WO2014125630A1 - 放電イオン化電流検出器 - Google Patents
放電イオン化電流検出器 Download PDFInfo
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- WO2014125630A1 WO2014125630A1 PCT/JP2013/053752 JP2013053752W WO2014125630A1 WO 2014125630 A1 WO2014125630 A1 WO 2014125630A1 JP 2013053752 W JP2013053752 W JP 2013053752W WO 2014125630 A1 WO2014125630 A1 WO 2014125630A1
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- insulating member
- ionization current
- current detector
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/64—Electrical detectors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
- G01N27/68—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using electric discharge to ionise a gas
- G01N27/70—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using electric discharge to ionise a gas and measuring current or voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N2030/022—Column chromatography characterised by the kind of separation mechanism
- G01N2030/025—Gas chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/62—Detectors specially adapted therefor
- G01N30/64—Electrical detectors
- G01N2030/647—Electrical detectors surface ionisation
Definitions
- the present invention mainly relates to a discharge ionization current detector suitable as a detector for a gas chromatograph (GC), and more particularly to improvement of the characteristics of the detector at a high temperature.
- GC gas chromatograph
- FID Flame Ionization detector
- PDD Pulsed Discharge Detector
- TCD Thermal Conductivity detector
- FID is commonly used to detect organic substances in the detector.
- the FID ionizes sample components in the sample gas with a hydrogen flame and detects the ion current.
- FID has a feature that it has a wide dynamic range, since the sample components are burned with a hydrogen flame and ionized, the compounds to be analyzed are limited.
- FID has low sensitivity to incombustible gas and does not have sensitivity to inorganic gas.
- a PDD or the like that ionizes a sample by utilizing discharge has high sensitivity even for incombustible gases and inorganic gases, and is suitable for detecting almost all compounds required for gas chromatographs (for example, Patent Documents). 1 to 4).
- a method of exciting helium molecules is often used, and a PDD using this method is called a helium discharge ionization detector (HDPID: Helium Discharge Photo Ionization Detector).
- HDPID mainly includes a plasma generation unit and an ion collection unit.
- a plasma excitation electrode is disposed in the plasma generation unit.
- Helium gas is introduced into the plasma generation unit, and a high-pressure pulse is applied to the plasma excitation electrode, thereby exciting the helium gas and generating plasma.
- Light (such as vacuum ultraviolet light) emitted from the plasma reaches the ion collector.
- An ion collection electrode and a bias electrode are arranged in the ion collection unit.
- a sample gas is introduced into the ion collector, and the sample gas is ionized by irradiating the sample gas with light that has arrived from the plasma generator (sample ion).
- a voltage is applied to the bias electrode to form an electric field, and sample ions are guided to the ion collection electrode.
- the ion collection electrode collects sample ions and detects them as an ion current through an amplifier connected to the ion collection electrode.
- An insulating member thickness of about several mm
- such as ceramic is inserted between the ion collecting electrode and the bias electrode to electrically insulate them (see, for example, Patent Documents 1 to 4).
- Gas chromatographs sometimes analyze high-boiling components. In order to promote ionization of such components, it is necessary to heat the HDPID ion collector to about 400 ° C. However, when the ion collector is heated, temperature drift and noise suddenly increase at 300 ° C. or higher, and as a result, the background level increases and the SN ratio of the detection signal decreases.
- the present invention has been made to solve the above-mentioned problems, and its object is to prevent discharge ionization current detection suitable for the analysis of high-boiling components while preventing a decrease in the S / N ratio of detection signals at high temperatures. Is to provide a vessel.
- the present invention made to solve the above problems is a discharge ionization current detector used in a gas chromatograph, a) a plasma generator for generating plasma; b) A bias electrode for generating an electric field for guiding sample ions ionized by light generated by the plasma generated by the plasma generation unit to an ion collection electrode described later, and for ion collection for collecting the sample ions
- An ion collector having an electrode and an insulating member made of aluminum oxide or sapphire having a purity of 99.5% or more, disposed between the ion collection electrode and the bias electrode; Is provided.
