US3379968A

US3379968A - Method and means for detection of gases and vapors

Info

Publication number: US3379968A
Application number: US658949A
Authority: US
Inventors: Yamane Mikiya
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-10-13
Filing date: 1967-08-07
Publication date: 1968-04-23
Anticipated expiration: 1985-04-23
Also published as: GB1042409A; DE1208913B

Description

April 23, 1968 MIKIYA YAMANE 3,379,968

METHOD AND mums FOR DETECTION 0E GASES AND VAPORS Original Filed Oct. 9, 1963 2 Sheets-Sheet 1 G RECORDER I? I38 I? HIGH ELECTRO- HIGH VOLTAGE METER VOLTAGE SOURCE AMPLIFIER SOURCE I ---FI owMETER-- GAS SEPARATION COLUMN ARG ON GAS TANK ELECTROMETER 8 ELECTROMETER -|8 AMPLIFIER AMPLIFIER l 1 HIGH VOLTAGE HIGH VOLTAGE SOURCE SOU RCE April 1968 MlKlYA YAMANE 3,379,968

METHOD AND MEANS FOR DETECTION OF GASES AND VAPORS 2 Sheets-Shee 2 SENSING CHAMBER ANODE VOLTAGE United States Patent 3,379,968 METHOD AND MEANS FOR DETECTIGN 0F GASES AND VAPORS Mikiya Yamane, 27 of 201 Kunitachi, Kunitachi-machi, Kitatama-gun, Tokyo-to, Japan Continuation of application Ser. No. 315,011, Oct. 9, 1963. This application Aug. 7, 1967, Ser. No. 658,949 Claims priority, application Japan, Oct. 13, 1962, 37/ 45,419 4 Claims. (Cl. 324-33) The application is a continuation of my copending application Ser. No. 315,011, filed Oct. 9, 1963, now abandoned.

This invention relates to a method and means for detecting minute concentrations of gases and vapors in gas chromatographic analysis, and more specifically it relates to an improvement of the method of the argon ionization detector.

The argon ionization detector, which was developed by J. E. Lovelock, has heretofore been used widely as a highly sensitive detector for gas chromatography. In this detector a radioactive source is contained, and argon as the carrier gas is ionized by the high-velocity ionizing particles radiated from this radioactive source to generate primary electrons. These primary electrons are accelerated by a voltage applied between the anode and the cathode of the detector, thereby gaining energy, and collide with argon atoms to produce metastable argon atoms. If a minute quantity of other gases and vapors exists, the metastable argon atoms can transfer their energies to these gases and vapors, leading to their ionization when the potential of the metastable atom is higher than the ionization potentials of the gas or vapor molecules. By measuring the ionization current which is produced in this manner, it is possible to detect these gases and vapors.

This conventional argon detector described above can be modified by replacing the radioactive source by a gaseous discharge which is excited in the vicinity of the sensing electrodes.

It is an object of the present invention to provide a method and circuit which can supply etiectively a copious stream of electrons from such a discharge in order to increase the sensitivity of the detector.

The nature, principle, and details of the invention, as well as the manner in which the said and other objects of the invention may best be achieved, will be most clearly apparent by reference to the following description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings, in which like parts are designated by like reference characters, and in which:

FIGURE 1 is a schematic diagram, partly as a block diagram, showing the compositional arrangement of a gas chromatograph wherein a gas detection circuit according to the invention is used;

FIGURE 2 is schematic diagram, as a sectional view, showing the construction of the detector of the gas chromatograph shown in FIGURE 1;

FIGURES 3 and 4 are schematic circuit diagrams showing states of voltage application on the discharge electrodes of the detector shown in FIGURE 2; and

FIGURE 5 is a graphical representation showing curves respectively indicating the relationships between the anode voltage and the background current of the gas detection circuit of the invention in the cases of the states indicated in FIGURES 3 and 4.

In the gas chromatograph shown by the schematic diagram of FIGURE 1, in which the gas detection circuit of the invention is incorporated, there is provided a first flow path in which argon is used as a carrier 3,379,968 Patented Apr. 23, 1968 ice gas, and which comprises a tank 1 for storing argon gas for separating the sample gas, a flow regulating valve 2, a sample inlet line 3, and a column 4 for separating the sample gas. In addition, there is provided a second flow path I; which is for causing flow of helium gas and causing subsidiary discharge to take place within this flow, and which comprises a helium tank 5 and a flow regulating valve 6. These two flow paths a and b are connected to a detector 7, whose gas outlet flow is measured by a fiowmeter 8.

