JPH03222298A - Microwave plasma trace element analyzing device - Google Patents

Abstract

PURPOSE:To highly sensitively and efficiently analyze a trace element by forming a plasma torch into a double tube structure consisting of a discharge tube outer tube and a discharge tube inner tube, and thickening the top end part of the inner tube. CONSTITUTION:A plasma torch system is formed of a double tube consisting of an outer tube 10 and an inner tube 20, and the difference between the inner diameter of the outer tube 10 and the outer diameter of the top end part of the inner tube 20 is less than 2mm. The other end of the inner tube 20 is connected to a sample introducing system 30. The top end of the outer tube 10 is extended over the top end of the inner tube 20, and the other end is terminated in a plasma gas introducing tube 40 connected in the tangential direction. In this case, by thickening the top end part 21 of the inner tube 20 of the plasma torch of double tube structure, the plasma gas flow rate can be reduced, and also the pressure in the center part of a plasma generating part 80 can be reduced, so that a doughnut plasma can be easily formed. Hence, the analysis of a trace element can be highly sensitively and efficiently performed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to the improvement of a trace element analyzer using plasma generated by microwave power, and particularly to the improvement of a microwave plasma generation system and a plasma torch system therein. Regarding the improved structure of.

[Conventional technology]

This type of conventional apparatus is described, for example, in Applied Spectroscopy, 39.2 (1985, pp. 214 to 222) (Appl, 5pectroscopy).
39, 2 (1985) pp214-222) and Spectrochemistry Acta 40B, 3 (1985) No. 49
Pages 3 to 499 (Spectrochimica
Acta 40B, 3 (1985) pp493-4
99), and each has a configuration as shown in FIGS. 3 and 4.

That is, in the former conventional example, as shown in FIG. 3, the microwave plasma generation system uses TMo technology. mode cavities are used and microwave power is supplied via a coaxial cable connector. Furthermore, a through hole is provided in the center of the cavity, and the discharge tube outer tube 1 is placed inside the through hole.
A plasma torch consisting of a discharge tube inner tube 20 and a discharge tube inner tube 20 is installed as shown.

In the configuration of FIG. 3, the TMo process is caused by heat generation, as shown in FIG. The mode cavity is water-cooled, the plasma torch has a triple tube structure, and the discharge tube outer tube 10 is forcedly air-cooled. As a result, the microwave input power can be increased to 500 W, and compared to FIG. 3, the analysis sensitivity has been improved and the types of samples that can be analyzed have been expanded. In FIG. 4, reference numeral 10 indicates an outer tube of the discharge tube, 20 indicates an inner tube of the discharge tube, and 22 indicates a plurality of slots provided at the tip of the inner tube of the discharge tube.
2 is the same as in FIG. 3, TM, 0. It is installed in the center of the mode cavity.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, the plasma shape is made into a donut and the resulting high sensitivity (lower detection limit), the high sensitivity is achieved by increasing the microwave power supply (500 W or more), and the discharge tube inner tube 20 Not enough consideration was given to reducing damage to the tip, and there were problems with sensitivity (detection limit), the types of samples that could be analyzed, and the stability of the analysis.

An object of the present invention is to stably generate donut-shaped plasma with high power and solve the above problems.

[Means to solve the problem]

In order to achieve the above object, in the present invention, as shown in FIG.
It has a double tube structure consisting of a discharge tube inner tube 20, etc., and the tip 21 of the inner tube 20 is thickened (see the detailed diagram in FIG. 2). (2) The microwave cavity is made of a flat waveguide 9.
0, an inner conductor 100, and an end plate 111;
This is set at a distance f backward from the tip of 00.

[Effect]

In (1), making the tip 21 of the inner tube 20 thick as shown in FIG. This acts to reduce the pressure on the central axis of the plasma generating part 80.Thereby, it acts to facilitate generation of doughnut-shaped plasma.

The flat waveguide 90 (thickness in electric field direction: a
<20 mm) serves to facilitate impedance matching with the plasma, and also serves to supply large power (500 W or more). As a result, reflected power is drastically reduced and efficiency is improved. moreover,
It operates so that solution samples can be directly analyzed, and the range of samples that can be analyzed is also expanded. Further, by using the inner conductor 100 and the end plate 111, a surface wave is excited in the gap e between them. This weakens the electric field strength on the central axis, making it easier to generate donut-shaped plasma. Furthermore, by adjusting the gap e, any electric field strength can be obtained. That is, the electric field strength is inversely proportional to the gap e. The microwave power absorbed by the plasma is proportional to the square of the electric field strength.