- the inventors of the present application have found that the fact that the insulation resistance of the insulating member rapidly decreases at 300 ° C. or higher due to the heating of the ion collector is the main cause of the decrease in the SN ratio of the detection signal. That is, conventional insulation members such as aluminum oxide and heat-resistant resin that have been used in the past have a significant decrease in insulation resistance at a high temperature of 300 ° C. or higher. As a result, there is a problem between the bias electrode and the ion collection electrode. Isolation is insufficient, current flows from the bias electrode to the ion collection electrode, and is detected as drift or noise.
- the insulating resistance of the insulating member is 300. It has been found that it can be prevented from abruptly becoming smaller than °C.
- These insulating members have a volume resistivity of about 10 10 ⁇ cm or more even at the maximum operating temperature of the detector (about 400 ° C), and provide sufficient isolation between the ion collection electrode and the bias electrode. Realize.
- generation part shall produce
- the inventors of the present application have found that the emission of gas from the inner wall of the detector including the plasma generation unit due to the heating of the ion collection unit is one of the causes of the decrease in the SN ratio of the detection signal.
- the released gas is mainly an inorganic gas such as hydrogen or oxygen.
- the detector using discharge detects the inorganic gas with high sensitivity, and therefore the discharged gas is also detected excessively. For this reason, the background level increases and the S / N ratio of the detection signal decreases.
- the discharge ionization current detector using the plasma generating means having the above configuration is generally called a low frequency dielectric barrier discharge ionization current detector (BID).
- the BID generates a plasma in the space by providing a space surrounded by a dielectric in the plasma generation unit and disposing an electrode for plasma excitation outside the dielectric. This suppresses generation of electrode sputtering and emission gas due to direct exposure of the inner wall of the electrode or detector to plasma or the like. By utilizing such a dielectric barrier discharge, the amount of gas emitted from the inner wall of the detector can be greatly reduced even at high temperatures.
- a metal O-ring may be disposed between each of the ion collecting electrode, the insulating member, and the bias electrode, and these may be pressed and fixed by an elastic member.
- the metal O-ring is preferably a nickel-base superalloy with gold or silver plating.
- a leaf spring can be used as the elastic member.
- a gasket is disposed on the contact surfaces of the ion collecting electrode, the insulating member, and the bias electrode to ensure the airtightness of the ion collecting portion.
- the gasket is plastically deformed by the temperature cycle, and the airtightness of the ion collector is lowered. For this reason, the inorganic gas may enter the ion collector from the contact surface, and the SN ratio of the detection signal may be reduced.
- the metal O-ring has excellent resilience, and even if the detector is used for a long period of time, there is almost no plastic deformation due to the temperature cycle.
- the ion collecting electrode, the insulating member, and the bias electrode may be airtightly bonded using a bonding member.
- the first joint surface joined to the ion collecting electrode and the second joint surface joined to the bias electrode were metallized with molybdenum (Mo) and manganese (Mn), respectively. It is plated with nickel (Ni), and the insulating member and the ion collecting electrode are brazed at the first joint surface, and the insulating member and the bias electrode are brazed at the second joint surface. May be.
- nickel (Ni) plating may be applied to a position of the brazing material used for the first bonding surface and the second bonding surface that is exposed to the outside of the ion collector.
- the collecting electrode and the biasing electrode may be electrodes made of stainless steel or nickel so that, for example, a passivation can be formed on the surface and oxidation can be prevented. It is desirable that it be formed of an alloy made of Such an alloy can prevent oxidation by applying nickel (Ni) plating.
- the thermal expansion coefficient of an alloy made of iron, nickel and cobalt is close to that of aluminum oxide or sapphire, and the ion collecting electrode and bias electrode are made of such an alloy, so It can withstand temperature cycles due to long-term use.
- the junction surfaces of the ion collection electrode, the insulating member, and the bias electrode are exposed to the atmosphere outside the ion collection unit. Therefore, at a high temperature, the brazing material exposed from the joint surface may oxidize and expand, and the airtightness may be reduced.
- nickel (Ni) plating is also applied to the brazing material exposed to the outside of the ion collector, this becomes a barrier layer and can prevent oxidation.
- the electrode for ion collection is also connected to an amplifier or the like outside the ion collection unit, it is exposed to the atmosphere. In that case, when the ion collecting part is heated, the collecting electrode may be oxidized at the connecting part.
