Discharge ionization detector and gas chromatograph analyzer

Abstract

To provide a technique for reducing changes in sensitivity accompanying changes in concentration of a sample component in a discharge ionization detector and a gas chromatograph analyzer that uses the discharge ionization detector.SOLUTION: A preparative liquid chromatograph includes a discharge ionization detector 10. In the discharge ionization detector 10, sample gas is supplied to a charge collection part 120 through an aperture 126X. Between a dielectric tube 111 and the aperture 126X, a shield plate 190 is placed to shield at least part of the aperture 126X against the dielectric tube 111.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a discharge ionization detector and a gas chromatograph analyzer.

Background Art

[0002] As a trace gas detector for a gas chromatograph (GC), a discharge ionization detector (BID: dielectric Barrier discharge Ionization Detector) is used. In the discharge ionization detector (BID), dielectric barrier discharge in which the electrode surface is covered with a dielectric is used (see, for example, Patent Document 1). In the discharge ionization detector, sample components in the sample gas are ionized by excitation light, the ionized sample components are collected by an electrode for sample detection by an electric field generated by the electrode, and the amount of the sample components is detected based on the current value flowing between the electrodes.

Prior Art Documents

Patent Documents

[0003]

Patent Document

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a discharge ionization detector, a technique for making the sensitivity (detection value / concentration of sample components) constant regardless of changes in the concentration of sample components is required.

[0005] An object of the present invention is to provide a technique for obtaining stable sensitivity in a discharge ionization detector and a gas chromatograph analyzer using the discharge ionization detector.

Means for Solving the Problems

[0006] A discharge ionization detector according to a certain aspect of the present disclosure comprises a dielectric tube that constitutes at least a portion of a gas flow path through which a discharge gas flows and extends in the direction of the tube axis, a high-voltage electrode provided on the outer wall of the dielectric tube, a ground electrode unit provided on the outer wall of the dielectric tube and electrically grounded, a voltage application unit connected to the high-voltage electrode and applying an alternating voltage between the high-voltage electrode and the ground electrode unit in order to generate a discharge in the dielectric tube and generate plasma from the discharge gas, and a charge collection unit including a collection electrode that collects ions generated from sample components in a sample gas by light emitted from the plasma, wherein the charge collection unit includes an opening for introducing the sample gas into the gas flow path and further comprises a shielding unit located between the dielectric tube and the opening, which shields at least a portion of the opening from the dielectric tube.

[0007] A gas chromatograph analyzer according to a certain aspect of the present disclosure comprises a discharge ionization detector and an analytical column for separating sample components in the sample gas into components, and introduces the sample components separated by the analytical column into the gas flow path of the discharge ionization detector. [Effects of the Invention]

[0008] In accordance with certain aspects of this disclosure, in a discharge ionization detector and a gas chromatograph analyzer utilizing a discharge ionization detector, the change in sensitivity due to changes in the concentration of sample components is reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the configuration of a gas chromatograph analyzer according to this embodiment. [Figure 2] This figure shows an example of how the sensitivity of a typical discharge ionization detector changes in response to changes in the concentration of a sample component. [Figure 3] This figure shows an example of the structure of the shielding plate 190. [Figure 4] This is a diagram showing a first modified example of the shielding plate 190. [Figure 5] This diagram shows a second modified example of the shielding plate 190. [Figure 6] This figure shows a first comparative example of the shielding plate 190. [Figure 7] This figure shows a second comparative example of the shielding plate 190. [Figure 8] This figure illustrates an example of the change in sensitivity in the discharge ionization detector 10. [Figure 9] This figure illustrates another example of the change in sensitivity in the discharge ionization detector 10. [Figure 10] This figure illustrates yet another example of the change in sensitivity in the discharge ionization detector 10. [Figure 11] This figure shows another example of the configuration of a gas chromatograph analyzer. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0011] [1. Configuration of a gas chromatograph analyzer] Figure 1 shows an example of the configuration of a gas chromatograph analyzer according to this embodiment. As shown in Figure 1, the gas chromatograph analyzer includes a discharge ionization detector 10, a sample introduction unit 34, and an analysis column 36.

[0012] The gas chromatograph analyzer transports the sample to the sample introduction section 34 using a carrier gas, and then transports the sample to the analysis column 36. The analysis column 36 separates the sample components in the sample gas into their respective components. The gas chromatograph analyzer then introduces the sample components separated in the analysis column 36 into the gas flow path of the discharge ionization detector 10.

