Sampling Valve And System For The Detection Of Predetermined Compounds In Air

Abstract

A sampling valve for use with a chromatographic column or any other appropriate detection device for enabling the detection of predetermined compounds in an ambient medium, such as air. The valve includes a housing member having a plurality of apertures therein for enabling respective communication with at least a carrier medium, the ambient medium and the chromatographic column. A movable valve body member is mounted within the housing and is provided with a plurality of apertures for selective communication with predetermined ones of the housing member apertures. A platinum gauze member is retained within a predetermined one of the valve body member apertures and is selectively exposed to the ambient medium. The valve body member is then moved and the platinum gauze member is heated to desorb the predetermined compound in the presence of the carrier medium, such as helium, and the carrier medium together with the predetermined compound are passed through the chromatographic column to enable detection of the presence of the predetermined compound.

Description

The present invention relates to a sampling valve and detector system and more particularly to a sampling valve for use with a chromatographic column or any other appropriate detection device for enabling the detection of at least one predetermined compound in an ambient medium, such as air.

Detection of specific organic or other compounds in air is required for various scientific applications. With the recent increased interest in the problems of pollution of the atmosphere, the requirement for a suitable gas detection device has become extremely important. The need for a highly sensitive, continuously operating, portable, automatic, highly selective and versatile compound detector is not only present in the field of pollutant detection but is also a need which has existed for considerable time in other areas, such as mine safety, where the detection of explosive gases in the air is highly important for the safety of lives and property.

Numerous attempts have been made to develop a suitable detection device to detect specific compounds in air. Plasma chromatographic detectors, mass spectrometers, U. V. and I. R. spectrophotometers, fuel cells, gas chromatographs and various ionization detectors are among the instruments that have been developed in attempting to provide a highly sensitive, continuously operating, portable, automatic, highly selective, and versatile detection device.

Although most of these instruments are used successfully in particular fields, none of them satisfies all of the aforementioned requirements which should be present in an instrument adapted to accurately and conveniently detect specific compounds in air. Gas chromatography seems to be the method with the widest range of applications; however, two major problems are encountered when the gas chromatograph is adapted to selective and sensitive detection of organic compounds in air. These problems are sampling and selectivity. High selectivity may be obtained by choosing a suitable column and a selective detector, but sampling still remains a problem.

Injection of air samples into a gas chromatographic column or any other appropriate detection device is usually made with a syringe or by use of a gas sampling valve. Although these methods and the particular valves heretofore used have been found to be useful, they have several important disadvantages. For example, air may interfere when injected with the organic vapors to be analyzed, and this interference is due to the high concentrations of nitrogen and oxygen in air as compared to the low concentrations of organic vapors that may be present.

A sudden injection of 5 or 10 cc of air may cause serious interference in the flow rate of the carrier gas through the chromatographic column, the stability of which is very important. Furthermore, the maximum amount of 10 cc of air that may be injected into the gas chromatograph is insufficient for sensitive determinations of the presence of organic compounds. Air samples of sizes of several liters must be injected to allow the detection of quantities of one ppb and below.

It is, therefore, an object of the present invention to provide a unique sampling valve for use with a chromatographic column or any other appropriate detection device for enabling the detection of at least one predetermined compound in an ambient medium, such as air.

Another object is to provide a simply constructed, sturdy and inexpensive sampling valve for use with a chromatographic column system for enabling the detection of organic compounds in air.

A further object of the invention is to provide a highly sensitive, selective and versatile apparatus for detecting the presence of organic compounds in a large sample of air.

Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages are realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

To achieve these objects, this invention provides apparatus that embraces all the advantages of similarly employed detection devices and possesses none of the aforedescribed disadvantages. As embodied and broadly described the invention utilizes a single, unique sampling valve, that together with a chromatographic system, provides a highly sensitive detection system which has a minimal response time and which is highly selective and versatile so that it can be readily used for the detection of a number of compounds. The device of this invention is also compact and portable and may be operated automatically.

