JPH10307123A - Photoionization detection method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To also detect a small amount of organic constituent in an inorganic gas by selecting discharged gases being subjected to gas discharge from He, Ne, Ar, Xe, or H2 and changing the energy of ionization radiation. SOLUTION: A photoionization detector consists of a light source part 1 and a detection part 8. A sample flowing into a detection part 8 through the inside of a collector counter electrode 10 from a flow-in port 11 of a sample to be detected is generated by the gas discharge between a discharge cathode 2 and a discharge anode 3 of the light source part 1 and is exposed to light being applied to the detection part 8 from a light path 13. Then, an ionized sample constituent being ionized by receiving light from the light source part 1 is measured by measuring the flow of an ion current that flows to a collector electrode 9 being installed against the flow of the sample. In this case, discharge gases being subjected to gas discharge are selected from He, Ne, Ar, Xe, or H2 and the energy of ionization radiation is changed, thus achieving selectivity for a detection constituent. For example, a discharge stabilization resistor 7 with a resistance of 15-90 kΩ is required for using He as a discharge gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector in a gas chromatograph for separating a substance and performing quantitative or qualitative analysis, and a gas chromatograph apparatus provided with the detector. The present invention relates to a photoionization detector for irradiating and irradiating with ultraviolet light or ultraviolet light and measuring an ion current thereof, and a gas chromatograph apparatus provided with the detector.

[0002]

2. Description of the Related Art The structure, principle, detector and use range of a gas chromatograph are described in detail in, for example, "Latest Gas Chromatography" written by Funasaka and Ikegawa, Hirokawa Shoten (1967). In order to improve the performance of the gas chromatograph, use a small amount of sample at the lowest possible concentration,
It is required to separate and detect the components. Therefore,
Conventionally, research and development of high-sensitivity detectors have been continuously performed. Representative examples of detectors that have been developed and used so far include a thermal conductivity detector, a flame ionization detector, an electron capture detector, and a photoionization detector. With the development of these detectors, the gas chromatograph has been remarkably developed and has become an indispensable device for separation and analysis.

In particular, a photoionization detector (Photoionizatio
n Detector (hereinafter referred to as PID) and a PID using He gas discharge as a light source (hereinafter referred to as He-PID)
Is highly sensitive to inorganic and organic substances and is used as a universal detector. However, since He-PID has high sensitivity to inorganic gas, it is not suitable for analyzing trace organic substances in nitrogen (N ₂ ) gas, oxygen (O ₂ ) gas, or air. The reason is that the output peak of the inorganic gas covers the output peak of the trace component of the organic substance, and the analysis accuracy is reduced. Therefore, a flame ionization detector (FID) that does not respond to the inorganic gas and has high sensitivity only to organic substances is used for the analysis of the organic trace components in the inorganic gas. However, since FID uses hydrogen, it is necessary to always pay attention to safety.

[0004]

The principle of PID detection is as follows.
This is discussed in JE Lovelock: Nature 188, 401 (1960), and will be described below using this theory. The wavelength at the maximum energy generated by the He discharge is 58.4 nm,
Energy of about 20 eV. Primary ionization potentials of inorganic gases such as H ₂ , N ₂ , and O ₂ are 15.45 eV, 15.59 eV, and 12.07 eV, respectively. The ionization potential of organic matter is lower than that of inorganic gas, and is about 13 eV for the highest methane (CH ₄ ). Therefore, the sample to be detected is ionized by irradiating the inorganic gas or the organic gas of the sample to be detected with light generated by the He discharge. This phenomenon can be expressed as the following [Equation 1].

[0005]

[Number 1] ^{M + hν → M + + e} - where M is the molecular of the detected object, h is Planck's constant, [nu represents the frequency of light, e is an electron. That is, the test sample is ionized by being irradiated with light, and is detected by measuring the ion current.

