Detector for gas chromatography

FIELD: instrument industry.

SUBSTANCE: detector comprises housing which is the cathode of the detector, devices for supplying and discharging gas to be analyzed, anode, tritium target, and insulator housed in the space between the electrodes. The working surfaces of the electrodes are parallel and mounted with a spaced relation to each other with the use of the insulator. The detector is provided with current lead and current collectors. The insulator is made of a ring made of silicate-containing material and is interposed between the electrodes.

EFFECT: enhanced stability of operation and prolonged service life.

2 cl, 1 dwg

 

The invention relates to the field of creation of the detectors used for the analysis of gaseous media, and can be used in analytical instrumentation, in particular in gas chromatography for high-precision measurements of gas concentration.

In science and technology there are various detectors for gas chromatography - thermal conductivity detectors and conductivity detectors, flame ionization detectors, electronopaque detectors, nitrogen-phosphorus detectors, flame photometric detectors, photoionization detectors, mass-selective detectors, infrared detectors, atomic emission detectors, thermal ionization detectors, helium ionization detectors.

A universal problem in this area is to increase the sensitivity, or minimum detection level. For some types of detectors are working on improving their design to solve problems related to increased sensitivity, selectivity and expansion of dynamic range. For example, a known design of detectors for gas chromatography, proposed a specialized enterprise for the production of domestic chromatographs CJSC Special design Bureau ″CHROMATIC″. In particular the known flame photometric detector for getawayfrommejava by the RF patent №2176391, IPC G 01 N 30/74, 2001, or photoionization detector for RF patent No. 2132053, IPC G 01 N 27/62, 1999

However, the proposed techniques of constructive solution to the aforementioned detectors can only be applied to this type of detectors, i.e. are not universal to improve the performance of other detectors.

Our proposed design relates to ionization detectors, which are based on the fact that depending on the carrier gas, the electric field in the chamber is chosen so that under the action of ionizing radiation, electrons can excite the inert gas atoms to a metastable state. The mechanism of action of ionization detectors defines the basic elements of their design.

Known ionization detector for gas chromatography, containing a flow chamber with inlet and outlet fittings with the radiation source and the collector electrode and the electrometer, the camera detector placed additional electrode of the variable space, made of a material, the work function of electrons which differs from the work function of the electrons of the material of the collector electrode, an additional electrode in the form of metal screws and electrically connected with the collector electrode [With idealista of the Russian Federation No. 4830, IPC G 01 N 30/95, 1997].

Also known construction ionization detector for gas chromatography, containing a flow chamber with inlet and outlet fittings, with its collector and the contact electrodes, a source of radiation located on the contact electrode, and the electrometer, while the ionization chamber placed in her collector and the contact electrodes and the radiation source is included in the measuring circuit of the detector, in which the contact electrode of the detector is connected with the collector electrode of the ionization chamber, and having a collector electrode and a contact electrode of the ionization chamber is connected to the electrometer [the Testimony of the Russian Federation No. 4383, IPC G 01 N 30/95, 1997].

A known design of detectors do not provide opportunities to improve the basic characteristics associated with the detection threshold gases. This is due to such defects, as the tightness of the structure and used insulating material having, as shown, a very high ″memory″ on Gaza.

Closest to the present invention is ionization detector, consisting of input and output gas, two electrodes, the operating surfaces of which are parallel to each other, a device for supplying voltage to the electrodes, the radiation source is placed in the interelectrode simple is ansto, which is used as tritium on zirconium foil [Metzner, K., Struppe HG, Leibniz Century, Rise X., Engewald Century, Perlman J., Popp P., Boote, K., Vow D., Shen, "Guide for gas chromatography", in 2 hours, Transfer with it./Edited Alabina, Hegstrom, M., Mir, 1988, V.1, s-461].

According to conducted the search in respect of the helium ionization detectors there are no publications relating to constructive solutions workspace - interelectrode space. In practice, the production of ionization detectors to create the interelectrode space dielectric material, which used a rubber or Teflon.

However, it is widely known such properties of fluoropolymers as porosity. When using PTFE in the design of the detector seen in such property as ″memory″ on Gaza. After Assembly or after the change of the separation columns, when in the cavity of the detector gets air blow-off detector (decrease noise detector to the minimum operating level) is a long time.

Furthermore, the well known properties of fluoropolymers as fluidity. In the long run when exposed to even small temperature change in linear dimensions PTFE parts, the violation of the geometric dimensions of the detector, lasermedia the Oia and change the operating characteristics of the detector. The same applies to the rubber parts.

All this, eventually, leads to an increase of the lower limit of the defined concentrations.

It is known that helium ionization detectors are versatile and are characterized by very high sensitivity, however, yield stability and quality of the detector depends on the constancy in time of the geometric dimensions of the detector is the distance between the electrodes and the lack of outside influence on the measurement results. Use as dielectric PTFE or rubber material allows us to keep operating characteristics of the detector for a long time, because in the presence of high unit stresses in the interelectrode space, the polymeric material undergoes degradation - rubber ″lit″and PTFE ″floating″. The destruction of the dielectric strip leads to the selection in the workspace the degradation products and the change of distance between the cathode and the anode, which leads to an increase of the noise detector and a negative impact on the operating characteristics of the detector as a whole and the reliability of the results.

The technical problem of the invention is the improvement of performance of the detector by increasing the stability of its work in time, povertyalleviation and reliability in the measurement of low concentrations of gases and increase the service life of the detector.

The technical problem is achieved by the fact that the proposed detector consists of placed in a sealed casing, input and output of the sample gas, the two electrodes, the operating surfaces of which are parallel to each other and dissociated by an insulator, the tritium target is placed between the electrodes, compagnonnage and collector devices, and the insulator is made in the form of a ring and made of silikatmaterialiem material, and one of the electrodes is the body of the detector. As electroceramic materials use quartz, Topaz, chalcedony, and other varieties of quartz minerals.