The sampling valve includes a housing member having a plurality of apertures therein for enabling respective communication with at least a carrier medium, an ambient medium, and a chromatographic column. A valve body member is movably mounted within the housing member and has a plurality of apertures therein for selective movement into communication with predetermined ones of the housing member apertures. In addition, the valve comprises means for adsorbing a predetermined compound from the ambient medium, and this adsorbing means, preferably platinum gauze, is in operative relationship with the valve body member for being retained within a predetermined one of the valve body member apertures at least during selective exposure to the ambient medium. Means are also provided in operative relationship for selectively heating the adsorber means to desorb any compounds previously adsorbed by the platinum gauze and the desorbed compounds are carried into the through the chromatographic column by a carrier gas, such as helium.

It should be understood that both the foregoing description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

The accompanying drawings illustrate examples of preferred embodiments of the invention and together with the description serve to explain the principles of the invention.

FIG. 1 is a sectional view of one embodiment of the sampling valve of this invention in a first position which respect to a chromatographic column;

FIG. 2 is a sectional view of the embodiment illustrated in FIG. 1 showing movement of an adsorber ball into the sampling valve;

FIG. 3 is a sectional view of the arrangement illustrated in FIG. 1 wherein the sampling valve is in a second position;

FIG. 4 is a sectional view of the embodiment shown in FIG. 1 representing return of the adsorber ball to a position adjacent the chromatographic column;

FIG. 5 is a detailed view, partly in section, of another embodiment of the sampling valve of this invention in a first position;

FIG. 6 is a view, partly in section, of the valve illustrated in FIG. 5 in a second position;

FIG. 7 is a view, partly in section, of the sampling valve embodiment shown in FIG. 5 and wherein the valve is in a third position;

FIG. 8 is a section of the sampling valve taken on the line 8--8 of FIG. 7 looking in the direction of the arrows;

FIG. 9 is a view, partly in section, of still another embodiment of the sampling valve of this invention wherein the valve is in a first position;

FIG. 10 is a view, partly in section, of the valve shown in FIG. 9 and wherein the valve is in a second position;

FIG. 11 is a view, partly in section, of the valve shown in FIG. 9 and wherein the valve is in a third position;

FIG. 12 is a partial section of the sampling valve taken on the line 12--12 of FIG. 9 looking in the direction of the arrows;

FIG. 13 is a diagrammatic view of one embodiment of a detector system of this invention; and

FIG. 14 is a diagrammatic view of another embodiment of a detector system in accordance with this invention.

Basically, the detector system of this invention utilizes a valve body member which is preferably made of polytetrafluoroethylene and which is free to rotate in a housing member preferably made of stainless steel. Other suitable materials can be used for the valve body member and for the housing member. The housing member is connected to a gas chromatographic column and is designed in such a way that at one position ambient atmospheric air flows through the valve while at a second position the valve is open to the chromatographic column and closed to the ambient air.

A small ball of platinum gauze which may be coated with the appropriate liquid phase is used for the adsorption of the compounds to be detected. When air is forced through the valve and through the porous ball, organic compounds, for example, will be adsorbed by the ball while other gases will pass through the ball without being adsorbed thereby. Selective adsorption is achieved through the use of the proper phase as is well known in the art. After adsorption is complete, the platinum ball is heated and all the compounds previously adsorbed on the ball are immediately desorbed and are carried into the chromatographic column by an inert carrier gas, such as helium, for analysis and for indication of the presence or absence of the compounds.

With specific reference now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIGS. 1-4 one embodiment of the sampling valve of this invention in various positions of operation.

A housing member 20 having a plurality of apertures 22, 24, 26, and 28 therein is mounted with aperture 26 in communicating relationship with a chromatographic column 30 via a tubular member 32. Apertures 22 and 24 are in communicating relationship with an ambient medium, such as the atmosphere, while aperture 28 is in communicating relationship with a supply of carrier gas, such as helium.

A valve body member 34 is movably mounted within housing member 20 to be rotated about a centrally located axis. Valve body member 34 has a plurality of apertures 36 and 38 therein which are in communication with each other in a substantially V-shaped configuration.