[0013] The discharge ionization detector 10 is a detector for detecting sample components. The discharge ionization detector 10 includes a dielectric tube 111, a high-voltage electrode 112, a ground electrode 113, a ground electrode 114, a voltage application unit 115, a control unit 22, and a light source 23. In one implementation example, the dielectric tube 111 has a cylindrical shape. The voltage application unit 115 functions as a power source for high-voltage alternating current for excitation. The ground electrode 113 and the ground electrode 114 are arranged to be spaced apart from each other in the tube axis direction of the dielectric tube and constitute a ground electrode unit.

[0014] The dielectric tube 111 forms a gas flow path through which a discharge gas (also referred to as a "plasma generation gas") flows and extends in the tube axis direction. For the plasma generation gas, for example, any one of helium (He), argon (Ar), nitrogen (N2), neon (Ne), xenon (Xe), or a mixed gas thereof may be used. Hereinafter, for the sake of convenience of explanation, the upstream side in the gas flow direction (the direction indicated by the downward arrow in FIG. 1) in the dielectric tube 111 is defined as "up" and the downstream side as "down" in the vertical direction. However, these definitions are for convenience only and do not limit the direction during the use of the BID.

[0015] On the outer wall surface of the dielectric tube 111, annular electrodes (high-voltage electrode 112, ground electrode 113, and ground electrode 114) made of a conductor such as SUS or copper are provided along the above-described gas flow direction. The high-voltage electrode 112, the ground electrode 113, and the ground electrode 114 may be collectively referred to as "electrodes for plasma generation" in some cases.

[0016] <� The high-voltage electrode 112 is connected to the voltage application unit 115 and provided on the outer wall of the dielectric tube 111. The ground electrode 113 and the ground electrode 114 are electrically grounded and provided on the outer wall of the dielectric tube 111. The high-voltage electrode 112 is provided between the ground electrode 113 and the ground electrode 114.

[0017] The voltage application unit 115 applies an alternating voltage between the high-voltage electrode 112 and the ground electrodes 113 and 114. As a result, discharge occurs within the dielectric tube 111, generating plasma from the plasma generation gas. The voltage application unit 115 generates a high-voltage alternating voltage with a frequency in the range of 1 kHz to 100 kHz, more preferably around 5 kHz to 30 kHz (low frequency) and a voltage of about 5 kV to 10 kV. Note that the waveform shape of the alternating voltage may be any of a sine wave, rectangular wave, triangular wave, sawtooth wave, etc.

[0018] In this specification, the region above the lower end of the ground electrode 114 in FIG. 1 is referred to as the discharge part 110, and the region below the lower end of the ground electrode 114 is referred to as the charge collection part 120. The discharge gas may reach both the inside of the discharge part 110 and the charge collection part 120. In this sense, the inside of both the discharge part 110 and the charge collection part 120 is referred to as the gas flow path.

[0019] A gas supply pipe 116a is connected to the pipe tip member 116 provided at the upper end of the dielectric tube 111, and the plasma generation gas is supplied into the dielectric tube 111 through this gas supply pipe 116a. The plasma generation gas also serves as a dilution gas. There is a wall surface of the dielectric tube 111 between the plasma generation electrodes (high-voltage electrode 112, ground electrode 113, and ground electrode 114) and the plasma generation gas. Therefore, the wall surface inside the dielectric tube 111 itself functions as a dielectric coating layer covering the surface of the plasma generation electrodes, enabling dielectric barrier discharge.

[0020] Downstream of the dielectric tube 111, a shielding plate 190, a connection member 121, a bias electrode 122, and a collection electrode 123 are arranged along the gas flow direction.

[0021] The shielding plate 190 is arranged to prevent the light emitted by the plasma in the dielectric tube 111 from reaching near the opening 126X. The structure of the shielding plate 190 will be described later with reference to FIG. 3 and the like.

[0022] An insulator 125a is interposed between the connecting member 121 and the bias electrode 122. An insulator 125b is interposed between the bias electrode 122 and the collecting electrode 123. The insulators 125a and 125b are made of, for example, alumina or PTFE (polytetrafluoroethylene) resin. The connecting member 121, the bias electrode 122, the collecting electrode 123, and the insulators 125a and 125b are cylindrical bodies having the same inner diameter as the dielectric tube 111.

