KR20020033984A - Corona Discharge Photo-Ionization Detector Assisted by Stabilizers. - Google Patents

Abstract

PURPOSE: A corona discharge photoionization detector is provided to maintain stable corona discharge and maximize selectivity of detector, while achieving improved accuracy of detection. CONSTITUTION: A detector comprises a discharge unit(1) for generating helium and corona discharge light; an ionization detection unit(2) for detecting ionized sample; and a filter/buffering unit(3) for stabilizing flow of gas and light generated from the discharge unit, and prevents back flow of the sample being introduced into the detection unit. The filter/buffering unit includes a mesh(9) having a mesh diameter of 0.3mm, and which attenuates the noise caused due to the ionized particles; a buffering space(10) of 200mm3 for preventing back flow of the sample; a hole(11) having a diameter of 3 to 4mm and which maximizes movement of the helium and discharge light and prevents back flow of the helium and discharge light; a sensitive electrodes(13) having a diameter of 3 to 4mm, and which increases detection sensitivity; and a large electrode(12) having a diameter of 6 to 8mm and length of 2 to 5mm.

Description

Corona Discharge Photo-Ionization Detector Assisted by Stabilizers.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector for measuring a sample separated-eluted from a gas chromatograph. Among the various types of gas chromatography detectors, the present invention relates to a discharge ionization detector and a photo ionization detector for ionizing and analyzing eluted materials. .

Discharge ionization detectors are described in H. Kawaguchi, et al., Anal. Sci., Vol. 12. Apr, 1996. As described in p. 195, it is known to have a high sensitivity compared to a thermal conductivity detector and a flame ionization detector, which are widely used as a detector of a gas chromatograph. In particular, unlike the helium ionization detector, this detector is known to be very safe because it does not use a radioactive material as an ionization source. On the other hand, the photoionization detector uses an ultraviolet lamp as an ionization source, and the light emitted from the ultraviolet lamp ionizes the sample, and is used to analyze the eluted sample with relatively good sensitivity and selectivity. However, since some of the light used as the ionization source cannot penetrate the lamp window or the transmission efficiency is poor, it is impossible to analyze components requiring ionization energy of 10.5 eV or more.

In discharge ionization detectors, see R. P. W. Scott, Chromatographic detector, Marcel Dekker, Inc. As described in New York, p132, 1996, USA, a high voltage is applied between two electrodes located at a helium-filled discharge to induce atmospheric gas discharge. In this process, light in the vacuum ultraviolet region and the quasi-stabilized gas are ionized into the detector. The electrons generated during the ionization process are rejected by the counter electrode applied with a negative voltage, induced to the sensitive electrode, and detected by a micro current meter connected to the sensitive electrode. Since the vacuum ultraviolet rays generated during this process and the gas in the quasi-stabilized state ionize the trace amount sample, it is known that the structure of the discharge portion and the detection portion, and the shape and position of each electrode have a very important effect on the detection sensitivity. However, the discharge ionization detector does not effectively move the helium and photons in the quasi-stabilized state, and the sample flowing into the ionization unit flows back to the discharge unit, which is problematic in improving detection sensitivity and securing signal stability due to the phenomenon. Accordingly, the detector is manufactured and used in the same form as in the paper, WE Wentworth, et al., Chromatographia, vol 34. 1992. p.219 and in US Pat. No. 4975648, but with US Pat. Nos. 5889404 and 6037179. Similarly, structural improvements for lowering the detection limit and increasing selectivity continue to this day.

Helium, which is mainly used as the discharge gas in the discharge ionization detector, generates light in the vacuum ultraviolet region of 13.5 to 17.7 eV and forms quasi-stabilized atoms with energy of 19.8 and 20.7 eV, thus all lower ionization energy than these. Samples of organic elements and inorganic gases are ionized. However, G. Gremand, et al., J. Chromatogr., A, vol. 724. As in p. 235, helium gas containing a small amount of inert gas may be used as the discharge gas to increase the selectivity of sample detection. When helium containing a small amount of inert gas is used as the discharge gas, the mixed inert gas is sufficiently excited due to the relatively stabilized helium atoms in which diffusion is relatively slow. If a small amount of argon is used, the 11.62 and 11.83 eV resonances of argon play an important role in sample ionization. Therefore, since only eluted samples having ionization energy lower than these resonance lines are ionized, it is known that the selectivity of sample detection is improved. However, pure inert gases, except helium, do not discharge because of their high breakdown voltage at atmospheric pressure. Therefore, in the case of helium gas having a high mixing ratio of other inert gas, it is known that the mixing ratio should be kept below 1% because it does not show stability enough to be used as a discharge gas.