However, the energy level of the light source of He-PID is as high as about 20 eV, and both the inorganic gas and the organic gas are ionized, so that it becomes difficult to analyze the trace organic components in the inorganic gas. The present invention has been made in view of such problems of the related art, and has as its object to provide a PID capable of detecting a trace organic component in an inorganic gas. Also,
The present invention provides a method for detecting a trace amount of organic components in an inorganic gas.
An object of the present invention is to provide a gas chromatograph device incorporating an ID.

[0007]

In order to achieve the above object, it is sufficient that the PID has a function of changing the light energy of the light source according to the sample to be detected. The energy of the light source in the PID is determined by the gas supplied to the discharge unit, which is the light source of the PID. For example, H
When e is supplied, light having an energy of about 20 eV is generated, but when Ar is supplied, light having an energy of about 12 eV is generated.

At the energy level of light generated by Ar discharge, inorganic gases such as O ₂ , N ₂ , CO and CO ₂ cannot be ionized. However, since the ionization potential of an organic compound is 9 to 11 eV, it is almost always used. Has high sensitivity to organic substances. However, PID by Ar
Has no or low sensitivity to organic substances having a high ionization potential such as methane, ethane and acetonitrile.

An organic compound having a high ionization potential can be detected with high sensitivity by using light having an energy of about 16 eV generated by Ne discharge as a light source. Ne
When discharge is used as the light source, the inorganic gas can be detected with moderate sensitivity. As described above, the energy of light from the light source can be changed by changing the gas supplied to the discharge unit of the PID. Therefore, when measuring trace organic impurities in an inorganic gas, a PID using Ar discharge as a light source (hereinafter referred to as PID)
By using Ar-PID), only organic trace components can be detected without detecting inorganic gas.

In the prior art, trace organic impurities in inorganic gas were measured using FID. However, since hydrogen was used, it was necessary to always pay attention to safety. Since the Ar-PID provided by the present invention does not use a combustible gas, it is a detector superior in safety to the conventional FID. The control of the light energy level of the light source of the PID
It is also possible to use a mixed gas as the discharge gas. For example, when a discharge gas in which Ar is mixed in He is used, light having an energy of about 11.6 eV, which is a resonance line derived from Ar, is obtained. Similarly, in a discharge gas in which H ₂ is mixed in He, light having an energy of about 10 eV derived from H ₂ is obtained. As described above, by mixing a gas having a low-energy resonance line in He by several percent or more and discharging it, the light energy level of the light source of the PID can be changed.

The reason why light of energy derived from a gas having a low energy resonance line can be obtained when a mixed gas is used as a discharge gas can be explained as follows. In the discharge with other gas mixed in He,
Two phenomena occur: (1) a phenomenon in which the mixed gas component is ionized or excited by the light generated from He, and (2) a phenomenon in which the mixed gas component is ionized or excited by the quenching effect of the excited component of He. It is thought that there is. Light is generated when the excited component of the mixed gas component generated by the actions (1) and (2) returns to the ground state. Here, since the energy of light generated from the gas component mixed with He is much lower than the excitation energy and ionization energy of He, the phenomenon of being absorbed by He does not occur. Therefore, light emission is obtained from the gas component mixed with He, and can be used as a light source of a photoionization detector.

Table 1 below shows examples of the ionization potentials of organic substances and inorganic substances having relatively high ionization potentials.

[0013]

[Table 1]

As described above, the gas is generated by gas discharge in consideration of the ionization potential of a substance to be detected, the ionization potential of a substance (interfering substance) not to be detected, and the energy of light generated by gas discharge. Reduce the sensitivity to interfering substances by selecting the type of gas used for PID gas discharge so that the light energy is greater than the ionization potential of the substance to be detected and smaller than the ionization potential of the substance you do not want to detect. In addition, the sensitivity to the substance to be detected can be increased.

Table 2 shows types of gas used for gas discharge of PID, light energy generated by the discharge, and an example of a substance suitable for detection.

