JP2557435B2 - Sample introduction device for inductively coupled plasma mass spectrometry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a sample introduction device for inductively coupled plasma mass spectrometry, and particularly measures ultratrace amounts of uranium (U) and thorium (Th). The present invention relates to a sample introduction device attached to an inductively coupled plasma mass spectrometer.

(Prior Art) When a semiconductor material forming a dynamic memory contains a trace amount of impurities U or Th, the U or Th emits α rays by spontaneous decay, which causes a soft error in the memory cell. Becomes In order to miniaturize and highly integrate the memory for the purpose of speeding up and increasing the capacity, it is important to improve the packaging material and the chip constituent material to lower the α ray. U and
In order to select a manufacturing method of LSI constituent materials with low Th content and materials suitable for practical use, it is necessary to develop a simple and highly sensitive analyzer with a short measurement time.

Conventional U and Th analysis is based on the inductively coupled plasma emission method,
Fluorescence method and activation analysis method are adopted. However, the methods described above have a problem that the sensitivity to a small amount of U and Th is insufficient, a very complicated chemical pretreatment operation is required, and the analysis time is long. Although the above method is widely applied to the analysis of U and Th, it requires a nuclear reactor and is not practical as an analysis method for quality control.

For these reasons, analysis of U and Th by inductively coupled plasma mass spectrometry has been attempted in recent years. In this method, a solutionized sample is atomized with a neprizer and introduced into an inductively coupled plasma for excited ionization. The ions are mass-separated by a quadrupole mass filter and the contents of U and Th in the sample are measured. Although such a method has higher sensitivity than the above method, the sample introduction efficiency into the plasma is low and the detection sensitivity is insufficient at 10 ^-12 g, so that it is practical for a minute amount of sample such as a semiconductor thin film. Could not be applied to.

Therefore, as a method for increasing the efficiency of introducing a sample into plasma and improving the detection sensitivity, a sample introducing device for evaporative vaporization is attached to the inductively coupled plasma mass spectrometer. Such a sample introduction device places a solution sample on a heating substance, applies current or voltage in an inert gas stream, heats the sample step by step, evaporates and vaporizes a target component in the sample, and efficiently converts it into plasma. It is to be introduced. As a heating substance provided in the sample introduction device, a high melting point metal such as graphite, tantalum, and tungsten is generally used. However, when graphite is used as the exothermic substance, when the sample is evaporated and vaporized, U
And Th react with graphite to form carbides,
The ionization efficiency of U and Th remarkably decreases, and a memory effect in which U and Th remain remains. As a result, there has been a problem that detection sensitivity and accuracy are significantly deteriorated. On the other hand, when a refractory metal such as tantalum or tungsten is used as the exothermic substance, U and Th are slightly contained as impurities in these metals, and thus U and Th are detected together with U and Th in the sample. To be measured. As a result, there is a problem that it is difficult to analyze a sample containing U or Th that is less than the content of U or Th in the refractory metal.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to detect an extremely small amount of U or Th in a sample in an inductively coupled plasma mass spectrometer with high sensitivity and high accuracy. Further, the present invention is intended to provide a sample introduction device that enables rapid analysis.

[Structure of the Invention] (Means for Solving the Problems) The first invention of the present application is a heating furnace provided with an electrode made of a good electrical conductor and a tubular cuvette made of a heat-generating substance having a sample injection hole in a central portion, And a gas control mechanism for controlling the flow of the inert gas while flowing the inert gas from one end of the cuvette through the inside and the other end of the cuvette to the plasma torch part of the inductively coupled plasma mass spectrometer. In the sample introduction device, the cuvette surface and the electrode surface, which are brought into contact with a heated inert gas or a vaporized sample gas, are coated with an oxide film or a nitride film of a refractory metal, thereby forming an inductive coupling. It is a sample introduction device for plasma mass spectrometry.

The above electrodes and cuvettes are electric good conductors at 2600 ~ 3000 ℃
Any material that can withstand the above temperature can be used, for example, it can be formed of heat resistant metal such as Clafite or tantalum, tungsten, rhenium or zirconium.

Examples of the refractory metal oxide coating the cuvette surface and the electrode surface which are contacted with the heated inert gas or the vaporized sample gas include tantalum oxide, tungsten oxide, zirconium oxide and the like. As the refractory metal nitride that covers the surface of the cuvette, for example, tantalum nitride, tungsten nitride, hafnium nitride, zirconium nitride, titanium nitride and the like can be mentioned.

