JP5136300B2 - Discharge ionization current detector - Google Patents

Description

  The present invention relates to a discharge ionization current detector suitable mainly as a detector for gas chromatograph (GC).

  Gas chromatograph detectors include thermal conductivity detector (TCD), electron capture detector (ECD), hydrogen flame ionization detector (FID), flame photometric detector (FPD), flame thermionic detector. Various types of detectors such as (FTD) have been proposed and put into practical use. Of these detectors, the most commonly used, particularly for detecting organic matter, is a flame ionization detector. The hydrogen flame ionization detector ionizes a sample component in a sample gas by a hydrogen flame and measures its ion current, and achieves a wide dynamic range of about 6 digits.

  However, the flame ionization detector has a low ionization efficiency, so a sufficiently low minimum detection amount cannot be obtained, and since it requires highly dangerous hydrogen, it is necessary to install special equipment such as explosion-proof equipment. Has the disadvantage of being troublesome.

  On the other hand, a pulse discharge ionization current detector (PDD: Pulsed Discharge Detector) has been conventionally known as a detector that can detect inorganic substances to low boiling point organic compounds with high sensitivity (see Patent Document 1, etc.). (See Non-Patent Document 1, etc.). The pulse discharge ionization current detector excites helium molecules by high-pressure pulse discharge, and ionizes molecules to be analyzed using light energy generated when molecules in the excited state return to the ground state. Then, the ion current is detected, and a detection signal corresponding to the amount (concentration) of the molecule to be analyzed is obtained.

  Therefore, unlike the flame ionization detector, the pulse discharge ionization current detector does not require hydrogen and is easy to handle. In addition, its ionization efficiency is higher than that of the flame ionization detector. As an example, the ionization efficiency for propane is only 0.0005 [%] for the flame ionization detector, whereas 0.07 [%] is realized for the pulse discharge ionization current detector. However, in spite of this, the dynamic range of the pulse discharge ionization current detector does not reach that of the flame ionization detector, and is actually about one digit lower. This is one reason why pulse discharge ionization current detectors are not as popular as flame ionization detectors.

  Although the limiting factor of the dynamic range in the conventional pulse discharge ionization current detector has not been clearly clarified, the following factors can be considered. That is, in a conventional general pulse discharge ionization current detector, a plasma is generated by applying a short high voltage pulse between electrodes arranged at a minute interval of several [mm] or less. I try to let them. This is an improvement of DC discharge, and is intended to suppress electrode heat generation and plasma instability due to DC discharge by pulsing the applied voltage.

  However, as a result, periodic fluctuations of the plasma accompanying the transition of the voltage state such as the rise of the pulse voltage, the peak voltage, and the fall occur, which causes the periodic fluctuation of ionization as it is. That is, since efficient excitation is performed only periodically, the average excitation efficiency is thereby lowered, and it can be estimated that the resulting plasma instability results in ionization instability. In addition, periodic fluctuations in the plasma state can cause background noise. Therefore, as a result, it is considered that the conventional pulse discharge ionization current detector does not sufficiently increase the SN ratio of the detection signal, which is a limiting factor of the dynamic range.

  In order to stabilize the plasma state, it is conceivable to use a high-frequency discharge. However, if this happens, the plasma becomes high temperature, and various problems are expected to occur. Specifically, thermoelectrons generated when the electrodes and the like are heated may affect the plasma and may make the plasma state unstable. In addition, the detector needs to have a structure and structure in consideration of heat resistance, which causes a large increase in cost.

  Accordingly, the inventors of the present application have come up with the idea of using the low-frequency AC-excited dielectric barrier discharge reported in Non-Patent Document 2 or the like in order to generate plasma for ionization. It was experimentally confirmed that it was possible to detect sample components using plasma generated by barrier discharge (see Non-Patent Document 3). Prior to the publication of Non-Patent Document 3, the present inventors have proposed a basic configuration of a discharge ionization current detector using a low-frequency AC-excited dielectric barrier discharge in Japanese Patent Application No. 2008-76917. Since the discharge ionization current detector using the low-frequency AC-excited dielectric barrier discharge has high stability of the plasma itself, the influence of noise on the ionization current output caused by plasma such as abnormal discharge is small.