[0016]

[Table 2]

Ne, Ar or H as a PID light source
In the case of utilizing the gas discharge of the mixed gas with e, the discharge is not stabilized unless the electric discharge electrode is provided with an electric resistance. In order to stabilize the gas discharge of a mixed gas of Ne, Ar or He, not only an electric resistance is provided between the discharge cathode and the power supply, but also a certain level or more between the discharge anode and the ground. It is necessary to install an electric resistance.
This is to prevent the avalanche phenomenon of the plasma in the discharge gas generated by the discharge.

In general, voltage-current characteristics in gas discharge based on glow discharge show constant voltage characteristics. That is, even if the applied voltage is changed, the voltage between the discharge electrodes hardly changes, and only the discharge current changes. However, the discharge starting voltage differs depending on the composition of the discharge gas. For example, the discharge starting voltage for He gas is 600 to 750V, and the discharge starting voltage for Ar gas is 700 to 900V. Regardless of the type of the discharge gas, once the discharge starts, the voltage for maintaining the discharge (discharge maintaining voltage) is 100 to 200 V lower than the discharge start voltage. The phenomenon that the discharge sustaining voltage is lower than the discharge starting voltage supports that the discharge has a constant voltage characteristic.

The discharge current is determined by factors such as applied voltage, electrode spacing, type of discharge gas, and pressure of discharge gas. If no ballast resistor is provided between the power supply and the negative electrode, the discharge will be an intermittent discharge. The discharge current is not stable. In other words, when a discharge starts between the discharge electrodes installed in a certain gas atmosphere, secondary electrons generated by the collision between the cations of the gas molecules and the negative electrode, the collision between the gas molecules and the electrons, and the like are caused by the discharge. As a result, the current flowing between the discharge electrodes gradually increases, and finally, the discharge reaches an arc, and a current exceeding the power supply capacity flows, leading to intermittent discharge.

In order to prevent such an unstable discharge phenomenon, a current limiting resistor is generally provided between a power supply and a discharge cathode. However, depending on the type of the discharge gas, the discharge is not always stable only by providing the current limiting resistor (ballast resistor). In order to ideally stabilize gas discharge, it is necessary to provide a resistor (hereinafter, this resistor is referred to as a discharge stabilizing resistor) between the discharge anode and ground. The discharge stabilization resistance varies depending on the discharge gas. The stable region of the discharge current is several tens μA to 150 μA.

The present invention has been made based on the above considerations, and irradiates ionization radiation consisting of ultraviolet rays or vacuum ultraviolet rays generated by gas discharge to a sample to be detected, and reduces the ionization current of the sample to be detected. in photoionization detection method for detecting a sample component by measuring the discharge gas of the gas discharge He, Ne, Ar, by selected from Xe or H ₂ changing the energy of the ionizing radiation,
It is characterized in that it has selectivity for a detected component.

The present invention also provides a photoionization detection method for irradiating a sample to be detected with ionizing radiation generated by a gas discharge and detecting a sample component by measuring an ionization current of the sample to be detected. Discharge gas is He
Mixed gas of He and Ar, mixed gas of He and Ar, He and Xe
A mixed gas of He, H _2, a mixed gas of Ne and Ar, a mixed gas of Ne and Xe, a mixed gas of He and N ₂ ,
Alternatively, by changing the energy of ionizing radiation by selecting from a mixed gas of He and CO ₂ , selectivity is given to a detection component.

The present invention also provides a photoionization detection method for irradiating a sample to be detected with ionizing radiation generated by gas discharge and measuring the ionization current of the sample to detect sample components. Ar gas discharge
Alternatively, by using a mixed gas of Ar and He, an organic component in a sample to be detected including an inorganic gas is detected.

The present invention also provides a discharge electrode for generating ionizing radiation by gas discharge, a sample flow path exposed to ionizing radiation, and an ion current of the sample ionized by irradiation with ionizing radiation. A photoionization detector provided with a measuring electrode for changing the energy of ionizing radiation by switching a discharge gas of a gas discharge.