The thickness of the refractory metal oxide film or the refractory metal nitride film is determined by the reaction between the vaporized sample and the electrode material coated with the film, the constituent material of the cuvette, or the vaporization of the impurity vapor in the constituent material. It is desirable that the thickness be as thick as possible from the viewpoint of suppressing mixing into the sample, but practically it is 0.1 to 10 μm. The coating of such a refractory metal oxide film or refractory metal nitride film may be performed by any method such as a CVD method, a thermal oxidation method, a sputter deposition method, and a coating / firing method.
The coating-baking method is preferable in consideration of easiness of operation.

Examples of the above-mentioned inert gas include argon and helium, and if necessary, a small amount of hydrogen may be added to the gas.

In the second invention of the present application, the cuvette is formed of graphite, and the cuvette has a sample injection hole,
A sample introduction device is configured by inserting a tube made of a refractory metal whose surface is coated with an oxide film or a nitride film of a refractory metal similar to that described above.

A third invention of the present application is a heating furnace provided with an electrode made of a good electric conductor and a cylindrical cuvette made of a heat generating substance having a sample injection hole in a central part, and one end of the cuvette to the inside and the other end thereof. In an apparatus for introducing a sample into a plasma torch part of an inductively coupled plasma mass spectrometer through which the inert gas is flown and a gas control mechanism for controlling the flow of the inert gas is heated, evaporative vaporization The cuvette surface and the electrode surface, which are in contact with the sample gas, are coated with a double-layered structure film in which a carbide film of a refractory metal and an oxide film or a nitride film of a refractory metal are laminated in this order. And a sample introduction device for inductively coupled plasma mass spectrometry.

The electrodes and cuvettes are formed of a heat-resistant metal such as graphite or tantalum, tungsten, rhenium, zirconium, or the like, as described in the first invention of the present application.

Examples of the refractory metal carbide coating the surface of the cuvette and the surface of the electrode with which the heated inert gas or the vaporized sample gas is contacted include, for example, tantalum carbide, tungsten carbide, hafnium carbide, zirconium carbide, and titanium carbide. Can be mentioned. Further, as the refractory metal oxide or refractory metal nitride laminated on the carbide film of the refractory metal, tantalum oxide, tungsten oxide, zirconium oxide are used as described in the first invention of the present application. Examples thereof include tantalum nitride, tungsten nitride, hafnium nitride, zirconium nitride, titanium nitride and the like.

The thickness of each of the refractory metal carbide film, the refractory metal oxide film and the refractory metal nitride film forming the above two-layer structure coating film is
It is desirable to be as thick as possible from the viewpoint of suppressing the reaction between the electrodes coated with these films and the constituent material of the cuvette itself and the vaporized sample, and mixing of the impurity vapor in the constituent materials into the vaporized sample. 0.1-10 respectively
It may be μm. The coating of such a two-layer structure coating is CV
The method may be any method such as D method, thermal oxidation method, sputter vapor deposition method, and coating / firing method, but the coating / firing method is preferable in consideration of the ease of operation.

Examples of the above-mentioned inert gas include argon and helium, and if necessary, a small amount of hydrogen may be added to the gas.

In the fourth invention of the present application, the cuvette is formed of graphite, and further, a sample injection hole is provided in the cuvette, and the surface thereof has the same refractory metal carbide and refractory metal oxide film or nitride as described above. A sample introduction device is constructed by inserting a high melting point metal tube coated with a two-layer structure coating of a physical film.

(Function) According to the first invention of the present application, the surface of the cuvette and the surface of the electrode which are brought into contact with the heated inert gas or the vaporized sample gas are coated with a refractory metal oxide film or nitride film. Thus, when graphite is used as the base material of the cuvette or the like, it is possible to prevent U and Th in the sample to be analyzed from reacting with graphite to generate a carbide. As a result, the ionization efficiency can be significantly improved and the memory effect can be eliminated. On the other hand, when a refractory metal is used as a base material for a cuvette or the like, U or Th contained as impurities in the refractory metal evaporates due to the barrier action of the refractory metal oxide film or nitride film. Can be suppressed. Moreover, the vaporization start time of U or Th in the refractory metal can be delayed from the vaporization start time of U or Th in the sample by coating the oxide film or the nitride film of the refractory metal. Therefore, the ion spectrum of U or Th in the sample can be temporally separated from the ion spectrum of U or Th in the heat-resistant metal that is the base material. Therefore, according to the first invention of the present application, an extremely small amount of U or Th in a sample in inductively coupled plasma mass spectrometry can be analyzed with high sensitivity, high precision and speed.