U.S. Pat.No. 5,394,092 “Inorganic gas analysis goes to the ppb range PDD high-sensitivity analysis system”, [online], Shimadzu Corporation, [searched August 15, 2008], Internet <URL: http: //www.an.shimadzu. co.jp/products/gc/pdd.htm> M. Teschke and four others, "High-Speed Photographs of a Dielectric Barrier Atmospheric Pressure Plasma Jet" ”, IEEE Transaction on Plasma Science, Vol. 33, No, 2, April 2005, pp.310-311 Megumi Shinada and three others, "Ionization current detector for gas chromatograph using atmospheric pressure microplasma", Proceedings of the 55th Joint Lecture on Applied Physics in Spring 2008, March 28, 2008

  The inventor of the present application has made various studies for the purpose of further improving the performance of the discharge ionization current detector, and in the process, a trace amount of impurities contained in the plasma generation gas and the inner wall of the pipe constituting the gas flow path It was found that a small amount of impurities released from the etc. contribute to noise. That is, although these impurity components are in a minute amount, they are directly excited with high efficiency by plasma, and therefore, when the sample component to be detected is in a minute amount, it can be at a level that cannot be ignored compared to its ionization current. For this reason, the ionization current derived from such impurities becomes an offset current in the ionization current detection output, which destabilizes the output or causes noise. In order to reduce noise caused by such impurities, use a pipe material that emits less impurities, increases the purity of the plasma generating gas, supplies the plasma generating gas to the detector after passing through the gas purifier, Such measures can be considered. However, these measures have limitations and there are problems that analysis costs are high.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to eliminate noise caused by impurities mixed in the plasma generating gas or released from the piping of the gas flow path. An object of the present invention is to provide a discharge ionization current detector capable of improving the analysis accuracy and the analysis sensitivity by reducing them.

The present invention made to solve the above problems is a discharge ionization current detector that ionizes and detects a sample component in a sample gas using plasma generated by discharge,
a) A dielectric barrier discharge is generated by an AC electric field having a frequency range of 1 [kHz] to 100 [kHz] in the gas flow path through which the plasma generating gas flows, and plasma is generated from the plasma generating gas by the discharge. Plasma generating means for generating;
b) a sample gas introduction flow path for introducing a sample gas into the gas flow path on the downstream side of the plasma generation region by the plasma generation means;
c) current detection means for detecting an ionic current due to a sample component in the sample gas in the gas flow path downstream of the plasma generation region by the plasma generation means and ionized by the action of the plasma;
d) a branch exhaust flow path for branching and discharging a part of the plasma generation gas flowing in the gas flow path between the plasma generation area by the plasma generation means and the ion current detection area by the current detection means; ,
It is characterized by having.

  As the plasma generating gas, one of helium, argon, nitrogen, neon, xenon, or a mixed gas thereof can be used.

  The plasma generating means applies a pair of discharge electrodes having at least one surface covered with a dielectric, and a low frequency AC voltage having a frequency range of 1 [kHz] to 100 [kHz]. And an AC power source.

  In the discharge ionization current detector according to the present invention, when the dielectric barrier discharge is generated by the plasma generating means, plasma is generated from the plasma generating gas in the vicinity thereof. This is a stable atmospheric pressure microplasma. Part of the plasma generation gas that has passed through this plasma generation region in the gas flow path flows into the branch exhaust flow path, and the remaining plasma generation gas is mixed with the sample gas through the sample gas introduction flow path, thereby detecting the current. Toward the ion current detection region. Therefore, the flow rate of the plasma generation gas passing through the ion current detection region is smaller than the flow rate of the plasma generation gas passing through the plasma generation region.