In accordance with the invention, means for adsorbing a predetermined compound are provided in operative relationship with valve body member 34 for being retained within a predetermined one of the valve body member apertures at least during selective exposure to the ambient medium or atmosphere. As here embodied, the adsorbing means is a platinum gauze ball 40 which is normally held within a magnetizable iron holder 42 located within tubular member 32. In accordance with this embodiment of the invention, electromagnetic means are provided in operative relationship for selectively moving holder 42 within tubular member 32 to cause the adsorbing ball 40 to be impelled into a first one 38 of the valve body member apertures. As here embodied, the electromagnetic means is an electromagnet 44 which surrounds tubular member 32. The invention also provides means in operative relationship for selectively heating the adsorber means 40. As here embodied, the heating means is an oven 46, a portion of which is illustrated in FIGS. 1-4 and which is shown in its entirety in FIGS. 13 and 14. The oven 46 encloses electromagnet 44 and at least a portion of tubular member 32.

In operation of the sampling valve embodiment illustrated in FIGS. 1-4, the small platinum gauze ball 40 is initially situated in the magnetizable (iron) gauze holder 42. The holder is at the lower end of tubular member 32 and is surrounded by electromagnet 44. As previously stated, the electromagnet and tube 32 are situated within oven 46 so that the temperature of chromatographic column 30 and of the column inlet is controlled. The valve body member 34 is rotated to a first position (the sampling position) whereby a first one of the valve body member apertures 36 is sealed at one end by housing member 20 while a second one of the valve body member apertures 38 is in communication with chromatographic column 30 and with tubular member 32. This position is illustrated in FIG. 1.

A plurality of voltage pulses are then applied to electromagnet 44 via two connections 50 and 51 so that iron gauze holder 42 together with platinum gauze sphere 40 are caused to jump upwardly. As a result, the ball 40 is thrown into valve body member 34 and into the aperture 36 where it remains. Tubular member 32 and the entire assembly illustrated in FIGS. 1-4, are preferably located at a relatively slight angle with respect to the vertical so that platinum gauze ball 40 is readily retained within aperture 36 (FIG. 2).

Valve body member 34 is then rotated clockwise until apertures 36 and 38 are in communication with apertures 24 and 22, respectively. See FIG. 3. If air is then passed through the apertures and over the platinum gauze ball, certain compounds, if present in the atmosphere, will be adsorbed by the ball. Thus, air is conventionally passed through the apertures by means of a pump 124 (FIGS. 13 and 14) which forces air through apertures 22, 38, 36, and 24 so that platinum gauze ball 40 adsorbs the compound or compounds which may be in the atmosphere and the detection of which is desired.

After the atmosphere has been passed over platinum gauze ball 40 with valve body member 34 in the second position (FIG. 3) for the desired length of time, valve body member 34 is rotated back to its first or sampling position (FIG. 4) where the apertures 36 and 38 as well as ball 40 are sealed from the atmosphere and so that ball 40 will drop down to its original position within gauze holder 42. Because the platinum gauze ball 40 is now located within the oven 46, any compounds which may have been adsorbed by the gauze ball are immediately desorbed and are carried into chromatographic column 30 by a carrier gas, such as helium entering through aperture 28.

The presence of predetermined compounds in the atmosphere is then determined by means of chromatographic column 30 together with additional detection and indicating elements, which will be described later with respect to FIGS. 13 and 14.

FIGS. 5-8 illustrate another embodiment of the sampling valve of this invention. A housing member 20' is provided with a plurality of apertures therein for enabling respective communication with at least a carrier medium, an ambient medium, such as the atmosphere, and a chromatographic column. As here embodied, housing member 20' includes apertures 52 and 54, which are in communication with a carrier gas, such as helium. Additional apertures 56 and 58 are provided in communication with the ambient medium, such as air. A purge aperture 60 is also provided in communication with the ambient medium and an aperture 62 is provided in communication with chromatographic column 30.

Valve body member 34' is movably mounted within housing member 20' and includes a plurality of apertures therein for selective movement into communication with predetermined ones of the housing member apertures. As here embodied, valve body member 34' includes apertures 64 and 66 which are in different planes with respect to one another and which may be perpendicular with respect to one another. Although apertures 64 and 66 are shown and described as being perpendicular with respect to one another, it should be understood that they need not be perpendicular and that they can be oriented at any number of angles with respect to one another as long as the apertures in the housing member 20' are appropriately located.