The detector 7, which is shown in detail in relatively enlarged view in FIGURE 2, comprises a sensing chamber 10, a discharge chamber 9 communicating with the sensing chamber 10, an inlet 11 for introducing discharge gas into the discharge chamber 9, an inlet 12 for introducing carrier gas into the sensing chamber 10, a common gas outlet 13 for exhausting gases from the sensing chamber 10, a pair of discharge electrodes 14 consisting of two metal wires mounted in the discharge chamber 9, and a semispherical cathode 16 and a tubeshaped anode 17 provided in mutually confronting disposition in the sensing chamber 10.

The discharge electrodes 14 are connected to a high voltage source 15 shown in FIGURE 1 and are adapted to accomplish D.C. discharge of several tens of microamperes of discharge current. The cathode 16 and anode 17 are respectively connected to a recorder 22 by way of an electrometer amplifier 18 and to a high voltage source 19 as indicated in FIGURE 1.

In the operation of the detector 7, a portion of the electrons generated by the discharge in the discharge chamber 9 flows into the sensing chamber 10, is accelerated in the gap between the cathode 16 and anode 17, and ionizes the sample gas injected through the anode 17. The resulting ionized current is measured by the electrometer amplifier 18 connected to the cathode 16.

The sensitivity of this detection system has a relationship to the magnitude of the ionizing current, and, furthermore, the ionizing current is proportional to the number of electrons flowing from the discharge chamber 9 into the sensing chamber 10.

The gas detection circuit of the present invention is designed to supply a large quantity of primary electrons from the discharge chamber 9 into the sensing chamber 10 by accomplishing discharge by means of a high voltage source of negative polarity and, at the same time, impressing a high positive voltage on the anode 17 in the sensing chamber 10, and thereby to increase the sensitivity of detection of the system.

In order to indicate still more fully the nature of the invention, the operation and effectiveness of the detection circuit of the invention is described hereinbelow with respect to a preferred embodiment of the invention.

FIGURE 3 is a schematic diagram indicating the case wherein the discharge within the discharge chamber 9 of the invention is accomplished by means of a highvoltage source of negative polarity, while FIGURE 4 is a diagram indicating the case wherein the discharge is accomplished by means of a high-voltage source of positive polarity. In each of FIGURES 3 and 4, the highvoltage source and a current limiting resistor connected in series are respectively designated by

reference numerals

20 and 21.

Under each of the circuit conditions as indicated in FIGURES 3 and 4, the discharge of 30 microamperes was accomplished in a stream of helium of a fiowrate of cc./rnin. by means of the high-voltage source 20, and measurements were made with argon used as the carrier gas flowing at a flowrate of 60 cc./ min. The relationships between the measured background currents and the respective anode voltages for the two cases indicated in 3 FIGURES 3 and 4 are indicated by

curves

1 and 2, respectively, shown in FIGURE 5. These two cases will be considered separately in greater detail hereinbelow.

( 1) The case in which the discharge is excited by a negative high-voltage source As can be observed in FIGURES 3 and 5, when discharge is caused, by means of a negative power source, with one discharge electrode grounded and the other electrode at a potential of minus 270 volts (resulting from a voltage of 870 volts of the power source 20 and a voltage drop of 600 volts across the current limiting resistor 21), the space potential in the vicinity of the electrodes 14 is negative. Accordingly, when the anode voltage is zero volt, the potential of the sensing chamber is zero, which is higher than the potential of the discharge chamber 9. Consequently, the electrons produced are attracted to the cathode 16 and the anode 17, and a negative current flows to the electrometer amplifier 18.

When the anode voltage becomes several tens of volts,

7 the potential of the sensing chamber 10 becomes high.

Consequently, the number of electrons attracted increases. However, since most of these electrons are collected at the anode 17, the number of electrons moving to the cathode 16 becomes less. When the anode voltage reaches several hundreds of volts, the number of electrons drawn into the sensing chamber 10 increases even further, but all of these electrons are collected at the anode 17, and a small quantity of ions generated by photo-ionization and other causes flow to the cathode 16. Consequently, a positive current flows to the electrometer amplifier 18. Accordingly, this state conforms to the ideal condition wherein electrons necessary for ionizing the sample gas collect at the anode 17 which is injecting the sample gas, and, moreover, the background current is very low.

Next, when the anode voltage is caused to be of the order of minus 50 volts, most of the electrons drawn into the sensing chamber 19 collect at the cathode 16, and a large negative current flows to the electrometer amplifier 18. When the anode voltage is further lowered, the potential of the sensing chamber 10 becomes low, tending to suppress the flow of electrons. Consequently, the number of electrons flowing to the cathode 16 decreases, and, at the same time, ions begin to flow to the anode 17. Accordingly, the electron current to the electrometer amplifier 18 is reduced. When the anode voltage is lowered still further and recahes a value of the order of minus 1,000 volts, ions are drawn into the sensing chamber and flow to the anode 17, and electrons such as secondary electrons due to photo-ionization flow to the cathode 16.