  In general, ionization of a sample by plasma excitation is considered to be caused by the action of excitation light from the plasma and the excited species of the plasma generating gas generated by the plasma. Therefore, in order to obtain sufficient ionization efficiency, it has been considered that the best method is to flow all the plasma generation gas that has passed through the plasma generation region to the ion current detection region. However, according to the study of the present inventor, in the case of the low-frequency AC excited dielectric barrier discharge, the contribution of the excited species generated by the plasma to ionization is quite small, and most of the ionization is due to plasma emission. It has been found. In other words, in order to ionize the sample in the low-frequency AC-excited dielectric barrier discharge, it is only necessary to make the excitation light from the plasma reach the ion current detection region without waste, and all of the plasma generating gas is ionized. There is little need to pass through the detection area.

On the other hand, if a part of the plasma generation gas is discharged after passing through the plasma generation region and the flow rate of the plasma gas generation gas passing through the ion current detection region is reduced, the following advantages can be obtained.
(1) Impurities originally contained in the gas for generating plasma, impurities released from the inner wall of the gas flow passage, etc. (especially in the vicinity of the plasma generating region where impurities are relatively easily released) and ions derived therefrom A part of is also discharged together with the plasma generating gas before reaching the ion current detection region. Therefore, since the amount of impurities that reach the ion current detection region and are directly excited by plasma is reduced, offset current and noise caused by the impurities can be reduced.

(2) Since the sample gas is diluted by the plasma generation gas passing through the ion current detection region, reducing the flow rate of the plasma generation gas means that the concentration of the sample component is relatively high, and ionization is performed. This leads to an increase in the current signal.
(3) Even if the flow rate of the plasma generating gas passing through the ion current detection region is reduced, it is not necessary to change the flow rate of the plasma generating gas passing through the plasma generating region. Therefore, the dilution degree of impurities released from the pipe inner wall of the gas flow path does not decrease, and the effect of reducing the amount of impurities shown in (1) can be sufficiently exerted.

  That is, in the discharge ionization current detector according to the present invention, a part of the plasma generation gas is exhausted after passing through the plasma generation region and before reaching the ion current detection region. You can enjoy the benefits. On the other hand, even if a part of the plasma generating gas is discharged halfway, the excitation light emitted from the vicinity of the plasma generating region does not weaken, and even if the excited species of the plasma generating gas decreases as described above, There is almost no effect on ionization. Therefore, the ionization efficiency can be kept high.

  In the discharge ionization current detector according to the present invention, a gas flow path is provided between the plasma generation region and the ion current detection region in order to introduce the excitation light emitted from the vicinity of the plasma generation region into the ion current detection region without waste. It is good to set it as the structure which is linear.

  In addition, the appropriate branching ratio of the plasma generating gas through the branch exhaust channel depends on the direction of sample gas introduction into the gas channel and the flow rate of the sample gas. Half of the flow rate of the plasma generating gas passing therethrough may be discharged through the branch exhaust passage. As described above, although the excited species of the plasma generating gas hardly contributes to ionization of the sample components, the flow rate of the sample gas is generally much smaller than the flow rate of the plasma generating gas. If the ratio is increased too much, the flow rate of the plasma generating gas passing through the ion current detection region becomes too small, which hinders the smooth flow of the sample gas. In consideration of such a situation, it is preferable to determine the branching ratio so that at least about 1/10 of the plasma generating gas that has passed through the plasma generating region flows to the ion current detecting region.

  According to the discharge ionization current detector according to the present invention, noise caused by impurities can be reduced without impairing the conventional good ionization efficiency. Thereby, the SN ratio of the ion current derived from the sample component that is the detection target can be improved, and the dynamic range can be expanded.

  A discharge ionization current detector according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a discharge ionization current detector according to the present embodiment.