According to the second invention of the present application, the cuvette is formed of graphite, and the cuvette has a sample injection hole,
By inserting a tube made of a refractory metal whose surface is covered with an oxide film or a nitride film of a refractory metal similar to that described above, an extremely small amount of U in the sample in the inductively coupled plasma mass spectrometer described above is inserted. And Th can be analyzed with high sensitivity, high precision and speed, and the evaporative vaporization part space of the sample introduction device can be downsized. That is, the cuvette is made of a heat-resistant metal, and the surface thereof is coated with an oxide film or a nitride film of a refractory metal. Although it can be analyzed, since the heat-resistant metal has good thermal conductivity, the space for evaporation and vaporization of the sample introduction device becomes large due to the necessity of heat insulation. Therefore, by forming the cuvette with graphite having excellent heat insulating properties, it is possible to reduce the space of the evaporation / vaporization section of the sample introduction device. In this case, not only the cuvette but also the electrode is made of graphite, so that the size can be further reduced. However, if the cuvette is made of graphite, a trace amount of graphite may be released even when the cuvette surface is coated with a refractory metal oxide film or nitride film. If such graphite release occurs especially in the evaporative evaporation space of the sample, U and Th in the sample
Reacts with graphite to form a carbide, which significantly reduces the ionization efficiency of U and Th, and causes a memory effect. In other words, even if the cuvette is made of graphite and its surface is coated with a refractory metal oxide film or nitride film, the release of graphite causes the cuvette to be made of a heat-resistant metal, and its surface is the same. Compared with the release of impurities in the refractory metal, which may occur even when the oxide film or the nitride film is coated, the analysis accuracy is significantly reduced. Therefore, by inserting a tube made of a refractory metal whose surface is coated with a high-precision metal oxide film or nitride film into the cuvette, and evaporating and evaporating the sample here, the memory effect is eliminated and the temperature is high. It is possible to reduce the size of the space in the evaporative vaporization section of the sample introduction device while maintaining the ionization efficiency.

According to the third invention of the present application, a cuvette surface and an electrode surface, which come into contact with a heated inert gas or a vaporized sample gas, are provided with a refractory metal carbide film and a refractory metal oxide film or nitride film. Are coated in this order with a two-layer structure coating, and when graphite is used as a base material for such cuvettes, U and
It is possible to prevent Th from reacting with graphite to form a carbide. As a result, the ionization rate can be significantly improved and the memory effect can be completely eliminated. Further, by covering the cuvette surface and the electrode surface with a refractory metal oxide film or a nitride film through a refractory metal carbide film, compared to a case where the oxide film or the like is directly coated on the cuvette surface. Adhesion can be significantly improved. On the other hand, when a refractory metal is used as a base material for a cuvette or the like, U or impurities contained in the refractory metal as impurities due to a more excellent barrier action due to the inclusion of a carbide film of a refractory metal having excellent gas impermeability. It is possible to effectively suppress the vaporization of Th. Moreover, the vaporization start time of U or Th in the heat-resistant metal can be delayed by the coating of the two-layer structure coating film compared to the vaporization start time of the sample, so that an ion spectrum due to U or Th in the sample can be obtained. U in the heat resistant metal that is the base material
The ion spectrum due to Th can be temporally separated. Further, by coating the oxide film or the nitride film of the refractory metal on the surface of the cuvette made of a heat resistant metal and the electrode surface through the carbide film of the refractory metal, the oxide film or the like is directly coated on the cuvette surface. The heat resistance can be significantly improved as compared with the case of Therefore, according to the third invention of the present application, as compared with the first invention of the present application, an extremely small amount of U or Th in the sample in the inductively coupled plasma mass spectrometer can be analyzed with higher sensitivity, higher accuracy and speed.

According to the fourth invention of the present application, the cuvette is formed of graphite, and the cuvette has a sample injection hole,
By inserting a tube made of a refractory metal whose surface is coated with a two-layer structure coating of a refractory metal carbide film and a refractory metal oxide film or a nitride film similar to those described above,
Ultra small amounts of U and Th in the sample in the above-mentioned inductively coupled plasma mass spectrometer can be analyzed with high sensitivity, high accuracy and speed, and the space of the evaporative vaporization section of the sample introduction device can be reduced.