An object of the present invention is to provide a method for designing, fabricating, and applying a chromatographic detector having a low detection limit, versatility and selectivity, and having the following three detailed purposes.

First, the present invention is to enable a trace amount analysis of various organic samples and inorganic gas samples by designing a corona photo ionization detector equipped with a stabilization device to have the characteristics of the discharge-ionization detector and the photo-ionization detector at the same time . Secondly, an inert gas is added to helium for the purpose of increasing the selectivity of detection, and it is for constructing and applying a discharge unit capable of stable discharge phenomenon even if the added amount is increased. Third, to provide a general structure and method for maintaining the airtight inside the detector to the outside air.

1 is an overall view of a corona discharge photo ionization detector.

2nd and 3rd degree filter-buffers.

4, 5, 6 or a view of the discharge portion.

7, 8, 9 are views of the ionization-detection section.

10 is a diagram of a sensitive electrode.

11 is a view of a counter electrode.

12 shows the filter-buffer-gasket part, the discharge part and the ionization-detection part assembled.

In order to achieve the above object, the corona discharge photoionization detector of the present invention comprises a discharge portion, an ionization-detection portion, and a filter-buffer portion disposed on the same concentric axis.

Hereinafter, described in detail by the accompanying drawings as follows. 1 is an overall view of a corona discharge photo ionization detector. The detector is composed of a discharge part 1, an ionization-detection part 2 and a filter-buffer part 3 on the same axis. The discharge part has a discharge gas injection port 4, and the ionization-detection part has a sample gas injection port 5 injected through a separation tube of a gas chromatograph, and a discharge hole 6 through which discharge gas and sample gas are discharged. The two electrodes 7 and 8 are discharge electrodes, and corona discharge is formed when a high voltage is applied in an atmosphere filled with discharge gas. The metastable helium and photons emitted at this time are ionized through an ion filter 9 located at the filter-buffer 3, a buffer space 10 and a hole 11 installed to prevent backflow of the analyte gas. The sample introduced through the sample inlet 5 is ionized while being guided to the detection unit. In order to start the discharge, a high voltage DC voltage is induced to the two discharge electrodes of the discharge unit through the electronic circuit. The ionization-detecting section 2 is composed of a counter electrode 12, a sensitive electrode 13, a sample gas inlet 5, and an outlet 6. As a negative voltage is added to the counter electrode, electrons generated by the sample ionization are induced to the sensitive electrode 13. The sensitive electrode 13 is connected to the microcurrent meter to obtain an ionization signal proportional to the sample amount. The sensitizing electrode is located on the same axis as the hole of the filter-buffer part to increase the trapping efficiency of the electrons.

2 and 3 are cross-sectional and top views of the filter-buffer 3, which is an important feature of the present invention. The filter-buffered part 3 uses copper having a diameter of 14-18 mm and a length of 4-8 mm in order to be used as a gasket connecting the discharge part 1 and the ionization-detection part 2 on the same axis. In addition, the filter-buffer has a metal mesh filter (9) to effectively move a large amount of quasi-stabilized helium and emitted light to the ionization-detector and to effectively remove signal noise caused by ions generated in the corona discharge. For this purpose, the size of the hole 11 is 3-4 mm in diameter. At the same time, the filter-buffer 3 has a diameter of 8 mm, a length of 4 mm, and a volume of 200 mm ³ in order to prevent backflow of the sample gases in the discharge direction and to prevent degradation of the resolution due to dragging of the detection peak. The buffer space 10 is provided.

4, 5 and 6 are detailed views of the discharge portion. The discharge electrodes 7, 8 are located at the center of the cylindrical discharge part body 2 and are sealed with a cloisonne glaze 14 for electrical insulation. The materials of the electrodes 7 and 8 were platinum wires of 1 mm in diameter with good mechanical stability, and the ends were needle-shaped and installed as close to the filter 9 as possible for the stability of the discharge. The discharge electrode is connected to the DC high voltage power supply by the wires 15 and 16.

7, 8 and 9 are detailed views of ionization-detection. The counter electrode 12 and the sensitive electrode 13 were each sealed with a cloisonne glaze 14 to be bonded while maintaining electrical insulation to the ionization-detector body 3. Since the counter electrode was supplied with a negative voltage, 150-250V from an external power source, a cylindrical mesh 18 having a diameter of 6-8 mm and a length of 2-5 mm was welded so as to keep the field distribution spatially constant. The sensitive electrode is located in the center of the cylindrical ionization-detection part and is located in series with the hole through which the light passes from the filter-buffer part. The upper surface is provided with a metal disk 19 having a diameter of 3-4 mm to detect the sensitivity. Is maximized. The upper end of the mesh of the counter electrode surrounding the sensitive electrode is positioned 1 mm above the original plate of the collecting electrode and 0.5 mm below the position of the sample inlet, and the sample flowing through the sample inlet 5 and the discharge part are perpendicular to each other. Installed to maximize detection sensitivity. The incoming sample and the discharge gas are discharged through the outlet 6 of FIG. The counter electrode and the sensitive electrode are connected to the DC voltage power source and the micro current meter by wires 20 and 21 of FIG. 8, respectively.