- the discharge ionization current detector detects a minute ion current of about several pA flowing through the collecting electrode. For this reason, if the electrode for ion collection is oxidized, and even a slight contact failure occurs with the amplifier or the like, the sensitivity of the detector is greatly reduced.
- the bias electrode is also connected to a power source or the like outside the ion collector, it is exposed to the atmosphere. When the bias electrode is oxidized, it causes noise.
- the bias electrode is preferentially oxidized by anodic oxidation. In that case, it is preferable to apply nickel (Ni) plating to both electrodes to prevent this.
- the ion collecting electrode and / or the bias electrode is formed of a conductive surface obtained by plating a part of the insulating member with a conductor and a conductive pin passing through the insulating member and electrically connected to the conductive surface. You may make it do.
- the ion collection electrode and / or the bias electrode By forming the ion collection electrode and / or the bias electrode in this manner, it is possible to prevent the atmosphere from entering the ion collection section from the contact surface between the electrode and the insulating member.
- each of the ion collecting electrode, the insulating member, and the biasing electrode has a cylindrical shape with a hole having the same diameter in the center, and the holes are made to coincide with each other. It is desirable that a through hole is formed by disposing the collecting electrode, the insulating member, and the bias electrode, and the sample ions are confined in the through hole.
- the discharge ionization current detector According to the discharge ionization current detector according to the present invention, it is possible to prevent a decrease in the S / N ratio of the detection signal at a high temperature, and it is possible to obtain a good measurement result even in the analysis of the high boiling point component.
- the figure which shows schematic structure of the discharge ionization current detector by 1st Example of this invention The figure which shows the schematic block diagram of the ion collection part in the conventional discharge ionization current detector.
- the set temperature of the ion collector is 200 ° C.
- the set temperature of the ion collector is 300 ° C.
- the set temperature of the ion collector is 400 ° C.
- the figure which shows the chromatogram of the conventional discharge ionization current detector using the aluminum oxide whose purity is less than 99.5% for an insulating member. (a) When the set temperature of the ion collector is 200 ° C and (b) is 450 ° C.
- FIG. 1 is a schematic configuration diagram of a discharge ionization current detector according to a first embodiment of the present invention, and shows a cross section of a discharge ionization current detector 10 having a cylindrical shape.
- the discharge ionization current detector 10 mainly includes a plasma generation unit 20 and an ion collection unit 30.
- a gas inlet 23 is provided above the plasma generator 20 and a cylindrical tube 21 made of a dielectric such as synthetic quartz is provided below the gas inlet 23.
- a plasma generating electrode 22 is disposed outside the cylindrical tube 21, and a low frequency AC power supply 24 is connected to the electrode 22.
- the AC power supply 24 is configured so that the controller 25 can control the voltage and frequency.
- the ion collecting unit 30 is provided with an insulating member 33, a bias electrode 32, an insulating member 33, an ion collecting electrode 31, and an insulating member 33 in this order from the top.
- the ion collecting electrode 31 and the bias electrode 32 are insulated, and both electrodes are also insulated from the ground potential.
- the ion collecting electrode 31 and the bias electrode 32 are preferably formed of stainless steel or nickel in order to prevent oxidation.
- the insulating member 33 for example, aluminum oxide or sapphire having a purity of 99.5% or more is used, and the thickness is about 1 to 4 mm, preferably about 1.5 mm.
- the capillary 34 for introducing the sample gas is inserted from below and fixed so that the tip of the capillary is located near the center of the bias electrode 32.
- the ion collection electrode 31 is connected to an external circuit (not shown) through an amplifier 36, and the bias electrode 32 is connected to a DC power source 35. Further, the ion collector 30 can be adjusted to a temperature of about 450 ° C. by a heat source (not shown) such as a heater so that the sample having a high boiling point can be analyzed.
- the operation of the discharge ionization current detector 10 will be described.
- the plasma generation unit 20 helium gas is introduced into the inside through the gas introduction port 23.
- the controller 25 controls the AC power source 24 to apply a low frequency AC voltage having a frequency of about 5 to 50 kHz and a voltage of about 4 to 8 kVp-p to the plasma generating electrode 22 to cause discharge.
