Flame Ionization Detector

Abstract

To suppress a deterioration in insulation properties between a collector and a collector housing to prolong the life of an FID.SOLUTION: A hydrogen flame ionization detector (1) comprises: a nozzle (8) that ejects sample gas upward; a cylindrical collector (16) that is provided above the nozzle (8) so that its longitudinal direction is vertical, and collects ions generated by the hydrogen flame formed at the tip of the nozzle (8); an insulation body (18) holding the collector (16) thereinside, and provided extending radially outward with respect to the collector (16); and a collector housing (4) housing the collector (16) thereinside so as to surround the outer peripheral surface of the collector (16) while holding the periphery of the insulation body (18). Above the insulation body (18), provided are deposition suppression structures (24, 26, 30) that suppress deposition of substances discharged from the upper end of the collector (16) on the insulation body (18) so as to shorten an insulation distance between the collector (16) and the collector housing (4).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a flame ionization detector. [Background technology]

[0002] Flame ionization detectors (FIDs) are known as detectors for gas chromatographs (hereafter referred to as GCs). FIDs are configured to mix hydrogen gas with the sample gas flowing out from the outlet of the GC separation column, release it from the tip of the nozzle, form hydrogen gas at the tip of the nozzle to ionize the components in the sample gas, collect the generated ions with a collector, and detect the amount of ions collected by the collector as an electric current.

[0003] The collector that captures ions generated by the hydrogen flame is fixed in a metal collector housing while being disposed above the nozzle. An insulator is attached to the collector so as to extend radially outward from the collector, and the collector is electrically insulated from the collector housing by being held by the insulator (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-206091 A Summary of the Invention [Problem to be solved by the invention]

[0005] Deterioration of an FID can be manifested by an increase in noise in the output signal, a rise in the baseline, etc. It was found that the cause of such deterioration is a decrease in the insulation between the collector and the collector housing.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to extend the life of an FID by suppressing the deterioration of the insulation between the collector and the collector housing. [Means for solving the problem]

[0007] The present inventor has found that one of the causes of the deterioration of the insulation between the collector and the collector housing is the deposition of conductive materials on the insulator insulating the collector and the collector housing. For example, when a sample gas containing carbon disulfide (CS2) is introduced into an FID, sulfide ions ionized by a hydrogen flame react with stainless steel metal parts constituting the FID to produce conductive materials. When such conductive materials are deposited on the insulator insulating the collector from the collector housing, problems occur such as a shortening of the insulation distance between the collector and the collector housing and electrical conduction between the collector and the collector housing. The present invention has been made based on such findings, and the main subject is to suppress the deterioration of the insulation between the collector and the collector housing caused by the deposition of conductive materials on the insulator insulating the collector and the collector housing.

[0008] That is, the hydrogen flame ionization detector (hereinafter referred to as FID) according to the present invention comprises a nozzle which sprays sample gas upward, a cylindrical collector which is arranged above the nozzle with its longitudinal direction oriented vertically and which collects ions generated by a hydrogen flame formed at the tip of the nozzle, an insulator which holds the collector inside and is arranged so as to extend radially outward from the collector, and a collector housing which has an insulator holding portion which holds the peripheral portion of the insulator and which contains the collector inside so as to surround the outer circumferential surface of the collector by holding the peripheral portion of the insulator with the insulator holding portion, and a deposition suppression structure is provided above the insulator to suppress shortening of the insulation distance between the collector and the collector housing due to deposition of material released from the upper end of the collector on the insulator. Effect of the Invention

[0009] In the FID of the present invention, a deposition prevention structure is provided above the insulator to prevent shortening of the insulation distance between the collector and the collector housing due to deposition of material emitted from the upper end of the collector on the insulator, thereby preventing a decrease in insulation between the collector and the collector housing and extending the life of the FID. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an embodiment of an FID. [Diagram 2] FIG. 2 is an enlarged view of an insulator holding portion of a collector housing in the FID of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of an FID according to the present invention will be described with reference to the drawings.

[0012] 1, the FID 1 includes a housing body 2 and a collector housing 4. The collector housing 4 is attached to the upper part of the housing body 2.