[0023] A bottomed cylindrical pipe end member 124 is positioned downstream of the collection electrode 123. An insulator 125c is interposed between the collection electrode 123 and the pipe end member 124. The internal space formed by the connecting member 121, bias electrode 122, collection electrode 123, pipe end member 124, and insulators 125a, 125b, and 125c is in communication with the internal space of the dielectric tube 111.

[0024] A bypass exhaust pipe 121a is connected to the circumferential surface of the connecting member 121, and a sample exhaust pipe 124a is connected to the circumferential surface of the pipeline end member 124. A portion of the plasma generation gas is discharged to the outside from the bypass exhaust pipe 121a. The sample is discharged to the outside from the sample exhaust pipe 124a.

[0025] A sample introduction tube 126 is inserted through the lower surface of the pipe end member 124. The sample introduction tube 126 supplies the sample gas into the charge collection unit 120 through the opening 126X at its tip. The charge collection unit 120 is heated to a maximum of approximately 450°C by an external heater (not shown) to maintain the vaporized state of the sample gas.

[0026] The connecting member 121 is grounded and acts as a bounce electrode to prevent charged particles in the plasma, which are traveling on the gas flow, from reaching the collection electrode 123. The bias electrode 122 is connected to the bias DC power supply 127. The collection electrode 123 is connected to the current amplifier 128.

[0027] [2. Detection operation of sample components in the discharge ionization detector] The detection operation of sample components contained in the sample gas in the discharge ionization detector 10 will be described in general terms.

[0028] As indicated by the rightward arrow in the upper part of Figure 1, a plasma generation gas, which also serves as a diluent gas, is supplied to the dielectric tube 111 through the gas supply pipe 116a.

[0029] The plasma generation gas flows downward through the dielectric tube 111, a portion of which is discharged to the outside through the bypass exhaust pipe 121a, and the remainder flows downward through the charge collection unit 120 as a diluent gas and is discharged to the outside through the sample exhaust pipe 124a.

[0030] Meanwhile, the sample gas containing the sample components is supplied to the charge collection unit 120 through the opening 126X of the sample introduction tube 126. The sample gas is discharged from the opening 126X in the opposite direction to the flow direction of the diluent gas, but as shown by the arrow in Figure 1, the sample gas is immediately pushed back and merges with the diluent gas and moves downward.

[0031] While the plasma-generating gas flows through the dielectric tube 111, the voltage application unit 115 applies a high-voltage AC voltage between the high-voltage electrode 112 and the ground electrode 113, and between the high-voltage electrode 112 and the ground electrode 114. This causes dielectric barrier discharge to occur in the dielectric tube 111, ionizing the plasma-generating gas and generating plasma (atmospheric pressure non-equilibrium plasma).

[0032] The collection electrode 123 collects ions generated from the sample components by light emitted from the plasma. Specifically, excitation light emitted from the atmospheric pressure non-equilibrium plasma passes through the discharge section 110 and the charge collection section 120 to reach the area where the sample gas is present, and ionizes the sample components in the sample gas. The ions thus generated move towards the collection electrode 123 due to the electric field formed by the DC voltage applied to the bias electrode 122, and exchange electrons with the collection electrode 123.

[0033] As a result, an ion current corresponding to the amount of ions (amount of sample component) generated by the excitation light is input to the current amplifier 128. The current amplifier 128 amplifies this ion current and outputs a detection signal.

[0034] In this way, the discharge ionization detector 10 outputs a detection signal corresponding to the amount (concentration) of the sample components contained in the sample gas introduced through the aperture 126X.

[0035] [3. Changes in sensitivity due to changes in the concentration of sample components] Figure 2 shows an example of how the sensitivity of a typical discharge ionization detector changes in response to changes in the concentration of a sample component. In the graph in Figure 2, the horizontal axis represents the concentration of the sample component, and the vertical axis represents the sensitivity. Sensitivity is an index calculated by dividing the amount of the sample component detected based on the detection signal output from the current amplifier 128 by the concentration of the sample component.

[0036] Figure 2 shows the change in sensitivity in a typical discharge ionization detector, indicated by line L1. Line L2 represents the ideal change in sensitivity.

[0037] Line L2 indicates that the sensitivity remains constant regardless of the concentration of the sample component. On the other hand, line L1 indicates that the sensitivity decreases as the concentration of the sample component increases. One possible reason for this decrease in sensitivity is the so-called Lambertian rule.