As illustrated in FIG. 8, housing member 20' includes two keyways 70 and 72 in communication with apertures 54 and 62 for enabling selective communication of each of the valve body member apertures 64 and 66 with housing member apertures 54 and 62 whereby flow of the carrier medium through the chromatographic column is maintained substantially constant during operation of the valve. This feature will be explained in more detail infra where the operation of this valve embodiment is set forth.

In this embodiment, platinum gauze ball 40' is captured within valve body member aperture 64. A storage capacitor 74, for example, or any other suitable electrical energy storage means, is electrically coupled to platinum gauze 40' via leads 76 and 78, and a switch 80 is located in circuit with capacitor 74 together with an electrical source 82 whereby capacitor 74 is selectively charged by energy source 82 and discharged by closing of the switch 80. Capacitor 74 through leads 76 and 78 is utilized to heat the gauze since the gauze is not dropped into the oven, as was the case with the embodiment illustrated in FIGS. 1-4. In addition, gauze 40' need not be spherical in shape but may be of a flat configuration, for example.

In operation of the sampling valve embodiment shown in FIGS. 5-8, valve body member 34' is rotated to a first position as shown in FIG. 5, valve body member aperture 64 is in communication with housing apertures 56 and 58 and with the atmosphere or ambient medium. At the same time second valve body member aperture 66 is in communication with keyways 70 and 72 and with housing apertures 54 and 62. In this first position the carrier gas, such as helium, passes through tube 90, aperture 54, aperture 66 and aperture 62 so as to pass into and through chromatographic column 30. Simultaneously, air from the ambient medium is drawn through apertures 56, 64, and 58 by means of a pump (124 in FIGS. 13 and 14) so that air passes through platinum gauze 40' whereby certain compounds that are present in the atmosphere are adsorbed by the gauze.

Accurate temperature control and a steady carrier gas flow rate through chromatographic column 30 are required to obtain accurate and reproducable results in the detection of predetermined compounds. Accordingly, an important feature of this embodiment of the sampling valve is that it provides a substantially continuous and steady carrier gas flow rate through the chromatographic column via aperture 66 even when the platinum gauze 40' is being subjected to the atmosphere.

After gauze 40' has been exposed to the air for the desired length of time valve body member 34' is rotated clockwise to the position shown in FIG. 7. Before reaching that position, however, valve body member 34' passes through a second position (FIG. 6) whereby first valve body aperture 64 containing the gauze ball 40' is placed in communication with the carrier medium via apertures 52 and 60 whereby first aperture 64 is flushed of any residual air from the atmosphere by means of the carrier gas. At this position second aperture 66 is sealed by housing member 20'. By flushing the apertures the accuracy of the results is markedly enhanced since all air is expelled from the system prior to the desorbing step. In this way, extraneous readings are avoided and only the presence of the predetermined compound as it is absorbed from the platinum gauze 40' is detected as it passes through the chromatographic column 30. The ball 40' is not heated at this time so the carrier gas does not flush out any of the compounds adsorbed by the ball.

Valve body member 34' is then rotated to the third position (FIG. 7) and first aperture 64 is placed in communicating relationship with the carrier medium via aperture 54 and with the chromatographic column via aperture 62. The second valve body member aperture 66 is offset and is not in communication with housing apertures 56 and 58 and is therefore sealed by housing member 20' when the valve body member is in the third position.

The flow of carrier gas from tube 90 into column 30 is interrupted only for the very short time that it takes for valve body member 34' to rotate approximately 90.degree. from its first position (FIG. 5) to its third position (FIG. 7). Thus, substantially constant gas flow through the chromatographic column 30 is maintained.

In the third position (FIG. 7) carrier gas flow through aperture 54, aperture 64, platinum gauze 40', aperture 62 and into and through chromatographic column 30. As soon as valve body member 34' reaches the third position, switch 80 (FIG. 8) is closed so that capacitor 74 is discharged and the current passing through platinum gauze 40' heats it so as to desorb any compounds which had previously been adsorbed thereby. The carrier gas together with the desorbed compounds then pass through the chromatographic column 30 and the presence of the compounds is determined by the determining and indicating means shown and described in more detail with respect to FIGS. 13 and 14.

