JPS6130761A - Electron trap detector - Google Patents

Abstract

PURPOSE:To obtain a safe-to-handle detector, by providing a light generating means, a photoelectron generating means, a means of trapping photoelectrons, a sample gas supplying means, a means of restricting the light irradiation surface and a means of detection ionized state of the sample gas. CONSTITUTION:A discharge gas He or Ar is released into the atmosphere via a discharge gas flow inlet 21, a discharge chamber 22, an optical path 23 provided on a discharge anode 23 and a gas outlet 25. On the other hand, after a carrier gas is adjusted 38 and 29 in the pressure, a sample gas is injected at a sample injection port 27 and then, released into the atmosphere together with the discharge gas from a gas outlet 25 via a column 28. Negative potential is applied to a discharge cathode 30 from a DC power source 32 to cause a discharge between anodes 23 and light generated irradiates an electron generation source 33 given the negative potential by the DC power source 34 to generate photoelectrons. Moreover, the photoelectron energy is adjusted depending on the potential gradient between the generation source 33 and a collector 35 given positive potential by a DC power source containing an electrometer 36. Then, a grid 42 given negative potential by a DC power source 43 is provided to prevent photoelectrons from moving through a housing 31.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electron capture detector, and particularly to an electron capture detector that does not use radiation to ionize a carrier gas.

[Background of the invention]

Various types of electron capture detectors have traditionally been used, especially detectors for gas chromatography, but electron capture detectors have a high sensitivity specifically for compound samples containing strongly electronegative atoms such as halogens. Capture type detectors (hereinafter referred to as ECDs) exist.

Therefore, the general concept of ECD will be explained using FIG. 2. In the figure, the pressure is adjusted by a pressure regulator 11 and carrier gas is supplied to a chromatography column 13. There is a sample gas receiving part 12 that supplies the sample gas in the middle of the carrier gas being supplied to the chromatograph 2m 13, from which the sample gas is introduced into the force 2m 13 together with the carrier gas, and this force 2m Receive distribution at 13. The column 13 is connected to a detector 14, which detector (ECD) 1
The sample gas in 4 is ionized, and the ionization state of each component is recorded by a recorder 15 connected to a detector 14. This ECD was developed by Robert Lovelock, and its principle is as follows. That is, first, carrier gas 1) is ionized (A+10e-) by β rays (e-), a certain amount of ion current is generated in the detector, and the halogen compound CM) carried by the carrier gas is ionized (A+10e-). M collides inelastically with e- produced by ionization of dE carrier gas (A), and M becomes M''. Roughly, M- collides with A1 and discharges each other, returning to electrically neutral molecules. This is based on the fact that when this neutral molecule returns, a certain amount of ion current (pack-ground current) flowing in the detector decreases, and the amount of decrease in this ion current correlates with the amount of gas to be detected.

By the way, as mentioned above, radiation? The ECD used must be installed and managed based on legally established management standards. Therefore, not only is it not possible to change the installation location freely, but it also requires a controlled area, which requires an airspace that is wider than the size of the device itself. resulting β
Since the energy of the rays is high, ranging from tens of KeV to several hundred KeV, there is a problem with safety in emergencies.

Therefore, in order to solve the problems of ECD using radiation, ultraviolet light is irradiated onto the carrier gas to generate electrons.
There is a known example (Japanese Patent Publication No. 43-12800) that indicates D. In this known example, ultraviolet light is obtained by discharging He, but the structure is such that the sample gas is also irradiated with ultraviolet light. Therefore, it is necessary to mix a gas such as CH4 or CO□ into the carrier gas to prevent the sample gas from being ionized by residual light not absorbed by the carrier gas. In order to operate the detector stably, it is necessary to always mix in a certain amount of gas. This means that it will take several hours for the detector to stabilize upon startup.

Other known non-radioactive ff1EcD examples (Jouna
l of chromatography vol 2
35 pages 1-20 A, Neukermars” 19
In 82), a platinum filament is coated with barium zirconate, and a carrier gas is ionized using thermionic sound generated at a temperature of 650° to 750°C. In this thermionic method, in order to protect barium zirconate, which is the source of thermionic electrons, from highly corrosive halogen atoms, it is necessary to pass an inert guard gas in addition to the carrier gas.

Particularly recently, in addition to pollution caused by organic halogen compounds such as PCB, DDT, and BHC7Z, the carcinogenicity of trihalomecunes such as CHCl5°CHBr5 has become a social problem.