  The discharge ionization current detector includes a plasma generation unit 1 and an ion current detection unit 2 along a cylindrical tube 3 in which an upper portion of the discharge ionization current detector is a gas flow path 4. Here, the cylindrical tube 3 is made of quartz, but may be made of another dielectric material such as ceramic, glass, polymer, or the like. The upper end opening of the cylindrical tube 3 serves as a gas supply port 5 for introducing a plasma generating gas into the gas flow path 4. Here, helium (He) is used as the plasma generating gas. However, any gas that can be easily ionized may be used, such as argon, nitrogen, neon, xenon, or a mixture of two or more thereof. But you can.

  The plasma generation unit 1 includes metal plasma generation electrodes 7, 6, 8 and an excitation high-voltage power supply 9 that are disposed on the outer wall surface of the cylindrical tube 3 at a predetermined distance from each other. The plasma generating electrodes 6 to 8 can be easily provided by winding a conductive tape such as a copper foil around the cylindrical tube 3.

  Since the wall surface of the cylindrical tube 3 that is a dielectric is interposed between the plasma generation electrodes 6 to 8 and the gas flow path 4, this wall surface covers the surfaces of the plasma generation electrodes 6 to 8. Become a layer. That is, the metal plasma generation electrodes 6 to 8 and the dielectric coating layers covering the respective surfaces function as discharge electrodes for plasma generation. The plasma generating electrodes 7 and 8 on both the upper and lower sides along the flow of helium are grounded, and the excitation high voltage power source 9 is connected to the central plasma generating electrode 6. The excitation high-voltage power supply 9 generates a low-frequency high-voltage AC voltage, and its frequency is in the range of 1 [kHz] to 100 [kHz], more preferably in the range of 5 [kHz] to 50 [kHz]. The voltage amplitude is preferably in the range of about 1 [kVp-p] to 10 [kVp-p]. The waveform of the AC voltage may be any of a sine wave, a rectangular wave, a triangular wave, a sawtooth shape, and the like.

  The ion current detection unit 2 includes ion current detection electrodes 13 and 14 exposed in the cylindrical tube 3 and a detection circuit unit 20 provided outside the cylindrical tube 3. The ion current detection electrodes 13 and 14 are coaxial double tubes made of platinum or the like, and the outer tube is an ion current detection electrode 13 for applying a bias DC voltage, and the inner tube is an ion current detection for collecting a charge. Electrode 14 is formed. The inner tube is inserted into an insulating tube 15 made of aluminum oxide or the like, thereby ensuring electrical insulation between the electrodes 13 and 14. The inner ion current detection electrode 14 is connected to a charge collecting current amplifier 22 included in the detection circuit unit 20, and the other ion current detection electrode 13 is connected to a bias DC power source 21.

  A sample gas passage 16 is provided inside the ion current detection electrode 14 which is an inner tube, and the sample gas introduced from the sample gas supply port 17 at the lower end of the sample gas passage 16 is shown in FIG. Proceed as indicated by the up arrow. The helium supplied to the gas supply port 5 at the upper end of the cylindrical tube 3 flows downward in the gas flow path 4 and merges with the sample gas rising in the sample gas flow path 16 to form an ion that is an outer cylindrical pipe. The gas travels downward in the merged flow path 18 formed in the gap between the current detection electrode 13 and the insulating tube 15 and is discharged from the gas discharge port 19 at the lower end thereof.

  As a characteristic configuration of the discharge ionization current detector of the present embodiment, a branch exhaust pipe 10 is connected between the plasma generation unit 1 and the ion current detection unit 2 in the cylindrical tube 3. The helium flowing downward in the gas flow path 4 flows downward in the vicinity of the branch connection portion 12, that is, branches to the side of the ion current detection electrodes 13 and 14 and laterally, that is, to the branch exhaust pipe 10. When helium is supplied to the gas supply port 5 at a flow rate Qt, the ratio between the flow rate Qd of helium flowing on the ion current detection electrodes 13 and 14 side and the flow rate Qp of helium flowing on the branch exhaust pipe 10 side is It is determined by the ratio of the respective channel resistances after 12. Here, since the channel size and the like are designed so that both channel resistances are substantially equal, it can be considered that Qd = Qp = Qt / 2.