In this photoionization detector, it is preferable to provide an electric resistance between the discharge cathode and the power supply, and to provide an electric resistance between the discharge anode and the ground. Since the photoionization detector according to the present invention can change the light energy of the light source, it can be used as a universal detector or a detector dedicated to organic compounds, and has a wide range of applications.

According to the present invention, there is provided a gas chromatograph apparatus comprising a sample injection section, a separation column for separating the injected sample component, and a detector for detecting the separated sample component. It is characterized by comprising an ionization detector.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an example of the photoionization detector according to the present invention. The photoionization detector includes a light source unit 1 and a detection unit 8. The light source unit 1 includes a discharge cathode 2 and a discharge anode 3, and discharge gas is supplied to a discharge gas supply port 4 from cylinders 14a, 14b and the like. A current limiting resistor 6 is provided between the power supply 5 and the discharge cathode 2, and a discharge stabilizing resistor 7 is provided between the discharge anode 3 and the ground. The detection unit 8 is provided with a collector electrode 9 and a hollow collector counter electrode 10. Collector opposite pole 10
At one end of the sample is provided a sample inlet 11 to be detected,
The sample gas supplied from the detected sample inlet 11 passes through the collector counter electrode 10 and is guided to the detector 8, and is discharged from the detected sample outlet 16.

The light source unit 1 and the detection unit 8 are connected by an optical path 13 that guides light from the light source unit 1 to the detection unit 8. The optical path 13 also functions as a flow path through which the discharge gas supplied from the discharge gas supply port 4 flows into the detection unit 8. The sample that has flowed into the detection unit 8 from the sample inlet 11 through the inside of the collector counter electrode 10 is discharged to the discharge cathode 2 and the discharge anode 3 of the light source unit 1.
Is generated by the gas discharge during the exposure, and is exposed to light emitted from the optical path 13 to the detection unit 8. The sample component ionized by the light irradiation from the light source unit 1 is measured by an ionic current flowing through the collector electrode 9 installed facing the flow of the sample. Switching of the discharge gas for changing the emission wavelength of the light source unit 1 is performed by using the flow path switching valve 1.
5 is performed.

FIG. 2 shows the relationship between the resistance value of the discharge stabilizing resistor 7 and the stable discharge region when Ar gas discharge is used. From FIG. 2, the stable region of the gas discharge of Ar is the discharge current 1
It is found that the resistance value of the discharge stabilizing resistor 7 needs to be 50 kΩ or more. The stable region of the discharge varies depending on the type of the discharge gas. For example, when helium is used as the discharge gas, a discharge stabilization resistor of 15 kΩ to 90 kΩ is required.

FIG. 3 is a schematic configuration diagram of a gas chromatograph apparatus provided with the above-described photoionization detector in the detecting section. The main body of the gas chromatograph apparatus except for the detector has a well-known configuration. The flow rate of the carrier gas supplied from the carrier gas supply source 21 is adjusted by the carrier gas flow rate adjustment unit 22, and the separation gas is supplied to the separation column 2 via the sample injection unit 23.
5 is introduced. The separation column 25 is maintained at a constant temperature in the thermostat unit 24. The sample gas injected into the carrier gas from the sample injection unit 23 is separated while passing through the separation column 25, and is separated by the photoionization detector 26 shown in FIG.
Is introduced and detected. Carrier gas flow controller 2
2. The sample injection unit 23, the constant temperature bath unit 24, and the photoionization detection unit 26 operate according to the contents set in the control device 27.

The control device 27 includes an input means 2 such as a keyboard.
8 and a personal computer having a display device 29 such as a CRT. By operating the input means 28, the measurement conditions of the detector 26 can be automatically set according to the measurement components. For example, when measuring a trace amount of organic components in the air, when the measurement components are designated to the control device 27, the setting conditions of the detector 26 are displayed on the screen of the display device 29 at the same time as the measurement conditions of the gas chromatograph, and according to the instruction of the measurer. The measurement conditions are set automatically.