Embodiment of the Invention Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

Example 1 FIG. 1 is a schematic sectional view showing a sample introduction device for inductively coupled plasma mass spectrometry used in this example. 1 in the figure
Is a cuvette made of a heating substance, and a sample injection hole 2 is opened in the upper center of the cuvette 1. In the cuvette 1, a cylindrical tube 3 made of a high melting point metal is provided.
Is inserted so that the sample injection hole 4 opened at the upper center thereof matches the injection hole 2 of the cuvette 1. The cuvette 1 is surrounded by electrodes 5a, 5b made of a good electric conductor, which are divided in a direction perpendicular to the axial direction, and both edges of the cuvette 1 contact and support the inner surfaces of the electrodes 5a, 5b, respectively. Has been done. An insulating material layer (not shown) for electrically insulating the electrodes 5a and 5b from each other is provided on the divided surfaces. A pipette insertion hole 6 is opened in one electrode 5a. Each of the electrodes 5a, 5b is surrounded by electrode blocks 7a, 7b made of a good electric conductor which is divided in the direction perpendicular to the axial direction, and each electrode 5a
The outer peripheral surfaces of a and 5b are in contact with and supported by the inner peripheral surfaces of the electrode blocks 7a and 7b, respectively. An insulating material layer (not shown) for electrically insulating the electrode blocks 7a and 7b from each other is provided on the divided surfaces. The electrode block 7a,
The 7b is provided with cooling water passages 8a and 8b for cooling the blocks 7a and 7b. The electrode blocks 7a, 7b
A quartz pipe 9a that serves as a carrier gas outlet and a quartz pipe 9b that serves as a carrier gas inlet are inserted into the respective parts. Further, the electrode blocks 7a, 7b to the electrode 5a,
Carrier gas external flow channels 10a and 10b are bored over 5b, respectively, and carrier gas internal flow channels 11a and 11b are bored in the electrode blocks 7a and 7b near the insertion portions of the quartz pipes 9a and 9b. Has been done. Quartz pipe as the carrier gas inlet
9b and the carrier gas internal flow paths 11a and 11b are the same as those of the tube 3
It is used to flow an independent flow rate of carrier gas during the drying and ashing and evaporative vaporization stages of the sample. In addition,
The cuvette 1, the tube 3, the electrodes 5a and 5b, the electrode blocks 7a and 7b and the like constitute a heating furnace.

Further, 12 in the figure is a unitized gas control mechanism. The gas control mechanism 12 includes a first solenoid valve 14 arranged on the inert gas inlet 13 side. The solenoid valve 14 is connected to a pressure regulator 15, and a pressure meter 16 is connected to the regulator 15. The pressure regulator 15 and the pressure meter 16 are adjusted to proper pressure in advance. Also,
A pipe portion between the solenoid valve 14 and the pressure regulator 15 is connected to a pressure switch 17 for detecting whether or not the pressure of the inert gas introduced from the inert gas inlet 13 is sufficient. When the pressure detected by the pressure switch 17 is equal to or lower than a predetermined value, the detection signal is fed back to the control unit (not shown) of the power supply system of the electrode blocks 7a and 7b, and the cuvette 1 and the like are excessively fed. It also serves to prevent heat generation (around 3000 ° C) and oxidation. On the rear side of the pressure regulator 15, it is branched into three directions and connected to the flow meters 18 to 20 having a flow rate adjusting function. First flow meter
Reference numeral 18 is connected to the carrier gas external flow paths 10a and 10b of the heating furnace. The second flow meter 19 is connected to the carrier gas internal flow paths 11a and 11b of the heating furnace via a second electromagnetic valve 21. The third flow meter 20 includes a quartz pipe 9b which is a carrier gas inlet of the heating furnace via a third solenoid valve 22.
It is connected to. A fourth solenoid valve 23 is provided in a piping system connecting the heating furnace and a plasma torch (not shown) of the inductively coupled plasma mass spectrometer.

In the first embodiment, the surface of the cuvette 1, the surface of the tube 3 and the surfaces of the electrodes 5a and 5b, which are brought into contact with the heated inert gas or the vaporized sample gas, are covered with a refractory metal oxide film or nitride. It has a structure covered with a film.

