CA1191721A - Method and device for continuous, automatic air analysis - Google Patents
Method and device for continuous, automatic air analysisInfo
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- CA1191721A CA1191721A CA000416762A CA416762A CA1191721A CA 1191721 A CA1191721 A CA 1191721A CA 000416762 A CA000416762 A CA 000416762A CA 416762 A CA416762 A CA 416762A CA 1191721 A CA1191721 A CA 1191721A
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Abstract
Abstract of the Disclosure The present invention relates to a continuously working, automatic gas chromatograph, where air is used as carrier gas through a column and detector. The gas chromatograph is provided with a pre-concentrator which, besides the function of concentrating those substances that are to be analyzed in an air sample, also functions as a purification step. Because of this, the air present in the sample can be utilized as carrier gas. A separate carrier gas source or a complicated purification system is thus not required for using the atmospheric or ambient air as carrier gas.
Description
~9~
The present invention relates to a continuously working, automatic gac chromatograph that is useful for qualified air analysis, for instance Eor the determination and identiEication oE extremely small contents of impurities in air.
In a conventional gas chromatograph a definite amount of the sample is injected into a vaporization chamber Eor quick vaporization thereof if the sample is in the liquid state. It is then carried by a carrier gas into a chromatograph column and through a detector for the analysis of the sample com-ponents. If the sample is initially in the gaseous state, it is injected directly into the carrier gas flow. As carrier gas helium, argon or nitrogen is usually used. It has also been suggested to use air as carrier gas. As the carrier gas must be dry and free from impurities, the air must in such a case be taken from a separate gas bottle or, when atmospheric or ambient air is to be used, it must be purified before the use as carrier gas. For such a purpose hitherto it has been necessary to use relatively complicated purification equip-ment, for instance as described in United States patent 3,772,909. The gas chromatograph as a whole then becomes relatively large and complicated.
According to the present invention, there is provided a method relevant to a gas chromatograph for continuous, automatic, qualitative and quantitative air analysis, for instance for the determination and identification of extremely small contents of substances present in air, the gas chromatograph comprising an injector, a pre-concentrator, a chromatograph column, a detector, a computer for the control of the gas chromatograph, preparation and presentation of analysis results and a power supply unit, characterized in that sample air is passed continuously and at an even speed through the injector, the pre-concen-trator which comprises an adsorbent, the column and the detector, during which period of time substances present in the air are adsorbed on the adsorbent in Z~
the pre-concen-tratillg step at the same time as the air is purified and can be used as carrier gas through the column and the detector, and then the adsorbent is heated Eor a short time so that the substances that have become concentrated on the adsorbent in the pre-concentrating step are desorbed and are carried by carrier gas, consisting of sample air purified in the pre-concentrating step, through column and detector for analysis thereof at the same time as new sample air is being passed through the injector and the adsorbent in the pre-concentrat-ing step; the above steps during said period of time being repeated, whereby a continuous sampling and analysis method is achieved.
The gas chromatograph of the invention may be small, compact, easily operated and portable and because of this, useful for qualitative and quantita-tive air analysis at the place of sampling, if so is desired. The inventiwl particularly makes possible a simplified method for purification of the air in the sample to be used as carrier gas.
The present invention makes possible a simplified method of purifying the atmospheric or ambient air for use as the carrier gas through the column and detector. As the air that is present at the very place of sampling and analysis can be used, no separate gas source is required for the supply of carrier gas.
This circumstance together with the fact that the gas chromatograph is battery operated and that you can go "down in scale", for instance by using a capillary column, contributes in making the gas chromatograph according to the invention small, simplified, portable and useful for field use.
When analyzing air one has previously been forced to carry out a pre-paratory step of collecting the sample at a particular location and then analyz-ing the sample later on in a laboratory. As the gas chromatograph of the inven-tion can be pre-calibrated for possible substances in the air analysis at the sampling spot becomes possible so that a very quick indication of the presence of certain subs-tance5 and the percentages of such substances present in the air at a certain place can be ob-tainecl. The gas chromatograph is of course also suitable for conventional laboratory use.
As those substances that are to be determined are concentrated in a pre-concentrating step by means of an adsorbent before the analysis thereof, the gas chromatograph oE the invention is, in spite of its compact construction, extremely sensitive and reliable and makes possible analysis of for instance nerve gases, dangerous substances at places of work, such as benzene, toluene, xylene etc, present in concentrations as low as 0.005 mg/m3.