[0013] An introduction tube 6 is inserted into the housing body 2 from below. Although not shown in the figure, the outlet of a GC separation column is connected to the lower end of the introduction tube 6, and sample gas that has passed through the GC separation column is introduced upward through the introduction tube 6. A nozzle 8 is provided directly above the introduction tube 6. The nozzle 8 is held by the housing body 2 so that it is fluidly connected to the outlet of the introduction tube 6. The upper end of the nozzle 8 protrudes upward from the housing body 2 and is located within the space surrounded by the collector housing 4. The nozzle 8 is equipped with a nozzle cap 10 at its tip. Although not shown in the figure, a constant voltage is applied to the nozzle cap 10.

[0014] The housing body 2 is provided with a hydrogen gas introduction flow path 12 and an air introduction flow path 14. The hydrogen gas introduction flow path 12 is a flow path for introducing a mixed gas of hydrogen gas and makeup gas, and is connected to the connection part between the introduction tube 6 and the nozzle 8. The mixed gas of hydrogen gas and makeup gas introduced from the hydrogen gas introduction flow path 12 is mixed with the sample gas introduced through the introduction tube 6 and is ejected upward from the tip of the nozzle cap 10. The air introduction flow path 14 is a flow path for introducing a combustion supporting gas (air) toward the periphery of the nozzle cap 10. At the tip of the nozzle cap 10, the hydrogen gas is ignited by an igniter (not shown), and a hydrogen flame is formed above the nozzle cap 10. The components to be analyzed in the sample gas ejected from the tip of the nozzle cap 10 are ionized by the hydrogen flame.

[0015] A cylindrical collector 16 having a longitudinal direction is provided immediately above the nozzle 8 in the collector housing 4. The collector 16 is arranged so that its longitudinal direction is vertical. The collector 16 is for collecting ions generated by a hydrogen flame formed at the tip of the nozzle cap 10. The collector 16 is provided with terminals 20 on its outer circumferential surface, and a measuring circuit 22 is electrically connected to the collector 16 via the terminals 20. The measuring circuit 22 is an electronic circuit for extracting the ion current of the ions collected by the collector 16 and detecting the components in the sample gas based on the ion current.

[0016] The insulator 18 includes a lower insulator 18a and an upper insulator 18b. The lower insulator 18a and the upper insulator 18b are each a disk-shaped insulating member having a through hole in the center for holding the collector 16 inside, and are each provided so as to extend from the outer circumferential surface of the collector 16 in the radially outward direction of the collector 16. The lower insulator 18a and the upper insulator 18b are made of, for example, ceramic.

[0017] The collector housing 4 includes a lower part 4a and an upper part 4b. The lower part 4a and the upper part 4b are fixed to each other with the peripheral parts of the lower insulator 18a and the upper insulator 18b sandwiched between them, thereby holding the peripheral parts of the insulator 18. The collector housing 4 includes a purge gas inlet 24 at a position lower than the upper end of the collector 16 and higher than the upper insulator 18. The purge gas inlet 24 is for introducing purge gas into the inside of the collector housing 4. By introducing purge gas into the collector housing 4 from the purge gas inlet 24, an ascending air current is formed above the upper insulator 18, and the material discharged from the upper end of the collector 16 is prevented from accumulating on the upper surface of the upper insulator 18b. That is, the purge gas inlet 24 has a deposition suppression structure that suppresses the material discharged from the upper end of the collector 16 from accumulating on the insulator 18 so as to shorten the insulation distance between the collector 16 and the collector housing 4.

[0018] The purge gas introduced into the collector housing 4 from the purge gas inlet 24 may be any type of gas as long as it does not affect the measurement. For example, the combustion supporting gas supplied into the collector housing 4 through the air introduction passage 14 and the purge gas supplied into the collector housing 4 through the purge gas inlet 24 may be supplied from a common supply source. In addition, since the introduction of the purge gas from the purge gas inlet 24 does not necessarily need to be performed all the time, the supply of the purge gas to the purge gas inlet 24 may be configured to be switched on / off. In this way, when no conductive material is released from the upper end of the collector 16, the introduction of the purge gas from the purge gas inlet 24 can be stopped, and the consumption of the purge gas is reduced.