Next, the operation of the sample introduction device shown in FIG. 1 will be described.

First, the sample is dropped into the cylindrical tube 3 through the pipette insertion hole 6 and the sample injection holes 2 and 4 with the second to fourth electromagnetic valves 21 to 23 closed. Subsequently, according to the heating programming of the control unit from the power supply, the electrode block 7a,
7b is energized, and a voltage is applied to both ends of the cuvette 1 through the electrodes 5a and 5b connected to the electrode blocks 7a and 7b to heat the cuvette 1 and the tube 3 to a predetermined temperature, and the sample 24 in the tube 3 is heated. Along with drying and ashing,
The third solenoid valves 21 and 22 are opened to supply an inert gas (carrier gas) to the internal passages 11a and 11b of the heating furnace and the quartz pipe 9b as an inlet. As a result, water vapor and coexisting substances generated in the steps of drying and ashing the sample 24 are removed to the outside of the heating furnace through the sample injection holes 4 and 2 and the pipette insertion hole 6 together with the carrier gas. Then, after plugging the pipette insertion hole 8 and the sample injection holes 2 and 4 with a graphite plug, a boron nitride plug, or a heat-resistant metal plug (not shown) whose surface is covered with a refractory metal oxide film or nitride film, , The cuvette 1 is energized to generate heat at a higher temperature to vaporize and vaporize the target component in the sample 24, and at the same time, open the fourth electromagnetic valve 23 to incinerate the vaporized target component. It is introduced into the plasma torch and is excited and ionized. The ions are measured by mass separation using a quadrupole mass filter, and the concentration of the target component is calculated from the ion intensity using a calibration curve. After the above operation is completed, cuvette 1 and tube 3
After cooling, the second to fourth solenoid valves 21 to 23 are closed, the sample is injected again, and the same operation is repeated to perform the measurement.

When evaporating and vaporizing the above-described sample, the surface of the cuvette 1, the surface of the tube 3 and the surfaces of the electrodes 5a and 5b, which are brought into contact with the heated inert gas or the vaporized and sampled gas, are covered with a refractory metal oxide film or nitride Since graphite is used as the base material of the cuvette 1 and the electrodes 5a and 5b, U and Th in the sample 24 dropped in the tube 3 react with graphite to generate carbides because they are covered with a physical film. Can be prevented. As a result, the ionization efficiency can be significantly improved and the memory effect can be completely eliminated. Therefore, ultra trace amounts of U and Th in the sample in the inductively coupled plasma mass spectrometer can be analyzed with high sensitivity, high precision and speed.

In fact, it was confirmed that ultra-trace amounts of U and Th in the sample can be accurately analyzed by performing the following experiment using the sample introduction device for inductively coupled plasma mass spectrometry of the first embodiment.

Example 1-1 Electrodes 5a and 5b made of graphite, cuvette 1 made of graphite having an outer diameter of 8 mmφ, an inner diameter of 6 mmφ, a length of 28 mm, and a sample injection hole of 2 mmφ in the central portion were cylindrical. Tube 3 has an outer diameter of 5.5 mmφ, an inner diameter of 4.5 mmφ, a length of 26 mm, and a sample injection hole of 2 mmφ in the center.
Ones each made of high-purity tantalum were used. The electrodes 5a, 5b, the cuvette 1, and the cylindrical tube 3 were coated with a tantalum nitride film having a thickness of about 0.5 μm on the surfaces of the portions in contact with the heated inert gas and the vaporized sample gas. Note that the coating of the tantalum nitride film was performed by applying an organic tantalum compound on a predetermined member surface and then firing in a nitrogen atmosphere.

Comparative Example 1-1 Except that the tantalum cylindrical tube was not used and the electrode and the cuvette were not coated with the tantalum nitride film,
A sample introduction device similar to that of the above Example 1-1 was assembled.

Comparative Example 1-2 Example 1 above except that the electrode, cuvette and tantalum cylindrical tube were not coated with a tantalum nitride film.
A sample introduction device similar to -1 was assembled.

Therefore, the present Example 1-1 and Comparative Examples 1-1 and 1-2
Using the sample introduction device and the inductively coupled plasma mass spectrometer, the ionic strength of the 10 μm sample of 100 pg / ml uranium standard solution and the 10 μm sample of 0 pg / ml standard solution were measured under the following conditions.