(2) The case in which the discharge is excited by a positive high-voltage source As can be observed in FIGURES 4 and 5, when discharge is caused, by means of a positive power source, with one discharge electrode grounded and the other electrode at a potential of plus 270 volts (resulting from a voltage of 870 volts of the power source 20 and a voltage drop of 600 volts across the current limiting resistor 21), the space potential in the vicinity of the electrodes 14 is positive. Since, at the same time, the cathode 16 of the sensing chamber 10 is grounded by way of an input resistor (not shown) of the electrometer amplifier 18, it may be considered to be at approximately the ground potential. Accordingly, when the anode voltage is zero volt, the potential of the sensing chamber 10 is zero, which is lower than the potential of the discharge chamber 9, and positive ions created by the discharge are drawn by the force of the electric field. Although the flow of electrons is also to be expected at this time, the quantity of ions is relatively greater. These ions flow to the anode 17 and the cathode 16, wherefore a positive current flows to the electrometer amplifier 18.

When the anode voltage becomes approximately 50 volts, the ions are drawn into the sensing'chamber 10, but in the interior of the sensing chamber, the ions are repelled by the anode 17 and fiow to the cathode 16. Accordingly, a large positive current flows to the electrometer amplifier- 18. When the anode voltage is further increased, the potential of the sensing chamber becomes high, tending to suppress the flow of ions, and the quantity of ions flowing to the cathode 16 is reduced. At the same time, electrons begin to flow to the anode 17, and the reading of the electrometer amplifier 18 becomes less. The ion current decreases with increase in the anode voltage. When the anode voltage eXceeds'LOOO volts, ionization of the electrons flowing to the anode begins. Accordingly, the quantity of ions flowing to the cathode 16 increases once again.

Next, when the anode voltage becomes negative, the potential of the sensing chamber 10 becomes negative, and a large quantity of ions flows into the sensing chamber 10. However, since the greater portion of these ions flows to the anode 17, the current flowing to the electrometer amplifier 18 decreases. When the anode voltage is further lowered, a negative current flows to the electrometer amplifier 18. Although this indicates that electrons are flowing to the cathode 16, this indication is believed to be due to electrons such as secondary electrons emitted by the impact of ions against the anode 17 and electrons generated by photo-ionization.

As will be apparent from the foregoing disclosure, the background current is determined by the relationship between the potentials of the discharge chamber 9 and the sensing chamber 10 and by the relationship between the potentials of the cathode and anode within the sensing chamber. It is to be observed that by carrying out discharge with a negative power source and, at the same time, impressing a positive high voltage on the anode, electrons necessary for ionization of the sample gas are supplied at a high rate, and, moreover, an ideal operational condition wherein the background current is low is obtained. Accordingly, the gas detection method and circuit according to the present invention, wherein such an ideal condition is realized, is highly effective in practical applications, particularly in increasng sensitivty of measurements by gas chromatography.

It should be understood, of course, that the foregong disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all variations and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A device for detecting gases and vapors by ionization due to irradiation of primary electrons generated by the ionization action of an electric discharge, comprising a discharge chamber; a sensing chamber connected to said discharge chamber by a constricted and concentrically aligned connector; a pair of discharge electrodes disposed in said discharge chamber in mutually opposed position facing in the direction of said connector; a first power source; one of said electrodes being connected to the negative terminal of said first power source; the other electrode being grounded; a discharge gas inlet leading into said discharge chamber in the direction of its center axis; a carrier gas inlet leading in the direction of the center axis of said sensing chamber for the introduction of a sample gas therein; an anode and an opposing cathode disposed in said sensing chamber; a second power source; said anode being connected to the positive terminal of said second power source; said cathode being connected to a circuit for measuring electric current due to ionization of said sample gas; and gas outlet means from said discharge chamber and said sensing chamber.

2. The device as defined in claim 1, wherein said gas outlet means are a common outlet leading out of said sensing chamber opposite said connector.

3. A process for the detection of gases and vapors by ionization due to irradiation of primary electrons genertaed by the ionization action of an electric discharge, comprising the steps of introducing a discharge gas into a discharge chamber provided with a pair of mutually opposed electrodes, one of said electrodes being connected to the negative terminal of a first power source, the other being grounded; causing an electric discharge to occur between said electrodes; injecting primary electrons generated by said electric discharge into a sample gas introduced into a sensing chamber adjacent to said discharge chamber and connected thereto by a constricted and coaxially aligned connector; said sensing chamber being provided with an anode and an opposing cathode, said anode being connected to the positive terminal of a second power source; said sample gas being ionized betwen said cathode and said anode; said cathode being connected to a circuit which measures the electric current caused to flow by the ionization of said sample gas.

4. The process as defined in claim 3, wherein said discharge gas is helium and said carrier gas is argon.

References Cited RUDOLPH V. ROLINEC, Primary Examiner.

C. F. ROBERTS, Assistant Examiner.