GB2039777A

GB2039777A - Vaporization Injector for Gas Chromatographic Columns

Info

Publication number: GB2039777A
Application number: GB8001585A
Authority: GB
Original assignee: Carlo Erba Strumentazione SpA
Current assignee: Fisons Instruments SpA
Priority date: 1979-01-17
Filing date: 1980-01-17
Publication date: 1980-08-20
Also published as: NL8000240A; GB2039777B; DE3001425A1; FR2447032A1

Abstract

A vaporisation injector for gas chromatographic columns comprising an injector body (10) and an injection channel (38, 26) extending through said body and into which an injection needle (60) may be inserted to inject the sample to be analysed into a heated vaporisation chamber (24) into which the end of the column (16) extends and into which a carrier gas is fed to convey the vaporised sample into the column, wherein there is provided in said body (10) a valve member (44) movable between a first position closing said channel (35) against the insertion of said needle (60) and a second position in which said channel is open for the insertion of said needle, and wherein means (50, 52, 54) are provided intermediate the ends of said channel for feeding a secondary stream of said carrier gas into said channel intermediate the ends thereof to create a pressure gradient between the valve member and the vaporisation chamber. <IMAGE>

Description

SPECIFICATION Vaporization Injector for Gas Chromatographic Columns This invention reiates to a vaporization injector for gas chromatographic columns.

Vaporization injectors for gas chromatographic columns are already known. Generally, such vaporization injectors comprise a heated chamber in which the sample to be analysed is vaporized before being fed to the column in a stream of carrier gas. Usually, the sample to be analysed is injected into the vaporization chamber using a hollow needle which is inserted into the chamber through a sealable channel leading to the vaporization chamber. These injectors, due to the fact that the vaporization chamber must be kept pneumatically isolated from the outside before, during and after injection, are provided with a separating septum in correspondence with the injection channel, said septum being made of rubber, particularly silicon rubber, and being pierced by the injection syringe needle when said injection is performed.At the end of the injection of the substance to be examined, the needle is withdrawn and the opening in the septum caused by the needle closes again thanks to the elastic properties of the septum itself. This known arrangement has, however, some drawbacks, due to the presence of a heating element for the vaporization chamber which thermally affects the needle insertion channel and the separating septum, as well as the actual presence of the separating septum.

In fact, with the temperature increase above ambient values caused by the heating element of the vaporization chamber, the rubber forming the separating septum tends to alter and decompose, and the decomposition products negatively affect the chromatographic system. Attempts to overcome this drawback have been made by using a washing current constituted by the same carrier, which however does not always prove to be sufficient for the desired aims. Moreover, as a consequence of the mechanical action of the needle introduction through the septum, the detachment of small pieces of rubber occurs which fall into the vaporization chamber where they decompose and give rise to contamination of the sample which may alter the analysis in the gas chromatographic column.

A second drawback, more particularly related to the presence of a heated vaporization chamber, results from a discrimination occurring in the injection of the substance to be analysed through the syringe needle into the vaporization chamber.

In fact, as the heat of the vaporization chamber affects the needle insertion channel and therefore the needle itself, the substances it contains tend to undergo a discriminating vaporization in the needle itself and the volatile compounds come out of the needle, while the high boiling substances remain on the needle wall and do not penetrate or penetrate later into the vaporization chamber, thus altering the whole analysis.

According to this invention, there is provided a vaporization injector for gas chromatographic columns comprising an injector body and an injection channel extending through said body and into which an injection needle may be inserted to inject the sample to be analysed into a heated vaporization chamber into which the end of the column extends and into which a carrier gas is fed to convey the vaporized sample into the column, wherein there is provided in said body a valve member movable between a first position closing said channel against the insertion of said needle and a second position in which said channel is open for the insertion of said needle, and wherein means are provided intermediate the ends of said channel for feeding a secondary stream of said carrier gas into said channel intermediate the ends thereof to create a pressure gradient between the valve member and the vaporization chamber.

The use of a two-position valve member according to the invention in place of the rubber septum avoids any drawbacks due to rubber modification because of heating and any possibility of detachment of septum pieces during the needle insertion operation, while the introduction of at least part of the carrier gas along the insertion channel creates the cited pressure gradient which allows the necessary insulation of the vaporization chamber from the external environment, even when the valve is in its open position.Moreover, the mentioned introduction of carrier along the insertion channel and the subsequent formation of a current of carrier gas externally lapping the needle, until reaching the vaporization chamber provides a second fundamental advantage of the invention, due to the fact that this current cools the needle and avoids any premature vaporization of the substances within same, before it reaches the vaporization chamber. Therefore, said negative discrimination effect which can be noticed in some cases in the previous configurations is completely eliminated.