Thus, the adsorbent in the pre-concentrating step has a double func-tion, viz. to concentrate those substances in the air which are to be measured and to purify the air for use as carrier gas.
By arranging an air pump after the detector of the air analysis system, both a simplified sampling and asimplified purification of the air are obtained.
The air pump is working all the time and draws the air at an even speed through the adsorbent in the pre-concentrating step, through the column and the detector.
As the-air pump is positioned after the detector, the risk of contamination of impurities deriving from the pump can be avoided.
A computer, suitably a microcomputer, for the control of the gas chromatograph and Eor the preparation and presentation of the measurement results can be used and this makes the apparatus very easy to operate so it can be used by unqualified personnel for analysis at the actual sampling location. Thus, a highly field-adapted analytical instrument is obtained.
The invention will now be described in more detail with reference to the attached drawings, in which:
Figure 1 is a schematic diagram of the over-all construction of a gas chromatograph according to the invention;
7~
Figure 2 shows a suitable embodiment of an injector device used in chromatograph of Figure l;
Figure 3 shows a suitable embodiment of a detector device used in the chromatograph of Figure l; and Figure 4 shows in graphical format the working mode of the gas chroma-tograph.
The gas chromatograph of Figure 1 consists of an injector l, which in-cludes an adsorbent for purifying the air and concentrating the sample, a chroma-tograph column 2 and a detector 4 disposed in a thermostat-controlled oven 3, an air pump 5, a microcomputer 6 and a power supply unit 7, for instance a battery.
The injector l Isee Figure 2) suitably consists of a solid adsorbent material 8 in powder form, disposed between two glass-wool plugs 9 in a thin-walled glass tube lO that is provided with an electric resistance wire in the form of a heating coil ll wound round the tube. The heating coil connections to the power supply are designated 12. One end of the tube is connected directly to the chromatograph column 2 by means of a kind of quick-connect coupling via a rubber sealing joint 13. The other end opens directly to the ambient air but is so devised that it may be connected by means of a tubing, suitably of Teflon (trade mark), to another air sample. The entire adsorbent tube is disconnect-able so that it can be used for sampling separately from the gas chromatograph, for instance at exposition measurements. The adsorbent material inside the tube is chosen taking into consideration the air contaminants that are to be analy~ed.
However, it must be able to withstand being heated during the heat desorption stage. Liquids, for instance high temperature boiling silicone oil, may also be used as adsorbent material.
The column 2 is suitably a capillary column in the form of a glass tube helix, the coil thereof having a diameter of 11 cm and a relatively large '7~:~
tube inner diameter ~abou-t 0.4 mm). The inner surface has been deactivated and coated with a s-tationary phase with temperature stability even when air is used as carrier gas. The stationary phase operates to slow down to different degrees the various components of the sample, so they will leave the column scparated from each other, making possible separate detection thereof.
The oven 3 is designed to hold exactly the column 2 and the detector 4. The oven is well insulated with glass-wool or a similar fibre material and provided with a lining of thin aluminium foil so that the heat capacity will become low. The heating is carried out electrically by means of a resistance wire. The temperature is measured with a resistance sensor and is controlled by the microcomputer. There is a fan in order to avoid gradients and obtain a more effective temperature control.
The detector 4 is connected directly to the column 2. The choice of detection principle is made taking into consideration what substances are to be analyzed. It is desirable, however, that the detector has a small dead volume, small size and high sensitivity for the substances in question. It should also function without detector gases. There are several detectors that meet these requirements, for instance the photoionization detector and piezoelectric crys-tals coated with a specific liquid film.
The detector may be so constructed that, besides being used for gas chromatography as has been described, it can also be used as a direct-reading detector. In the latter case the sample air is directly furnished into the detector without previously passing the pre-concentrating adsorbent and the chromatograph column. In this case there is obtained an instantaneous value of the impurities the sample air contains.
