Hydrogen flame ionization detector

Abstract

A hydrogen flame ionization detector is provided with: a housing (2) having an internal space (3) to which a combustion gas is supplied; a nozzle (4) provided with a discharge port (18) at the upper end, for discharging a mixed gas of the sample gas and the combustion-supporting gas from the discharge port (18) to form a hydrogen flame at the upper end; and a hollow cylindrical collector electrode (8) provided above the nozzle (4) such that the central axis is in the vertical direction, the collector electrode (8) collecting components in the sample gas ionized by the hydrogen flame formed at the upper end of the nozzle (4), the upper end portion of the nozzle (4) being provided with a first tapered surface (22), the collector electrode (8) is provided with a first tapered surface (22) having a first taper angle ([theta] 1) and inclined such that the outer diameter becomes smaller toward the upper end side, and a second tapered surface (24) having a second taper angle ([theta] 2) larger than the first taper angle ([theta] 1) and inclined such that the inner diameter becomes smaller toward the upper side from the lower end.

Description

Technical Field

[0001] The present invention relates to a hydrogen flame ionization detector (hereinafter also referred to as FID). Background Art

[0002] As one of the detectors of gas chromatograph, FID is known. FID sprays a sample gas mixed with a combustion-supporting gas (hydrogen) and a supplementary gas upward from the front end of a nozzle inside a housing supplied with combustion gas, forms a hydrogen flame at the upper end of the nozzle to ionize the components in the sample gas, and uses a collector electrode arranged above the nozzle to capture the ions, thereby quantifying the components in the sample gas (see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-206091 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] In FID, the shorter the distance between the nozzle and the collector, and the further the nozzle enters the inner side of the collector, the higher the collector's collection efficiency for ions generated by the hydrogen flame, and the higher the detection sensitivity. However, in order to make the ions generated by the hydrogen flame fly toward the collector side and improve the collection efficiency of the collector, a potential difference of about 100 to several 100V is generally set between the nozzle and the collector. Therefore, the nozzle and the collector can only be brought close to the extent that the spatial insulation is not destroyed.

[0008] Furthermore, generally speaking, the inner diameter of the collector is smaller than the maximum outer diameter of the nozzle, so it is difficult to make the nozzle enter the inner side of the collector. Therefore, sometimes a structure is adopted in which a conical surface having the same cone angle as the conical surface provided at the upper end of the nozzle is provided on the inner surface of the lower end of the collector. By adopting such a structure, not only is it easy to make the nozzle enter the inner side of the collector, but also the combustion gas is guided to the vicinity of the upper end of the nozzle, which can stabilize the formation of the hydrogen flame at the upper end of the nozzle.

[0009] An object of the present invention is to improve the above-mentioned structure, stabilize the formation of the hydrogen flame at the upper end of the nozzle, and improve the efficiency of collecting ions by the collector electrode.

[0010] Solutions for solving the above technical problems

[0011] As in Patent Document 1, when the cone angle of the conical surface of the inner surface of the lower end of the collector is made the same as the cone angle of the upper end of the nozzle, if the nozzle is made to enter the inner side of the collector too much, the gap between the nozzle and the collector becomes smaller, and the opening area for introducing the combustion gas into the inner side of the collector becomes smaller. As a result, it is difficult for the combustion gas to be guided to the vicinity of the upper end of the collector, and the formation of the hydrogen flame may become unstable. Therefore, in the present invention, a hydrogen flame ionization detector having a structure that can ensure the opening area for introducing the combustion gas into the inner side of the collector even if the nozzle is made to enter the inner side of the collector is provided.

[0012] That is, the FID of the present invention comprises: a shell having an internal space supplied with combustion gas; a nozzle having a nozzle provided at the upper end, for ejecting a mixed gas of a sample gas and a combustion-supporting gas from the nozzle to form a hydrogen flame at the upper end; a collector in a hollow cylindrical shape, arranged above the nozzle with its central axis in a vertical direction, for capturing components in the sample gas ionized by the hydrogen flame formed at the upper end of the nozzle, the outer peripheral surface of the upper end of the nozzle having a first cone angle and being inclined in a manner that the outer diameter becomes smaller as it approaches the upper end side, and a conical surface is provided on the inner side of the lower end of the collector, the conical surface having a second cone angle larger than the first cone angle and being inclined in a manner that the inner diameter becomes smaller as it approaches from the lower end upward.