Moreover, by applying the previously described principles, it is possible to obtain a vaporization chamber separated from the injector itself, using an accessory device removably.assembled on a known injector for direct injection (on-column injector), this accessory device comprising, in a unit to be inserted between the on column injector and the oven housing the gas chromatographic column: an injection channel to be pneumatically inserted into the column seat within the injector, suitable for accepting the syringe needle and provide, at least for part of its length, with cooling means belonging to the injector; an expansion and vaporization volume for the sample, pneumatically connected on one side to the injection channel and submitted to the action of a heat source at least sufficient to determine the vaporization of the injected sample; and an outlet channel, pneumatically connected to the vaporization volume on the opposite side to the injection channel and provided with means to pneumatically receive the upper end of the gas chromatographic column.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is an axial section, with some details omitted for a better understanding of the drawing, of a vaporization injector for gas chromatographic columns according to the invention.

Figure 2 is an axial illustration of an accessory device applied in operative position to a direct oncolumn injector for vaporization injection.

Figure 3 is a section corresponding to the one of figure 2 but with the parts in a separated position.

With reference to figure 1 of the drawings, the illustrated injector comprises a first body 10, which may be fixed in a known way to an oven housing a gas chromatographic column and provided with an internal cylindrical cavity 12 ending in its lower section in a channel 14 axially crossed by the capillary gas chromatographic column 16 which penetrates into the cavity 12 through a sealing element 1 8. A channel 20 allows the introduction in a way known in itself of a cooling agent for the initial section of column 16, while 64 indicates a known "splitting line", which can be optionally used or not.The cavity 12 of the body 10 is internally coated with a glass jacket 22 forming a chamber 24 called vaporization chamber which gets narrower in its upper section and forms channel 26 through which the needle of a syringe is introduced into the vaporization chamber 24. The body 10 is surrounded, in correspondence with the vaporization chamber 24, by a heating device 28, of a type known in itself, while the channel 30 in the upper section of body 10 allows the carrier introduction over the glass coating 22, in correspondence with a small distribution chamber 32 from which the channel 26 comes out.

To the body 10, with the interposition of a metal packing 34, a second body 36 is fixed defining within itself a passage or channel 38 for the injection syringe needle introduction, said passage or channel being suitably dimensioned using a small steel tube as indicated in 40. The body 36 also defines a conical seat 42 for a valve 44 designed to open and close respectively the passage 38 as a consequence of the rotation of same around its own axis 46, which rotation may be manually actuated, for instance by means of lever 48, or by any other suitable means. The seat 42 for valve 44 opens into a chamber 50 housed in the body 36 and connected to the outside by means of a channel 52 through which the auxiliary introduction of carrier is carried out, at a reduced rate and under a certain pressure kept constant by means of a pressure regulator.The chamber 50 communicates with a channel 54 in the valve 44 body and leading to the passage 56 which puts into communication the two branches of the channel 38. The passage 54 is placed along the axis 46 of the valve 44 and the auxiliary introduction of carrier into the injection channel 38 occurs only when the valve 44 is in its open position, said introduction forming a current in the passage 38 respectively directed towards the vaporization chamber 24, downstream the valve and towards the outside of body 36, upstream the valve 44. The carrier current through the channel 54 is carried out by means of a pressure regulator, which maintains a gas flow downstream the valve 44 even if the pneumatic resistance of the upstream section is lower than the one of the downstream section.

The introduction of the substances to be analysed is performed by means of a known syringe 58 equipped with a long needle 60 which penetrates into the channel 38 and into the channel 26 as far as the vaporization chamber 24 where the substance to be analysed is introduced by means of a suitable control of the piston 62 of syringe 58.

The valve 44 is advantageously constituted by a heat resistant polyamide and particularly a polyamide known on the market under the trademark Vespel of Du Pont de Nemours, or graphitized Vespel.

According to the invention, the introduction of carrier through channel 52 occurs at a pressure and a rate such as to cause a positive pressure gradient between the introduction point, in this particular case illustrated in correspondence to the valve 44, and any other point downstream the same, in particular the vaporization chamber 24 or the distribution chamber 32. This pressure gradient allows to perform the opening operation of channel 38 by means of valve 44 without causing any communication between the vaporization chamber 24 and the external environment.Moreover, as a consequence of the extremely small difference between the internal diameter of channel 38 and the external diameter of needle (of the order of 0.28 and 0.23 mm respectively), a very rapid current of carrier externally surrounds the needle, both downstream and upstream the valve 44, said current cooling the needle in spite of the presence of heated surrounding areas and keeping also the volatile substances introduced by means of the syringe in their liquid condition inside the needle, thus allowing their vaporization only in the appropriate chamber 24. This current continues even downstream the chamber 38, in the second section of the needle introduction channel, defined by the shaping of coating 22 and indicated by 26, this second section having a slightly larger diameter than the previous one (approximately 0.3 mm) and being fed with the whole current of the carrier introduced through the channel 30. This ensures constant cooling conditions of the needle as far as the vaporization chamber 24.

