JPH0963534A - Method and device for high-frequency induction coupled plasma massspectrometry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a shield from causing a discharge on a plasma and crossing magnetic flux by making the shield about as long as a work coil, and installing the shield inside the work coil. SOLUTION: A plasma 2 is formed inside a plasma torch 1 from power supplied from a high frequency power supply 6 to a work coil 4 and from gas supplied from a gas control part 5. A gap is provided between the work coil 4 and the plasma torch 1, and a shield 3 is inserted in such a way that the length of the shield 3 is about equal to the winding length of the work coil 4. Since the shield 3 and the plasma 2 are separated an appropriate amount equal to the projected length of the plasma torch 1 from the work coil 4, the plasma 2 is stably maintained without causing a discharge. Also, since the shield 3 is not projected beyond the work coil 4 to the opposite side of the plasma 2, it does not cross magnetic flux formed by the high-frequency power applied to the work coil 4, nor is it heated or damaged.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high frequency inductively coupled plasma mass spectrometry method and apparatus.

[0002]

2. Description of the Related Art In the structure shown in FIG. 3, the plasma has a potential with respect to the surrounding ground potential portion, and the plasma 2
Discharge at an interface part (sampling cone, skimmer cone, etc.) not shown in the figure, and generate molecular ions, oxide ions, and secondary ions that interfere with analysis.

In order to reduce the plasma potential in order to avoid this, conventionally, as shown in FIG. 3, a shield 3 is provided between the plasma torch 1 and the work coil 4 on the outer periphery of the plasma 2. At this time, the size of the shield 3 was set larger than that of the work coil 4 in order to lower the plasma potential.

For example, Japanese Utility Model Laid-Open No. 63-9761 discloses such a structure.

[0005]

However, conventionally, when the shield 3 largely protrudes from the work coil 4 toward the tip side of the plasma 2, discharge is likely to occur between the shield 3 and the plasma 2, and the shield 3 is damaged. Or, if the shield 3 largely protrudes from the work coil 4 on the side opposite to the plasma 2, the magnetic flux that supplies power to the plasma 2 from the work coil 4 by inductive coupling will be crossed.
There is a problem that induced electromotive force is generated in the shield 3 and the power supplied to the plasma is reduced to cause an error in the analysis value, and the shield 3 is heated and, in some cases, the shield 3 is damaged.

Therefore, an object of the present invention is to obtain a shield having a structure in which plasma is not discharged and a magnetic flux is not traversed in order to solve the conventional problems as described above.

[0007]

In order to solve the above-mentioned problems, the present invention makes the length of the shield approximately the same as that of the work coil in the shape (length) and position of the shield, and the shield is It is designed to be installed in the length.

[0008]

In the shield configured as described above,
The shield does not extend beyond the work coil to the plasma side, no discharge occurs between the shield and the plasma, and the shield does not extend beyond the work coil to the opposite side of the plasma, and the work coil inductively couples to the plasma. Therefore, the magnetic flux supplying the electric power is not crossed, and the induced electromotive force is not generated in the shield.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, plasma 2 is formed in the plasma torch 1 from the electric power supplied from the high frequency power source 6 to the work coil 4 and the gas supplied from the gas control unit 5.
A sample is introduced into the plasma 2 from a sample atomizer (not shown) through the plasma torch 1. A mass analyzer 7 is provided close to the plasma 2, and ions generated in the plasma 2 are introduced into the mass analyzer 7 and analyzed.

At this time, a space is provided so that the shield 3 can be inserted between the work coil 4 and the plasma torch 1. The shield 3 provided such that the length of the shield 3 is substantially equal to the winding length of the work coil 4, that is, the length in the axial direction, is substantially the same as the work coil 4 in the gap between the work coil 4 and the plasma torch 1. It is provided at a position corresponding to the inside. The shield 3 is grounded by the lead wire 8.

Since the shield 3 and the plasma 2 are separated by an appropriate amount (usually 1 to 10 mm, more usually 3 to 5 mm, preferably 4 mm) that the plasma torch 1 protrudes from the work coil 4, The plasma 2 is stably maintained without causing discharge. That is, the work coil 4 has an appropriate amount (usually 1 to 10 mm, more often 3 to 5 mm) from the tip end of the plasma torch 1.
It is preferable that the distance is 4 mm). It is 1m
When it is less than m, electric discharge easily occurs between the work coil 4 and the pulsar 2, and when it is more than 10 mm,
Since they are separated from each other, the ions generated by the plasma 2 cannot be efficiently introduced into the mass spectrometer 7.

