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USRE28417E - Cl golc - Google Patents

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USRE28417E
USRE28417E US36243273A USRE28417E US RE28417 E USRE28417 E US RE28417E US 36243273 A US36243273 A US 36243273A US RE28417 E USRE28417 E US RE28417E
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gas
electron capture
tracer gas
tracer
detector
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/0606—Investigating concentration of particle suspensions by collecting particles on a support
    • G01N15/0618—Investigating concentration of particle suspensions by collecting particles on a support of the filter type
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
    • G01N27/64—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber

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  • ABSTRACT F THE DISCLOSURE A method and apparatus for detecting the presence of an halogenated tracer gas, which is an electron absorber. in an environment which is itself, or comprises as a constituent, an electron absorber.
  • the apparatus comprises an electron capture detector and the environment to be sampled is rst drawn through a membrane which has a greater permeability to the tracer gas than the remainder of the environment before being carried into the detector by a carrier gas. This results in a diminution of the concentration of any electron capture agents present in the environment and which if drawn into the detector could swamp the effect of the tracer gas.
  • the present invention relates to a method and apparatus for detecting the presence of electron capture tracer gases.
  • electron capture tracer gases there can be mentioned SP3, CZHZCIZ, C2H3BI'4, C2H2Cl4, CClgFg and CBI'CIFZ.
  • tracer gases are electron absorbers and the apparatus is particularly concerned with the detection of such tracer gases present in an environment which is itself, or comprises as a constituent, an electron absorber.
  • tracer gases One use for tracer gases is the detection of leaks in a gas system.
  • the tracer gas has been helium, which is detectable by a mass spectrometer and freon which is detectable by a halogen detector.
  • the mass spectrometer is both bulky and expensive.
  • the halogen detectors are not suciently sensitive for a number of applications.
  • A11 electron capture detector for detecting the presence of the tracer gas.
  • A11 electron capture detector generally comprises an ionization chamber containing a particle emitter, such as tritium, as the primary source of ionizing radiation.
  • a particle emitter such as tritium
  • a carrier gas such as nitrogen possessing no affinity for electrons
  • the carrier gas contains a compound having an aflinity for electrons
  • negative ion formation occurs which is accompanied by an observed decrease in current.
  • the present invention seeks to provide a method and apparatus which can be used to monitor atmospheric air or other gas samples for the presence and concentration of sulphur hexauoride and other halogenated tracer gases.
  • Oxygen itself is capable of electron capture and it could therefore saturate the detector.
  • a method of detecting and monitoring the presence of ha1ogenated tracer gas in a gas supply having as a major constituent thereof an electron capture material comprises selectively isolating said tracer gas from the remainder of the supply by diifusion through a membrane having a greater permeability to said tracer gas than to the remainder of the supply, and thereafter conveying the tracer gas into an electron capture detector by means of a gas stream substantially inert to electron capture.
  • an apparatus for detecting and monitoring the presence of halogenated tracer gas supply comprises a probe carrying a membrane having a greater permeability to said halogenated tracer gas or gases than the remainder of the gas supply, means for conveying a carrier .gas to the side of the membrane remote from the gas supply and an electron capture detector to receive said carrier gas containing the halogenated tracer gas whereby to detect the latter.
  • halogenated tracer gas When the halogenated tracer gas is present in the atmosphere it is necessary to separate the tracer gas from the oxygen of the atmosphere prior to introduction into the detector. Oxygen is itself an electron absorber and its presence would saturate the detector and effectively blanket the presence of the tracer gas. Suflicient amount of the tracer gas must be introduced intothe detector to obtain a useful response of the detector and it is therefore necessary to separate the tracer gas from the atmospheric oxygen prior to its introduction into the detector.
