US3828184A

US3828184A - Ionization chamber with a porous anode

Info

Publication number: US3828184A
Application number: US00232721A
Authority: US
Inventors: J Lupton
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-03-08
Filing date: 1972-03-08
Publication date: 1974-08-06
Anticipated expiration: 1991-08-06

Abstract

An Ionization Detector analyses a flowing fluid stream for a specific gas or gases. The recirculation of gases between electrodes is eliminated, and the gas between the anode and cathode is not restrained. The anode is made of a porous, electrically conductive material and the cathode is a beta emitting foil positioned adjacent to, but physically and electrically isolated from, the anode. The detector will function with or without an added cell voltage. The response of the detector to the water of aqueous solutions is so limited in duration that a characteristic response from organic substances can be obtained even when the substance is introduced in an aqueous solution to the chromatographic column.

Description

0 United States Patent 1191 [111 3,828,184 Lupton Aug. 6, 1974 IONIZATION CHAMBER WITH A POROUS ANODE Primary Examiner-Harold A. Dixon [76] Inventor: Joseph D. Lupton, 2653 Henderson Attorney Agent or Flrm james Gaffey k 3 I Rd Tuc er Ga 0084 ABSTRACT 2 Filed: 1972 An Ionization Detector analyses 21 flowing fluid stream [21] Appl. No.: 232,721 for a specific gas or gases. The recirculation of gases between electrodes is eliminated, and'the gas between the anode and cathode is not restrained. The anode is if 5 250/83'6 made of a porous, electrically conductive material and l d R 6 FT the cathode is a beta emitting foil positioned adjacent 1 o are 21 O to, but physically and electrically isolated from, the anode. The detector will function with or without an 56 R f d added cell voltage. The response of the detector to the 1 e erences water of aqueous solutions is so limited in duration UNITED STATES PATENTS that a characteristic response from organic substances 2,499,830 3/1950 Molloy 250/83.6 R can be obtained even when the substance is intro? 76 0/1953 Firminhac... 250/835 FT duced in an aqueous solution to the chromatographic 3,009,098 11/196] Simons 250/83.6 FT column, 3,154,682 10/1964 Hartz et al.. 250/816 FT 3,247,315 4/1966 Lovelock 250/83.6 PT 19 Claims, 3 Drawmg Figures I 5 E 28 I ///////AI as 5 as Z 4 Z 37 37 29 26 Z 36 57 Q 32 POROUS 7 ANODE 4 37 37 2 a] RADIOACTIVE co ATlNG minnow Y IONIZATION RECORDER CHAMBER FIG .1

RADIOACTIVE 1 COATING FIG 2 FIG 3' Sun rel!!! mlmnl mv IONIZATION CHAMBER WITH A POROUS ANODE BACKGROUND OF THE INVENTION In general, ionization detectors consist of a chamber having fluid inlet and outlet ports, a radiation source in the chamber, and an external DC. voltage source. The radiation source is a radioactive isotope, usually deposited on a stainless steel foil. A standing current is created by passing a gas such as N through the ionization chamber. Ionization chambers function as detectors because specific gases produce changes in the standing current which can be measured as a sample passes through the detector.

While a discussion of ionized gas theory is beyond the scope of this patent, some insight to the theory can be gained from Ionized Gases by VonEngle, Oxford University Press, New York, N.Y., 1965, and examples of gas analysis systems are disclosed in U.S. Pat. No. 2,641,710, issued June 9, 1953, to D. J. Pompeo, and in U.S. Pat. No. 3,247,375, issued Apr. 19, 1966, to .I. E. Lovelock.

Ionization chambers, including detectors of the type described in U.S. Pat. No. 2,641,710 operate on the basis of the magnitude of the voltage used across the anode and cathode. A DC. voltage is applied between the cathode and ground in order to increase the standing current over that noted when the cathode is at ground potential (U.S. Pat. No. 3,247,375).

Ionization chambers have been used as components in systems to detect and analyze specific gases in recirculating-systems (U.S. Pat. No. 2,547,874), to obtain timed current responses (U.S. Pat. No. 2,547,874), and for other purposes. With the prior art devices, an organic compound has to be extracted from an aqueous solution before injection into a gas chromatograph. Furthermore, the sample should be separated from as many contaminants as possible to keep the detector clean. Failure to inject samples with limited residues increases base line noise of the detector and reduces the overall sensitivity of the detector, and the interior surfaces of the detector become coated with contaminants such as hydrocarbons. The coating eventually produces a high-resistance short circuit within the detector which is a source of increased base line noise and drift.

As a result of contamination, some detectors in use today are returned to the factory for cleaning, which increases cost of operation of the instrument and reduces the time an instrument is in service. In order to reduce the frequency of cleaning the detectors, an aqueous solution having high purity can be utilized; however, the requirement for high solvent purity for sample extraction from aqueous solutions contributes to higher cost per sample.