A suitable embodiment of the detector 4 is shown in Figure 3. The detector is concentrically built ;n a holder 14, which by means oE a double-threaded fixing screw 19, screws 25 and with intermediate insulation pieces 15 of Teflon Eixes an W lamp 16, a detector cell l7 and an anode 1~ in a gastight way to each other. The sample air is drawn into the detector, either through a column connecting element 23 or through a direct-delivering tube 24. ~Only one of the connections has an open communication with the sample air, and a shut-off device or switching device is positioned where the sample air is furnished into the gas chromatograph.) The air sample is brought centrally into the detector cell 17 through a tubular part 22 of the anode 18 and exhausted by suc-tion through a tube 20. The two tubes 20 and 24, that are insulated with I`eflon tubing 21, also serve as electric conduits for the ionization current that arises between the detector cell and the anode, i.e. the detector signal. In order to tighten the column connection to the detector there is also provided an O-ring gasket of rubber 26 between the anode 18 and the fixing screw 19 ~between the column connecting element 23 and the insulation 15).
The air pump ~ is connected to the detector 4 via flow resistances and buffer volumes, in which way a continuous flow is obtained through the system.
I~ is suitably of the plunger type in order to achieve a sufficient suction height.
The microcomputer 6 is arranged to control the oven temperature, the air pump and the heating of the adsorbent, to register detector signal and time, and to prepare and present measured values and results. The microcomputer is suitably of the CMOS-type, which makes it possible to run the gas chromatograph for about eight hours using a battery.
Additional equipment comprises among other things a key set for control instructions to the gas chromatograph, a display and a sound alarm device for
The present invention relates to a continuously working, automatic gac chromatograph that is useful for qualified air analysis, for instance Eor the determination and identiEication oE extremely small contents of impurities in air.
In a conventional gas chromatograph a definite amount of the sample is injected into a vaporization chamber Eor quick vaporization thereof if the sample is in the liquid state. It is then carried by a carrier gas into a chromatograph column and through a detector for the analysis of the sample com-ponents. If the sample is initially in the gaseous state, it is injected directly into the carrier gas flow. As carrier gas helium, argon or nitrogen is usually used. It has also been suggested to use air as carrier gas. As the carrier gas must be dry and free from impurities, the air must in such a case be taken from a separate gas bottle or, when atmospheric or ambient air is to be used, it must be purified before the use as carrier gas. For such a purpose hitherto it has been necessary to use relatively complicated purification equip-ment, for instance as described in United States patent 3,772,909. The gas chromatograph as a whole then becomes relatively large and complicated.
According to the present invention, there is provided a method relevant to a gas chromatograph for continuous, automatic, qualitative and quantitative air analysis, for instance for the determination and identification of extremely small contents of substances present in air, the gas chromatograph comprising an injector, a pre-concentrator, a chromatograph column, a detector, a computer for the control of the gas chromatograph, preparation and presentation of analysis results and a power supply unit, characterized in that sample air is passed continuously and at an even speed through the injector, the pre-concen-trator which comprises an adsorbent, the column and the detector, during which period of time substances present in the air are adsorbed on the adsorbent in Z~
the pre-concen-tratillg step at the same time as the air is purified and can be used as carrier gas through the column and the detector, and then the adsorbent is heated Eor a short time so that the substances that have become concentrated on the adsorbent in the pre-concentrating step are desorbed and are carried by carrier gas, consisting of sample air purified in the pre-concentrating step, through column and detector for analysis thereof at the same time as new sample air is being passed through the injector and the adsorbent in the pre-concentrat-ing step; the above steps during said period of time being repeated, whereby a continuous sampling and analysis method is achieved.
The gas chromatograph of the invention may be small, compact, easily operated and portable and because of this, useful for qualitative and quantita-tive air analysis at the place of sampling, if so is desired. The inventiwl particularly makes possible a simplified method for purification of the air in the sample to be used as carrier gas.
The present invention makes possible a simplified method of purifying the atmospheric or ambient air for use as the carrier gas through the column and detector. As the air that is present at the very place of sampling and analysis can be used, no separate gas source is required for the supply of carrier gas.
This circumstance together with the fact that the gas chromatograph is battery operated and that you can go "down in scale", for instance by using a capillary column, contributes in making the gas chromatograph according to the invention small, simplified, portable and useful for field use.
When analyzing air one has previously been forced to carry out a pre-paratory step of collecting the sample at a particular location and then analyz-ing the sample later on in a laboratory. As the gas chromatograph of the inven-tion can be pre-calibrated for possible substances in the air analysis at the sampling spot becomes possible so that a very quick indication of the presence of certain subs-tance5 and the percentages of such substances present in the air at a certain place can be ob-tainecl. The gas chromatograph is of course also suitable for conventional laboratory use.