[0038] More specifically, the absorption of excitation light by sample components follows Lambert's law. Therefore, in regions with high concentrations of sample components, the ratio of excitation light absorption to the amount of sample component is expected to decrease. Consequently, when the concentration of sample components is high, especially in regions where the concentration of sample components is high, i.e., near aperture 126X, the ratio of excitation light absorption to the amount of sample component decreases, which is expected to reduce sensitivity.

[0039] To address these challenges, the discharge ionization detector 10 of this embodiment includes a shielding plate 190. The shielding plate 190 prevents excitation light from the plasma from irradiating the aperture 126X, regardless of changes in the concentration of the sample components. As a result, the discharge ionization detector 10 can reduce the change in sensitivity due to changes in the concentration of the sample components.

[0040] [4. Structure of the shielding plate] Figure 3 shows an example of the structure of the shielding plate 190. Note that Figure 1 shows a longitudinal section of the shielding plate 190, while Figure 3 corresponds to a plan view of the shielding plate 190.

[0041] The shielding plate 190 has a disc shape and has windows 190A and 190B. A shielding section 190C is located between windows 190A and 190B. Each of the windows 190A and 190B is approximately rectangular in shape. The length of the long side is indicated by D1, and the length of the short side is indicated by D2. The width of the shielding section 190C is represented by D3. In one implementation example, the shielding plate 190 is made of an aluminum plate. In windows 190A and 190B, the length of the long side D1 is approximately 2.4 mm, the length of the short side D2 is approximately 1.0 mm, and the width D3 of the shielding section 190C is approximately 0.4 mm.

[0042] In Figure 3, the dashed circle 190X represents the position of the opening 126X in the state shown in Figure 1. The shielding portion 190C covers the entire surface of circle 190X. More specifically, at the connection point between the discharge portion 110 and the charge collection portion 120, when viewing the charge collection portion 120 from the discharge portion 110 side, the shielding portion 190C has a shape that covers the entire surface of the opening 126X. An example of the diameter of the opening 126X is approximately 0.3 mm.

[0043] The shielding plate 190 shields the excitation light from the plasma generated in the discharge section 110. However, the excitation light passes through windows 190A and 190B. That is, the shielding plate 190 supplies the excitation light from the plasma generated in the discharge section 110 to the charge collection section 120 via windows 190A and 190B, while the shielding section 190C suppresses the supply of the plasma excitation light to the aperture 126X. This suppresses changes in sensitivity due to changes in the concentration of sample components caused by the irradiation of the aperture 126X with excitation light from the plasma.

[0044] [5. Variations of the shielding plate] Figure 4 shows a first modified example of the shielding plate 190. In the modified example 191 of Figure 4, a string-like member 181 is wrapped around the shielding portion 190C of the shielding plate 190 of Figure 3 in order to increase the width of the shielding portion 190C. As a result, the modified example 191 suppresses the irradiation of excitation light from the plasma not only to the opening 126X but also to the outer edge of the opening 126X.

[0045] Figure 5 shows a second modified example of the shielding plate 190. In the modified example 191 of Figure 5, a string-like member 182 is wrapped around the shielding portion 190C of the shielding plate 190 of Figure 3 in order to further increase the width of the shielding portion 190C. Member 182 is thicker than member 181 in Figure 4. As a result, modified example 192 suppresses the irradiation of excitation light from the plasma not only to the aperture 126X but also to the outer edge of the aperture 126X. The range over which modified example 192 suppresses the irradiation of excitation light is wider than the range over which modified example 191 suppresses the irradiation of excitation light. That is, modified example 192 can suppress the irradiation of excitation light to a range further away from the aperture 126X than modified example 191.

[0046] [6. Examples of Shielding Plates] Figure 6 shows a first comparative example of the shielding plate 190. Comparative example 210 in Figure 6 is a disc having the same outer shape as the shielding plate 190 in Figure 3, and has a window 211 in the center. The shape of the window 211 is a circle with a diameter R1 (approximately 0.5 mm). The diameter R1 of the window 211 is larger than the diameter of the opening 126X.

[0047] Figure 6, similar to Figure 3, shows a circle 190X representing the position of aperture 126X in the state shown in Figure 1. In comparative example 210, excitation light from the plasma is supplied to aperture 126X through window 211.

[0048] Figure 7 shows a second comparative example of the shielding plate 190. Comparative example 220 in Figure 7 is a disc having the same outer shape as the shielding plate 190 in Figure 3, and has a window 221 in the center. The shape of the window 221 is a circle with a diameter R2 (approximately 1.0 mm). The diameter R2 of the window 221 is larger than the diameter R1 in Figure 6, and therefore larger than the diameter of the opening 126X.