12 is a coupling diagram of the corona discharge photoionization detector, in which the discharge part 1 and the filter-buffer part 3 at the middle part and the ionization-detection part 2 at the lower part are coaxially fastened with four screws 22. Structure. To enable airtight and electrical bonding of the three components, a filter-buffer made of copper is used as the gasket. In addition, the front of the discharge portion and the detection portion is provided with a blade-shaped (17 in Figs. 6 and 9) of 12-15mm in diameter and fastened with four bolts to maintain airtightness with the outside air and to electrically connect the three bodies to ground Keep the state

Since the discharge part is equipped with two needle-shaped discharge electrodes with short intervals, stable corona discharge is maintained even when discharged at a level of DC 150-250V using helium containing 1-7% argon as the discharge gas. The selectivity of the detector is maximized.

The filter-buffer part is provided with a buffer space of 200 mm ³ , a metal mesh net is installed toward the discharge part, and a hole of 3-4 mm in diameter is provided at the ionization-detection part, so that detection noise and ionized particles generated from discharge are generated. The detection noise caused by the mesh is suppressed and the reverse flow of the analysis sample gas flowing into the detection unit is alleviated, thereby increasing the stability of the discharge and increasing the stability of the detection signal.

In the ionization-detection unit, a counter electrode is installed and a negative voltage is applied to guide the electrons generated by the ionization of the sample to the sensing electrode.Because the counter electrode of the metal mesh is widely installed in the detection unit, electrons present in the entire detection unit It is effectively guided to the sensitive electrode. In addition, since the surface of the sensitive electrode electrode is provided with a wide plate, there is an effect of increasing the detection sensitivity.

All electrodes are attached by cloisonne glaze, and the filter-buffer part made of copper is used as a gasket, and the front part of the discharge part and the detection part is made in the shape of a blade and fastened with four bolts. Airtightness is maintained and electrical bonding is possible.

The detector of the present invention can detect trace elements in organic samples and inorganic gas samples up to 0.01 pg / s, and can maintain an accuracy of 1-2% in an analysis of 10 pg / s. Then, helium or 1-7% of argon-added helium is used as the discharge gas, which enables stable discharge, thereby increasing selectivity.

Claims (3)

A discharge unit 1 for generating helium and corona discharge light in a metastable state, An ionization-detector 2 in which the ionized sample is detected, A corona discharge photoionization detector, comprising: a filter-buffer 3, which stabilizes the flow of light formed in the discharge portion and gases in a quasi-stabilized state, and blocks back flow of a sample flowing into the detector; In the filter-buffer 3, a 0.3 mm mesh network 9 for attenuating noise caused by ionized particles, In the filter-buffer section 3, a 200 mm ³ buffer space 10 provided to prevent backflow of the sample and In the filter-buffer 3, a hole 11 having a diameter of 3-4 mm for maximizing the movement of the helium and the discharge light in the quasi-stabilized state and preventing backflow, In the ionization-detecting section 2, disc-shaped sensitive electrodes 13 and 19 having a diameter of 3-4 mm, which are manufactured to increase the detection sensitivity, In the ionization-detection section, a detector for a gas chromatograph having a diameter of 6-8 mm, a length of 2-5 mm, and counter electrodes 12 and 18 of a metal mesh. 2. The filter-buffer is made of pure copper 14-14 mm in diameter and 4-8 mm in length, according to claim 1, to enable airtight and electrical bonding of the three critical components (1, 2 and 3). And use it as a gasket, and the discharge part and the detection part are made of stainless steel with a blade shape of 12-17 mm in diameter and fastened with four bolts to maintain airtightness; A method of manufacturing a detector comprising using a cloisonne glaze to maintain and seal electrical discharge, counter electrode and sensitive electrode in the body. The spacing of the needle-shaped discharge electrodes 7 and 8 in the discharge portion of claim 1 is kept within 0.2 mm, using helium or helium added with 1-7% of argon as the discharge gas, respectively, at a DC voltage of 150-250 V. Analytical method for detecting a sample while maintaining corona discharge.