Also applying the principles of this invention, figures 2 and 3 illustrate a vaporization injector obtained by connection of a known direct oncolumn injector with a vaporization chamber, in the form of an accessory device.

With reference to said figures, an on column injector 110 is constituted in a known way by a body 112 in which a channel 114 is obtained which can be closed by means of a valve 11 6 placed in correspondence to an area provided with a coating 11 8 for guiding the injection needle 120 of an injection syringe 122 of a type known in itself. The body 11 2 shows, in a zone under the valve 11 6, a section 124 designed in such a way as to allow cooling from outside, for instance finned to receive a cooling permanent air current and to transmit said cooling to channel 114. A channel 126 leads to channel 114 in order to introduce a carrier gas.Also in a known way, the channel 114 ends downstream with an opening 128 which houses the head 130 of a cylindrical sleeve 1 32 kept in position by means of a threaded locking ring 134 applied at the basis of body 112 and acting on the sleeve head 130.

The latter keeps in position a truncated coneshaped gasket 1 36 having an axial opening through which it is possible to introduce the upstream end of a capillary gas chromatographic column, which passes through a corresponding axial opening of sleeve 132 and penetrates into channel 114. The axial opening of sleeve 132 forms, around the capillary column, a hollow space 138 which is open at its lower end and is connected at its upper section, by means of connections 140 of head 130, to the chamber 128, where a channel 142 for cooling air introduction comes in; said air introduction is performed only during injection and constitutes a so-called secondary cooling system.The accessory device, which can be applied to the above described on column injector, substantially comprises an injection channel 144, of capillary size equal to the one of the upstream end of gas chromatographic column, said channel being able to be introduced into the sleeve 132 and through the gasket 136, in a position corresponding to the one normally belonging to the upper end of the capillary column, as indicated in figure 2. Said injection channel 144 is connected, at the end opposite to the one to be freely introduced into the injector, to a vaporization and expansion volume 146 essentially constituted by an extension of said channel 144, large enough to form a vaporization chamber which on its turn is connected, in position opposite to the channel 144, to an outlet channel 148.As can be seen in figure 2, the volume or vaporization chamber 146 has a size substantially equal to that of the outlet channel 148, but it is obviously possible to consider even different sizes.

The vaporization volume 146, together with at least part of the outlet channel 148, is inserted into a supporting block 150, preferably made of heat conducting material, the lower section of which, namely on the side of the outlet channel 148, is connected to a threaded ring 152, with threading in 154, having an axial opening 148' appertaining to the outlet channel 148, said ring 1 52 being assembled with interposition of a gasket 1 56. The ring 1 52 has a fitting 1 58 coming out at the channel 148' and through which it is possible to draw a splitting stream of part of the sample, while at the lower side, downstream the fitting 158, said ring 1 52 has a truncated cone-shaped gasket 1 60 sealing the upper end 1 62 of the gas chromatographic column. The metal block 1 50 incorporates a heating resistance 1 64 and is therefore suitable for transmitting heat, by conduction, to the vaporization chamber 146, said block 1 50 terminating at its upper section in correspondence to the initial fitting of the vaporization chamber, in a position at least slightly spaced from the lower end of the sleeve 1 32 in order to allow the outlet from this end of the air coming from the secondary cooling system.

As illustrated in figure 2, the injection is carried out by introducing the needle 120 of the syringe 122 into the initial section of channel 114 and into the injection channel 144, actually until reaching the end of this latter, and then injecting the sample into the vaporization volume 146 together with the carrier gas introduced in 126.In this volume 146, thanks to the temperature reached by actuating the resistance 164, a sample vaporization occurs and part of the sample, together with part of the carrier, goes to the splitting channel 158, while the remaining part penetrates into the gas chromatographic column 1 62. During injection, the secondary cooling system is actuated in order to maintain, together with the permanent primary cooling system, in cooled conditions the whole direct injector and actually the whole injection channel 144, so that no untimely and discriminating sample volatilization occurs inside needle 1 20.

Simultaneously, the low temperature kept in the above mentioned components, together with the carrier gas rate of the carrier gas entering the fitting 126 allow the formation of a "barrier" preventing any coming back of the vaporized sample from the vaporization volume 146 backwards along the injection channel 144.

Therefore, it is possible to perform in this way a vaporization injection avoiding the inconveniences of the known vaporization septum injectors. From what has been said, it must become obvious that the described and illustrated embodiments might undergo several changes and modifications, in particular relating to the position and number of the points for carrier introduction, provided that said introduction creates the mentioned pressure gradient, as well as the described needle cooling current. Other changes and modifications will possibly be found in relation to the valve structure as well as to the other means and accessory devices, not directly affecting the present invention.