Therefore, from the standpoint of public health, the fiEcD has good operability.
development is awaited.

[Purpose of the invention]

The purpose of the present invention is to ionize the carrier gas with radiation? An object of the present invention is to provide an electron capture detector (ECD) that is safe to use and handle, and does not require a gas for removing residual ultraviolet light or a guard gas for a thermionic source.

[Summary of the invention]

The first aspect of the invention is to form an ionized region between a light generating means that generates light, a photoelectron generating means that generates all photoelectrons upon irradiation with the light generated by the light generating means, and the electron generating means. a collection means arranged at a predetermined distance so as to collect photoelectrons generated by the electron generation means; and a sample gas supply means for supplying a sample gas to the ionization chamber; The ionization state of the sample gas ionized by the photoelectrons generated by the photoelectron generation means in the ionization region is detected. This is a characteristic electron capture detector.

The invention of cylinder 2 of the present application includes a thermionic generation means for generating thermionic electrons,
a collecting means arranged at a predetermined distance from the thermionic electron generating means to form an ionization region therebetween, and collecting the thermionic electrons generated by the thermionic electron generating means; and a gas injection port in the ionization region. and a sample gas supply means that is arranged to protrude and supply a sample gas to the ionized region, so as to prevent the sample gas from directly touching the thermionic source, and to prevent the sample gas from directly touching the thermionic electron source in the ionized region. This is an electron capture detector characterized by detecting the ionization state of a sample gas ionized by thermionic electrons generated by a generating means.

Light irradiation surface in the first invention of the present application? Is it possible to restrict and prevent light from directly hitting the sample gas by shifting the light irradiation axis and the sample gas supply port, or by directing the light to the photoelectron generation source through an optical fiber? Various methods are conceivable, such as irradiation using the electron capture detector, or furthermore, providing a billboard inside the electron capture detector.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an ECD for gas chromatograph among electron capture detectors according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, and is a block diagram of an ECD for a gas chromatograph.

In the figure, an electron generation source 33 is located in the lower part of the housing 31, which is an insulator, and a collector 35 and a purge gas inlet 41 are located on the side horizontally opposite to the electron generation source. A carrier gas inlet pipe 29 and an inlet 50 are provided respectively. A DC power supply 34 is connected to this electron generation source 33, and a grid to which a DC power supply 43 is connected is provided above the electron generation source 33. Further, an electrometer 36 to which a recorder 37 is connected is connected to the collector 35 . Further, an outlet pipe 25 is connected to this collector 35 .

On the other hand, a discharge chamber 22 is provided at the upper part of the housing 31. A discharge anode 23 is supported and fixed by a housing 31 below the discharge chamber 22, and an optical path 24 is provided in the discharge anode 23. A discharge gas inflow pipe 21 is provided in the discharge chamber 22, and an inflow port 51 is connected to this inflow pipe 21. A discharge cathode 30 is supported and fixed to a housing 31 within the discharge chamber 22 . A DC power source 32 is connected to this discharge cathode 30.

On the other hand, a pressure regulator 38 is connected to the carrier gas storage tank 26.
, 39, a carrier gas is introduced into the inlet 50 through the entire inlet tube 29 through a gas flow path system including the carrier gas inlet tube 44, the sample injection port 27, and the column 28. Further, a purge gas passage system consisting of pressure regulators 38 and 39 from the carrier gas storage tank 26 is connected to the purge gas inlet 41.

Next, the operation of this embodiment will be explained.

The discharge gas He or Ar passes through the discharge gas inlet 21 and the inlet 51, flows into the discharge chamber 22, passes through the optical path 24 provided in the discharge anode 23, and is emitted into the atmosphere from the gas outlet 25.

On the other hand, the pressure of the carrier gas is adjusted by pressure regulators 38 and 39, and then introduced into the carrier gas introduction pipe 44.
After the sample gas is injected at the sample injection port 27, it is vented into the column 28, passes through the inflow pipe 29 and the inflow port 50, and is discharged into the atmosphere from the gas outlet 25 together with the discharge gas.

A negative potential is applied to the discharge cathode 30 by a DC power supply 32, and a discharge occurs between it and the anode 23 which is in a grounded state. Due to this discharge, light having an energy of about 21 ev is generated when He<< is used as the discharge gas. In addition, when Ari is used as the discharge gas, it is approximately 11.6e.
V light is generated.