[0013] Effects of the Invention

[0014] According to the FID of the present invention, the outer peripheral surface of the upper end portion of the nozzle has a first cone angle and is inclined in such a manner that the outer diameter becomes smaller as it approaches the upper end side, and a conical surface is provided on the inner side of the lower end portion of the collecting electrode, the conical surface has a second cone angle larger than the first cone angle and is inclined in such a manner that the inner diameter becomes smaller as it approaches from the lower end upward. Therefore, even if the nozzle is made to enter the inner side of the collecting electrode, an opening area for introducing combustion gas into the inner side of the collecting electrode can be ensured, the formation of the hydrogen flame at the upper end of the nozzle can be stabilized, and the ion capture efficiency of the collecting electrode can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a cross-sectional view showing the internal structure of an embodiment of an FID.

[0016] Figure 2 This is a diagram for explaining the relationship between the taper angle of the taper surface of the nozzle and the taper angle of the taper surface of the collecting electrode according to this embodiment.

[0017] Figure 3 This is a diagram showing a case where the taper angle of the taper surface of the nozzle and the taper angle of the taper surface of the collecting electrode are the same as a comparative example.

[0018] Figure 4 This is a diagram showing a case where no tapered surface is provided on the inner surface of the lower end portion of the collecting electrode as a comparative example. DETAILED DESCRIPTION

[0019] Hereinafter, an embodiment of the FID of the present invention will be described with reference to the drawings.

[0020] Figure 1 FIG. 1 shows the internal cross-sectional structure of an embodiment of a FID.

[0021] The FID 1 includes a lower housing 2 , a nozzle 4 , a collecting electrode holding member 6 , a collecting electrode 8 , an insulator 10 , and an upper housing 12 .

[0022] The lower shell 2 is a hollow cylindrical member with an open upper surface, and has an internal space 3. Combustion gas is supplied to the internal space 3 of the lower shell 2 through a pipe 20. A hole 14 leading to the internal space 3 is provided at the lower portion of the lower shell 2 in the vertical direction.

[0023] The nozzle 4 is mounted on the lower housing 2 in a state where the upper part protrudes upward from the hole 14. The nozzle 4 has a jet outlet 18 at the upper end, and the downstream end of the separation column 100 of the gas chromatograph is inserted at the lower end. The combustion-supporting gas (hydrogen) and the supplementary gas are supplied to the hole 14 through the pipe 16. The combustion-supporting gas and the supplementary gas supplied to the hole 14 go around the lower end of the nozzle 4 and enter the inner side of the nozzle 4 through the gap between the nozzle 4 and the separation column 100, mix with the sample gas from the separation column 100, and are ejected upward from the jet outlet 18 of the nozzle 4.

[0024] The collector holding member 6 is mounted on the upper part of the lower housing 2, and the upper housing 12 is mounted above the collector holding member 6 in such a manner as to sandwich the two insulators 10. Although not shown in the figure, an igniter for forming a hydrogen flame at the front end of the nozzle 4 is provided in the upper housing 12. The two insulators 10 are disc-shaped insulating members that hold the outer peripheral surface of the collector 8, respectively.

[0025] The collector 8 is a hollow cylindrical component with both ends open, and the insulator 10 is mounted on the outer peripheral surface of the collector 8 in a manner extending from the outer periphery of the collector 8 to the circumferential direction. By sandwiching the peripheral edge of the insulator 10 between the collector holding component 6 and the upper shell 12, the collector 8 is arranged above the nozzle 4 in a manner such that the axial direction becomes a vertical direction. The collector 8 is an electrode for capturing ions generated by the hydrogen flame formed at the front end of the nozzle 4.