[0049] Figure 7, like Figure 3, shows a circle 190X representing the position of aperture 126X in the state shown in Figure 1. In comparative example 220, excitation light from the plasma is supplied to aperture 126X through window 221.

[0050] [7. Sensitivity of the discharge ionization detector 10] <Presence or absence of shielding plates> Figure 8 illustrates an example of the change in sensitivity in the discharge ionization detector 10. The graph in Figure 8 shows the change in sensitivity in response to a change in the amount of sample component (sample gas) introduced into the charge collection unit 120 through the aperture 126X. The horizontal axis represents the amount of sample component (sample gas) introduced, and the vertical axis represents the sensitivity. Sensitivity is calculated by dividing the amount of the sample component detected based on the detection signal output from the current amplifier 128 by the amount of sample component (sample gas) introduced. Since the charge collection unit 120 is constant, the concentration of the sample component in the charge collection unit 120 follows the amount of sample component introduced through the aperture 126X. Therefore, the above amount of introduction corresponds to the concentration of the sample component.

[0051] Figure 8 shows the results for the following four types of examples. (1) No shielding plate (2) Example (Figure 3) (3) Modified example (Figure 4) (4) Modified example (Figure 5) "Without shielding plate" represents an example in which the shielding plate 190 is removed from the discharge ionization detector 10. "Example (Figure 3)" represents an example in which the shielding plate 190 is installed in the discharge ionization detector 10, as shown in Figure 1. "Modified example (Figure 4)" represents an example in which modified example 191 (Figure 4) is installed in place of the shielding plate 190 in the discharge ionization detector 10. "Modified example (Figure 5)" represents an example in which modified example 192 (Figure 5) is installed in place of the shielding plate 190 in the discharge ionization detector 10.

[0052] As shown in Figure 8, in the "no shielding plate" configuration, the sensitivity decreases significantly with increasing input dose. More specifically, the sensitivity at an input dose of approximately 0.33 ng is approximately 1350 mVsec / ng, while the sensitivity at an input dose of approximately 330 ng is approximately 350 mVsec / ng.

[0053] On the other hand, in the "Example (Figure 3)," the degree of decrease in sensitivity with increasing introduction amount is lower than in the "without shielding plate" case. More specifically, the sensitivity at an introduction amount of about 0.33 ng is about 500 mVsec / ng, while the sensitivity at an introduction amount of about 330 ng is about 300 mVsec / ng. This suggests that the change in sensitivity is reduced because the irradiation of excitation light to aperture 126X is suppressed.

[0054] Furthermore, the degree of reduction described above is lower in the "modified example (Figure 4)" than in the "example (Figure 3)". More specifically, the sensitivity at an introduced dose of about 0.33 ng is about 250 mVsec / ng, while the sensitivity at an introduced dose of about 330 ng is about 200 mVsec / ng. This suggests that if the irradiation of excitation light is suppressed not only to aperture 126X but also to the outer edge of aperture 126X, the change in sensitivity will be further reduced.

[0055] Furthermore, the degree of reduction described above is even lower in the "modified version (Figure 5)" than in the "modified version (Figure 4)". More specifically, the sensitivity at an introduced dose of approximately 0.33 ng and the sensitivity at an introduced dose of approximately 330 ng are both approximately 60 mVsec / ng. This suggests that if the suppression of excitation light irradiation extends to a wider area of ​​the outer edge of the 126X aperture, the change in sensitivity will be further reduced.

[0056] <Presence or absence of shielding of openings (1)> Figure 9 illustrates another example of the change in sensitivity in the discharge ionization detector 10. The graph in Figure 9, similar to the graph in Figure 8, shows the change in sensitivity to changes in the amount of sample component (sample gas) introduced into the charge collection unit 120 through the aperture 126X.

[0057] Figure 9 shows the results for the following three types of examples. (1) Modified example (Figure 5) (2) Comparative example (Figure 6) (3) Comparative example (Figure 7) "Modified Example (Figure 5)" shows an example in which modified example 192 (Figure 5) is installed in place of the shielding plate 190 in the discharge ionization detector 10. "Comparative Example (Figure 6)" shows an example in which comparative example 210 (Figure 6) is installed in place of the shielding plate 190 in the discharge ionization detector 10. "Comparative Example (Figure 7)" shows an example in which comparative example 220 (Figure 7) is installed in place of the shielding plate 190 in the discharge ionization detector 10.