The generated light passes through an optical path 24 provided in the discharge anode 23,
The metal surface, which is the electron source 33, is irradiated with light. Since the work function of most metals is 1 OeV or less, photoelectrons are generated in He or ' by the ultraviolet light generated by the discharge of Ar. The energy of photoelectrons emitted from the metal surface approximates the difference between the work function (ψ) of the metal and the irradiation energy (hy').

A negative potential is applied to the electron source 33 by a DC power supply 34, and a positive potential is applied to the collector 35 from a DC power supply built into an electrometer 36. Therefore, a potential envelope is generated between the electron generation source 33 and the collector 35, and the photoelectrons generated by the ultraviolet light irradiation move toward the collector 35, so that the total energy of the photoelectrons can be adjusted.

Further, a grid 42 is provided near the electron generation source 33 of the housing 31 so as not to obstruct the optical path 24, and a negative potential is applied to this grid 42 by a DC power source 43. As a result, it is possible to prevent the electrons generated in the electron generation source 33 from moving into the optoelectronic housing 31 .

By the way, when N2 is used as a carrier gas, N
Electron (e-) energy of approximately 15.5 eV or more, which is the ionization potential of 2, is required to obtain a constant pack ground current.

The energy of the generated electrons is achieved by adjusting the potential of the electron source 33 and the collector 35 as described above, and the background current, that is, the ionization of the carrier gas (N
;+e-) can be adjusted based on the ion current. In order to stabilize the detector in which a constant background current flows, a halogen compound (M
) flows into the detector together with the carrier gas, M absorbs electrons and becomes a negative ion (M-), and this M- ion becomes N2
Collisions with +, does not lose charge to electrically neutral molecules, and as a result, the background current decreases.
An electrical signal related to the amount of halogen compound is obtained, and a second
The entire electrometer 36 in the figure is recorded by a recorder 37.

An inlet 29 for a carrier gas containing a sample gas is open to an electron generation source 33 and a collector 35 .

Further, the housing 31 is disposed perpendicularly above the electron generation source, so that the discharge light passing through the optical path 24 is irradiated only on the electron generation source, but not on the carrier gas containing the sample gas.

The residence time of the carrier gas containing the sample gas in the detector is controlled by introducing a purge gas having the same composition as the carrier gas from the carrier gas supply source 26 through the pressure regulators 38 and 40 through the inlet 41. be done. The function of this purge gas is to control the intensity of the signal obtained by the recorder 37, but in some cases, the function of the purge gas can be replaced by increasing the flow rate of the discharge gas. However, when l(e) is used as the discharge gas, the purge gas receives light of about 2 ieV and is ionized, giving a background current, and the total background current is the sum of the background current due to photoelectrons in the electron source 43. However, the background current due to the purge gas is the main source.

As described above, according to this embodiment, since the carrier gas inlet 50 is offset from the optical path 24, the sample gas in the carrier gas is not irradiated with ultraviolet light.

FIG. 3 is a configuration diagram of an ECD showing a second embodiment of the present invention.

3 is different from the embodiment shown in FIG. 2 in that a grid 45 is provided on the purge gas inlet 41 side of the electron generation source 33, and a negative potential is applied to this by a DC power source 334. It is a point.

As a result, photoelectrons generated by the electron generation source 33 can be prevented from moving in the opposite direction to the collector 35 side. The configuration and operation of other parts in FIG. 3 remain the same as in the embodiment shown in FIG. 2. Therefore, in FIG. 3, the same parts as in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and the carrier gas introduction part and the purge gas introduction part are omitted.

FIG. 4 is a configuration diagram of an ECD showing a third embodiment of the present invention.

The difference in FIG. 4 from the embodiment shown in FIG. 2 is that the purge gas inlet 41'fr is removed and the action of the purge gas is performed by increasing the flow rate of the discharge gas.
The background current has a structure obtained by the action of only photoelectrons in the electron generation source 33. The configuration and operation of other parts are the same as in the case of FIG. 3.

FIG. 5 is a configuration diagram of E C' D showing a fourth embodiment of the present invention, and is a modification of the embodiment of FIG. 4.

The difference in FIG. 5 from the embodiment shown in FIG.
It is located in a place that has the function of assisting movement to the 5th side. The configuration and operation of other parts are the same as in the case of FIG. 4.

FIG. 6 is a block diagram of an ECD showing a fifth embodiment of the present invention, which is a modification of the embodiment shown in FIG.

In FIG. 6, the differences from the embodiment shown in FIG. 2 are as follows:
The ultraviolet light is not obtained by electric discharge, but an ultraviolet light bulb 546 that emits light of 9 to 11 eV is used as a light source, and an inert gas inlet 47 is used to protect the window of the ultraviolet lamp. The point is that gas is introduced.