- This discharge is a dielectric barrier discharge using the cylindrical tube 21 as a dielectric, thereby exciting the helium gas and generating helium plasma.
- the helium plasma emits light (mainly vacuum ultraviolet light), and the light reaches the ion collector 30.
- an external circuit including the amplifier 36 is operated so that ions collected by the ion collecting electrode 31 can be detected as an ion current. Further, a voltage is applied to the bias electrode 32 by the DC power source 35. This voltage is a DC voltage of about +50 to 200 V, and is preferably about +170 V in terms of linearity of signal response. In this state, the sample gas is introduced from the capillary 34.
- the introduced sample gas is blown upward from the tip of the capillary 34.
- the sample gas 34 is irradiated with vacuum ultraviolet light generated by the plasma generation unit 20.
- the sample gas 34 is ionized and becomes sample ions.
- the sample ions are influenced by the electric field formed by the voltage applied to the bias electrode 32 and are guided to the ion collection electrode 31 located below.
- the sample ions reaching the ion collection electrode 31 are detected as an ion current through the amplifier 36.
- sample components can be ionized and detected.
- an excellent effect can be obtained by using aluminum oxide or sapphire having a purity of 99.5% or more as the insulating member 33. The effect will be described below with reference to FIGS.
- FIGS. 6, 7, and 8 are graphs in which the base line signal (A), which is the ion current obtained from the ion collecting electrode, is plotted on the vertical axis, with the horizontal axis representing the bias voltage (V) applied to the bias electrode.
- A base line signal
- V bias voltage
- FIGS. 6, 7, and 8 are obtained by setting the temperature of the ion collector to 200 ° C., 300 ° C., and 400 ° C., respectively.
- the baseline signal is almost constant at the bias voltage (eg, 50 V or more) when the detector is used.
- the baseline signal is substantially zero regardless of the bias voltage. It can be said that such a preferable state is obtained when the temperature of the ion collector is set to 200 ° C. (FIG. 6). On the other hand, when the temperature of the ion collector is set to 300 ° C., it can be seen that the baseline signal increases as the bias voltage increases even when helium plasma is not excited (FIG. 7).
- the fluctuation range of the baseline signal at this time is usually about 0.1 to 10 nA, and the baseline signal exceeds 10 nA when there is an exhaust gas.
- a discharge ionization current detector that detects a minute ion current of about several pA, it becomes background noise. Furthermore, this tendency becomes remarkable when the temperature of the ion collector is set to 400 ° C., and when the helium plasma is not excited, the baseline signal rapidly increases as the bias voltage increases. Further, when helium plasma is excited, the baseline signal is not constant even in a region where the bias voltage is 100 V or more (FIG. 8).
- the above means that when the temperature of the ion collector exceeds 300 ° C., the insulation resistance is lowered in the conventional insulating member, and the isolation between the ion collecting electrode and the bias electrode is insufficient. . Due to the lack of isolation, a current flows from the bias electrode to the ion collecting electrode, which is detected as drift or noise.
- FIG. 9 shows a chromatogram obtained by a conventional discharge ionization current detector having such a baseline signal temperature characteristic, with the horizontal axis representing time and the vertical axis representing detection intensity.
- 9A shows a graph when the temperature of the ion collector is set to 200 ° C.
- FIG. 9B shows a graph when the temperature of the ion collector is set to 450 ° C.
- the measurement for the same sample is repeated three times, and the obtained three chromatograms are displayed in an overlapping manner.
- the set temperature is 200 ° C.
- the three chromatograms are almost overlapped (FIG. 9 (a)).
- FIG. 10 shows a chromatogram obtained by the discharge ionization current detector of Example 1 above.
- the background noise level is almost the same as when the set temperature is 200 ° C.
- the three chromatograms are almost overlapped (FIGS. 10 (a) and 10 (b)). That is, even if the temperature of the ion collector increases, the SN ratio of the detection signal and the measurement accuracy do not decrease. This is because in Example 1 described above, sufficient isolation was realized between the ion collection electrode and the bias electrode by using aluminum oxide or sapphire having a purity of 99.5% or more for the insulating member.
- Aluminum oxide with a purity of less than 99.5% (that is, a conventional insulating member) has a volume resistivity of about 10 14 ⁇ cm near room temperature, but decreases to about 10 8 ⁇ cm at a high temperature of 300 to 500 ° C. End up.