[0019] Furthermore, the collector housing 4 is provided with an overhanging portion 26 that protrudes inward from the inner circumferential surface. The overhanging portion 26 is provided to receive material that is discharged from the upper end of the collector 16 and falls toward the insulator 18. The provision of the overhanging portion 26 prevents the material discharged from the upper end of the collector 16 from accumulating on the insulator 18. In other words, the overhanging portion 26 also forms a deposition suppression structure that suppresses the deposition of conductive material on the insulator 18.

[0020] Furthermore, the lower insulator 18a and the upper insulator 18b have an outer diameter larger than the inner diameter of the main part of the collector housing 4 that surrounds the periphery of the collector 16. The lower part 4a and the upper part 4b of the collector housing 4 are in contact with the lower insulator 18a and the upper insulator 18b, respectively, at a position farther from the collector 16 than the inner circumferential surface that surrounds the periphery of the collector 16.

[0021] 2 is an enlarged view of a portion of the collector housing 4 that holds the insulator 18. The upper part 4b of the collector housing 4 has a first surface 30 and a second surface 32 that face the upper surface of the upper insulator 18b. Both the first surface 30 and the second surface 32 are provided at positions farther from the collector 16 than the inner peripheral surface 28 of the main part of the collector housing 4. The second surface 32 is provided on the outside of the first surface 30, the first surface 30 is spaced from the upper surface of the upper insulator 18b, and the second surface 32 is in contact with the upper surface of the peripheral portion of the upper insulator 18b. The lower part 4a of the collector housing 4 is also in contact with the lower insulator 18a in a structure similar to that of the upper part 4b.

[0022] With the above structure, the distance L2 between the contact point between the insulator 18 and the collector housing 4 and the collector 16 is longer than the distance L1 between the outer peripheral surface of the collector 16 and the inner peripheral surface 28 of the collector housing 4, making it difficult for the collector 16 and the collector housing 4 to be electrically conductive. Furthermore, since an area covered by the first surface 30 of the collector housing 4 is formed on the upper surface of the upper insulator 18b, conductive materials do not accumulate in this area. That is, the provision of the first surface 30 not only increases the insulation distance between the collector 16 and the collector housing 4, but also prevents conductive materials from accumulating on the upper surface of the upper insulator 18b so as to electrically connect the collector 16 and the collector housing 4. That is, the first surface 30 of the collector housing 4 forms a structure that suppresses the accumulation of conductive materials on the insulator 18.

[0023] In this embodiment, three structures, the purge gas inlet 24, the eaves 26, and the first surface 30, are provided as the deposition suppression structure, but the present invention is not limited to this, and it is not necessary to provide all of these three structures. Each of the purge gas inlet 24, the eaves 26, and the first surface 30 has the effect of suppressing the deterioration of the insulation between the collector 16 and the collector housing 4 due to the deposition of a conductive material on the upper surface of the insulator 18, and any one of the structures may be adopted alone, or any two of the three structures may be adopted in combination. It is clear that when two or more deposition suppression structures are adopted in combination, the effect of suppressing the deterioration of the insulation between the collector 16 and the collector housing 4 is higher than when one deposition suppression structure is adopted alone due to the synergistic effect.

[0024] The embodiment described above is merely one example of the embodiment of the flame ionization detector according to the present invention. The embodiment of the flame ionization detector according to the present invention is as follows.

[0025] In one embodiment of the hydrogen flame ionization detector according to the present invention, the detector comprises a nozzle which sprays sample gas upward, a cylindrical collector arranged above the nozzle with its longitudinal direction oriented vertically for collecting ions generated by the hydrogen flame formed at the tip of the nozzle, an insulator which holds the collector inside and is arranged to extend radially outward from the collector, and a collector housing which contains the collector inside so as to surround the outer circumferential surface of the collector while holding the peripheral portion of the insulator, and a deposition suppression structure is provided above the insulator to suppress deposition of material released from the upper end of the collector on the insulator so as to shorten the insulation distance between the collector and the collector housing.

[0026] In a first aspect of the above embodiment, the deposition suppression structure includes a purge gas inlet provided at a position lower than the upper end of the collector and higher than the insulator, and is configured to form an ascending air current above the insulator by gas introduced into the collector housing from the purge gas inlet. In this manner, the material discharged from the upper end of the insulator is prevented from descending toward the insulator, thereby preventing a deterioration in insulation between the collector and the collector housing.