A commercially available UV lamp can be used, and an insulator 48
A plug 49 is provided for connection to a power source.

Note that the inert gas that protects the window of the ultraviolet lamp is discharged into the atmosphere from the gas outlet. The configuration and operation of other parts are similar to the embodiment shown in FIG.

FIG. 7 shows a sixth embodiment of the present invention, which is different from the above embodiments in that it is an embodiment of an ECD using a thermoelectron generation source as an electron generation source. FIG.

In the figure, a heat source 52 is connected to a platinum filament 51 coated with barium zirconia 1. The configuration of other parts is the same as the embodiment described above.

The operation of this embodiment differs from other embodiments in that the heat source 52 applies heat to the platinum filament 50 so that the temperature of the platinum filament 51 is 650° to 750°C. Then, thermoelectrons are generated from the Fifmet 50, and these thermoelectrons move to the collector 35.

As described above, according to this embodiment, the carrier gas inlet 50
Since the sample gas is provided between the filament 51 and the collector 350, the sample gas is not directly attached to the filament 51, so there is no risk of corrosion of the filament.

(Comparative Example 1) - Next, i ppm of tetrachlorethylene (CC12=C
C1ff) was measured according to the first embodiment of the present invention shown in FIG. The results are shown in FIG.

Also, for reference, the measurement results according to the conventional example (Japanese Patent No. 43-12800) are shown in FIG.

In Figures 1 and 5, the horizontal axis shows the entire measurement elapsed time,
The vertical axis indicates the intensity of the detection signal recorded by the recorder.

In this embodiment, the attenuation rate is measured at -.

According to this embodiment, the detection signals of tetrachlorethylene are detected at the same time and with the same intensity as shown in FIGS. 8 and 9. Therefore, the gas chromatograph ECD according to the present invention has no problem in terms of sensitivity.

〔Effect of the invention〕

As described above, according to the present invention, all measurements of the sample gas can be performed without using radiation to ionize the carrier gas. Furthermore, since the structure is such that the sample gas is not directly irradiated with ultraviolet light, there is no need for a gas to remove residual ultraviolet light. Furthermore, since the structure is such that the sample gas does not come into direct contact with the thermionic source, there is no need for a gas to guard the electron source. Therefore, it does not take a long time to stabilize the equipment.

[Brief explanation of the drawing]

FIG. 2 is a conceptual diagram showing the configuration of a conventional gas chromatograph, and FIGS. 1, 3 to 7 are configuration diagrams showing an embodiment of the electron capture detector according to the present invention. Figures 3 to 6 are block diagrams of an electron capture detector for gas chromatographs that use photoelectrons to ionize gas, Figure 7 is a block diagram of a detector for gas chromatographs that uses thermoelectrons to ionize gas, and Figure 8 is a block diagram of an electron capture detector for gas chromatographs that uses photoelectrons to ionize gas. The graph showing the detection results of 11)I)m according to the embodiment shown in FIG. 1, and the graph shown in FIG. 9 using the conventional gas chromatograph ECDK! 11) It is a graph showing the detection results of RI m. 22...Discharge chamber, 33...Electron generation source, 46...
Purge gas inlet, 50...Carrier gas inlet, 5
1...Platinum filament, 52...Heat source.

Claims (1)

[Scope of Claims] 1. Between a light generating means that generates light, a photoelectron generating means that generates photoelectrons upon being irradiated with light generated by the light generating means, and the electron generating means. a collection means arranged at a predetermined distance to form an ionization region and collecting photoelectrons generated by the electron generation means; a sample gas supply means for supplying a sample gas to the ionization chamber; limiting means for restricting the light irradiation surface so that the sample gas is not irradiated with the generated light; and detecting the ionization state of the sample gas ionized by the photoelectrons generated by the photoelectron generation means in the ionization region. An electron capture detector characterized in that it has means for. 2. Thermionic generation means for generating thermoelectrons, and a trap arranged at a predetermined distance to form an ionization region between the thermoelectron generation means and collecting the thermoelectrons generated by the thermionic electron generation means. a collection means, a sample gas supply means arranged such that a gas injection port projects into the ionization region and supplies a sample gas to the ionization region, and thermionic electrons generated by the thermionic generation means in the ionization region. 1. An electron capture detector comprising: means for detecting the ionization state of a sample gas ionized by the electron capture detector.