Next, the sample component detection operation in the discharge ionization current detector of the present embodiment will be described.
As described above, helium as a plasma generating gas is supplied to the gas supply port 5 at a predetermined flow rate, and the sample gas containing the sample component to be analyzed is supplied to the sample gas supply port 17 at a predetermined flow rate. For example, when this detector is used as a detector of a gas chromatograph, a sample gas separated by a column may be introduced into the sample gas supply port 17. As will be apparent from an actual measurement example to be described later, the sample gas flow rate is usually much smaller than the supply flow rate of the plasma generating gas.

  Helium flows downward in the gas flow path 4, branches near the branch connection portion 12, and a part (about half in this example) is discharged to the outside through the branch exhaust path 10, and the remaining helium further proceeds downward. . Since the flow rate of the sample gas flowing upward is small, the sample gas merges with helium in the vicinity of the upper edge of the sample gas channel 16, spreads outward, flows downward in the merge channel 18, and finally exhausts the gas. It is discharged from the outlet 19.

  As described above, the excitation high-voltage power supply 9 is driven by a control signal from a control circuit (not shown) in a state where helium flows in the gas flow path 4, and the excitation high-voltage power supply 9 generates a low-frequency high-voltage AC voltage as plasma. It is applied between the generation electrode 6 and the plasma generation electrodes 7 and 8. As a result, a dielectric barrier discharge is generated between the plasma generating electrode 6 and the plasma generating electrodes 7 and 8 through the dielectric coating layer (a part of the wall surface of the cylindrical tube 3). Due to this dielectric barrier discharge, helium flowing through the gas flow path 4 is ionized to generate plasma. This plasma is an atmospheric pressure nonequilibrium microplasma.

  In this discharge ionization current detector, the structure in which the plasma generating electrode 6 to which a high voltage is applied is sandwiched between two grounded plasma generating electrodes 7 and 8 is generated in the vicinity of the plasma generating electrode 6. This is to suppress the plasma from spreading to the upstream side and the downstream side as much as possible, and to limit the plasma generation region between the two plasma generation electrodes 7 and 8 (for example, Kitano et al., “Low-frequency atmospheric pressure microplasma jet "Applied Physics Vol.77, No.4, 2008, pp.383-389 etc.)

  Since the plasma generating electrodes 6 to 8, which are metals, are not exposed in the gas flow path 4, there is no emission of secondary electrons from the metals. Further, in the atmospheric pressure non-equilibrium plasma, since the supply of electric power by the applied voltage is once interrupted before the rapid heating of the plasma proceeds, the plasma does not easily reach a high temperature. Moreover, since the power is supplied at a low frequency here, the plasma temperature is kept low. Therefore, the temperature rise of the pipe inner wall face facing the gas flow path 4 is suppressed, and the release of impurities from the pipe inner wall face is suppressed. Therefore, stable plasma can be formed in the plasma generation region described above.

  Excitation light and helium excited species are generated by the plasma generated as described above. A part of the helium-excited species is discharged from the gas outlet 11 through the branch exhaust pipe 10 along with the flow of helium. At this time, a small amount of impurities originally mixed in helium and a small amount of impurities released from the inner wall surface of the cylindrical tube 3 are also divided and discharged out of the tube at almost the same ratio as the gas division ratio. become. Thereby, the amount of impurities reaching the ion current detection region between the ion current detection electrodes 13 and 14 can be reduced.

  On the other hand, since the excitation light generated from the plasma travels straight without being affected by the helium branch, almost all reaches the ion current detection region. Then, sample component molecules (or atoms) in the sample gas are ionized. The sample ions generated in this way give and receive electrons at the ion current detection electrode 14 by the action of the bias DC voltage applied to the ion current detection electrode 13. As a result, the amount of sample ions generated, that is, an ion current corresponding to the amount of sample components is input to the current amplifier 22, and the current amplifier 22 amplifies this and outputs it as a detection signal. In this way, the discharge ionization current detector outputs a detection signal corresponding to the amount (concentration) of the sample component contained in the introduced sample gas.