- aluminum oxide or sapphire having a purity of 99.5% or more (that is, the insulating member of the above example) can obtain a volume resistivity of about 10 10 ⁇ cm even at a high temperature of 300 to 500 ° C. That is, the volume resistivity at high temperature differs by two orders of magnitude.
- FIG. 2 shows a schematic configuration of an ion collector of a conventional discharge ionization current detector.
- description of the amplifier connected to the electrode for ion collection, the direct current power source connected to the electrode for bias, and the like is omitted (the same applies to FIGS. 3 and 4).
- the gasket 45 is disposed on the contact surface of the ion collecting electrode 41, the insulating member 43, and the bias electrode 42, and airtightness is ensured by pressing with the leaf spring 46.
- the gasket is plastically deformed and the airtightness cannot be maintained. For this reason, for example, air enters through the contact surface between the electrode and the insulating member, and as a result, the SN ratio of the detection signal decreases.
- the ion collector may be configured as shown in FIG. 3, for example.
- a metal O-ring 55 is disposed on the contact surface of the ion collecting electrode 51, the insulating member 53, and the bias electrode 52, and airtightness is ensured by pressing with the leaf spring 56.
- Inconel registered trademark
- Inconel is a nickel-base superalloy excellent in restoring force at high temperatures, and by using this, plastic deformation due to the temperature cycle of the O-ring can be prevented.
- the surface of the O-ring may be plated with gold or silver.
- the configuration shown in FIG. 4 may be adopted (third embodiment).
- the ion collection electrode 61, the insulating member 63, and the bias electrode 62 are joined with silver brazing or the like (joining layer 65).
- the insulating member 63 cannot be brazed as it is. Therefore, the surface of the insulating member 63 to be bonded to the ion collecting electrode 61 and the bias electrode 62 is preliminarily metallized with molybdenum (Mo) and manganese (Mn) and then plated with nickel (Ni).
- an alloy made of iron, nickel and cobalt having linear expansion coefficients close to those of aluminum oxide and sapphire is preferable.
- An example of such an alloy is Kovar (registered trademark).
- Kovar is preferably plated with nickel (Ni).
- the ion collecting electrode 61 is connected to an external circuit through an amplifier in the same manner as the ion collecting electrode 31 shown in FIG.
- the brazing material exposed from the joint surface with the insulating member 63 may be oxidized by heating of the ion collector.
- the brazing material exposed to the outside of the ion collector is also preferably plated with nickel (Ni).
- the ion collector can be configured as shown in FIG. 5 (fourth embodiment).
- the ion collecting electrode is formed by a conductive surface 71 a obtained by metallizing a part of the insulating member 73 and a conductive pin 71 b penetrating the insulating member 73.
- the bias electrode is formed of a conductive surface 72 a obtained by metallizing a part of the insulating member 73 and a conductive pin 72 b penetrating the insulating member 73. This also maintains the airtightness of the ion collector.
- the ion collecting electrode, the bias electrode, and the insulating member in the ion collecting portion are each formed in a cylindrical shape having the same hole in the center. Are stacked to form a through hole. With such a configuration, the dead space where sample ions are wasted is reduced as much as possible.