In accordance with a third embodiment of the invention, as illustrated in FIGS. 9-12, a housing member 20" is provided which has a plurality of apertures therein for enabling respective communication with at least a carrier medium, an ambient medium such as air, and a chromatographic column. As here embodied, the housing member 20" includes apertures 92 and 94, which are in communicating relationship with the ambient medium or atmosphere. In addition, housing member 20" includes a purge outlet or aperture 96 which is also in communicating relationship with the atmosphere. An aperture 26' is in communicating relationship with chromatographic column 30, and aperture 28' is provided in communicating relationship with the carrier medium or gas, such as helium.

Valve body member 34" of this embodiment has first and second apertures 102 and 104, respectively, which are in a substantially V-shaped configuration with one another. The second aperture 104 is closed at one end 106 thereof, and a purge aperture 108 is provided in communicating relationship with the V-shaped configuration. In addition, a support member 110 is located across purging aperture 108 and adjacent to apertures 102 and 104 for holding the platinum gauze ball when valve body member 34" is in a third position (FIG. 11).

As illustrated in FIG. 12, valve body member 34" of the embodiment illustrated in FIGS. 9-12, has a tapered cross section for enabling a better sealing fit within housing member 20". This configuration also represents a preferred arrangement for the previously described embodiments. Body member 34" is provided with an extension 112 which has a member 114 fitted thereover and a knob 116 attached thereto for enabling manual rotation of valve body member 34" about the axis 118.

In operation of the embodiment illustrated in FIGS. 9-12, the small ball of platinum gauze is initially located in the cylindrical iron holder 42. As in the embodiment of FIGS. 1-4, the holder is located at the lower end of tubular member 32 which is surrounded by electromagnet 44. The electromagnet and the tubular member are both located in an oven 46 in which the temperature is controlled by a temperature controller 121 (FIGS. 13 and 14). The valve is first positioned as illustrated in FIG. 9. In the first position the first one of the apertures 102 is in communication with tubular member 32 and with chromatographic column 30 while purge aperture 108 is sealed at one end by housing member 20".

A plurality of voltage pulses are applied to electromagnet 44 via leads 50 and 51, and iron gauze holder 42 is caused to jump upwardly so as to throw the platinum gauze ball 40 into the valve body member 34" and into closed aperture 104 where it remains. If desired, the entire assembly, as illustrated in FIGS. 9-12, may be located at an angle with respect to the vertical so that the gauze ball is readily retained within the closed aperture 104.

Valve body member 34" is then rotated clockwise to a second position, as illustrated in FIG. 10, to enable purge aperture 108 to be in communication with purge outlet 96. At the same time, first aperture 102 in the V-shaped configuration is still in partial communication with the carrier medium and aperture 28' so that the carrier gas passes through aperture 102 and through purge aperture 108 to purge the valve body member of any residual gases prior to sampling which might remain therein. Valve body member 34" is then rotated to a third position (FIG. 11) so that the first aperture 102 is in communication with the atmosphere and with housing aperture 92 and so that purge aperture 108 is in communication with the atmosphere and with housing aperture 94. The platinum gauze ball 40 falls onto and is supported by support member 110.

With valve body member 34" in the third position (FIG. 11) the ambient medium, such as air, is caused by means of a pump 124 (FIGS. 13 and 14) to pass through apertures 92, 102, 108, and 94. If certain compounds are present in the atmosphere it will be adsorbed on the gauze ball 40.

The valve body member 34" is then rotated in a counter-clockwise direction from its position as illustrated in FIG. 11, and as member 34" passes through the second position (FIG. 10) the carrier gas again purges apertures 102, 104, and 108 of air to avoid contamination of chromatographic column 30. Member 34" continues to rotate in the counterclockwise direction until the first position (FIG. 9) is reached. The platinum gauze ball then drops from its position on support member 110 down and through tubular member 32 until it comes to rest within gauze holder 42. Any compounds which may have been adsorbed by the platinum ball are desorbed immediately within the heated environment of oven 46 and are carried into chromatographic column 30 by the carrier gas which passes into tubular member 32 via aperture 28.