From the tip of the inner conductor 100 in (3) above to the inner tube 2
Setting the distance Mf to the tip 21 of 0 operates so that the plasma gas pressure and the plasma pressure are balanced at a constant ratio. This makes it possible to stably hold the donut-shaped plasma, and also serves to reduce damage to the tip 21 caused by the plasma.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a sectional view showing the structure of a surface wave excitation type microwave cavity and a plasma torch, which are the main parts of the apparatus of the present invention, and the installation positional relationship between the two. Further, FIG. 2 is a detailed sectional view of the plasma torch shown in FIG. 1.

In Fig. 1, numerals 10 and 20 indicate the outer and inner tubes of the discharge tube made of quartz that form the plasma torch, and 90 indicates a flat waveguide made of copper (thickness in the electric field direction when the microwave frequency is 2.45 GHz). Sa = 2~20mm, usually 8.6mm
, the magnetic field direction is a regular shape of 109.2 mm), and 100 is an inner conductor made of copper, for example, cylindrical (inner diameter: 6 to 20 mm, for example).
φ) cavity 10L is provided. The shape of the inner conductor 100 is, for example, a truncated cone, and the height b thereof is usually 0<b.
<50 mm. 110 is a cylindrical shape made of copper (
An outer conductor with an inner diameter of, for example, 40 to 100 mmφ.

A copper end plate 111 is provided at one end.

The end plate 111 is provided with a circular hole through which the discharge tube outer tube 10 passes, and the length d of the end plate 111 is
From the tip of the inner conductor 100 to the end plate 111
The distance e is set to (e=1 to 30 mm). Also.

A plurality of coolant discharge ports 11 are provided on the outer periphery of the outer conductor 110.
3 is provided at equal intervals. 120 is a coolant (usually air) introduction system made of copper or the like, and the coolant is introduced into the discharge tube outer tube 10.
The cavity 10 flows in a spiral manner around the outer periphery of the
It was configured to be introduced from the connecting direction to the inner circumferential wall surface of No. 1. Note that it is preferable to set the distance C from the tip of the inner conductor 100 to the other end where the coolant introduction system is provided to be about 1/4 of the microwave wavelength used (to reduce leakage of microwave power). ). Reference numeral 130 is a plasma sampling cone made of nickel or the like, which is used when performing mass spectrometry.

FIG. 2 shows a detailed sectional view of the plasma torch. Here, 10 is a discharge tube outer tube made of quartz, and its inner diameter A is 3.
~20 mmφ (when the plasma gas is a rare gas such as Ar, A=3 to 10 mmφ, and when the plasma gas is a molecular gas such as N2, A□=6 to 20 mmφ: due to the large thermal conductivity coefficient).

20 is a discharge tube inner tube made of quartz, and the outer diameter B0 of its tip 21 is 2.8 to 19 mmφ, and the gap E between the outer tube 10 and the inner tube 20 is set to 0.2 to 1 mm. It is. Here, if E is smaller than 0.2 mm, manufacturing accuracy is required and manufacturing becomes difficult. On the other hand, if E exceeds 1 mm, it becomes difficult (unstable) to generate donut-shaped plasma, and the consumption of plasma gas also increases. Therefore, the inner diameter A□ of the outer tube 10 and the outer diameter B of the inner tube tip 21. It is preferable that the difference is 2 mm or less. Reference numeral 30 denotes a carrier gas and sample introduction tube made of quartz, which is directly connected to the inner tube 20. Reference numeral 40 denotes a plasma gas introduction tube made of quartz, and a p
- It is attached from the tangential direction as shown in the p' cross section.

5o is a gap between the outer tube 10 and the inner tube 20 (plasma gas swirling section), which is larger than the gap 60 at the tip end 21 of the inner tube (plasma gas acceleration section). Plasma gas (He, N
2. Air, 02. Ar, etc., flow rate 1 to 20 Q/
m1n) is transported to the discharge space 80 while rotating uniformly). 7o is a carrier gas provided in the inner tube 20 (same as normal plasma gas, flow rate 0.3-1.
Q/win) and the sample outlet, its diameter D0 beam.

= 0, 6 to 1, 5 mmφ, which is narrower than the other parts (to increase the flow velocity and forcefully introduce the sample into the plasma center). Also,
The distance f from the distal end 21 of the inner tube 2o to the distal end of the inner conductor 100 (see the construction drawing) is for reducing damage to the distal end 21, forming a donut of plasma, and stabilizing it.