[0026] The outer peripheral surface 22 of the upper end of the nozzle 4 is inclined in such a manner that the outer diameter decreases toward the upper end to form a first tapered surface (hereinafter referred to as the first tapered surface 22). The outer diameter of the nozzle 4 is smallest at the upper end. The inner surface 24 of the lower end of the collector 8 is inclined in such a manner that the inner diameter increases toward the lower end to form a second tapered surface (hereinafter referred to as the second tapered surface 24). The inner diameter of the main part of the collector 8 located above the upper end of the second tapered surface 24 is smaller than the outer diameter of the maximum outer diameter part of the nozzle 4.

[0027] like Figure 2 As shown, the taper angle θ2 (second taper angle) of the second taper surface 24 of the collecting electrode 8 is larger than the taper angle θ1 (first taper angle) of the first taper surface 22 of the nozzle 4 , and the inner diameter of the lower end of the collecting electrode 8 is larger than the outer diameter of the upper end of the nozzle 4 .

[0028] The upper end of the nozzle 4 is located above the lower end of the collector 8 and enters the inner side of the collector 8. Regarding the distance between the nozzle 4 and the collector 8, the distance L between the upper end of the nozzle 4 and the upper end of the second tapered surface 24 of the collector 8 is minimized. The distance L is designed to be a size that does not destroy the spatial insulation between the nozzle 4 and the collector 8.

[0029] Here, it is sufficient to make the taper angle θ2 of the second taper surface 24 of the collector 8 larger than the taper angle θ1 of the taper surface 22 of the nozzle 4, but it is necessary to have a size that can obtain the effect of guiding the combustion gas in the internal space 3 to the inner side of the collector 8, that is, near the upper end of the nozzle 4. Therefore, the larger the taper angle θ2 is, the better, and it is not preferred to have a size that is infinitely close to 180°. For example, θ2 can be set to about θ1+30 degrees. If the taper angle θ1 is 60 to 90°, the taper angle θ2 can be set to 90 to 120°.

[0030] By making the taper angle θ2 of the second taper surface 24 of the collector 8 larger than the taper angle θ1 of the first taper surface 22 of the nozzle 4, even if the upper end of the nozzle 4 is inserted into the inner side of the collector 8, the interval D between the lower end of the collector 8 and the nozzle 4 can be enlarged. By enlarging the interval D between the lower end of the collector 8 and the nozzle 4, it is possible to sufficiently ensure the opening area for introducing the combustion gas in the internal space 3 into the collector 8, and to achieve stabilization of the hydrogen flame formed at the upper end of the nozzle 4. That is, by appropriately increasing the taper angle θ2 of the second taper surface 24 of the collector 8 relative to the taper angle θ1 of the first taper surface 22 of the nozzle 4, it is possible to achieve both improvement in the ion capture efficiency brought about by bringing the upper end of the nozzle 4 into the inner side of the collector 8 and bringing the nozzle 4 close to the collector 8, and stabilization of the hydrogen flame brought about by guiding the combustion gas to the vicinity of the upper end of the nozzle 4.

[0031] Figure 3As Comparative Example 1, a case where a collector 8' having a taper angle θ2 that is the same as the taper angle θ1 of the nozzle 4 is used is shown. As in Comparative Example 1, even if the taper angle θ2 is made the same as the taper angle θ1, the upper end of the nozzle 4 can be made to enter the inner side of the collector 8' to some extent. However, since the taper angle θ2 of the collector 8' is the same as the taper angle θ1 of the nozzle 4, the distance between the nozzle 4 and the collector 8' is the shortest due to the distance L in the perpendicular direction of the first tapered surface 22 and the second tapered surface 24. Therefore, if the spatial insulation between the nozzle 4 and the collector 8' is considered, there is a limit to the entry of the nozzle 4 into the inner side of the collector 8'. In addition, since the taper angle θ2 of the collector 8' is the same as the taper angle θ1 of the nozzle 4, if the shortest distance L between the nozzle 4 and the collector 8' is shortened, the interval D between the lower end of the collector 8' and the nozzle 4 is also narrowed, and the opening area for introducing the combustion gas into the inner side of the collector 8 is reduced.