  Sample component molecules are ionized by the action of excitation light from plasma or helium-excited species, but ionization by excitation light is dominant in low-frequency excitation dielectric barrier discharge. Therefore, even if some helium excited species are discharged through the branch exhaust passage 10, there is almost no effect on the ionization of the sample component molecules. On the other hand, about half of the helium is discharged through the branch exhaust passage 10, so that the trace amount of impurities originally mixed in helium or released from the inner wall of the cylindrical tube 3 is reduced to about half as described above. The ion current detection region is reached. Such impurities are easily excited directly by the plasma, and noise is generated when the impurities reach the ion current detection electrodes 13 and 14, but noise can be reduced by reducing these impurities.

  In addition, a decrease in the flow rate of helium flowing through the merging flow path 18 increases the concentration of the sample component in the merged gas, which leads to an increase in the ionization current derived from the sample component. Thereby, the SN ratio of the detection signal can be improved. Further, in order to obtain the same effect, the flow rate of helium supplied to the gas supply port 5 may be reduced. However, in this case, although the amount of impurities originally mixed in helium is reduced, the inner wall of the cylindrical tube 3 is reduced. The degree of dilution of impurities released from, for example, decreases, and the influence of impurities becomes relatively large. On the other hand, in the discharge ionization current detector of the present embodiment, for example, the flow rate of helium flowing in the plasma generation region can be made the same as the conventional one while reducing the helium flowing in the ionization current detection region in half. For this reason, it is not necessary to reduce the dilution of impurities in the vicinity of the plasma generation region, which is advantageous for stabilization of plasma formation.

Next, an actual measurement example using the discharge ionization current detector of the above embodiment will be described. The dimensions of each part of the detector used in the experiment are as follows. The outer diameter of the cylindrical tube 3 is 3.9 [mm] and the inner diameter is 2.5 [mm]. The diameter is 0.7 [mm], the outer diameter of the outer tube serving as the ion current detection electrode 13 is 2.0 [mm], and the outer diameter of the insulating tube 15 is 1.2 [mm]. Plasma generation conditions and measurement conditions were as follows.
・ Plasma excitation frequency: 11 [kHz]
・ Plasma excitation voltage: 5.4 [kVp-p]
・ Ion current detection bias voltage: 100 [V]
・ Sample gas: Methane ・ Sample gas flow rate: 1 [ml / min]
In the experiment, the ionization current when the helium gas supply flow rate was changed while the sample gas was kept constant was measured, and the ionization efficiency was calculated from the obtained ionization current. Also, the ionization current fluctuation was measured when the sample gas concentration was zero (100% helium), and the relationship with the helium flow rate was examined. As described above, the flow path resistance of the branch exhaust passage 10 from the branch connection point 12 to the gas discharge port 11 and the flow path resistance of the gas flow path 4 and the merge flow path 18 from the branch connection point 12 to the gas discharge port 19 Therefore, when the gas discharge port 11 is opened, the relationship is Qd = Qp = Qt / 2, and when the gas discharge port 11 is closed, Qd = Qt (Qp = 0). .

  FIG. 2 is a graph in which the ionization efficiency when the gas discharge port 11 is opened and when the gas discharge port 11 is closed is plotted with respect to the gas flow rate Qd flowing in the ion current detection region (discharged from the gas discharge port 19). FIG. 3 is a graph in which the ionization current noise is plotted against the gas flow rate Qd flowing in the ion current detection region. As apparent from the graph of ionization efficiency in FIG. 2, when the gas outlet 11 is opened and closed, there is no significant difference in ionization efficiency for the same gas flow rate Qd (within the error range). is there). From the measurement conditions described above, the gas flow rate Qt flowing through the plasma generation region is twice that when the gas discharge port 11 is closed.