Carrier gas in sample introduction device; Argon at 4.0 / min.

Drying in the sample introduction device; 150 ° C, 30 sec.

Ashing in the sample introduction device; 1000 ° C, 30 sec.

Evaporative vaporization in sample introduction device; 2800 ° C, 7 sec.

Frequency of high frequency power supply with plasma torch; 27.12 MHz.

High frequency output of high frequency power supply with plasma torch; 1.3kW.

Cooling gas with plasma torch; 15 / min.

Plasma gas with plasma torch; 0.8 / min.

As a result, in Example 1-1, the uranium standard solution 100 p
The ionic strength of the g / ml sample was 250, and the ionic strength of the same standard solution 0 pg / ml sample was 5. On the other hand, Comparative Example 1-
In 1, the ionic strength of the sample of 100 pg / ml uranium standard solution is 6, and the ionic strength of the sample of 0 pg / ml standard solution is 2.
Since the cuvette was made of graphite itself, uranium became a carbide and could not be detected. In Comparative Example 1-2, the uranium standard solution 100 pg / ml sample had an ionic strength of 280, and the uranium standard solution 0 pg / ml sample had an ionic strength of 42. The tantalum nitride film was not coated on the cylindrical tantalum. The ionic strength of uranium was measured even in the sample containing no standard solution due to the mixture of uranium vaporized from the tube.

Example 1-2 The electrodes 5a and 5b were made of graphite, and the cuvette 1 was made of graphite having an outer diameter of 8 mmφ, an inner diameter of 6 mmφ, a length of 28 mm, and a central 2 mmφ sample injection hole having a cylindrical shape. Tube 3 has an outer diameter of 5.5 mmφ, an inner diameter of 4.5 mmφ, a length of 26 mm, and a sample injection hole of 2 mmφ in the center.
Each of them was made of high-purity tungsten. The electrodes 5a and 5b, the cuvette 1 and the cylindrical tube 3 were coated with a tungsten nitride film having a thickness of about 0.5 μm on the surface where the heated inert gas or the vaporized sample gas was in contact. The tungsten nitride film was coated by applying an organotungsten compound on the surface of a predetermined member and then firing it in a nitrogen atmosphere.

Comparative Example 1-3 A sample introducing device similar to that in Example 1-2 was assembled except that the tungsten cylindrical tube was not used and the electrode and the cuvette were not covered with the tungsten nitride film.

Comparative Example 1-4 A sample introducing apparatus similar to that in Example 1-2 was assembled except that the electrode, the cuvette, and the cylindrical tube made of tungsten were not covered with the tungsten nitride film.

Then, the present Example 1-2 and Comparative Examples 1-3, 1-4
Using the sample introduction device and the inductively coupled plasma mass spectrometer of 10 μm of the thorium standard solution 100 μg / ml sample and 10 μm of the same standard solution 0 pg / ml, the ashing conditions were 600 ° C. for 30 s.
The ionic strength was measured under the same conditions as in Example 1-1 except that ec was used. As a result, in Example 1-2, the ionic strength of the sample containing 100 pg / ml of the thorium standard solution was 240, and the ionic strength of the sample containing 0 pg / ml of the standard solution was 7. On the other hand, in Comparative Example 1-3, the ionic strength of the sample containing 100 pg / ml of the thorium standard solution was 4, the ionic strength of the sample containing 0 pg / ml of the standard solution was 2, and the cuvette was formed of graphite itself. Thorium became a carbide and could hardly be detected. In Comparative Example 1-4, the ionic strength of the sample containing 100 pg / ml of the thorium standard solution was 280, and the ionic strength of the sample containing 0 pg / ml of the standard solution was 52, which was a cylindrical cylinder made of tungsten not coated with the tungsten nitride film. The ionic strength of thorium was measured even in the sample containing no standard solution by mixing thorium vaporized from the tube.

As described above, in the sample introduction device of the present Example 1, the measurement of uranium and thorium is about 100 times that of the conventional inductively coupled plasma mass spectrometry, and the comparison with the inductively coupled plasma mass spectrometry combined with the conventional evaporative vaporization method is performed. It can be seen that the detection sensitivity of uranium and thorium is improved by about 10 times. In addition, the sample introduction device of the first embodiment can be used for an inductively coupled plasma emission spectrometer, and the detection sensitivity is further improved by about 10 times as compared with the conventional inductively coupled plasma emission spectrometry using the vaporization method. Can be achieved.