As those substances that are to be determined are concentrated in a pre-concentrating step by means of an adsorbent before the analysis thereof, the gas chromatograph oE the invention is, in spite of its compact construction, extremely sensitive and reliable and makes possible analysis of for instance nerve gases, dangerous substances at places of work, such as benzene, toluene, xylene etc, present in concentrations as low as 0.005 mg/m3.
Thus, the adsorbent in the pre-concentrating step has a double func-tion, viz. to concentrate those substances in the air which are to be measured and to purify the air for use as carrier gas.
By arranging an air pump after the detector of the air analysis system, both a simplified sampling and asimplified purification of the air are obtained.
The air pump is working all the time and draws the air at an even speed through the adsorbent in the pre-concentrating step, through the column and the detector.
As the-air pump is positioned after the detector, the risk of contamination of impurities deriving from the pump can be avoided.
A computer, suitably a microcomputer, for the control of the gas chromatograph and Eor the preparation and presentation of the measurement results can be used and this makes the apparatus very easy to operate so it can be used by unqualified personnel for analysis at the actual sampling location. Thus, a highly field-adapted analytical instrument is obtained.
The invention will now be described in more detail with reference to the attached drawings, in which:
Figure 1 is a schematic diagram of the over-all construction of a gas chromatograph according to the invention;
7~
Figure 2 shows a suitable embodiment of an injector device used in chromatograph of Figure l;
Figure 3 shows a suitable embodiment of a detector device used in the chromatograph of Figure l; and Figure 4 shows in graphical format the working mode of the gas chroma-tograph.
The gas chromatograph of Figure 1 consists of an injector l, which in-cludes an adsorbent for purifying the air and concentrating the sample, a chroma-tograph column 2 and a detector 4 disposed in a thermostat-controlled oven 3, an air pump 5, a microcomputer 6 and a power supply unit 7, for instance a battery.
The injector l Isee Figure 2) suitably consists of a solid adsorbent material 8 in powder form, disposed between two glass-wool plugs 9 in a thin-walled glass tube lO that is provided with an electric resistance wire in the form of a heating coil ll wound round the tube. The heating coil connections to the power supply are designated 12. One end of the tube is connected directly to the chromatograph column 2 by means of a kind of quick-connect coupling via a rubber sealing joint 13. The other end opens directly to the ambient air but is so devised that it may be connected by means of a tubing, suitably of Teflon (trade mark), to another air sample. The entire adsorbent tube is disconnect-able so that it can be used for sampling separately from the gas chromatograph, for instance at exposition measurements. The adsorbent material inside the tube is chosen taking into consideration the air contaminants that are to be analy~ed.
However, it must be able to withstand being heated during the heat desorption stage. Liquids, for instance high temperature boiling silicone oil, may also be used as adsorbent material.
The column 2 is suitably a capillary column in the form of a glass tube helix, the coil thereof having a diameter of 11 cm and a relatively large '7~:~
tube inner diameter ~abou-t 0.4 mm). The inner surface has been deactivated and coated with a s-tationary phase with temperature stability even when air is used as carrier gas. The stationary phase operates to slow down to different degrees the various components of the sample, so they will leave the column scparated from each other, making possible separate detection thereof.
The oven 3 is designed to hold exactly the column 2 and the detector 4. The oven is well insulated with glass-wool or a similar fibre material and provided with a lining of thin aluminium foil so that the heat capacity will become low. The heating is carried out electrically by means of a resistance wire. The temperature is measured with a resistance sensor and is controlled by the microcomputer. There is a fan in order to avoid gradients and obtain a more effective temperature control.
The detector 4 is connected directly to the column 2. The choice of detection principle is made taking into consideration what substances are to be analyzed. It is desirable, however, that the detector has a small dead volume, small size and high sensitivity for the substances in question. It should also function without detector gases. There are several detectors that meet these requirements, for instance the photoionization detector and piezoelectric crys-tals coated with a specific liquid film.
The detector may be so constructed that, besides being used for gas chromatography as has been described, it can also be used as a direct-reading detector. In the latter case the sample air is directly furnished into the detector without previously passing the pre-concentrating adsorbent and the chromatograph column. In this case there is obtained an instantaneous value of the impurities the sample air contains.