Set f=5 to 20 mm. Note that this value depends on the flow rate of the plasma gas, the microwave power, the inner diameter A of the outer tube 10 of the discharge tube, the outer diameter Bo of the inner tube 20, and the tip of the inner conductor 100 and the end plate 111. If the value of f becomes smaller than the above range, the tip 21 of the inner tube 20 will be damaged by the plasma, and the plasma will become unstable or even disappear. . On the other hand, if f is larger than the above range, the plasma will concentrate or swirl and become unstable.

Although the plasma torch shown in Fig. 2 has the inner and outer tubes integrated, it is also possible to assemble them separately, as in the prior art shown in Fig. 4, and the material may also be ceramic or the like. good.

Further, in FIG. 1, a metallic coil (usually 1 to 5 turns, diameter 6 to 30 mmφ) is provided between the inner conductor 100 and the end plate to excite circularly polarized waves and generate plasma. Good too.

The plasma is generated at atmospheric pressure or lower pressure (760
~I O-'T o r r).

〔Effect of the invention〕

According to the present invention, the inner tube 2 of the plasma torch has a double tube structure.
By making the tip 2 of 0 thicker.

Since the plasma gas flow rate can be reduced and the pressure at the center of the plasma generating section 80 can be reduced, there is an effect that doughnut-shaped plasma can be easily generated. In addition, by configuring the microwave cavity based on the flat waveguide 90, inner conductor 100, and end plate 111, it is possible to supply high power (500W or more) with good matching (without reflected power), and also to Because it can excite circularly polarized waves, it has the effect of generating donut-shaped plasma. By setting the distance f from the tip 21 of the inner tube 2o of the plasma torch to the tip of the inner conductor 100, it is possible to stably hold the donut-shaped plasma.

Stable generation and maintenance of such a doughnut-shaped plasma has the effect of stably and efficiently analyzing trace amounts of elements with high sensitivity (low detection limit).

[Brief explanation of drawings]

FIG. 1 is a sectional view of a device according to an embodiment of the present invention, FIG. 2 is a detailed sectional view of a plasma torch portion of the device of the present invention, and FIGS. 3 and 4 are sectional views of a device according to the prior art. . 10...discharge tube outer tube, 20...discharge tube inner tube, 21.
... Inner tube tip, 30 ... (carrier gas + sample) introduction tube, 40 ... plasma gas introduction tube, 70 ... (carrier gas + sample) outlet, 80 ... plasma generation part, 90... Flat waveguide, 100... Inner conductor, 110
... Outer conductor, 111 ... End plate, 120.
... Coolant introduction system.

Claims (1)

[Claims] 1. A microwave plasma trace element analyzer comprising at least a microwave plasma generation system, a plasma torch system, a sample introduction system, and a measurement system, wherein the plasma torch system is comprised of an outer tube and an inner tube. It is composed of a double tube, and the difference between the inner diameter of the outer tube and the outer diameter of the tip of the inner tube is 2 mm.
The other end of the inner tube is connected to the sample introduction system,
A microwave plasma trace element analyzer characterized in that a tip of the outer tube extends longer than a tip of the inner tube, and the other end is terminated with a plasma gas introduction tube connected tangentially. 2. The micro device according to item 1 above, characterized in that the outer shape of the inner tube constituting the plasma torch system is cup-shaped, and the outer diameter of the tip of the inner tube is larger than the outer diameter of other parts. Wave plasma ultratrace element analyzer. 3. In the above item 1 or 2, the microwave plasma generation system is configured with at least a flat waveguide, and a through hole is provided in the direction of the electric field, and the plasma torch system is installed through the through hole. Features Microwave plasma ultratrace element analyzer. 4. In the above item 3, a metal truncated cone having a cylindrical cavity is provided in the through-hole inside the flat waveguide so that their axes coincide with each other, and the plasma torch system is passed from the cavity to the through-hole. A microwave plasma ultratrace element analysis device characterized by being equipped with. 5. In item 3 or 4, one of the through holes provided in the flat waveguide has a diameter larger than the other, and the through hole is provided on the outside of the side surface of the flat waveguide having the large through hole. A microwave plasma ultratrace element analyzer, characterized in that a metal cylinder is provided with an end plate having a hole at its tip so that its mouth and axis coincide, and an outer tube of the plasma torch is inserted into the hole. . 6. In the third term, fourth term, or fifth term, the distance f from the tip of the inner tube constituting the plasma torch system to one side of the flat conduit in the electric field direction or the tip of the truncated cone is constant. A microwave plasma ultratrace element analysis device characterized in that the value is maintained at a value (5<f≦20mm). 7. The microwave plasma trace element analysis apparatus according to any one of items 1 to 6, characterized in that at least one of the flat waveguide and the plasma torch system is provided with a cooling system.