Hydrogen flame ionization detector

Abstract

To improve the ion collection efficiency by a collector while stabilizing the formation of the hydrogen flame at the upper end of a nozzle.SOLUTION: A hydrogen flame ionization detector includes a housing (2) having an internal space (3) into which combustion gas is supplied, a nozzle (4) provided with a discharge port (18) at the upper end, for ejecting a mixture of sample gas and auxiliary combustion gas from the discharge port (18) to form a hydrogen flame at the upper end, and a hollow cylindrical collector (8) provided on the upper side of the nozzle (4) so that the center axis is oriented vertically, for collecting components in the sample gas ionized by the hydrogen flame formed at the upper end of the nozzle (4). A first tapered surface (22) inclined so that the outer diameter decreases toward the upper end with a first taper angle (θ1), is provided at the upper end of the nozzle (4). On the inner side of the lower end part of the collector (8), a second tapered surface (24) is provided that is inclined so that the inner diameter decreases from the lower end toward the upper end with a second taper angle (θ2) larger than the first taper angle (θ1).SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] FID is known as one of the detectors for gas chromatographs. In an FID, a sample gas, which is a mixture of a combustion support gas (hydrogen) and a make-up gas, is ejected upward from the tip of a nozzle inside a housing to which combustion gas is supplied, and a hydrogen flame is formed at the top end of the nozzle to ionize the components in the sample gas, and the ions are collected by a collector provided above the nozzle, thereby quantifying the components in the sample gas (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-206091 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an FID, the shorter the distance between the nozzle and the collector, and the further the nozzle is inserted into the collector, the more efficient the collection of ions generated by the hydrogen flame by the collector and the higher the detection sensitivity. However, in order to improve the collection efficiency by the collector by directing the direction of the ions generated by the hydrogen flame toward the collector, a potential difference of about 100 to several hundred volts is generally provided between the nozzle and the collector. Therefore, the nozzle and the collector can only be brought close to each other to the extent that the spatial insulation is not broken down.

[0005] Furthermore, since the inner diameter of the collector is generally smaller than the maximum outer diameter of the nozzle, it is difficult to insert the nozzle into the inside of the collector. Therefore, a structure is sometimes adopted in which a tapered surface with the same taper angle as the tapered surface 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 easier to insert the nozzle into the inside of the collector, but the combustion gas is also guided near the upper end of the nozzle, making it possible to stabilize the formation of a hydrogen flame at the upper end of the nozzle.

[0006] An object of the present invention is to improve the above structure and to improve the efficiency of ion collection by the collector while stabilizing the formation of a hydrogen flame at the upper end of the nozzle. [Means for solving the problem]

[0007] As in Patent Document 1, when the taper angle of the tapered surface on the inner surface of the lower end of the collector is made the same as that of the tapered surface at the upper end of the nozzle, if the nozzle is inserted too far into the inside of the collector, the gap between the nozzle and the collector becomes small, and the opening area for drawing the combustion gas into the inside of the collector becomes small. This makes it difficult for the combustion gas to be guided near the upper end of the collector, which may cause the formation of a hydrogen flame to become unstable. Therefore, the present invention provides a hydrogen flame ionization detector having a structure that ensures an opening area for drawing the combustion gas into the inside of the collector even when the nozzle is inserted too far into the collector.

[0008] That is, the FID of the present invention comprises a housing having an internal space to which combustion gas is supplied, a nozzle having an outlet at its upper end for ejecting a mixed gas of sample gas and combustion supporting gas from the outlet to form a hydrogen flame at the upper end, and a hollow cylindrical collector arranged above the nozzle with its central axis oriented vertically for collecting components in the sample gas that have been ionized by the hydrogen flame formed at the upper end of the nozzle, wherein the outer peripheral surface of the upper end of the nozzle is inclined with a first taper angle so that the outer diameter becomes smaller toward the upper end, and a tapered surface is provided on the inside of the lower end of the collector, inclined with a second taper angle larger than the first taper angle so that the inner diameter becomes smaller as it extends from the lower end upward. Effect of the Invention

[0009] In the FID according to the present invention, the outer circumferential surface of the upper end of the nozzle is inclined at a first taper angle so that the outer diameter decreases toward the upper end, and a tapered surface is provided on the inside of the lower end of the collector, the tapered surface being inclined at a second taper angle larger than the first taper angle so that the inner diameter decreases toward the upper end from the lower end. Therefore, even when the nozzle is inserted into the inside of the collector, an opening area for drawing combustion gas into the inside of the collector is ensured, and the formation of a hydrogen flame at the upper end of the nozzle can be stabilized while the efficiency of ion collection by the collector can be improved. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing the internal structure of one embodiment of an FID. [Diagram 2] 13 is a diagram for explaining the relationship between the taper angle of the tapered surface of the nozzle and the taper angle of the tapered surface of the collector in the embodiment. FIG. [Diagram 3] 13 is a diagram showing a comparative example in which the taper angle of the tapered surface of the nozzle and the taper angle of the tapered surface of the collector are the same. FIG. [Figure 4] FIG. 13 is a diagram showing, as a comparative example, a case in which a tapered surface is not provided on the inner surface of the lower end portion of the collector. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the FID according to the present invention will now be described with reference to the drawings.