A suitable embodiment of the detector 4 is shown in Figure 3. The detector is concentrically built ;n a holder 14, which by means oE a double-threaded fixing screw 19, screws 25 and with intermediate insulation pieces 15 of Teflon Eixes an W lamp 16, a detector cell l7 and an anode 1~ in a gastight way to each other. The sample air is drawn into the detector, either through a column connecting element 23 or through a direct-delivering tube 24. ~Only one of the connections has an open communication with the sample air, and a shut-off device or switching device is positioned where the sample air is furnished into the gas chromatograph.) The air sample is brought centrally into the detector cell 17 through a tubular part 22 of the anode 18 and exhausted by suc-tion through a tube 20. The two tubes 20 and 24, that are insulated with I`eflon tubing 21, also serve as electric conduits for the ionization current that arises between the detector cell and the anode, i.e. the detector signal. In order to tighten the column connection to the detector there is also provided an O-ring gasket of rubber 26 between the anode 18 and the fixing screw 19 ~between the column connecting element 23 and the insulation 15).
The air pump ~ is connected to the detector 4 via flow resistances and buffer volumes, in which way a continuous flow is obtained through the system.
I~ is suitably of the plunger type in order to achieve a sufficient suction height.
The microcomputer 6 is arranged to control the oven temperature, the air pump and the heating of the adsorbent, to register detector signal and time, and to prepare and present measured values and results. The microcomputer is suitably of the CMOS-type, which makes it possible to run the gas chromatograph for about eight hours using a battery.
Additional equipment comprises among other things a key set for control instructions to the gas chromatograph, a display and a sound alarm device for
2~
direct-indication o~ detector signal, oven temperature etc. and connecting taps for recorder, printer, external source of power supply and other fittings.
The gas chromatograph operates continuously in accordance with the following description which will be understood more readily with reference to Figure 4.
A; The sample air is drawn in through the injector 1 during a preset time. The air contaminants will get caught on the adsorbent.
B; The adsorbent is then heated for a short while. This is done almost instantaneously. The adsorbent becomes cooler and once more functions according to A.
C; Substances that are desorbed, when the adsorbent is heated, are drawn into the column 2, where they are subject to chromatography in the usual way but where the air is Eunctioning as carrier gas.
The adsorbent, which is now cold, puri~ies new sample air from contaminants, i.e. at the same time as the just desorbed substances are subject to chromatography, a new sample is furnished to the adsorbent.
D; The detector 4 registers each of the substances individually as they leave the column.
E; The microcomputer 6 prepares the detector signal and presents the result qualitatively and quantitatively.
The next work cycle starts with the adsorbent being heated again ~B;).
It can be observed that the air pump is working all the time and is drawing the air at an even speed through the adsorbent in the pre-concentrating step, the column and the detector.
The per se previously known principle of concentrating the air con-7æ~
taminants on an adsorbent before the chromatography and detection will here maXe the detection limit of the detector about 100 times better. This means that con-tents of about 0.01 mg/m3 (benzene, toluene or xylene) can be determined by means of a photoionization detector without difficulty. The good separation ability of the capillary column makes it possible to determine for instance each of the xylene isomers individually.
Every sample value that is obtained, becomes an average value of the con~ent in question during the sampling period concerned. A time period of 15 minutes is usual for industrial hygienic measurements.
By making the adsorbent tube connec-tion in such a way that it is easily disconnectable, it can be used for exposition measurements, in which case sample air is collected from the breathing zone by means of a conventional, portable air pump. As an alternative it is possible to carry the gas chromatograph about having a sampling hose, for instance of Teflon, opening out into the breathing zone. The described embodiment of the gas chromatograph would weigh about 4 kilogrammes, and can be battery operated for about 4 hours. The measurement results that are collected, during Eor instance every quarter of an hour, are stored in a storage device and can later on be taken out and then plotted/tabu-lated.
The gas chromatograph can, as has previously been pointed out, also be so constructed that the detector can be used as a direct-reading instrument.
To be able to change-over the gas chromatograph in an easy way to a direct-reading instrument is especially valuable in regard to leak searches and so-called emission measurements at working places. It is also useful when one tries to make as quickly as possible a survey of the variations of a known sub-stance in a room. It can also be used for comparison measurements, for in-'7~
stance when one wishes to make a comparison witll the background signal in a gas chromatogram.