In each of the three embodiments heretofore described organic compounds that may have been adsorbed by the platinum gauze are desorbed immediately when subjected to a preselected heat, and the valve body member rotates back to the sampling position to again expose the platinum gauze to the atmosphere and to accept another sample. By the time the compounds reach the detector 138 (FIG. 14) associated with the chromatographic column, a new sample will be ready for injection. Thus, the entire cycle (retention time) will last only as long as it takes for the compounds to reach the detector 138 from the time of injection into the column.

The sampling apparatus of this invention and the sampling valve can be operated completely automatically by means of systems as illustrated in FIGS. 13 and 14.

The embodiment of FIG. 13 includes an automatic control circuit 120, which may be a conventional timing circuit and which acts as the master control for operation of the entire system. In operation, a motor 122 is activated to rotate the sampling valve of this invention to the sampling position. Depending upon whether the valve is of the embodiment illustrated in FIGS. 1-4, FIGS. 5-8, or FIGS. 9-12, the platinum gauze is already located within the valve or a series of voltage pulses applied to the electromagnet 44 cause the iron gauze holder to jump upwardly so that the ball is thrown into the valve body member where it is trapped. Motor 122 is again activated by automatic control circuitry 120 and rotates until stopped by a controlling microswitch (not shown) so that the platinum ball is exposed to the atmosphere and air is passed through the ball by means of fan 124.

After adsorption is complete, the valve rotates backwardly until it is stopped by another controlling microswitch (not shown) at such an angle that the ball drops down to its initial position, or in the case of the embodiment of FIGS. 5-8, the ball is placed in communication with the carrier gas and with the chromatographic column. The ball is then heated so that any compounds which may have been adsorbed by the platinum gauze are now desorbed immediately and carried into the chromatographic column by the carrier gas, which enters from aperture 28 and which is supplied by carrier gas supply 124. Simultaneously, recorder 126 is activated by automatic control circuitry 120 for a specified time, e.g. 1-3 minutes.

The compounds and carrier gas advance along the separation column and the flow rate of the carrier gas through the column remains constant. Both temperature and flow rate are chosen in each case in accordance with the characteristics of the specific compound to be detected. Any compound will reach the end of the chromatographic column at a particular fixed time, depending upon the temperature and flow rate and on the column packing, and this time is specific to each compound.

Downstream of the column the compound reaches a conventional ionization detector (not shown). This detector responds to organic compounds by generating a current which is displayed on recorder 126 after being amplified by an electrometer amplifier 140.

Another arrangement for detecting the presence of compounds in air is shown in FIG. 14. This particular apparatus is illustrated in combination with the sampling valve of FIGS. 1-4 or of FIGS. 9-12; however, the sampling valve embodiment illustrated in FIGS. 5-8 could be readily utilized with this system.

In operation of the system shown in FIG. 14, the ball of platinum gauze 40 is thrown upwardly into the valve and is trapped there as previously explained. Movement of the ball is observed by a photoelectric cell 130, which is located under the valve. The tubular member 32 in this embodiment has two windows 132 which allow a beam of light from a small bulb 134 to reach the photoelectric cell 130. A signal is generated each time the ball, moving upwardly, intercepts the beam, and a different signal results when the ball moves downwardly.

After the ball is received by the valve, motor 122 is activated to rotate the valve until it is stopped by a controlling microswitch (not shown). The platinum ball is then exposed to the atmosphere and air containing the sample is passed through the ball by means of the pump 124. During this operation the carrier gas (helium) enters column 30 through the aperture 28 at the lower end of the valve so that the flow of carrier gas through the column is not affected by rotation of the valve. This is true for the valve embodiments of FIGS. 1-4 and of FIGS. 9-12 while the helium flow is only slightly interrupted as the valve body member of the embodiment shown in FIGS. 5-8 rotates 90.degree..

