JPH0522866B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a thermal ionization detector, and particularly to a thermal ionization detector used as a detector for a gas chromatograph device. (b) Prior Art A thermal ionization detector is a device that provides an emission electrode in a hydrogen flame or hydrogen plasma to selectively detect phosphorus, nitrogen, halogen, sulfur compounds, etc. with high sensitivity. As the emission electrode, for example, a spiral wire made of copper, stainless steel, platinum, platinum-iridium, etc., an alkali metal salt such as cesium (Cs), rubidium (Rb), potassium (K), etc. of Group 1 of the periodic table, For example, materials to which sodium hydroxide (NaOH), potassium chloride (KCl), potassium bromide (KBr), cesium bromide (CsBr), rubidium silicate (Rb ₂ SiO ₃ ), etc. are attached are used. Since all of the alkali metal salts have low melting points, the lifetime of the emission electrode is shortened, and the sensitivity of the detector changes greatly over time, making it difficult to stabilize the sensitivity, which is a problem. (c) Purpose The present invention aims to provide a thermal ionization detector that stabilizes the sensitivity of the thermal ionization detector and extends the life of the emission electrode. That is, a thermal ionization detector using a new type of emission electrode using lanthanum hexaboride is provided. (d) Configuration The present invention resides in a thermal ionization detector characterized by comprising an emission electrode containing at least lanthanum hexaboride. In the present invention, lanthanum boride, especially lanthanum hexaboride (LaB ₆ ), is a substance with a melting point of 2210°C, a small work function, and a very high electron emissivity on the solid surface. Any type of material can be used, but commercially available products are usually used. It is preferable to manufacture the powder by fusing this mixed powder of lanthanum hexaboride crystal and silicic anhydride (SiO ₂ ) to a coil of metal wire such as platinum. The emission electrode of the present invention can be adjusted to an appropriate potential with respect to the frame electrode depending on the measurement mode, and can also be formed so as to be electrically heated to an arbitrary temperature. (E) Embodiment The figure is a schematic sectional view showing an embodiment of the thermal ionization detector of the present invention. Hereinafter, the present invention will be explained in detail with reference to the drawings, but the present invention is not limited to this explanation in any way. The thermal ionization detector of the present invention is indicated generally at 1. The separation column 2 is connected to a quartz nozzle 3 of the detector, and a tube 4 communicates with a hydrogen gas supply (not shown). The open end 5 of the quartz nozzle 3 opens into the detector cell, and a nozzle electrode 7 is arranged at the end 5.
The electrode 7 is connected to a high voltage power source 8. The detector cell 6 is provided with an air or oxygen supply port 9 around the quartz nozzle 5 . This air or oxygen supply port 9 is preferably provided with a diffusion plate or the like so that the hydrogen gas and oxygen gas can be sufficiently mixed. A cylindrical inner collector electrode 10 is provided opposite the nozzle electrode 7, and surrounding the outer periphery of the collector electrode 10,
An electrically insulating cylinder 11 made of ceramics is provided,
A cylindrical outer collector electrode 12 is provided on the outside thereof. The emission electrode 14 uses lanthanum hexaboride (LaB ₆ ) with a melting point of 2210 as an emission source.
℃ crystals were used. Lanthanum hexaboride is attached by mixing its crystals with silicic anhydride powder and fusing this powder mixture to a 0.2 mm coiled platinum wire. The emission electrode 14 is located directly above the nozzle end 5, for example, at a height of about 6 mm,
One end thereof is electrically connected to the end of the inner collector electrode 10, and the other end is electrically connected to the inner end of the outer collector electrode 12, and can be electrically heated. The other end of the outer collector electrode 12 is connected to a power controller 15 via a transformer.
The other end of the inner collector electrode 11 is connected to one end of a power controller 15 and an electrometer 16. Since the thermal ionization detector 1 of the present invention has such a structure, the sample gas flowing out from the separation column 2 mixes with hydrogen gas and burns compounds containing hydrocarbons and hetero elements. The emission electrode is made of platinum wire through alternating current.
Heats to a dark red color. If the amount of hydrogen gas and the amount of air are adjusted appropriately, the background current can be adjusted by changing the voltage supplied to the platinum wire. The selectivity and reproducibility of nitrogen compounds with respect to hydrocarbons are as follows:
The selectivity was 7.2×10 ⁴ gC/gN, the coefficient of variation was 1.3%, and the dynamic range was 10 ⁴ or more. Also, azobenzene 3.8ng - eicosane 7.6μg
When rubidium sulfate (RbSO ₄ ) is used as the emission source, the selectivity is 3.7×10 ⁴
It was gC/gN. On the other hand, when the lanthanum hexaboride (LaB ₆ ) of the present invention was used as the emission source, the selectivity was 5.22×10 ⁴ gC/gN. Furthermore, as shown in the following table, its intelligence was extremely reproducible and highly accurate, and it remained unchanged even after 500 hours of use.

【table】

[Table] These results are based on the inner diameter of the column.
A 2.6 mm, 1 m long Pyrex (trade name) glass column was used, and Chromosolve W was used as a carrier.
-HP (product name) with a particle size of 80 to 100 mesh is used, and the liquid phase is SP2250 (product name), a high boiling point liquid based on metal phenyl, silicone, etc. The amount of liquid phase coating is It was 5%. In addition, the temperature of the sample introduction part is 300℃,
Column temperature was 210°C. Helium gas is used as the carrier gas, and its flow rate is 42
ml/min. The thermal ionization detector was used at a temperature of 300° C. with hydrogen gas supplied at 5.5 ml/min and air at 102 ml/min. (f) Effects By using lanthanum hexaboride as an emission source, the present invention eliminates the short lifetime and sensitivity of the emission source, which are found in conventional thermal ionization detectors using alkali metal salts. Therefore, compared to conventional thermal ionization detectors, analysis of nitrogen and phosphorus compounds is stable over long periods of time.
In addition, it has become possible to perform it with high sensitivity and good reproducibility. These results are due to the performance of lanthanum hexaboride provided by the present invention, and have a large influence.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view showing one embodiment of the thermal ionization detector of the present invention. 1 is a thermal ionization detector, 2 is a separation column, 3 is a quartz nozzle, 4 is a hydrogen gas supply pipe, 5 is a quartz nozzle end, 6 is a detector cell, 7 is a nozzle electrode, 8 is a high voltage power supply, 9 is oxygen 10 is an inner collector electrode, 11 is a cylindrical insulator, 12 is an outer collector electrode, 13 is an end of the electrode 12, 14 is an emission electrode, 15 is a power controller, and 16 is an electrometer.

Claims (1)

[Claims] 1. A thermal ionization detector comprising an emission electrode containing at least lanthanum hexaboride.