Example 2 In the sample introduction apparatus of Example 2, the surface of the cuvette 1 to which the heated inert gas or the vaporized sample gas is contacted, the surface of the tube 3 and the surfaces of the electrodes 5a and 5b are made of a refractory metal. It has a structure in which a carbide film and a refractory metal oxide film or a nitride film are covered with a two-layer film laminated in this order.

According to such a configuration, when evaporating and evaporating the sample, the surface of the cuvette 1, the surface of the tube 3 and the electrodes 5a and 5b which are brought into contact with the heated inert gas and the evaporatively evaporated sample gas are similar to those in the first embodiment. The surface of the cuvette 1 and the electrode are covered with a double-layered film in which a refractory metal carbide film and a refractory metal oxide film or nitride film are laminated in this order.
When, for example, graphite is used as the base material of 5a and 5b,
It is possible to prevent U and Th in the sample 24 dropped in the tube 3 from reacting with graphite to generate a carbide. As a result, the ionization efficiency can be significantly improved and the memory effect can be completely eliminated. Therefore, ultra trace amounts of U and Th in the sample in the inductively coupled plasma mass spectrometer can be analyzed with high sensitivity, high precision and speed.

In fact, it was confirmed that ultra-trace amounts of U and Th in the sample can be accurately analyzed by performing the following experiment using the sample introduction device for inductively coupled plasma mass spectrometry of the second embodiment.

Example 2-1 The electrodes 5a and 5b made of graphite, the cuvette 1 made of graphite having an outer diameter of 8 mmφ, an inner diameter of 6 mmφ, a length of 28 mm, and one sample injection hole of 2 mmφ in the central portion were cylindrical. Tube 3 has an outer diameter of 5.5 mmφ, an inner diameter of 4.5 mmφ, a length of 26 mm, and a sample injection hole of 2 mmφ in the center.
Ones each made of high-purity tantalum were used. The electrodes 5a and 5b, the cuvette 1 and the cylindrical tube 3 are coated with a tantalum carbide film having a thickness of about 0.3 μm on the surface of a portion which comes into contact with the heated inert gas and the vaporized sample gas. It was coated with a tantalum nitride film having a thickness of about 0.2 μm. The coating of the tantalum carbide film was performed by applying an organic tantalum compound to the surface of a predetermined member and then firing it in an argon gas atmosphere, and the coating of the tantalum nitride film was performed by applying the organic tantalum compound to the surface of the predetermined member. After that, firing was performed in a nitrogen atmosphere.

Comparative Example 2-1 A sample introducing device similar to that in Example 2-1 was assembled except that a cylindrical tube made of tantalum was not used and the electrode and the cuvette were not covered with the tantalum carbide film and the tantalum nitride film.

Comparative Example 2-2 A sample introduction device similar to that in Example 2-1 was assembled except that the electrode, the cuvette, and the tantalum cylindrical tube were not covered with the tantalum carbide film and the tantalum nitride film.

Then, the present example 2-1 and the comparative examples 2-1, 2-2
Using the sample introduction device and the inductively coupled plasma mass spectrometer of 10 μg of the uranium standard solution of 100 μg / ml and 10 μm of the standard solution of 0 pg / ml, the ionic strength was measured under the same conditions as in Example 1-1. . As a result, the present Example 2-
In 1, the ionic strength of the sample of 100 pg / ml uranium standard solution is 25
The ionic strength of the sample of 0 and the standard solution of 0 pg / ml was 2. On the other hand, in Comparative Example 2-1, uranium standard solution 100p
The ionic strength of the sample of g / ml was 6, the ionic strength of the sample of 0 pg / ml of the same standard solution was 2, and since the cuvette was formed of graphite itself, uranium became a carbide and could hardly be detected. Further, in Comparative Example 2-2, the ionic strength of the sample of 100 pg / ml of the uranium standard solution was 280, and the ionic strength of the sample of 0 pg / ml of the standard solution was 42, which was a cylindrical shape of tantalum not coated with the tantalum nitride film. The ionic strength of uranium was measured even in the sample containing no standard solution due to the mixture of uranium vaporized from the tube.