After the air is passed over the ball and the compounds have been adsorbed thereby, the motor is activated so that the valve rotates in a backward direction until the system is stopped by another controlling microswitch (not shown) so that the ball drops down into its initial position within the gauze holder 42. The ball movement is again observed by the photoelectric cell 130. Any compounds which may have been adsorbed by the platinum ball are desorbed immediately as a result of the heat applied by the oven 46 and are carried into the column 30 by the carrier gas originating from the source 124.

The gases from the platinum advance along the column, which is kept at a constant temperature. As one example, the column may be made of polytetrafluoroethylene tubing 30 cm long and 1 1/2 mm I. D. and is packed with 15 percent D.E.G.S. on 60-80 chromosorb W.A.W. The flow rate of the carrier gas through the column 30 is constant and both the temperature and flow rate are chosen in each case to identify the specific compound sought to be detected. Any compound will reach the end of the column 30 at a particular fixed time, depending upon the temperature and flow rate and in other cases the column packing. This time is characteristic for each compound.

At the end of the column the compound reaches a conventional ionization detector 138. This detector responds to organic compounds by generating a current which is displayed on recorder 126 after being amplified by electrometer 140'. Thus, if a compound is present the recorder will indicate its presence to the operator.

Because the time required for each compound to reach the end of the column 30 is specific and depends on the temperature and gas flow conditions, this time may be used for identification. An alarm system is connected in parallel to the recorder and is activated when a peak signal arrives in order to indicate when a specific compound is present in the atmosphere.

The present invention, thus, provides for a unique sampling valve and for unique apparatus for detecting the presence of compounds in the atmosphere wherein the device is highly sensitive, has a short time response, is portable, automatic, highly selective, and versatile and wherein a gas chromatograph or any other suitable detection device is utilized to enable the detection of extremely low concentrations of organic vapors in the atmosphere.

The invention in its broader aspects is not limited to the specific details shown and described and departures may be made from such details without departing from the principles of the invention and without sacrificing its chief advantages.

Claims

What is claimed is:

1. In a detection device, a sampling valve for concentrating at least one predetermined compound in an ambient medium comprising:

a housing having a first aperture having an inlet and outlet end, both communicating with the ambient medium and a second aperture communicating with the detection device;

a valve body movably mounted within the housing and having a V-shaped aperture therein for selective communication with the housing apertures;

means for adsorbing said predetermined compound locatable in the valve body aperture;

means for sequentially moving the valve body between a first position where the valve body aperture communicates with the first housing aperture to expose the adsorbing means located in the valve body aperture to the ambient medium and to a second position where the valve body aperture communicates with the second housing aperture;

a tubular member in communicating relationship between the second housing aperture and the detection device; said adsorbing means passing into the tubular member when the valve body aperture is moved to the second position from the first position;

means for selectively heating the adsorber means in the tubular member to desorb the predetermined compound from the adsorber means;

means for passing a carrier medium over the heated adsorber means to pick up the desorbed compound and transmit it to the detection device; and

means for returning the adsorbing means back to the valve body aperture.

2. The device of claim 1, wherein the valve body aperture is sealed to the ambient medium when in the second position.

3. The device of claim 1, in which the means for returning the adsorbing means comprises:

a holder located within the tubular member for holding the adsorbing means; and

means for selectively moving the holder within the tubular member to impell the adsorbing means back into the valve body aperture.

4. The device of claim 3, wherein the tubular member is inclined to the vertical.

5. The device of claim 3, wherein the adsorbing means include a substantially spherical mass of adsorptive material.

6. The device of claim 3, wherein the heating means includes an oven surrounding the tubular member for selectively heating the adsorbing means in its holder.

7. The device of claim 3, wherein the holder is of magnetizable material and the moving means includes an electromagnet surrounding the tubular member.

8. The device of claim 3, wherein the carrier medium is supplied to the tubular member between the valve body and the holder.

9. The device of claim 8, including means for purging the valve body aperture with the carrier medium as the valve body aperture moves between said first and second positions.

10. The device of claim 9, where the purging means includes a purge aperture in the housing that communicates with the valve body aperture and permits the carrier medium to pass through the valve body aperture.