SUMMARY OF INVENTION Briefly described, the present invention relates to gas analysis and provides a method and apparatus for detecting and measuring even small concentrations of gaseous substances. An ionization chamber detector is provided with a porous anode positioned in a housing and the gas flowing into the housing must flow through the porous anode before being exhausted from the housing. The porous anode provides for irradiation of the specific gas as it emerges from the anode while the gas is present at a high concentration in the carrier gas until they are both detected. The radiation source need not be enclosed in asealed chamber around the anode and cathode as is true in other detectors. This nonsealed or open arrangement eliminates recirculation between the outer surface of the anode and the cathode. The open cell concept makes possible injection of currently unacceptable solvents without interrupting normal operation at the detector. Base line return after injections of 50 p. 1 of H 0 in 30 seconds is about normal for the present chamber configuration. The flowthrough arrangement causes the surfaces of the system to be self-cleaning and the system can accept aqueous solutions without prior chemical or physical cleanup. The accumulation of contaminants is therefore avoided. The surfaces of the system are therefore not inclined to become coated with contaminants and a short circuit is avoided. Each of the openings in the porous anode acts as a separate anode for sensing the energy transfer. The net effect from the anode as a whole is the summation of current from the smaller openings which accounts for a standing current in the 20 nano ampere range.

A major contribution of the present detector lies in its capacity to accept aqueous and nonaqueous solutions directly. Using the new detector, a sample dissolved in any common solvent, including water, is injected into the column directly for testing. With an aqueous solvent and operating above C. this detector is steam cleaned with each injection and hence remains clean. The time and expense of chemical clean up of samples is thus eliminated.

The DC. voltage applied between the radioactive source and ground serves to reduce the space charge between the anode and cathode. An electrical ground surrounds the anode and cathode, hence, any electrical leakage between the anode and cathode is shorted to ground. Recirculation of carrier gas and samples which is common to other ionization detectors is eliminated by the porous anode which provides unidirectional gas flow from the anode and the lack of back pressure on the gases from the detector chamber.

The outer shell of the detector serves as a physical support for the anode and cathode and maintains their relative position. A single fluid outlet port in the outer shell insures entrapment of all gases and radioactive particles from the source when necessary. The significance of this feature is discussed by J. R. I-Iowley in Health Physics, vol. l8, no. l,.lanuary, 1970. The relatively large volume of the chamber insures dispersement of incoming gases as well as electrical isolation between the anode and cathode.

Thus, it is an object of the present invention to provide a detector which is inexpensive to operate, which is reliable for detecting and measuring even small concentrations of organic substances.

Another object of this invention is to provide an ionization detecting apparatus which allows the use of all common solvents, including water, to carry a substance with a gas stream, thus reducing the cost to the user of the system by eliminating several steps of extracting a sample from an unacceptable solution.

Another object of the present invention is to provide an ionization detection method and apparatus which is self cleaning, simple to operate, and which is reliable.

Other objects, features and advantages of the present invention will become apparent when reading the following specification, when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a gas-liquid chromatograph.

FIG. 2 is a detailed illustration of the ionization chamber.

FIG. 3 is a detailed illustration of an ionization chamber, showing a modified ionization chamber.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now in more detail to the drawing, FIG. 1 illustrates the ionization detection method and apparatus which isbroadly designated bythe numeral 10 and includes a source 11 of gas under pressure, such as nitrogen, argonor other rare gas. The gas should be substantially free from impurities. The gas passes in the form of a stream of gas from the source 11 through conduit 12 to a chromatograph column 13 which includes a heat shield 14, heating means 15, a granular heat conducting medium 16, and a column 18 filled with capillary material. An on-off valve 19 is placed in conduit 12, and a branch conduit 20 communicates through on-off valve 21. Branch conduit 20 and valve 21 are used to inject the sample in the gas flow stream through conduit 12 to the chromatograph column 13. The sample would include the substance to be detected together with a carrier solvent, such as water, etc.

Ionization chamber 22 communicates with the end of column 18 of chromatograph column 13, and recorder 24 records the detection of the substances in the ionization chamber and creates a print out 25.

As is illustrated in FIG. 2, ionization chamber 22 comprises a radiation shielded housing 26 having a gas inlet opening 28 and a gas outlet opening 29. Conduit 30 extends through the gas inlet opening 28 from the chromatograph column 13 into the housing 36. Exhaust conduit 31 extends through the gas outlet opening 29 and functions to exhaust the gas, etc., from the shielded housing to a radiation trap (not shown).