[0027] In a second aspect of the embodiment, the deposition suppression structure includes a visor portion provided to receive material discharged from an upper end of the collector and falling toward the insulator. This aspect prevents the material discharged from the upper end of the insulator from falling toward the insulator, thereby suppressing a decrease in insulation between the collector and the collector housing. This second aspect can be combined with the first aspect.

[0028] In a second aspect of the above embodiment, the overhanging portion may be provided so as to protrude further inwardly of the collector housing from an inner circumferential surface of the collector housing at a position above an upper end of the collector.

[0029] In a third aspect of the above embodiment, the insulator has an outer diameter larger than the inner diameter of a main part of the collector housing that surrounds the outer peripheral surface of the collector, and the collector housing has a first surface as the deposition suppression structure that faces the upper surface of the insulator at a position farther from the collector than the inner peripheral surface of the main part and is spaced from the upper surface, and a second surface that contacts the peripheral upper surface of the insulator at a position further from the collector than the first surface. In this manner, an area covered by the first surface is formed on the upper surface of the insulator, and conductive material is not deposited in the area. This prevents electrical conduction between the collector and the collector housing due to the conductive material deposited on the upper surface of the insulator. [Explanation of symbols]

[0030] 1. Flame ionization detector (FID) 2 Housing body 4 Collector housing 4a Upper part 4b Lower part 6 Introductory tube 8 Nozzles 10 Nozzle cap 12 Hydrogen gas introduction channel 14 Air inlet passage 16 Collector 18 Insulators 18a Lower insulator 18b Upper insulator 20 Terminals 22 Measurement circuit 24 Purge gas inlet 26 Eaves 28 Inner surface of collector housing 30 First Side 32 The Second Side

Claims

1. A nozzle that ejects the sample gas upward; a cylindrical collector disposed above the nozzle with its longitudinal direction oriented vertically, for collecting ions generated by a hydrogen flame formed at the tip of the nozzle; an insulator that holds the collector on the inside and extends radially outward from the collector; a collector housing that holds the collector in a manner to surround an outer peripheral surface of the collector while holding a peripheral portion of the insulator, a deposition suppression structure is provided above the insulator to suppress deposition of a substance discharged from the upper end of the collector on the insulator so as to shorten an insulation distance between the collector and the collector housing; a purge gas inlet provided at a position lower than an upper end of the collector and higher than the insulator, and configured to form an ascending air current above the insulator by gas introduced into the collector housing from the purge gas inlet.

2. A nozzle that ejects sample gas upward; a cylindrical collector disposed above the nozzle with its longitudinal direction oriented vertically, for collecting ions generated by a hydrogen flame formed at the tip of the nozzle; an insulator that holds the collector on the inside and extends radially outward from the collector; a collector housing that holds the collector in a manner to surround an outer peripheral surface of the collector while holding a peripheral portion of the insulator, a deposition suppression structure is provided above the insulator to suppress deposition of a substance discharged from the upper end of the collector on the insulator so as to shorten an insulation distance between the collector and the collector housing; The deposition suppression structure includes a canopy configured to receive material discharged from an upper end of the collector and falling toward the insulator.

3. 3. The hydrogen flame ionization detector according to claim 2, wherein the visor portion is provided so as to protrude further inwardly of the collector housing from an inner circumferential surface of the collector housing at a position above an upper end of the collector.

4. A nozzle that ejects sample gas upward; a cylindrical collector disposed above the nozzle with its longitudinal direction oriented vertically, for collecting ions generated by a hydrogen flame formed at the tip of the nozzle; an insulator that holds the collector on the inside and extends radially outward from the collector; a collector housing that holds the collector in a manner to surround an outer peripheral surface of the collector while holding a peripheral portion of the insulator, a deposition suppression structure is provided above the insulator to suppress deposition of a substance discharged from the upper end of the collector on the insulator so as to shorten an insulation distance between the collector and the collector housing; the insulator has an outer diameter larger than an inner diameter of a main portion of the collector housing that surrounds an outer peripheral surface of the collector; the collector housing includes a first surface facing the upper surface of the insulator at a position farther from the collector than an inner circumferential surface of the main portion and spaced apart from the upper surface, and a second surface in contact with the peripheral portion upper surface of the insulator at a position farther from the collector than the first surface, The deposition suppression structure is defined by the first surface.

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