Further, since the shield 3 is not protruded beyond the work coil 4 on the side opposite to the plasma 2 (the root side of the plasma torch 1), it is used for inductive coupling formed by the high-frequency power applied to the work coil 4. Does not cross the magnetic flux.
Therefore, induced electromotive force is unlikely to occur in the shield 3. Therefore, the power supplied to the plasma 2 is not reduced, an error is not caused in the analysis value, the shield 3 is not heated, and the shield 3 is not damaged.

Since the shield 3 is installed close to the plasma torch 1 close to the plasma 2, it is desired to have high heat resistance. Further, it is desired that it is non-magnetic so as not to cause inductive coupling. Furthermore, in order to function as the shield 3, it must have electrical conductivity. Therefore, the material of the shield 3 needs to be a high heat resistant non-magnetic conductive material.

As such a material, it is desirable to use pure metals such as tantalum, molybdenum, titanium and platinum, and alloys thereof. When the shield 3 is arranged inside the work coil 4, it becomes difficult for the plasma 2 to be generated (started) in the plasma torch 1. Therefore, the shield 3 can be further moved by the shield moving means 10 to the axial base side of the plasma torch 1 (left side in FIG. 1). A person may be used as the moving means, or a rod-shaped object may be moved. Further, in order to regulate the movement amount of the shield 3, a bank-shaped projection 11 is formed on the outer periphery of the plasma torch 1.
Is provided. When the plasma 2 is turned on, the shield 3 is arranged (moved) on the base side of the plasma torch 1 by the shield moving means. After the plasma is turned on by the high frequency power of the work coil, the shield 3 is arranged (moved) on the base side of the plasma torch 1 by the shield moving means.

[0015]

As described above, according to the present invention, the length of the shield is set to be approximately the same as that of the work coil, and the shield is installed in the winding length of the work coil. Since it does not extend beyond the coil to the plasma side and discharge does not occur between the shield and the plasma, the shield does not break and the shield does not extend beyond the work coil to the side opposite the plasma, Since the magnetic flux that supplies power to the plasma by inductive coupling is not crossed and no induced electromotive force is generated in the shield, the power supplied to the plasma does not decrease, and there is no error in the analysis value. It also has the effect of not damaging the shield.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of a main part of an example of a conventional method.

[Explanation of symbols]

 1 Plasma torch 2 Plasma 3 Shield 4 Work coil 5 Gas control unit 6 High frequency power supply 7 Mass spectrometer 8 Lead wire

Claims (4)

[Claims] 1. A high frequency power supply for supplying high frequency power, a work coil connected to the high frequency power supply, a plasma torch for supplying a gas for forming plasma by the high frequency power supplied to the work coil, and a gas control unit. And a gas control unit for supplying the gas to the plasma torch, and a shield having a length substantially equal to the winding length of the work coil and disposed on the outer periphery of the plasma torch. A high frequency inductively coupled plasma mass spectrometer, comprising a plasma ion source according to claim 1, wherein a gap is provided between the work coil and the plasma torch so that the shield can be inserted. 2. The high frequency inductively coupled plasma mass spectrometer according to claim 1, wherein the material of the shield is a high heat resistant non-magnetic conductive material. 3. The high frequency inductively coupled plasma mass device according to claim 2, wherein the material of the shield is a pure metal such as tantalum, molybdenum, titanium, platinum which is a high heat resistant non-magnetic conductive material, and an alloy thereof. . 4. A high-frequency power source for supplying high-frequency power, a work coil connected to the high-frequency power source, a plasma torch for supplying a gas for forming plasma by the high-frequency power supplied to the work coil, and a gas control unit. And a gas control unit for supplying the gas to the plasma torch, and a shield having a length substantially equal to the winding length of the work coil and disposed on the outer periphery of the plasma torch. High-frequency inductively coupled plasma mass, characterized in that the shield is movable in the axial direction of the plasma torch, and the shield is provided with an air gap so that the shield can be inserted between the work coil and the plasma torch. Analysis equipment.