[0012] FIG. 1 shows the internal cross-sectional structure of one embodiment of an FID.

[0013] The FID 1 comprises a lower housing 2 , a nozzle 4 , a collector holder 6 , a collector 8 , an insulator 10 , and an upper housing 12 .

[0014] The lower housing 2 is a hollow cylindrical member with an open top, and has an internal space 3. Combustion gas is supplied to the internal space 3 of the lower housing 2 through piping 20. A hole 14 that communicates with the internal space 3 is provided vertically in the lower part of the lower housing 2.

[0015] The nozzle 4 is attached to the lower housing 2 with its upper portion protruding upward from the hole 14. The nozzle 4 has an outlet 18 at its upper end, and the downstream end of a separation column 100 of a gas chromatograph is inserted into its lower end. A combustion supporting gas (hydrogen) and a make-up gas are supplied into the hole 14 through a pipe 16. The combustion supporting gas and the make-up gas supplied into the hole 14 go around to the lower end of the nozzle 4 and enter the inside of the nozzle 4 through the gap between the nozzle 4 and the separation column 100, where they are mixed with the sample gas from the separation column 100 and are ejected upward from the outlet 18 of the nozzle 4.

[0016] A collector holding member 6 is attached to the top of the lower housing 2, and an upper housing 12 is attached on top of the collector holding member 6 with two insulators 10 sandwiched between them. Although not shown, an igniter for forming a hydrogen flame at the tip of the nozzle 4 is provided inside the upper housing 12. Each of the two insulators 10 is a disk-shaped insulating member that holds the outer circumferential surface of the collector 8.

[0017] Collector 8 is a hollow cylindrical member with both ends open, and insulator 10 is attached to the outer circumferential surface of collector 8 so as to spread in the circumferential direction from the outer periphery of collector 8. The peripheral edge of insulator 10 is sandwiched between collector holding member 6 and upper housing 12, so that collector 8 is disposed above nozzle 4 with its axial direction oriented vertically. Collector 8 is an electrode for collecting ions generated by a hydrogen flame formed at the tip of nozzle 4.

[0018] The outer peripheral surface 22 at the upper end of the nozzle 4 is inclined so that the outer diameter becomes smaller toward the upper end, forming 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 at the lower end of the collector 8 is inclined so that the inner diameter becomes larger toward the lower end, forming a second tapered surface (hereinafter referred to as the second tapered surface 24). The inner diameter of the main part above the upper end of the second tapered surface 24 of the collector 8 is smaller than the outer diameter of the maximum outer diameter part of the nozzle 4.

[0019] As shown in FIG. 2, the taper angle θ2 (second taper angle) of the second tapered surface 24 of the collector 8 is larger than the taper angle θ1 (first taper angle) of the first tapered surface 22 of the nozzle 4, and the inner diameter of the lower end of the collector 8 is larger than the outer diameter of the upper end of the nozzle 4.

[0020] The upper end of the nozzle 4 is positioned above the lower end of the collector 8 and extends inside the collector 8. The distance between the nozzle 4 and the collector 8 is minimum at 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. This distance L is designed to be large enough so that the spatial insulation between the nozzle 4 and the collector 8 is not broken down.

[0021] Here, the taper angle θ2 of the second taper surface 24 of the collector 8 may be larger than the taper angle θ1 of the taper surface 22 of the nozzle 4, but must be large enough to induce the combustion gas in the internal space 3 to the inside of the collector 8, i.e., near the upper end of the nozzle 4. Therefore, the larger the taper angle θ2, the better, and a value as close to 180° as possible is not preferable. For example, θ2 can be set to about θ1+30°, and if the taper angle θ1 is 60 to 90°, the taper angle θ2 can be set to 90 to 120°.

[0022] Since the taper angle θ2 of the second tapered surface 24 of the collector 8 is larger than the taper angle θ1 of the first tapered surface 22 of the nozzle 4, the interval D between the lower end of the collector 8 and the nozzle 4 can be made wide even if the upper end of the nozzle 4 is advanced inside the collector 8. Since the interval D between the lower end of the collector 8 and the nozzle 4 is wide, a sufficient opening area for drawing the combustion gas in the internal space 3 into the collector 8 is ensured, and the hydrogen flame formed at the upper end of the nozzle 4 is stabilized. That is, by making the taper angle θ2 of the second tapered surface 24 of the collector 8 appropriately larger than the taper angle θ1 of the first tapered surface 22 of the nozzle 4, it is possible to improve the ion collection efficiency by advancing the upper end of the nozzle 4 inside the collector 8 and bringing the nozzle 4 close to the collector 8, and to stabilize the hydrogen flame by guiding the combustion gas to the vicinity of the upper end of the nozzle 4.