FIG. 4 shows an example of a screen display of the display device.
FIG. 4A shows an example of an initial screen for setting measurement conditions.
(B) shows an example of a detailed condition setting screen of the detector. FIG.
As shown in (a), on the display screen of the display device 29, the candidate to be analyzed is displayed by key input of a component to be analyzed, a component concentration, a separation column, a detector, a temperature (inlet port temperature, a detector temperature), or the like. The measurement conditions are set by selecting and inputting from. When you enter a component to be analyzed, various separation columns suitable for the component to be analyzed are displayed in the column of the separation column.Select the most appropriate column from the displayed separation columns, and select the selected column. Attach to In addition, at the detector, various detectors corresponding to the components to be analyzed and the component concentrations are displayed, so that the most appropriate detector is selected from among them, and the carrier gas flow path piping is selected. Connected to the detector.

In selecting a detector, for example, a helium photoionization detector (He-PI) using He gas as a discharge gas is used.
Suppose that D) is selected. Then, by switching the display screen of the display device 29 to the detailed setting screen, for example, FIG.
As shown in (b), the details of the He-PID, such as the flow rate of the discharge gas, the discharge current, and the applied voltage, can be set. The He-PID is automatically operated according to the conditions set here.

FIG. 5 is a diagram showing an example of analysis by the gas chromatograph of the present invention. This gas chromatograph device includes an Ar-PID of the present invention using argon gas as a discharge gas as a detector. The sample is unleaded regular gasoline. 0.25 id inside column
A liquid phase OV-1 (manufactured by Hitachi, Ltd.) having a length of 60 mm and a length of 60 mm was used. Column temperature is 1 ° C / min from 30 to 45 ° C,
This is an example in which the temperature is raised at a rate of 7.5 ° C./min from 45 to 200 ° C. and separated. Sample injection temperature is 230 ° C, Ar-PI
The temperature of D was 250 ° C. The gap between the discharge electrodes of the light source section of the PID was 1.5 mm, the current limiting resistor 6 was 3 MΩ, and the discharge stabilizing resistor 7 was 100 kΩ. Ar as a discharge gas
Is supplied at a rate of 50 ml / min, and the discharge current is 100
μA. FIG. 5 shows that the detection of an organic compound composed of multiple components is sufficiently possible with a stable baseline.

FIG. 6 is a diagram showing another example of analysis by a gas chromatograph using Ar-PID as a detector according to the present invention. The sample is a lower hydrocarbon whose concentration is adjusted with nitrogen gas. In the column, 2 squalane on alumina
A column having a diameter of 3 mm and a length of 2 m packed with a% -coated filler was used. The column temperature was 40 ° C. Nitrogen (N ₂ ) was used as the carrier gas, and the flow rate was 40 ml /
It was measured in min.

In the figure, 1 is the peak of ethane (1 ppm),
2 is the ethylene peak (1 ppm). As described above, even a trace amount of organic components in the inorganic gas can be separated and analyzed without being affected by the inorganic gas at all. FIG. 7 is a diagram showing an example in which a trace component in air is analyzed by a gas chromatograph using He-PID as a detector according to the present invention. The detection unit of He-PID has a discharge gas flow rate of 50 ml.
/ Min and a discharge current of 100 μA. MS5A (manufactured by GL Sciences) was used for the separation column, and the column temperature was 50 ° C. He is used as a carrier gas at a flow rate of 25.
It flowed at ml / min. Here air sample used was 0.5ppm the H _2, and the CH ₄ containing 0.8 ppm. As shown in the figure, the peaks of O ₂ and N _{2 as} air components overlap with the peak of CH ₄ as a trace component in air, which clearly affects the quantitative accuracy.

FIG. 8 is an explanatory view of another example of the photoionization detector according to the present invention. The same functional portions as those of the photoionization detector shown in FIG. 1 are assigned the same reference numerals as those in FIG. The only difference between the photoionization detector of FIG. 8 and the photoionization detector shown in FIG. That is, as the discharge anode 33, a platinum plate having a hole serving as an optical path at the center is used. By forming the discharge anode in a plate-like structure having a hole at the center, light generated in the discharge unit is efficiently incident on the detection unit.