[0058] As shown in Figure 9, in the "modified version (Figure 5)," the change in sensitivity with increasing dose is small. More specifically, the sensitivity at a dose of approximately 0.33 ng and at a dose of approximately 250 ng are both approximately 60 mVsec / ng.

[0059] On the other hand, in the "Comparative Example (Figure 6)," the change in sensitivity with increasing introduction volume is greater than in the "Modified Example (Figure 5)." More specifically, the sensitivity at an introduction volume of approximately 0.33 ng is approximately 55 mVsec / ng, while the sensitivity at an introduction volume of approximately 250 ng is approximately 35 mVsec / ng. In other words, it changes by about 20 mVsec / ng.

[0060] Furthermore, in the "Comparative Example (Figure 7)," the change in sensitivity with increasing introduction volume is even greater than in the "Comparative Example (Figure 6)." More specifically, the sensitivity at an introduction volume of approximately 0.33 ng is approximately 120 mVsec / ng, while the sensitivity at an introduction volume of approximately 250 ng is approximately 60 mVsec / ng. In other words, it changes by approximately 60 mVsec / ng.

[0061] In the "modified example (Figure 5)," the aperture 126X is shielded, whereas in the "comparative example (Figure 6)" and "comparative example (Figure 7)," the aperture 126X is not shielded. Therefore, from the results shown in Figure 9, it can be said that shielding the aperture 126X suppresses the change in sensitivity associated with changes in the amount of introduced.

[0062] Furthermore, the results shown in Figure 9 indicate that in "Comparative Example (Figure 7)," the change in sensitivity with increasing introduction amount is even greater than in "Comparative Example (Figure 6)." The window 221 of Comparative Example 220 is larger than the window 211 of Comparative Example 210, and Comparative Example 220 introduces more excitation light near aperture 126X than Comparative Example 210. This suggests that the more excitation light introduced near aperture 126X, the greater the change in sensitivity with changing introduction amount. In other words, the less excitation light introduced near aperture 126X, the more the change in sensitivity with changing introduction amount is suppressed.

[0063] <Presence or absence of shielding of openings (2)> Figure 10 illustrates yet another example of the change in sensitivity in the discharge ionization detector 10. The horizontal axis of the graph in Figure 10 represents the amount of sample component introduced, similar to the graph in Figure 8. The vertical axis of the graph in Figure 10 represents the relative sensitivity. In each example, the relative sensitivity is calculated as the sensitivity corresponding to a given amount introduced (3.3 ng).

[0064] Figure 10 shows the results for the following three types of examples. (1) No shielding plate (2) Modified example (Figure 5) (3) Comparative example (Figure 6) "Without shielding plate" represents an example in the discharge ionization detector 10 where the shielding plate 190 has been removed. "Modified example (Figure 5)" represents an example in the discharge ionization detector 10 where modified example 192 (Figure 5) is installed instead of the shielding plate 190. "Comparative example (Figure 6)" represents an example in the discharge ionization detector 10 where comparative example 210 (Figure 6) is installed instead of the shielding plate 190.

[0065] As shown in Figure 10, in the "modified version (Figure 5)," the change in sensitivity with increasing dosage is small. More specifically, the relative sensitivity from approximately 0.33 ng to approximately 330 ng is all close to 1.0.

[0066] On the other hand, in the "Comparative Example (Figure 6)," the change in sensitivity with increasing dosage is greater than in the "Modified Example (Figure 5)." More specifically, the relative sensitivity is about 1.4 at a dosage of approximately 0.33 ng, while it decreases to about 0.8 at a dosage of approximately 330 ng.

[0067] Furthermore, in the "no shielding plate" case, the change in sensitivity with increasing introduction rate is even greater than in the "comparative example (Figure 6)". More specifically, the relative sensitivity is about 2.4 at an introduction rate of about 0.33 ng, while at an introduction rate of about 330 ng, the relative sensitivity drops to about 0.7.

[0068] In the "modified example (Figure 5)," the aperture 126X is shielded, whereas in the "comparative example (Figure 6)," the aperture 126X is not shielded. Therefore, from the results shown in Figure 10, it can be said that shielding the aperture 126X suppresses the change in sensitivity associated with changes in the amount of introduced.

[0069] Furthermore, the results shown in Figure 10 indicate that, in the "no shielding plate" case, the change in sensitivity with increasing input amount is even greater than in the "comparative example (Figure 6)". This suggests that even when excitation light is introduced into aperture 126X, reducing the amount of excitation light introduced near aperture 126X suppresses the change in sensitivity with changing input amount.