  On the other hand, looking at the ionization current noise in FIG. 3, it can be seen that the noise increases remarkably when the gas outlet 11 is closed, particularly when the gas flow rate Qd is small. In other words, it can be seen that about half of the helium is discharged through the branch exhaust passage 10, so that an increase in noise can be avoided even when the gas flow rate Qd is small. This is because it is possible to reduce noise caused by impurities contained in the ionization current detection region by removing part of the helium that has passed through the plasma generation region and reducing the amount of gas flowing to the ionization current detection region. it can. From the experiment, it is possible to reduce noise while maintaining the ionization efficiency by removing a part of helium after passing through the plasma generation region and reaching the ion current detection region. It could be confirmed.

  In the above embodiment, about half of the flow rate of helium that has passed through the plasma generation region is discharged through the branch exhaust passage 10 and the remaining half of the flow rate is allowed to flow to the ion current detection region. The branching ratio of the working gas is not limited to this. From the viewpoint of reducing the amount of impurities reaching the ion current detection region, it can be said that it is preferable to discharge a larger amount of helium through the branch exhaust passage 10, but in this case, the flow rate of helium flowing through the ionization current detection region is reduced. , It becomes difficult for the sample gas to smoothly flow into the merge channel 18. In particular, in the case of the structure shown in FIG. 1, since the flow of the sample gas and the flow of helium are opposed to each other at the upper end of the sample gas flow path 14, if the flow rate of helium is too small, a turbulent flow of the sample gas may occur. It becomes easy to stay. As a result, a phenomenon that the ionization current detection signal becomes unstable may occur. From the experiment, it is considered that about 1 to 1/10 of the helium that has passed through the plasma generation region needs to flow to the ion current detection region. However, this is assumed to change depending on the direction of introduction of the sample gas.

  Each of the above-described embodiments is an example of the present invention, and it will be understood that the present invention is encompassed by the scope of the claims of the present application even if appropriate changes, modifications, and additions are made within the scope of the present invention.

The block diagram of the discharge ionization current detector by one Embodiment of this invention. The graph which plotted the ionization efficiency at the time of opening and closing a gas exhaust port with respect to the gas flow rate Qd which flows into an ion current detection area | region. The graph which plotted the ionization current noise at the time of opening and closing a gas exhaust port with respect to the gas flow rate Qd which flows into an ion current detection area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plasma generation part 2 ... Ion current detection part 3 ... Cylindrical tube 4 ... Gas flow path 5 ... Gas supply port 6, 7, 8 ... Electrode 9 for plasma generation ... High voltage power supply 10 for excitation ... Branch exhaust path 11 ... Gas exhaust Outlet 12 ... Branch connection part 13, 14 ... Ion current detection electrode 15 ... Insulating tube 16 ... Sample gas flow path 17 ... Sample gas supply port 18 ... Merge flow path 19 ... Discharge port 20 ... Detection circuit part 21 ... Bias DC power supply 22 ... Current amplifier

Claims (3)

A discharge ionization current detector for ionizing and detecting a sample component in a sample gas using plasma generated by discharge,
a) A dielectric barrier discharge is generated by an AC electric field having a frequency range of 1 [kHz] to 100 [kHz] in the gas flow path through which the plasma generating gas flows, and plasma is generated from the plasma generating gas by the discharge. Plasma generating means for generating;
b) a sample gas introduction flow path for introducing a sample gas into the gas flow path on the downstream side of the plasma generation region by the plasma generation means;
c) current detection means for detecting an ionic current due to a sample component in the sample gas in the gas flow path downstream of the plasma generation region by the plasma generation means and ionized by the action of the plasma;
d) a branch exhaust flow path for branching and discharging a part of the plasma generation gas flowing in the gas flow path between the plasma generation area by the plasma generation means and the ion current detection area by the current detection means; ,
A discharge ionization current detector. The discharge ionization current detector according to claim 1,
The discharge ionization current detector, wherein the gas flow path is linear between the plasma generation region and the ion current detection region. The discharge ionization current detector according to claim 1 or 2,
A discharge ionization current detector characterized in that half of the flow rate of the plasma generation gas passing through the plasma generation region is discharged through the branch exhaust passage.

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