[0038]

According to the present invention, the sensitivity of the photoionization detector to the detection components can be changed, and the detection of trace organic components in the inorganic gas becomes possible. Further, by incorporating such a photoionization detector, the performance of the gas chromatograph can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a photoionization detector according to the present invention.

FIG. 2 is a diagram showing a relationship between a resistance value of a discharge stabilization resistor and a stable discharge region.

FIG. 3 is a schematic configuration diagram of a gas chromatograph device.

FIG. 4 is a diagram showing an example of a screen display of the display device.

FIG. 5 is a diagram showing an example of analysis by the gas chromatograph device of the present invention.

FIG. 6 is a diagram showing another example of analysis by the gas chromatograph device of the present invention.

FIG. 7 is a diagram showing another example of analysis by the gas chromatograph device of the present invention.

FIG. 8 is an explanatory diagram of another example of the photoionization detector according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source part, 2 ... Discharge cathode, 3 ... Discharge anode, 4 ... Discharge gas supply port, 5 ... Power supply, 6 ... Current limiting resistance, 7 ... Discharge stabilization resistance, 8 ... Detection part, 9 ... Collector electrode, 10 ... Collector counter electrode, 11 ... Sample inlet, 13 ... Optical path, 1
4a, 14b: cylinder, 15: flow switching valve, 16:
Outflow port of sample to be detected, 21 ... Carrier gas supply source, 22 ...
Carrier gas flow control unit, 23: sample injection unit, 24: constant temperature bath, 25: separation column, 26: photoionization detector, 2
7 control device, 28 input means, 29 display device, 33
… Discharge anode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Kurita 1040 Ichimo Ichimo, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Science Systems Co., Ltd. Within Science Systems (72) Inventor Hideyasu Chiba 1040 Ichimo Ichige, Hitachinaka City, Ibaraki Prefecture Within Hitachi Science Systems, Ltd.

Claims (6)

[Claims] 1. A photoionization detection method for irradiating ionization radiation generated by a gas discharge to a sample to be detected and measuring a sample component by measuring an ionization current of the sample to be detected, wherein the discharge gas of the gas discharge is He, Ne, Ar, Xe or by varying the energy of ionizing radiation selected from H _2, photoionization detector wherein the to have a selectivity for detection component. 2. A photoionization detection method for irradiating ionization radiation generated by a gas discharge to a sample to be detected and detecting a sample component by measuring an ionization current of the sample to be detected, comprising: He and Ne mixed gas, He
Mixed gas of He and Xe, mixed gas of He and Xe, He and H ₂
, Mixed gas of Ne and Ar, mixed gas of Ne and Xe, mixed gas of He and N ₂ , or mixed gas of He and CO ₂ to change the energy of ionizing radiation, A photoionization detection method characterized in that the photoionization detection method is provided with selectivity to the photoionization. 3. A photoionization detection method for irradiating ionization radiation generated by a gas discharge to a sample to be detected and measuring an ionization current of the sample to detect a sample component, wherein the discharge gas of the gas discharge is A photoionization detection method, wherein an organic component in a sample to be detected including an inorganic gas is detected by using Ar or a mixed gas of He and Ar. 4. A discharge electrode for generating ionizing radiation by gas discharge, a sample flow path to be exposed to the ionizing radiation, and a measurement for measuring an ion current of the sample to be ionized by irradiation with the ionizing radiation. A photoionization detector comprising: an electrode; and a means for changing an energy of the ionizing radiation by switching a discharge gas of the gas discharge. 5. The photoionization detector according to claim 4, wherein an electric resistance is provided between the discharge cathode and the power supply, and an electric resistance is further provided between the discharge anode and the ground. Photoionization detector. 6. A gas chromatograph apparatus comprising a sample injection section, a separation column for separating the injected sample component, and a detector for detecting the separated sample component, wherein the detector is used as the detector. A gas chromatograph apparatus comprising the photoionization detector of (1).