[0070] [7. Variations of gas chromatograph analyzers] Figure 11 shows another example of the configuration of a gas chromatograph analyzer. The gas chromatograph analyzer shown in Figure 11 differs from the gas chromatograph analyzer shown in Figure 1 in the configuration of the charge collection unit 120. In Figure 11, a charge collection unit 120X is shown instead of the charge collection unit 120.

[0071] Compared to the charge collection unit 120, the charge collection unit 120X further includes a guard electrode 129 and an insulator 125d between the insulator 125b and the collection electrode 123. The guard electrode 129 is interposed between the insulator 125b and the insulator 125d. The insulator 125d is interposed between the guard electrode 129 and the collection electrode 123.

[0072] The guard electrode 129 is grounded. The guard electrode 129 is positioned between the bias electrode 122 and the collection electrode 123 to prevent current from flowing from the bias electrode 122 to the collection electrode 123 through the insulator 125b.

[0073] The placement of the guard electrode 129 ensures that the current flowing from the bias electrode 122 through the insulator 125b to the collection electrode 123 is not mixed with the ion current from the collection electrode 123. As a result, the detection results based on the ion current from the collection electrode 123 accurately reflect the amount of sample components.

[0074] [8. Other variations] (1) The shielding section 190C shields the entire surface of the aperture 126X. However, in the discharge ionization detector 10, it is not necessary for the entire surface of the aperture 126X to be shielded, as long as at least a portion of it is shielded from the ionizer tube. By shielding at least a portion of the aperture 126X, the amount of excitation light introduced into the aperture 126X is reduced compared to when the aperture 126X is not shielded at all. This can reduce the change in sensitivity in accordance with changes in sample concentration.

[0075] (2) A sample introduction tube 126 is inserted into the charge collection unit 120, and a sample is introduced through the opening 126X of the sample introduction tube 126. The opening 126X may be provided on the wall surface of the charge collection unit 120. In other words, the sample introduction tube 126 does not have to be inserted into the charge collection unit 120.

[0076] (3) In the discharge ionization detector 10, a shielding plate 190 is installed to shield the aperture 126X, and is configured separately from the elements constituting the discharge section 110 (dielectric tube 111, etc.) and the elements constituting the charge collection section 120 (connecting member 121, etc.). This allows for the addition of a shielding section to an existing discharge ionization detector that does not have a shielding section by installing a shielding plate. However, the member that shields the aperture 126X does not need to be separate from the elements constituting the discharge section 110 and the elements constituting the charge collection section 120. That is, the aperture 126X may be shielded by changing the shape of the elements constituting the discharge section 110 and / or the elements constituting the charge collection section 120 without installing a shielding plate 190.

[0077] [Aspect] Those skilled in the art will understand that the above-described exemplary embodiments are specific examples of the following embodiments.

[0078] (Section 1) A discharge ionization detector according to one embodiment comprises a dielectric tube that constitutes at least a part of a gas flow path through which a discharge gas flows and extends in the direction of the tube axis, a high-voltage electrode provided on the outer wall of the dielectric tube, a ground electrode unit that is electrically grounded and provided on the outer wall of the dielectric tube, a voltage application unit connected to the high-voltage electrode and applying an alternating voltage between the high-voltage electrode and the ground electrode unit in order to generate a discharge in the dielectric tube and generate plasma from the discharge gas, and a charge collection unit including a collection electrode that collects ions generated from sample components in a sample gas by light emitted from the plasma, wherein the charge collection unit includes an opening for introducing the sample gas into the gas flow path and may further include a shielding unit located between the dielectric tube and the opening that shields at least a part of the opening from the dielectric tube.

[0079] According to the discharge ionization detector described in paragraph 1, the change in sensitivity due to changes in the concentration of sample components is reduced.

[0080] (Clause 2) In the discharge ionization detector described in paragraph 1, the shielding portion may be configured to shield the entire opening from the dielectric tube.

[0081] According to the discharge ionization detector described in Section 2, the change in sensitivity due to changes in the concentration of sample components is more reliably reduced.

[0082] (Clause 3) In the discharge ionization detector described in paragraph 1 or 2, the shielding portion may be configured to shield the entire opening and its outer edge from the dielectric tube.

[0083] According to the discharge ionization detector described in Section 3, the change in sensitivity due to changes in the concentration of sample components is more reliably reduced.