A microcomputer for control, preparation e-tc gives a great flexibility.
It may for instance have stored values for retention times (identifiers), sensibility factors for the detector and hygienic limit values for those sub-stances that the analysis concerns. Besides, alarm functions can be released when limit values have been exceedad. It has a capacity to run two or more measuring systems in the gas chromatograph at the same time, for instance for specific detectors or a direct-reading, quick detector. The presentation of measurement results can be done in several ways by means of the microcomputer, for instance with a direct-reading recorder/display or a table over collected measurement values. The greatest advantage with the computer is that it controls the gas chromatograph in such a way that it becomes an easily operated measuring system.
direct-indication o~ detector signal, oven temperature etc. and connecting taps for recorder, printer, external source of power supply and other fittings.
The gas chromatograph operates continuously in accordance with the following description which will be understood more readily with reference to Figure 4.
A; The sample air is drawn in through the injector 1 during a preset time. The air contaminants will get caught on the adsorbent.
B; The adsorbent is then heated for a short while. This is done almost instantaneously. The adsorbent becomes cooler and once more functions according to A.
C; Substances that are desorbed, when the adsorbent is heated, are drawn into the column 2, where they are subject to chromatography in the usual way but where the air is Eunctioning as carrier gas.
The adsorbent, which is now cold, puri~ies new sample air from contaminants, i.e. at the same time as the just desorbed substances are subject to chromatography, a new sample is furnished to the adsorbent.
D; The detector 4 registers each of the substances individually as they leave the column.
E; The microcomputer 6 prepares the detector signal and presents the result qualitatively and quantitatively.
The next work cycle starts with the adsorbent being heated again ~B;).
It can be observed that the air pump is working all the time and is drawing the air at an even speed through the adsorbent in the pre-concentrating step, the column and the detector.
The per se previously known principle of concentrating the air con-7æ~
taminants on an adsorbent before the chromatography and detection will here maXe the detection limit of the detector about 100 times better. This means that con-tents of about 0.01 mg/m3 (benzene, toluene or xylene) can be determined by means of a photoionization detector without difficulty. The good separation ability of the capillary column makes it possible to determine for instance each of the xylene isomers individually.
Every sample value that is obtained, becomes an average value of the con~ent in question during the sampling period concerned. A time period of 15 minutes is usual for industrial hygienic measurements.
By making the adsorbent tube connec-tion in such a way that it is easily disconnectable, it can be used for exposition measurements, in which case sample air is collected from the breathing zone by means of a conventional, portable air pump. As an alternative it is possible to carry the gas chromatograph about having a sampling hose, for instance of Teflon, opening out into the breathing zone. The described embodiment of the gas chromatograph would weigh about 4 kilogrammes, and can be battery operated for about 4 hours. The measurement results that are collected, during Eor instance every quarter of an hour, are stored in a storage device and can later on be taken out and then plotted/tabu-lated.
The gas chromatograph can, as has previously been pointed out, also be so constructed that the detector can be used as a direct-reading instrument.
To be able to change-over the gas chromatograph in an easy way to a direct-reading instrument is especially valuable in regard to leak searches and so-called emission measurements at working places. It is also useful when one tries to make as quickly as possible a survey of the variations of a known sub-stance in a room. It can also be used for comparison measurements, for in-'7~
stance when one wishes to make a comparison witll the background signal in a gas chromatogram.
A microcomputer for control, preparation e-tc gives a great flexibility.
It may for instance have stored values for retention times (identifiers), sensibility factors for the detector and hygienic limit values for those sub-stances that the analysis concerns. Besides, alarm functions can be released when limit values have been exceedad. It has a capacity to run two or more measuring systems in the gas chromatograph at the same time, for instance for specific detectors or a direct-reading, quick detector. The presentation of measurement results can be done in several ways by means of the microcomputer, for instance with a direct-reading recorder/display or a table over collected measurement values. The greatest advantage with the computer is that it controls the gas chromatograph in such a way that it becomes an easily operated measuring system.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method relevant to a gas chromatograph for continuous, automatic, qualitative and quantitative air analysis, for instance for the determination and identification of extremely small contents of substances present in air, the gas chromatograph comprising an injector, a pre-concentrator, a chromatograph column, a detector, a computer for the control of the gas chromatograph, prepara-tion and presentation of analysis results and a power supply unit, characterized in that sample air is passed continuously and at an even speed through the in-jector, the pre-concentrator which comprises an adsorbent, the column and the detector, during which period of time substances present in the air are adsorbed on the adsorbent in the pre-concentrating step at the same time as the air is purified and can be used as carrier gas through the column and the detector, and then the adsorbent is heated for a short time so that the substances that have become concentrated on the adsorbent in the pre-concentrating step are desorbed and are carried by carrier gas, consisting of sample air purified in the pre-concentrating step, through column and detector for analysis thereof at the same time as new sample air is being passed through the injector and the adsorbent in the pre-concentrating step; the above steps during said period of time being re-peated, whereby a continuous sampling and analysis method is achieved.