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Abstract
Description
プラズマ生成部にはプラズマ励起用電極を配置する。プラズマ生成部にヘリウムガスを導入し、プラズマ励起用電極に高圧のパルスを印加することにより、ヘリウムガスを励起してプラズマを生成する。該プラズマが発する光(真空紫外光等)はイオン収集部に到達する。
イオン収集用電極とバイアス用電極の間には、セラミック等の絶縁部材(厚さ数mm程度)を挿入し、両者を電気的に絶縁する(例えば特許文献1から4参照)。
a)プラズマを生成するプラズマ生成部と、
b)前記プラズマ生成部が生成したプラズマが発する光によってイオン化された試料イオンを後記イオン収集用電極に導くための電場を発生させるためのバイアス用電極、前記試料イオンを収集するためのイオン収集用電極、及び該イオン収集用電極と該バイアス用電極との間に配置された純度が99.5%以上の酸化アルミニウム又はサファイアから成る絶縁部材を有するイオン収集部と、
を備える。
この知見をもとにさらに検討を行った結果、イオン収集用電極とバイアス用電極の間の絶縁部材に、純度が99.5%以上の酸化アルミニウム又はサファイアを用いることにより、絶縁部材の絶縁抵抗が300℃以上で急激に小さくなるのを防ぐことができることを見いだした。そして、これらの絶縁部材は、検出器の最高使用温度(400℃程度)においても約1010Ωcm以上の体積固有抵抗を有し、イオン収集用電極とバイアス用電極の間に十分なアイソレーションを実現する。
前記プラズマ生成部が、低周波交流電場による誘電体バリア放電を利用してプラズマを生成するものとすることができる。
上記構成のプラズマ生成手段を用いた放電イオン化電流検出器は、一般に、低周波誘電体バリア放電イオン化電流検出器(BID:Dielectric Barrier Discharge Ionization Detector)と呼ばれる。BIDは、プラズマ生成部に誘電体で囲んだ空間を設け、該誘電体の外側にプラズマ励起用電極を配置することで、該空間内にプラズマを生成する。これにより、同電極や検出器の内壁が直接プラズマ等に晒されることによる電極のスパッタや放出ガスの発生が抑えられる。
このような誘電体バリア放電を利用することで、高温時にも検出器の内壁から生じる放出ガスの量を大幅に減らすことができる。
金属製Oリングは、ニッケル基超合金に金メッキ又は銀メッキを施したものとすると良い。
弾性部材には、例えば板バネを用いることができる。
これに対し、金属製Oリングは復元性に優れ、検出器を長期にわたって使用し続けても温度サイクルによる塑性変形がほとんどないため、イオン収集部の気密性を維持できる。
この場合、前記絶縁部材のうち、前記イオン収集用電極と接合する第1接合面、及び前記バイアス用電極と接合する第2接合面が、それぞれモリブデン(Mo)およびマンガン(Mn)でメタライズされた上でニッケル(Ni)でメッキされ、該第1接合面において該絶縁部材と該イオン収集用電極がロウ付けされ該第2接合面において該絶縁部材と該バイアス用電極がロウ付けされるようにしてもよい。
さらに、前記第1接合面および第2接合面に使用するロウ材のうち、前記イオン収集部の外側に露出した位置にも、ニッケル(Ni)メッキを施すとよい。
収集用電極及びバイアス用電極は、例えば、表面に不動態を形成して酸化を防ぐことができるようにステンレス鋼又はニッケルで形成された電極としても良いが、ここでは特に、鉄、ニッケル及びコバルトから成る合金で形成されているものとすることが望ましい。
このような合金は、ニッケル(Ni)メッキを施すことで酸化を防ぐことができる。
イオン収集用電極、絶縁部材、及びバイアス用電極の接合面は、イオン収集部の外側において大気に晒されている。そのため、高温時には、接合面から露出したロウ材が酸化して膨張し、気密性が低下する恐れがある。しかし、上記のとおり、イオン収集部の外側に露出したロウ材にもニッケル(Ni)メッキを施しておけば、これがバリア層となり、酸化を防ぐことができる。
さらに、イオン収集部の温度を400℃に設定するとこの傾向が顕著となり、ヘリウムプラズマを励起していない場合は、バイアス電圧の上昇に伴いベースライン信号が急激に大きくなる。また、ヘリウムプラズマを励起している場合は、バイアス電圧が100V以上の領域においてもベースライン信号が一定とならない(図8)。
以上のことは、イオン収集部の温度が300℃を超えると、従来の絶縁部材では、絶縁抵抗が低下して、イオン収集用電極とバイアス用電極の間のアイソレーションが不足することを意味する。そして、該アイソレーションが不足することで、バイアス用電極からイオン収集用電極に電流が流れ、これがドリフトやノイズとし検出されてしまう。