[0084] (Clause 4) In the discharge ionization detector described in any one of paragraphs 1 to 3, the shielding portion may have a member disposed between the dielectric tube and the opening.

[0085] According to the discharge ionization detector described in Section 4, a shielding portion can be added to an existing discharge ionization detector by adding a component.

[0086] (Clause 5) In the discharge ionization detector described in Clause 4, the charge collection unit may further include a bias electrode for forming a DC electric field that promotes the movement of ions in the gas flow path, and a guard electrode disposed between the collection electrode and the bias electrode and grounded.

[0087] According to the discharge ionization detector described in Section 5, the detection results can more accurately indicate the amount of ionized sample components.

[0088] (Clause 6) A preparative liquid chromatograph according to one embodiment may include a discharge ionization detector according to any one of claims 1 to 5, an analytical column for separating sample components in the sample gas into components, and a channel for introducing the sample components separated by the analytical column into the gas channel of the discharge ionization detector.

[0089] According to the preparative liquid chromatography described in Section 6, the change in sensitivity due to changes in the concentration of sample components is reduced.

[0090] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. Furthermore, each technology in the embodiments is intended to be practiced individually or, as far as possible, in combination with other technologies in the embodiments. [Explanation of Symbols]

[0091] 10 Discharge ionization detector, 111 Dielectric tube, 120 Charge collection unit, 126X Aperture, 190 Shielding plate.

Claims

1. A dielectric tube extending in the axial direction of the tube, which constitutes at least a part of the gas flow path through which the discharge gas flows, A high-voltage electrode provided on the outer wall of the dielectric tube, A grounding electrode unit provided on the outer wall of the dielectric tube, which is electrically grounded, A voltage application unit is connected to the high-voltage electrode and applies an AC voltage between the high-voltage electrode and the ground electrode unit in order to generate a discharge in the dielectric tube and generate plasma from the discharge gas, The system includes a charge collection unit which includes a collection electrode that collects ions generated from sample components in a sample gas by light emitted from the plasma, The charge collection unit includes an opening for introducing the sample gas into the gas flow path, The opening is one end of the sample introduction tube that supplies the sample gas to the gas flow path. The shielding portion is located between the dielectric tube and the opening in the direction through which the discharge gas flows, and is located downstream of the dielectric tube, and further shields at least a portion of the opening from the dielectric tube. The shielding portion is a discharge ionization detector that shields at least a portion of the light reaching the aperture at a plane intersecting the extending direction of the sample introduction tube.

2. A dielectric tube extending in the axial direction of the tube, which constitutes at least a part of the gas flow path through which the discharge gas flows, A high-voltage electrode provided on the outer wall of the dielectric tube, A grounding electrode unit provided on the outer wall of the dielectric tube, which is electrically grounded, A voltage application unit is connected to the high-voltage electrode and applies an AC voltage between the high-voltage electrode and the ground electrode unit in order to generate a discharge in the dielectric tube and generate plasma from the discharge gas, The system includes a charge collection unit which includes a collection electrode that collects ions generated from sample components in a sample gas by light emitted from the plasma, The charge collection unit includes an opening for introducing the sample gas into the gas flow path, The opening is one end of the sample introduction tube that supplies the sample gas to the gas flow path. The shielding portion is located between the dielectric tube and the opening and further shields at least a portion of the opening from the dielectric tube, A discharge ionization detector wherein the shielding portion shields at least a portion of the light reaching the aperture with a plane that intersects the extending direction of the sample introduction tube, thereby preventing the aperture from being irradiated with light emitted from the plasma.

3. The discharge ionization detector according to claim 1 or claim 2, wherein the shielding portion is configured to shield the entire opening from the dielectric tube.

4. The discharge ionization detector according to any one of claims 1 to 3, wherein the shielding portion is configured to shield the entire opening and its outer edge from the dielectric tube.

5. The discharge ionization detector according to any one of claims 1 to 4, wherein the shielding portion has a member disposed between the dielectric tube and the opening.

6. The charge collection unit is A bias electrode for forming a DC electric field in the gas flow path to promote ion movement, A discharge ionization detector according to any one of claims 1 to 5, further comprising a guard electrode disposed between the collection electrode and the bias electrode and grounded.

7. A discharge ionization detector according to any one of claims 1 to 6, An analytical column for separating the sample components in the sample gas into individual components, A gas chromatograph analyzer comprising a channel for introducing sample components separated by the analytical column into the gas channel of the discharge ionization detector.

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