Cylindrical sleeve 32 is located inside housing 26 and is closed at its ends by end caps 33 and 34. Conduit 30 which protrudes through gas inlet opening 28 extends through end cap 34 so that the gas stream from conduit 30 is fed internally into sleeve 32. In one embodiment sleeve 32 is fabricated from molded granular bronze particles with the particles being in a range of sizes which provides a latticework of apertures or pores having approximately openings per square millimeter, with the openings being from about 0.l to 0.5 millimetors in diameter. The inside diameter of the sleeve in the particular embodiment illustrated is A inch, and the wall thickness of the sleeve is approximately l/ 16 of an inch thick. Of course, other sleeve sizes, thicknesses, grain and pore sizes can be utilized, as may be appropriate for the particular substances being detected.

Moreover, while bronze has been disclosed as the substance used in sleeve 32, it should be understood that various electrically conductive porous materials can be used, preferably a substance which is noncorrosive from the substances being detected and measured or the solvents or gases used in the system.

The arrangement of the sleeve 32 and its end caps 33 and 34 is such that the gases and substances passing into the sleeve from conduit 30 must pass through the pores of the sleeve. The end caps 33 and 34 are fabricated from an impervious substance, preferably a noncorrosive substance. For instance, the end caps 33 and 34 can be fabricated from Teflon or a ceramic material. Inlet conduit 30 is an electrical conductor connected inside housing 26 to sleeve 32 by means of conductor 35 or any conventional conducting means, and is electrically connected to recorder 24 by means of conductor 28.

Stainless steel foil 36 is wrapped around sleeve 32 so that it substantially covers the sleeve. The foil 36 is positioned closely adjacent to the sleeve. The inside surface of the stainless steel foil 36 is coated with a layer 57 of a radioactive substance such as radium, so that V the exterior surface of sleeve 32 is substantially uniformly exposed to beta radiation, the thickness of the stainless steel foil 36, herein referred to as a cathode, functions as a means to produce radiation within housing 26 at the exterior surface of sleeve 32. Other radioactive sources may be used other than radium, and other supports for the beta source such as a wire mesh, as an example, may be used.

As illustrated in FIG. 3, a modified ionization chamber 40 is provided which includes a radiation shield housing 41 having an inlet opening 62 and an outlet opening 43 defined therein. Conduit 44 extends through opening 42 into the mid-portion of housing 41. Cylindrical porous sleeve 45, on which has been coated a beta source, is a wire mesh in which incoming gases are ionized as they pass through.

The ends of cylinder 45 are closed by

nonconductive end plates

46 and 47. Cylindrical bronze porous sleeve 48 surrounds sleeve 45, being held in place by

end plates

46 and 47 functions as the anode for

cathodes

45 and 49. Cylindrical porous sleeve 49 is a radioactive coated wire mesh cathode which serves to reionize gas molecules as they emerge from anode 48.

Dual cathodes

45 and 49 are connected through insulated conductor 50, via electrical conductor 53.

Electrical conductor 51 passes through insulator 52 and serves as anode output from the detector. Electrical conductor 53 passes through insulator 54 and serves as the electrical output for the

dual cathodes

45 and 49. (NOTE: Electrical conductor 55 passing through insulator 56 could be installed to serve as a separate output for cathode 49.) Alternately, a DC voltage may be inserted between the

beta sources

45 and 49 and ground to reduce space charge within the detector. If the DC voltage is inserted with positive ground, the response of the detector is about three times that noted compared to the voltage source being connected with a negative ground.

The substances flowing with the gas through stainless steel conduit 44 into the inside area of wire mesh sleeve 45 will pass with the gas through the pores of the sleeve 45. As the substances reach and begin their passage through the plurality of small pores of sleeve 48, there will be a change in the standing current, which will be detected by the recorder. As the substances emerge from the outer surface of bronze sleeve 48, the detection process is repeated. Detection is made on both sides of the bronze sleeve 48 through the actions of the beta source facing each surface of the anode 48. The radioactive sources are

cathode

45 and 49. Thus, each molecule should be detected twice as the molecules flow with the gas stream through the system thus increasing the sensitivity of the detector. Changes in standing current within the detector will be noted when anode 48 and

dual cathodes

45 and 49 are connected to normal exterior electronic equipment. As with the device of FIG. 2, this generates a reliable indication as to the presence of the substances passing with the gas stream through the porous surface of the sleeve.

The ionization chambers illustrated in FIGS. 2 and 3 function reliably to detect the substances passing with the gas stream with the cathode at either ground potential or when a voltage is placed between the cathode and ground. When a voltage is used in this manner, the recorder can be adjusted to compensate for the increased potential and obtain a reading which corresponds to the substances being passed with the gas stream with the ionization chamber. Thus, both embodiments of the invention will function either with or without an additional voltage between the radioactive source (cathode) and ground.