[0032] As mentioned above, if Figure 2 The structure and Figure 3 By comparing the structure of , it can be seen that by making the cone angle θ2 larger than the cone angle θ1, it is easier to achieve both improved ion capture efficiency and stabilization of the hydrogen flame than when the cone angle θ2 is made the same as the cone angle θ1.

[0033] in addition, Figure 4 As Comparative Example 2, a case where a collector 8" having no tapered surface on the inner surface of the lower end is used is shown. As in Comparative Example 2, if a collector 8" having no tapered surface on the inner surface of the lower end is used, the effect of introducing the combustion gas near the upper end of the nozzle 4 cannot be obtained, and the nozzle 4 cannot enter the inner side of the collector 8", and the effect of improving the ion capture efficiency of the collector 8" cannot be obtained.

[0034] The above-described embodiment is only an example of the implementation of the FID of the present invention. The implementation of the FID of the present invention is as follows.

[0035] In one embodiment of the FID of the present invention, the FID comprises: a shell having an internal space supplied with combustion gas; a nozzle having a nozzle at the upper end, for ejecting a mixed gas of a sample gas and a combustion-supporting gas from the nozzle to form a hydrogen flame at the upper end; a collector in a hollow cylindrical shape, arranged above the nozzle with its central axis in a vertical direction, for capturing components in the sample gas ionized by the hydrogen flame formed at the upper end of the nozzle, a first conical surface being arranged at the upper end of the nozzle, the first conical surface having a first conical angle and being inclined in a manner such that the outer diameter becomes smaller as it approaches the upper end side, and a second conical surface being arranged on the inner side of the lower end of the collector, the second conical surface having a second conical angle larger than the first conical angle and being inclined in a manner such that the inner diameter becomes smaller as it approaches from the lower end to the upper side.

[0036] In the above-mentioned scheme [1] of one embodiment, the upper end of the nozzle is arranged at a higher position than the lower end of the collecting electrode. With such a scheme, the nozzle outlet is in a state of entering the inner side of the collecting electrode, so that the ions generated by the hydrogen flame formed at the upper end of the nozzle are difficult to scatter in the surrounding direction, and the collecting electrode improves the ion collection efficiency.

[0037] In the scheme [2] of the above-mentioned embodiment, the distance between the nozzle and the collector is minimized between the upper end of the nozzle and the upper end of the second conical surface of the collector. According to such a scheme, it is easy to make the nozzle enter the inner side of the collector, and the collector can improve the ion capture efficiency.

[0038] DESCRIPTION OF SYMBOLS 1F ID (Flame Ionization Detector) 2Lower housing

[0039] 3. Internal Space

[0040] 4 Nozzles

[0041] 6 Collector holding parts

[0042] 8 Collector

[0043] 10Insulator

[0044] 12 Upper shell

[0045] 14 holes

[0046] 16, 20 pipes

[0047] 18 Spout

[0048] 22 first tapered surface 24 second tapered surface.

Claims

1. A hydrogen flame ionization detector, characterized in that: have: a housing having an interior space supplied with combustion gas; The nozzle is provided with a jet outlet at the upper end, and is used to eject the mixed gas of the sample gas and the combustion-supporting gas from the jet outlet to form a hydrogen flame at the upper end; A collecting electrode in a hollow cylindrical shape is disposed above the nozzle with its central axis in a vertical direction, and is used to collect components in the sample gas ionized by the hydrogen flame formed at the upper end of the nozzle. A first tapered surface is provided at the upper end of the nozzle, the first tapered surface having a first tapered angle and being inclined so that the outer diameter decreases as it approaches the upper end side. A second tapered surface is provided inside the lower end of the collector electrode. The second tapered surface has a second tapered angle larger than the first tapered angle and is inclined so that the inner diameter decreases upward from the lower end.

2. The hydrogen flame ionization detector according to claim 1, characterized in that: The upper end of the nozzle is arranged at a higher position than a lower end of the collecting electrode.

3. The hydrogen flame ionization detector according to claim 1, characterized in that: The distance between the nozzle and the collecting electrode is minimized between the upper end of the nozzle and the upper end of the second tapered surface of the collecting electrode.

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