  • the tracer gas can pass through the membrane and is then swept into the detector by a stream of inert gas i.e. inert to electron capture.
  • a suitable carrier gas is nitrogen.
  • a suitable membrane is formed from a silastomer.
  • FIG. 1 is a diagrammatic representation of an apparatus according to the invention
  • land FIG. 2 shows a modification of part of the apparatus in which a sampling probe is contained in an outer sheath.
  • a sampling probe 10 for introducing a gas to be analyzed into an electron capture detector is closed at one end by a membrane 12.
  • the membrane is preferably formed from a silastomer as this has a permeability to some halogenated tracer gases which is of the order of ten times .greater than that to oxygen.
  • the opposite end of the probe is connected through a line 14 controlled by a valve 16 to a nitrogen supply, the nitrogen serving as a carrier gas to convey the gas to be analyzed into the electron capture detector 18 by way of a line 20.
  • the line 20 commences adjacent the membrane 12.
  • An amplifier 22 and a meter 24 are connected to the detector.
  • silastomer refers to a thin lm or sheet of silicone rubber.
  • the sampling probe 10 is contained within an outer sheath 30.
  • the end of the sheath 30 adjacent the membrane 12 is open to the atmosphere while the other end of the sheath commnuicates through line 32 with a suction means, for example an air pump (not shown).
  • the pump draws air or gas to be sampled into the sheath and into contact with the membrane
  • the exhaust from the detector 18 can be connected to the suction line 32. This provides a convenient method of determining ow from the detector.
  • the draft created by the suction makes the probe less directionally sensitive and it can pick up a tracer gas at greater distances from a leak than th apparatus of FIG.*1.
  • the apparatus can be used for detecting leaks in a gas system having a halogenated tracer gas.
  • tracer agents are sulphur hexauorideSF and Freon (registered trademark) such as dichlorodiuoromethane 1.
  • a method of detecting and monitoring the presenceof an electron capture halogenated tracer gas in a gas supply having as va constituent thereof an ⁇ electron capture material comprising the steps of selectively isolating said halogenated tracer gas from the remainder of thel supply by diiusion through a membrane formed from a silastomer having a greaterpermeability to'said halo genated tracer gas than to the remainder of the supply,
  • An appparatus for detecting and monitoring the pres- ⁇ ence of an electron capture halogenated tracer gas in a gas supply which is itself, or includes as a constituent, an electron capture material comprising a probe, a membrane at an end of said probe in which the membrane comprises a silastomer having a greater permeability to the halogenated tracer gas than the remainder of the gas supply, means for conveying a carrier gas to the side of the membrane remote from the gas supply and an electron capture detector to receive the carrier gas and tracer gas.
  • An apparatus including an outer .-sheathsurrounding thetprobe andeopen to theatmosphere at one end, suction means being connected to the other end of the sheath whereby to draw in a sample into the vicinity of the membrane.
  • a method of detecting and monitoring the presence of an electron capture nitro-compound tracer gas in a gas supply having as a constituent thereog an electron capture material comprising the steps of selectively isolating said nitro-compound tracer gas from the remainder of the supply by diffusion through a membrane formed from a silastomer having agreater permeability to said tracer gas than to the remainder of the supply, and thereafter' conveying the tracer gas into an electron capture detector by means of a gas stream substantially inert to electron capture.
  • the apparatus comprising a probe, a membrane at an end of said probe in which the ⁇ membrane comprises a sil'astomer having a greater permeability ⁇ to the nitro-compound tracer gais ⁇ than the regmainder of the gas supply, means for conveying a carrier gas' to the side 'of the membrane remote from the gas supply and an Aelectron capture detector to receive the carrier gas and tracer gas.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Pathology (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Toxicology (AREA)
  • Dispersion Chemistry (AREA)
  • Examining Or Testing Airtightness (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Sampling And Sample Adjustment (AREA)
  • Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)