A comparison of the proposed solution with the prototype shows that it is characterized by the following features:

As the dielectric material for the manufacture of the insulator used electroceramic material.

- Insulating gasket made in the form of a ring placed between the working surfaces of the electrodes.

One of the electrodes is the body of the detector.

The proposed solution meets the criterion of ″novelty″, as characterized by the features that distinguish it from known solutions.

The invention can be manufactured on standard equipment using known processes and materials that can do the ü conclusion on compliance with its criteria ″ industrial applicability″.

Ionization detectors are widely used for the analytical determination of the first permanent trace gases (gaseous substances). The use of our proposed design will improve the service life and stable in time high quality measurements by eliminating the negative influence of the processes of degradation of polymeric materials. Despite the fact that the use of electroceramic (quartz) materials as insulators known in science and technology, in our proposed detector design using silikatmaterialiem material for the manufacture of the insulator allows, in addition to the insulating effect, to obtain a new technical result is to increase the detection limit, to increase the stability of the sensitivity of the detector to increase the resource of stable operation of the detector and to achieve time-stable quality of analytical measurements.

All the above allows to make a conclusion on the conformity of the proposed solutions to the criterion of ″inventive step″, because the proposed design technique allows to achieve a new technical result in the detector as a whole.

The drawing shows a General view of the detector.

The device includes a housing 1, which is the cathode (contact electrode) detector is, the input device of the sample gas 2 and the device output 3, the anode (collector electrode) 4, tritium target 5, the insulator 6, located in the interelectrode space 7 on the dielectric spacer 8, which use Teflon tape. The detector is provided with a current supply and a current collector (not shown). The tightness of the connection of anode and cathode parts of the detector is provided mechanically by connecting each of the structural elements by means of known fastening devices, bolts, nuts, washers (POS. No. 11-14). The tightness of the anode side of the detector is provided by the creation inlet is screwed 9 and displacer 10.

The insulator 6 made in the form of a ring of silikatmaterialiem material. The presence of holes in the insulator is provided by the need to pass through unhindered flow of the analyzed gas mixture. Round-shaped holes of the insulator due to the need of creating a uniform electric field at each point of the interelectrode space. As shown by our experiments, electroceramic material has no effect on the mechanism of ionization of the inert gas or energy transfer from metastable helium to other atoms and molecules, i.e. silikatmaterialiem material directly in the interelectrode space does not introduce its own distortions as a result, the ATA measurements. In addition, the hardness silikatmaterialiem material resistant to the ravages of time and low sorption capacity, ceteris above data allows not only to solve the problem of the invention, but also to simplify the process of installation of the detector, since the interelectrode distance and parallelism between working surfaces of the electrodes is a function of the thickness of the insulator.

The detector works as follows.

The electrodes 1 and 4 is energized. The analyzed gas from the chromatographic column by means of the input device 2 enters the interelectrode space 7 where the ionization of helium with constant exposure, provide tritium target 5. Contained gaseous impurities affect the level of an electrical signal whose readings are taken through the collector device and recorded. The analyzed gas is output from the detector by the output device 3.

The proposed detector has the following technical features: working pressure up to 0.1 MPa, the design pressure of 0.15 MPa test pressure of 0.2 MPa, working temperature up to 50°C, the flow rate of 30-60 ml/min, the resource - 10 years.

A comparative analysis of the characteristics of the detector, manufactured using as an insulator PTFE (control) and quartz (claimed) allows the or to identify the following effects of the material of the insulator on the measurement results. The detectors were graduated in coarse, medium, and high sensitivity in eight gases: Ne, H2About2N2, CO, CH4Kg, Heh. The control detector after spent on grading 24 (8×3) working days needed ″podcastready″ adjustable interelectrode distance. The inventive detector in a similar situation does not require ″update″ after his graduation, that is stable in time the expected sensitivity.

In addition, as you know, one of the main characteristics of the detector is the detection limit, which is equal to 3-4 values of the noise level. The use of the quartz insulator reduces the noise level of the above gases in 3 times in comparison with PTFE, which helped to improve the limit of detection in 2-4 times.

For example, the inventive detector in the coarse mode sensitivity (U=150 (B) allows you to analyze impurities Of2in the range of 1-1000 million-1error 20-5%under the average sensitivity (U=340 (B) 0.05 - 200 million-1error 20-10%, high sensitivity mode (U=450 B) 0.001 to 20 million-1error 100-20%.

As we established, the velocity of the gas flow does not affect the noise level in the inventive detector, whereas in the control the detector noise increases with increasing flow velocity.

Savla the appropriate detectors due to its design can be made with the exception of the impact of the skill level of a particular artist, because working (interelectrode space structurally defined only by the thickness of the insulator, and the parallelism between working surfaces of the electrodes is set only by the uniformity in thickness of the insulator, which greatly simplifies the Assembly process and standardizes the characteristics of the detector. The stability of the proposed detector is largely determined by the fact that the interelectrode space during operation are not exposed to such factors as voltage, temperature and aging.

1. A detector for gas chromatography comprising placed in a sealed casing, input and output of the sample gas, the two electrodes, the operating surfaces of which are parallel to each other and distanced from each other by insulators, tritium target, placed between the electrodes, compagnonnage and collector device, characterized in that the insulator is made in the form of a ring and made of silikatmaterialiem material, and one of the electrodes is the body of the detector.

2. A detector for gas chromatography according to claim 1, characterized in that as silikatmaterialiem material used quartz, glass, Topaz, chalcedony.



 

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