In FIGS. 2 and 3, electrically conductive band 37 is connected to ground to provide electrical isolation between

active elements

45, 48 and 49.

While the invention is illustrated in FIG. 1 as being in combination with specific elements, it will be understood by those skilled in the art that the forms of the invention illustrated and variations thereof can be used in other and in different combinations. For example, the invention can be used with other combinations of elements wherein measurements are taken of pesticides in water, saturated and unsaturated fatty acids, steroids, alkeloids, amino acids, blood gases urinary aromatic acids and others. Thus, while this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

l claim:

1. A method of measuring small concentrations of gaseous substances comprising injecting a sample of a substance in a fluid carrier solvent into a rare gas stream, passing the gas stream through a gas chromatography column, passing the gas stream from the column through a porous solid electrically conductive surface, radiating the gas stream at the porous electrically conductive surface with beta radiation, and detecting a change in the flow of current from the porous electrically conductive surface.

2. Apparatus for detecting and measuring even small concentrations of substances in which said substances are introduced into an atmosphere of a rare carrier gas, said apparatus comprising a chamber defining a gas inlet and a gas outlet, at least one electrically conductive porous solid surface in said chamber, means for directing gas flow from said gas inlet through said porous surface and out of said outlet, means for producing ionization capabilities at said porous surface whereby molecules of the substances passing through said chamber are ionized at the surface of said porous surface, and detecting means for detecting substance ionized at said porous surface.

3. The apparatus of claim 2 and wherein said porous surface comprises an approximately cylindrical sleeve molded from bronze of varying porosities surrounding the gas inlet of said chamber, and said means for producing ionization capabilities comprising a stainless steel foil surrounding said sleeve without touching said sleeve and being coated with a radioactive isotope on its surface facing said sleeve.

4. The apparatus of claim 2 and wherein said porous surface comprises a bronze sleeve with its interior surface communicating with said gas inlet of said chamber, and said means for producing ionization capabilities is positioned outside said sleeve.

5. The apparatus of claim 2 and wherein said porous surface comprises a hollow cylindrical body, and said means for producing ionization capabilities at said porous material is positioned inside said cylindrical body.

6. The apparatus of claim 2 and wherein said porous surface comprises a hollow body, and said means for producing ionization capabilities at said porous material comprises means positioned both inside and outside the said hollow body.

7. The apparatus of claim 2 wherein the porous mate rial is arranged between the inlet and outlet to provide a pressure differential thereacross thereby providing unidirectional gas flow through the chamber.

8. The apparatus of claim 2 wherein the active elements of the detector are not grounded.

9. An ionization chamber for detecting a fluid sample of vaporized liquid and/or gas comprising a porous solid electrode connected for receiving said fluid, a source of ionization, a second electrode, a housing for supporting said electrodes in spaced relationship, said porous electrode providing a sufficient pressure drop to provide unidirectional flow thereby preventing any substantial condensation between the electrodes.

10. An ionization chamber having an inlet and outlet comprising a porous anode electrode having a lattice work of small apertures or pores for receiving and passing both gas and vaporized liquids from said inlet, said inlet normally having a positive pressure and said electrode and apertures providing a unidirectional flow of said gases to said outlet thereby providing a self cleaning without deposit of contaminants within the chamber.

11. A method according to claim 1, wherein said step of passing the gas stream from the column through a porous solid electrically conductive surface consists of passing the gas stream through a porous solid anode.

12. A method according to claim 11, wherein said step of passing the gas stream through a porous solid anode consists of passing the gas stream through a porous solid anode having a lattice work of small apertures or pores.

13. A method according to claim 1, wherein said step of passing the gas stream from the column through a porous solid electrically conductive surface consists of passing the gas stream through a porous solid electrode having a lattice work of small apertures or pores.

14. The apparatus of claim 2, wherein said at least one electrically conductive porous surface comprises a surface of a solid porous anode.

15. The apparatus of claim 14, wherein said solid porous anode is a porous solid electrode having a lattice work of small apertures or pores.

16. The apparatus of claim 2 wherein said at least one electrically conductive porous surface comprises a surface of a porous solid electrode having a lattice work of small apertures or pores.

17. The apparatus of claim 9, wherein said porous solid electrode is a porous solid anode.

18. The apparatus of claim 17, wherein said porous solid anode is a porous solid anode having a lattice work of small apertures or pores.

19. The apparatus of claim 9, wherein said porous solid electrode is a porous solid electrode having a lattice work of small apertures or; pores.

Claims

7. The apparatus of claim 2 wherein the porous material is arranged between the inlet and outlet to provide a pressure differential thereacross thereby providing unidirectional gas flow through the chamber.

19. The apparatus of claim 9, wherein said porous solid electrode is a porous solid electrode having a lattice work of small apertures or pores.