11. A device for the detection of a predetermined compound in air comprising:

a. a gas chromatographic column for separating compounds in a gas stream;

b. detection means downstream from said column for indicating the presence of said predetermined compound in the gas stream;

c. a sampling valve for concentrating the compound from the air and transferring the compound from the air in an air-free atmosphere to the gas column, said sampling valve comprising:

i. a valve housing having an air inlet and outlet, and a discharge outlet communicating with the gas chromatographic column,

ii. a valve body movably mounted within the valve housing and having an aperture therein for selective communication with the housing's air inlet and outlet when the valve body is in a first position and with the discharge outlet when the valve body is in a second position,

iii. means for moving said valve between said first and second positions, and

iv. adsorber means located within the valve body aperture for adsorbing and concentrating the compound from air;

d. means for passing air through the valve housing and the valve body aperture in said first position to expose the adsorber means to the air;

e. purge means communicating the valve body aperture with a supply of air-free carrier gas as the valve body passes through a position intermediate said first and second positions to purge the valve body aperture and the adsorber means of residual air;

f. heater means for selectively heating the adsorber means after it has adsorbed the compound and been purged of residual air to desorb the compound from the adsorber means; and

g. means for passing air-free carrier gas over the heated adsorber means when the valve body aperture is in said second position to pick up the desorbed compound and transmit it to the gas column.

12. The device of claim 11 wherein said heating means include:

a storage capacitor;

leads in circuit with said adsorbing means and said capacitor; and

a switch in circuit with said leads and said capacitor for enabling the selective discharge of said capacitor through said adsorber means.

13. The device of claim 11 wherein said adsorbing means include a piece of platinum gauze or any other adsorptive material of any metal or chemical fixidly mounted within the valve body aperture.

14. The device of claim 11, wherein the purge means comprises a carrier gas inlet and an outlet for the carrier gas in the valve housing, said inlet and outlet communicating with the valve body aperture as it passes through said intermediate position.

15. The device of claim 14, including a passage in the valve body communicating with the carrier gas inlet and the discharge outlet when the valve body is in said first position, said carrier gas inlet also communicating with the valve body aperture when the valve body is in said second position to transmit the desorbed compound to the gas column, thereby maintaining a substantially constant flow of carrier gas to the column.

16. The device of claim 15, wherein the carrier gas inlet comprises a first aperture in the housing communicating with the valve body aperture when said valve body is at said intermediate position and a second aperture in the housing communicating with the valve body aperture when the valve body is at said second position and with the valve body passage when the valve body is at said first position; said first and second apertures communicating with a common supply of carrier gas.

17. The device of claim 11, wherein the adsorber means is retained within the valve body aperture during exposure and heating.

18. A device for the detection of a predetermined compound in air comprising:

a. a gas chromatographic column for separating compounds in a gas stream;

b. detection means downstream from said column for indicating the presence of said predetermined compound in the gas stream;

c. a sampling valve for concentrating the predetermined compound from the air comprising a valve housing having an air inlet and outlet and a discharge outlet communicating with the gas chromatographic column;

d. a valve body movably mounted within the valve housing and having a V-shaped aperture therein for selective communication with the housing's air inlet and outlet when the valve body is in a first position and with the discharge outlet when the valve body is in a second position;

e. means for moving the valve body between said first and second positions;

f. adsorber means located in the V-shaped aperture when the valve body is in the first position for adsorbing and concentrating said predetermined compound from the air;

g. a tubular member in communicating relationship between the discharge outlet and the column, said adsorber means falling out of the valve body aperture and into the tubular member when the valve body is in the second position;

h. means for selectively heating the adsorber means to desorb the compound from the adsorber means when the adsorber means is located in the tubular member;

i. means for passing carrier gas over the heated adsorber means to pick up the desorbed compound and transmit it to the detection means; and

j. means for returning the adsorber means back into the valve body aperture.

19. The device of claim 18 including means for purging the valve body aperture of ambient medium as it moves between said first and second positions.

20. The device of claim 19, wherein the carrier medium is supplied to the tubular member and the purging means includes a purge outlet in the valve housing, said valve body aperture communicating with the purge outlet and the discharge outlet of the valve housing as the valve body moves between said first and second positions to flush the aperture and adsorber means of residual air.