ただし、絶縁部材63はそのままではロウ付けできない。そこで、予め、絶縁部材63のうち、イオン収集用電極61及びバイアス用電極62と接合する面に、それぞれモリブデン(Mo)・マンガン(Mn)をメタライズした上でニッケル(Ni)でメッキしておくとよい
また、イオン収集用電極及びバイアス用電極としては、線膨張係数が酸化アルミニウム及びサファイアに近い鉄、ニッケル及びコバルトから成る合金がよい。このような合金としては、例えばコバール(登録商標)がある。さらに酸化を防ぐために、コバールをニッケル(Ni)でメッキするとよい。
11…ボディ
20…プラズマ生成部
21…円筒管
22…プラズマ生成用電極
23…ガス導入口
24…交流電源
30…イオン収集部
31、41、51、61…イオン収集用電極
32、42、52、62…バイアス用電極
33、43、53、63…絶縁部材
34、44、54、64、74…キャピラリ
35…直流電源
36…アンプ
45…ガスケット
46、56…板バネ
55…Oリング
65…接合層
71a…導電面
71b…導電ピン
72a…導電面
72b…導電ピン
Claims (9)
- ガスクロマトグラフに用いられる放電イオン化電流検出器であって、
a)プラズマを生成するプラズマ生成部と、
b)前記プラズマ生成部が生成したプラズマが発する光によってイオン化された試料イオンを後記イオン収集用電極に導くための電場を発生させるためのバイアス用電極、前記試料イオンを収集するためのイオン収集用電極、及び該イオン収集用電極と該バイアス用電極との間に配置された純度が99.5%以上の酸化アルミニウム又はサファイアから成る絶縁部材を有するイオン収集部と、
を備える、放電イオン化電流検出器。 - 前記プラズマ生成部が、低周波交流電場による誘電体バリア放電を利用してプラズマを生成する、請求項1に記載の放電イオン化電流検出器。
- 前記イオン収集用電極、前記絶縁部材、及び前記バイアス用電極のそれぞれの間に金属製Oリングが配置され、これらが弾性部材で押さえ付けて固定される請求項1又は2に記載の放電イオン化電流検出器。
- 前記イオン収集用電極、前記絶縁部材、及び前記バイアス用電極が、接合部材を用いて気密に接合されている請求項1又は2に記載の放電イオン化電流検出器。
- 前記絶縁部材のうち、前記イオン収集用電極と接合する第1接合面、及び前記バイアス用電極と接合する第2接合面が、それぞれモリブデン(Mo)およびマンガン(Mn)でメタライズされた上でニッケル(Ni)でメッキされ、該第1接合面において該絶縁部材と該イオン収集用電極がロウ付けされ該第2接合面において該絶縁部材と該バイアス用電極がロウ付けされる請求項4に記載の放電イオン化電流検出器。
- 前記イオン収集部の接合部のうち、前記イオン収集部の外側に露出したロウ材にも、ニッケル(Ni)メッキが施されている請求項5に記載の放電イオン化電流検出器。
- 前記収集用電極及びバイアス用電極は、鉄、ニッケル及びコバルトから成る合金で形成されている請求項1~6のいずれか1項に記載の放電イオン化電流検出器。
- 前記イオン収集用電極及び/又はバイアス用電極が、絶縁部材の一部を導体でメッキした導電面と該絶縁部材を貫通して該導電面と電気的に接続された導電ピンとで形成されている請求項1又は2に記載の放電イオン化電流検出器。
- 前記イオン収集用電極、前記絶縁部材、及び前記バイアス用電極がそれぞれ中央に同一径の孔を設けた円筒形状とされ、各孔を一致させて該イオン収集用電極、該絶縁部材及び該バイアス用電極を配置することで貫通孔が形成され、該貫通孔に前記試料イオンを閉じこめる構成とされている請求項1~7のいずれか1項に記載の放電イオン化電流検出器。
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US14/767,191 US10585073B2 (en) | 2013-02-15 | 2013-02-15 | Discharge ionization current detector |
CN201380073114.2A CN104995504B (zh) | 2013-02-15 | 2013-02-15 | 放电离子化电流检测器 |
JP2015500066A JP5987969B2 (ja) | 2013-02-15 | 2013-02-15 | 放電イオン化電流検出器 |
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US10845345B2 (en) * | 2015-12-28 | 2020-11-24 | Shimadzu Corporation | Chromatograph with integrated display unit |
CN105606695B (zh) * | 2016-03-28 | 2019-01-22 | 青岛佳明测控科技股份有限公司 | Dbd离子化检测器及其检测方法 |
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