[0023] FIG. 3 shows a comparative example 1 in which a collector 8' having the same taper angle θ2 as the taper angle θ1 of the nozzle 4 is used. Even if the taper angle θ2 is the same as the taper angle θ1 as in this comparative example 1, it is possible to make the upper end of the nozzle 4 enter the inside 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 distance L in the perpendicular direction of the first and second tapered surfaces 22 and 24, so that there is a limit to how far the nozzle 4 can enter the inside of the collector 8' when considering the spatial insulation between the nozzle 4 and 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 also becomes narrower, and the opening area for drawing the combustion gas into the inside of the collector 8 becomes smaller.

[0024] As described above, by comparing the structure in Figure 2 with the structure in Figure 3, it can be seen that by making the taper angle θ2 larger than the taper angle θ1, it is easier to achieve both improved ion collection efficiency and stabilization of the hydrogen flame, compared to the case where the taper angle θ2 is the same as the taper angle θ1.

[0025] FIG. 4 shows, as Comparative Example 2, a case where a collector 8" that does not have a tapered surface on the inner surface of the lower end is used. When a collector 8" that does not have a tapered surface on the inner surface of the lower end is used as in Comparative Example 2, the effect of drawing the combustion gas into the vicinity of the upper end of the nozzle 4 cannot be obtained, and the nozzle 4 cannot enter the inside of the collector", and therefore the effect of improving the ion collection efficiency by the collector 8" cannot be obtained.

[0026] The embodiment described above is merely one example of the embodiment of the FID according to the present invention. The embodiment of the FID according to the present invention is as follows.

[0027] In one embodiment of the FID according to the present invention, the FID comprises a housing having an internal space to which combustion gas is supplied, a nozzle having an outlet at its upper end for ejecting a mixed gas of sample gas and combustion supporting gas from the outlet to form a hydrogen flame at the upper end, and a hollow cylindrical collector having a vertical central axis and disposed above the nozzle for collecting components in the sample gas that have been ionized by the hydrogen flame formed at the upper end of the nozzle, wherein a first tapered surface is disposed at the upper end of the nozzle and has a first taper angle such that the outer diameter becomes smaller as it approaches the upper end, and a second tapered surface is disposed on the inside of a lower end of the collector and has a second taper angle larger than the first taper angle such that the inner diameter becomes smaller as it approaches the lower end.

[0028] In the aspect [1] of the above embodiment, the upper end of the nozzle is disposed at a position higher than the lower end of the collector. With this aspect, the nozzle outlet is in a state of entering the inside of the collector, so that ions generated by the hydrogen flame formed at the upper end of the nozzle are less likely to scatter in the circumferential direction, improving the efficiency of ion collection by the collector.

[0029] In the aspect [2] of the above embodiment, the distance between the nozzle and the collector is minimum at the upper end of the nozzle and the upper end of the second tapered surface of the collector. This aspect makes it easier for the nozzle to enter the inside of the collector, thereby improving the efficiency of ion collection by the collector. [Explanation of symbols]

[0030] 1 FID (Flame Ionization Detector) 2 Lower housing 3. Interior space 4 Nozzles 6 Collector holding member 8 Collector 10 Insulators 12 Upper housing 14 holes 16,20 Piping 18 spout 22 First tapered surface 24 Second tapered surface

Claims

1. a housing having an interior space to which combustion gas is supplied; a nozzle having an outlet at an upper end thereof for ejecting a mixed gas of a sample gas and a combustion supporting gas from the outlet to form a hydrogen flame at the upper end; a hollow cylindrical collector disposed above the nozzle with its central axis oriented vertically, for collecting components in the sample gas ionized by a hydrogen flame formed at the upper end of the nozzle; a first tapered surface is provided at an upper end of the nozzle, the first tapered surface being inclined at a first taper angle so that an outer diameter becomes smaller toward the upper end; a second tapered surface is provided on the inside of the lower end of the collector, the second tapered surface being inclined such that the inner diameter becomes smaller as it goes upward from the lower end with a second taper angle larger than the first taper angle.

2. 2. The flame ionization detector of claim 1, wherein the upper end of the nozzle is disposed above a lower end of the collector.

3. 2. The flame ionization detector of claim 1, wherein the distance between the nozzle and the collector is minimum at the upper end of the nozzle and the upper end of the second tapered surface of the collector.

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