the sample vaporization, the duct 10&#34;&#39; is fed with inert gas. In more detail, when the syringe needle to inject the sample has been introduced into the duct 2, the valve 29 is regulated in such a way that only the duct 10&#34;&#39; communicates with the inert gas source, the valve 31 is regulated in such a way that the duct 10&#34;&#39; is connected to the duct 1&#39; while the valve 32&#34; of the discharge duct is open. The carrier gas sent to the duct 10&#34;&#39; comes out from the hole 10&#39; of the insert 9, partly penetrating into the gas chromatographic column and partly into the tube 12. 
     A small fraction of carrier gas introduced in the duct 10&#34;&#39; passes through the duct 30 and the neck 31 and flows into the duct 1&#39;. At this point the sample is injected into the tube 12 where it meets the opposite inert gas current coming in through the duct 10&#34;&#39;; in this way the more volatile substances present in the sample are swept by the carrier gas towards the opposite direction to that of sample introduction into the gas chromatographic column and sent out of the injector through duct 32 and under the control of valve 32&#39;, for example a needle valve. The small fraction of inert gas coming out from the duct 1&#39; prevents the volatile substances from entering the duct 1&#39; itself. 
     The heaviest part of the sample is held by the protrusions 20 of tube 12 when contacted by the carrier gas flow coming from hole 10&#39; of insert 9 and entraining the sample volatile substances. When this stage of elimination of the more volatile substances present in the sample is over and the sample vaporization stage begins, the valve 29 is regulated in such a way that the carrier gas flows only into the duct 1&#39; and the valve 32&#34; of the discharge duct is closed. The duct 10&#34;&#39; is kept in communication with duct 1&#39; so that a fraction of carrier gas flowing to the duct 1&#39; comes out from the radial hole 10&#39; of the insert 9 preventing the vaporized sample from entering the duct 10&#34;&#39;. 
     The adjustable neck 31 is designed to control the gas flow rate necessary to create a fluid seal, alternatively in the duct 1&#39; during the stage of elimination of the volatile substances present in the sample, and in the radial hole 10&#39; during the vaporization stage and the sample injection in the gas chromatographic column.