Moreover, the cooling means of the injector and the injection channel as well as the heating means of the vaporization volume will possibly be of any suitable type, different from the illustrated one. For example, it will be possible to consider an outer separating septum for the zone housing the vaporization volume with this vaporization volume directly or indirectly heated by a current of hot fluid, in substitution of the heating system with resistance and conducting block previously illustrated. All these changes and modifications must be considered as falling within the scope of the present invention.

Claims

1. A vaporisation injector for gas chromatographic columns comprising an injector body and an injection channel extending through said body and into which an injection needle may be inserted to inject the sample to be analysed into a heated vaporisation chamber into which the end of the column extends and into which a carrier gas is fed to convey the vaporised sample into the column, wherein there is provided in said body a valve member movable between a first position closing said channel against the insertion of said needle and a second position in which said channel is open for the insertion of said needle, and wherein means are provided intermediate the ends of said channel for feeding a secondary stream of said carrier gas into said channel intermediate the ends thereof to create a pressure gradient between the valve member and the vaporisation chamber.

2. A vaporisation injector according to claim 1, wherein valve member comprises a rotary member rotationally mounted in a seating extending into said injector housing to intersect said injection channel, said rotary member having a transverse port therethrough and being rotatable in said seating to bring said post into alignment with said injection channel to permit the insertion of said needle therethrough.

3. A vaporisation injector according to claim 1 or 2, wherein said feed means are positioned to feed said secondary stream of carrier gas through said insertion channel both upstream and downstream of the valve member.

4. A vaporisation injector according to claim 3, wherein said feed means for said secondary stream of carrier gas comprise a passageway in said valve member through which said secondary stream of carrier gas may be introduced into said transverse port.

5. A vaporisation injector according to any one of claims 1-4, wherein the valve member is of heat resistant polyamide.

6. A vaporisation injector according to claim 5, wherein the valve member is of graphitised polyamide.

7. A vaporisation injector according to any one of the preceding claims, comprising a second carrier gas feeding means axially spaced along said injection channel from said first gas feeding means for feeding a second carrier gas stream to said channel downstream of said second carrier gas stream.

8. A vaporisation injector according to any one of the preceding claims, wherein said injector body has said vaporisation chamber formed therein, said injection channel communicating with the vaporisation chamber, and said vaporisation chamber being open at one end to receive the end of the chromatographic column and provided with means for providing a gas-tight seal around said end of the column when received therein.

9. A vaporisation injector according to claim 8, wherein said vaporisation chamber has a lining member having a throat at one end in line with the needle injection channel and through which the end of the injection needle projects into said chamber during the injection process, said throat having a diameter greater than that of the needle injection channel.

10. A vaporisation injector according to claim 7 and 9, wherein said second carrier gas stream injection means is positioned to feed the second stream of carrier gas to said chamber through said throat surrounding the injection needle when positioned therein.

11. A vaporisation injector according to any one of claims 1-7, in the form of an adaptor for use with an on-column vaporisation injector comprising a vaporisation chamber having an injection capillary leading to said chamber, the said need injection channel in said injector body being open at one end to receive the injection capillary and provided means therein for forming a gas-tight seal around said capillary when received therein.

12. A vaporisation injector according to claim 11 , wherein said injector body is provided with external cooling fins.

13. A vaporisation injector according to claim 11 or 12, wherein the open end of said needle injection channel is of an enlarged diameter compared with the inlet portion of the channel, said inlet portion having an internal diameter substantially equal to the internal diameter of the injection capillary.

14. A vaporisation injector according to claim 12 or 13, wherein means are provided for externally cooling the end of the injection capillary when received into the open end of said needle injection channel.

1 5. A vaporisation injector according to claim 14, wherein said cooling means comprise a cylindrical jacket member which surrounds the inserted end of the injection capillary and means are provided to feed a stream of cooling air internally to said jacket to cool the external surface of the injection capillary.

1 6. A vaporisation injector according to any one of claims 11-15, including said vaporisation chamber and injection capillary, said vaporisation chamber having an open end which receives the end of the chromatographic column and being provided with means for providing an air-tight seal around the end of the column when received therein.

17. A vaporisation injector according to claim 16, wherein a splitting channel is provided communicating with said vaporisation chamber upstream of said seal to remove a split stream of vaporised sample and the carrier gas.

18. A vaporisation injector according to claim 16 or 17, wherein the vaporisation chamber is formed internally in a block provided with internal heating means and adapted to be mounted on the chromatographic column.

1 9. A vaporisation injector according to claim 1 6,1 7 or 18, wherein said vaporisation chamber and injection capillary comprise an integrally formed glass tube having a first section forming said capillary and a second section of increased internal diameter forming said chamber.