Abstract

1. A METHOD OF DETECTING AND MONITORING THE PRESENCE OF AN ELECTRON CAPTURE HALOGENATED TRACER GAS IN A GAS SUPPLY HAVING AS A CONSTITUENT THEREOF AN ELECTRON CAPTURE MATERIAL, COMPRISING THE STEPS OF SELECTIVELY ISOLATING SAID HALOGENATED TRACER GAS FROM THE REMAINDER OF THE SUPPLY THE DIFFUSION THROUGH A MEMBRANCE FORMED FROM A SILASTOMER HAVING A GREATER PERMEABILITY OF SAID HALOGENATED TRACER GAS THAN TO THE REMAINDER OF THE SUPPLY, AND THEREAFTER CONVEYING THE TRACER GAS INTO AN ELECTRON CAPTURE DETECTOR BY MEANS OF A GAS STREAM SUBSTANTIALLY INERT TO ELECTRON CAPTURE.

Description

May 6, `975 A JENKINS E'rAL Re. 28,417
METHOD AND APPARATUS FOR DETEGTING TRACER GAS Original Filed Aug. 15, 1970 United States Patent Re. 28,417 Reissued May 6, 1975 28,417 METHOD AND APPARATUS FOR DETECTING TRACER GAS Anthony Jenkins and Richard C. Cornell, Royston, England, assignors to Analytical Instruments, Ltd., Royston, England Original No. 3,699,342, dated Oct. 17, 1972, Ser. No. 63,571, Aug. 13, 1970. Application for reissue May 21, 1973, Ser. No. 362,432 Claims priority, application Gigas Britain, Apr. 27, 1970,
1 Int. Cl. G01c 1/18 U.S. Cl. Z50-302 5 Claims Matter enclosed in heavy brackets II] appears in the original patent but forms no part of this reissue specilicatlon; matter printed in italica indicates'the additions made by reissue.
ABSTRACT F THE DISCLOSURE A method and apparatus for detecting the presence of an halogenated tracer gas, which is an electron absorber. in an environment which is itself, or comprises as a constituent, an electron absorber. The apparatus comprises an electron capture detector and the environment to be sampled is rst drawn through a membrane which has a greater permeability to the tracer gas than the remainder of the environment before being carried into the detector by a carrier gas. This results in a diminution of the concentration of any electron capture agents present in the environment and which if drawn into the detector could swamp the effect of the tracer gas.
The present invention relates to a method and apparatus for detecting the presence of electron capture tracer gases. As examples of such gases there can be mentioned SP3, CZHZCIZ, C2H3BI'4, C2H2Cl4, CClgFg and CBI'CIFZ. Such tracer gases are electron absorbers and the apparatus is particularly concerned with the detection of such tracer gases present in an environment which is itself, or comprises as a constituent, an electron absorber.
One use for tracer gases is the detection of leaks in a gas system. In two known methods the tracer gas has been helium, which is detectable by a mass spectrometer and freon which is detectable by a halogen detector. The mass spectrometer is both bulky and expensive. The halogen detectors are not suciently sensitive for a number of applications.
The present invention utilizes an electron capture detector for detecting the presence of the tracer gas. A11 electron capture detector generally comprises an ionization chamber containing a particle emitter, such as tritium, as the primary source of ionizing radiation. Upon entry into the chamber of a carrier gas such as nitrogen possessing no affinity for electrons, recombination of positive ions nad free electrons formed by the ionizing radiation is unlikely to take place because of the free electrons high mobility. Thus by applying a small potential across the chamber all ions formed by the ionizing radiation can be collected. When the carrier gas contains a compound having an aflinity for electrons, negative ion formation occurs which is accompanied by an observed decrease in current.
The present invention seeks to provide a method and apparatus which can be used to monitor atmospheric air or other gas samples for the presence and concentration of sulphur hexauoride and other halogenated tracer gases. Oxygen itself is capable of electron capture and it could therefore saturate the detector.
According to one aspect of the present invention a method of detecting and monitoring the presence of ha1ogenated tracer gas in a gas supply having as a major constituent thereof an electron capture material comprises selectively isolating said tracer gas from the remainder of the supply by diifusion through a membrane having a greater permeability to said tracer gas than to the remainder of the supply, and thereafter conveying the tracer gas into an electron capture detector by means of a gas stream substantially inert to electron capture.
According to another aspect of the present invention, an apparatus for detecting and monitoring the presence of halogenated tracer gas supply comprises a probe carrying a membrane having a greater permeability to said halogenated tracer gas or gases than the remainder of the gas supply, means for conveying a carrier .gas to the side of the membrane remote from the gas supply and an electron capture detector to receive said carrier gas containing the halogenated tracer gas whereby to detect the latter.
When the halogenated tracer gas is present in the atmosphere it is necessary to separate the tracer gas from the oxygen of the atmosphere prior to introduction into the detector. Oxygen is itself an electron absorber and its presence would saturate the detector and effectively blanket the presence of the tracer gas. Suflicient amount of the tracer gas must be introduced intothe detector to obtain a useful response of the detector and it is therefore necessary to separate the tracer gas from the atmospheric oxygen prior to its introduction into the detector.
This is achieved by separating the detector from the atmosphere or other gas supply containing a preponderance of an electron capture material in addition to the electron capture tracer gas by means of a membrane. The tracer gas can pass through the membrane and is then swept into the detector by a stream of inert gas i.e. inert to electron capture. A suitable carrier gas is nitrogen.
A suitable membrane is formed from a silastomer.
The invention will be described further by way of example with reference to the accompanying drawings in which:
FIG. 1 is a diagrammatic representation of an apparatus according to the invention, land FIG. 2 shows a modification of part of the apparatus in which a sampling probe is contained in an outer sheath.
A sampling probe 10 for introducing a gas to be analyzed into an electron capture detector is closed at one end by a membrane 12. The membrane is preferably formed from a silastomer as this has a permeability to some halogenated tracer gases which is of the order of ten times .greater than that to oxygen. The opposite end of the probe is connected through a line 14 controlled by a valve 16 to a nitrogen supply, the nitrogen serving as a carrier gas to convey the gas to be analyzed into the electron capture detector 18 by way of a line 20. The line 20 commences adjacent the membrane 12. An amplifier 22 and a meter 24 are connected to the detector. When the gas to be analyzed contains tracer gas and is introduced into the detector this results in a change in the ionization current which charge is indicative of the concentration of tracer gas in the nitrogen carrier gas stream and is noted on the meter 24.
The term silastomer refers to a thin lm or sheet of silicone rubber.
In FIG. 2, the sampling probe 10 is contained within an outer sheath 30. The end of the sheath 30 adjacent the membrane 12 is open to the atmosphere while the other end of the sheath commnuicates through line 32 with a suction means, for example an air pump (not shown). The pump draws air or gas to be sampled into the sheath and into contact with the membrane Furthermore, as shown in FIG. 2, the exhaust from the detector 18 can be connected to the suction line 32. This provides a convenient method of determining ow from the detector. The draft created by the suction makes the probe less directionally sensitive and it can pick up a tracer gas at greater distances from a leak than th apparatus of FIG.*1.
The apparatus can be used for detecting leaks in a gas system having a halogenated tracer gas. Examples of tracer agents are sulphur hexauorideSF and Freon (registered trademark) such as dichlorodiuoromethane 1. A method of detecting and monitoring the presenceof an electron capture halogenated tracer gas in a gas supply having as va constituent thereof an `electron capture material, comprising the steps of selectively isolating said halogenated tracer gas from the remainder of thel supply by diiusion through a membrane formed from a silastomer having a greaterpermeability to'said halo genated tracer gas than to the remainder of the supply,
and thereafter conveying the tracer gas intoan electron capture detector by means of a gas stream substantially inert to electron capture.
2. An appparatus for detecting and monitoring the pres-` ence of an electron capture halogenated tracer gas in a gas supply which is itself, or includes as a constituent, an electron capture material, the apparatus comprising a probe, a membrane at an end of said probe in which the membrane comprises a silastomer having a greater permeability to the halogenated tracer gas than the remainder of the gas supply, means for conveying a carrier gas to the side of the membrane remote from the gas supply and an electron capture detector to receive the carrier gas and tracer gas.
3. An apparatus according to claim 2, including an outer .-sheathsurrounding thetprobe andeopen to theatmosphere at one end, suction means being connected to the other end of the sheath whereby to draw in a sample into the vicinity of the membrane.
4. A method of detecting and monitoring the presence of an electron capture nitro-compound tracer gas in a gas supply having as a constituent thereog an electron capture material, comprising the steps of selectively isolating said nitro-compound tracer gas from the remainder of the supply by diffusion through a membrane formed from a silastomer having agreater permeability to said tracer gas than to the remainder of the supply, and thereafter' conveying the tracer gas into an electron capture detector by means of a gas stream substantially inert to electron capture. v
45. An apparatus for detecting and monitoring the presence of 1an electron ,capture nitro-compound tracer gas in a gas supply which is itself,A or includes as a constituent,
an electron capture material, the apparatus comprising a probe, a membrane at an end of said probe in which the` membrane comprises a sil'astomer having a greater permeability `to the nitro-compound tracer gais` than the regmainder of the gas supply, means for conveying a carrier gas' to the side 'of the membrane remote from the gas supply and an Aelectron capture detector to receive the carrier gas and tracer gas.
References Cited i The followingl references,'cited by the Examiner, are of record in the patented le of this patent or the original patent.
UNITED STATES PATENTS 1/1968 Petitjean et al Z50-381 X 12/1970 McKinley, Jr. 55-16 ARCHIE R. BORCHELT, Primary Examiner l U.S. Cl. X.R. 250, 389
US36243273 1970-04-27 1973-05-21 Cl golc Expired USRE28417E (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4304752A (en) * 1979-03-23 1981-12-08 Anthony Jenkins Detection of tracer materials in the atmosphere
US4311669A (en) * 1980-08-21 1982-01-19 The Bendix Corporation Membrane interface for ion mobility detector cells
US4424067A (en) 1982-07-29 1984-01-03 Allied Corporation Purification of anhydrous hydrogen fluoride
US4793830A (en) * 1987-12-28 1988-12-27 Murphy Milton K Process for producing high quality gas for instrumentation application using gas separation membranes
US20050211949A1 (en) * 2003-11-13 2005-09-29 Bivens Donald B Detectable refrigerant compositions and uses thereof

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3361908A (en) * 1964-01-03 1968-01-02 Barber Colman Co Method and apparatus for electron attachment detection
US3545931A (en) * 1968-08-28 1970-12-08 Monsanto Co Ammonia analysis system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3361908A (en) * 1964-01-03 1968-01-02 Barber Colman Co Method and apparatus for electron attachment detection
US3545931A (en) * 1968-08-28 1970-12-08 Monsanto Co Ammonia analysis system

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