2. A method according to claim 1, characterized in that the sample air is drawn continuously and at an even speed through injector, pre-concentrator, column and detector by means of an air pump disposed after the detector, air purified in the pre-concentrating step carrying substances along with it that have been concentrated and vaporized and now is to be analyzed.
3. A device for carrying out the method according to claim 2 comprising an injector, also functioning as pre-concentrator for those substances that are to be analyzed, which includes an adsorbent that can be heated in order to de-sorb the substances adsorbed thereon; a temperature-controlled, fan-provided oven comprising a capillary column and a detector; a microcomputer for the control of the device and preparation and presentation of analysis results; and a power supply device, characterized in that there is provided after the de-tector an air pump that draws sample air at an even speed via flow resistances and buffer volumes through the injector, the capillary column and the detector, the air that is present in the sample forming a carrier gas through the capillary column and the detector for those substances that are to be analyzed.
4. A device according to claim 3, characterized in that the injector com-prises an adsorbent material in powder form which is held together by means of two glass-wool plugs in a thin-walled glass tube, which is provided with a helix-formed resistance wire tightly wound round it, the ends of the resistance wire being fixed to the glass tube by means of two metal rings, which at the same time are electric connecting taps and through which a current can be led and in a short while heat the resistance wire, the glass tube and the adsorbent material.
5. A device according to claim 3 or 4, characterized in that the detector is constructed from a detector cell in the form of a hollow cylinder; an anode that is concentric with the detector cell and comprises a tubular part surround-ed by the detector cell; an UV-lamp; a holder, which holds and is concentric with the detector cell and the anode and fixes the UV-lamp, the detector cell and the anode in a gas-tight way to each other by means of screw joints and in-termediate insulations, for instance of Teflon; an element connecting the column to the detector and provided with a through-hole for the delivery of sample air from the column to the detector; a tube, which is fixed to the anode and in com-munication with the ambient air for direct delivery of sample air; a suction tube, which is connecting the cavity of the detector cell with the air pump;
both the suction tube and the direct-delivering tube being insulated with for instance Teflon tubing and constituting electric conduits for the ionization current that arises between the detector cell and the anode; and a device posi-tioned outside the detector, which makes switching over or shutting off possible and with the help of which the sample air, that is drawn in by means of the air pump and furnished to the cavity of the detector cell through the tubular part of the anode, can be taken either from the column through the column connecting element or directly from the ambient air through the direct-delivering tube to be exhausted through the suction tube after the detection thereof.
both the suction tube and the direct-delivering tube being insulated with for instance Teflon tubing and constituting electric conduits for the ionization current that arises between the detector cell and the anode; and a device posi-tioned outside the detector, which makes switching over or shutting off possible and with the help of which the sample air, that is drawn in by means of the air pump and furnished to the cavity of the detector cell through the tubular part of the anode, can be taken either from the column through the column connecting element or directly from the ambient air through the direct-delivering tube to be exhausted through the suction tube after the detection thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416762A CA1191721A (en) | 1982-12-01 | 1982-12-01 | Method and device for continuous, automatic air analysis |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000416762A CA1191721A (en) | 1982-12-01 | 1982-12-01 | Method and device for continuous, automatic air analysis |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191721A true CA1191721A (en) | 1985-08-13 |
Family
ID=4124057
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000416762A Expired CA1191721A (en) | 1982-12-01 | 1982-12-01 | Method and device for continuous, automatic air analysis |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191721A (en) |
-
1982
- 1982-12-01 CA CA000416762A patent/CA1191721A/en not_active Expired
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