Example 2-2 The electrodes 5a and 5b made of graphite, the cuvette 1 made of graphite having an outer diameter of 8 mmφ, an inner diameter of 6 mmφ, a length of 28 mm and one sample injection hole of 2 mmφ in the central portion were cylindrical. Tube 3 has an outer diameter of 5.5 mmφ, an inner diameter of 4.5 mmφ, a length of 26 mm, and a sample injection hole of 2 mmφ in the center.
Each of them was made of high-purity tungsten. The electrodes 5a, 5b, the cuvette 1, and the cylindrical tube 3 cover the surface of the portion in contact with the heated inert gas or the vaporized sample gas with a tungsten carbide film having a thickness of about 0.3 μm. It was coated with a tungsten nitride film having a thickness of about 0.2 μm.

Comparative Example 2-3 A sample introducing device similar to that in Example 2-2 was assembled except that a cylindrical tube made of tungsten was not used and the electrode and the cuvette were not covered with the tungsten carbide film or the tungsten nitride film.

Comparative Example 2-4 A sample introducing device similar to that of the above Example 2-2 was assembled except that the electrode, the cuvette and the cylindrical tube made of tungsten were not covered with the tungsten carbide film or the tungsten nitride film.

Thus, the present example 2-2 and the comparative examples 2-3, 2-4
Using the sample introduction device and the inductively coupled plasma mass spectrometer of 10 μm of the thorium standard solution 100 μg / ml sample and 10 μm of the same standard solution 0 pg / ml, the ashing conditions were 600 ° C. for 30 s.
The ionic strength was measured under the same conditions as in Example 1-1 except that ec was used. As a result, in Example 2-2, the ionic strength of the sample containing 100 pg / ml of the thorium standard solution was 240, and the ionic strength of the sample containing 0 pg / ml of the standard solution was 2. On the other hand, in Comparative Example 2-3, the ionic strength of the sample of 100 pg / ml of the thorium standard solution was 4, the ionic strength of the sample of 0 pg / ml of the standard solution was 2, and the cuvette was formed of graphite itself. Thorium became a carbide and could hardly be detected. Further, in Comparative Example 2-4, the ionic strength of the sample of 100 pg / ml of thorium standard solution was 280, and the ionic strength of the sample of 0 pg / ml of standard solution was 52, which was a cylindrical cylinder made of tungsten not coated with the tungsten nitride film. The ionic strength of thorium was measured even in the sample containing no standard solution by mixing thorium vaporized from the tube.

As described above, in the sample introduction device of the present Example 2, the measurement of uranium and thorium is about 200 times that of the ordinary inductively coupled plasma mass spectrometry, and compared with the conventional inductively coupled plasma mass spectrometry combined with the evaporative vaporization method. It can be seen that the detection sensitivity of uranium and thorium is improved by about 20 times. In addition, the sample introduction device of the second embodiment can be used for an inductively coupled plasma optical emission spectrometer, and has a detection sensitivity about 20 times higher than that of the conventional inductively coupled plasma optical emission spectrometer combined with the vaporization evaporation method. Improvement can be achieved.

[Effects of the Invention] As described in detail above, according to the present invention, there is provided a sample introduction device capable of analyzing ultra-trace amounts of U and Th in a sample in an inductively coupled plasma mass spectrometer with high sensitivity, high accuracy and speed. It is possible.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a sample introduction device for inductively coupled plasma mass spectrometry showing one embodiment of the present invention. 1 ... Cuvette, 2, 4 ... Sample injection hole, 3 ... Cylindrical tube, 5a, 5b ... Electrode, 7a, 7b ... Electrode block, 10a, 10b ... Carrier gas internal flow path, 11a, 11b ......
Carrier gas external flow path, 12 …… Gas control mechanism, 17 …… Pressure switch, 21-23 …… Solenoid valve, 24 …… Sample.

Claims (4)

(57) [Claims] 1. A heating furnace provided with an electrode made of a good electric conductor and a cylindrical cuvette made of a heat-generating substance having a sample injection hole in the center, and from one end of the cuvette to the inside and the other end thereof. In a sample introduction device composed of a gas control mechanism for flowing an inert gas into the plasma torch part of an inductively coupled plasma mass spectrometer and controlling the flow of the inert gas, a heated inert gas or vaporized gas is introduced. A sample introduction device for inductively coupled plasma mass spectrometry, characterized in that the surface of the cuvette and the surface of the electrode which are brought into contact with the sample gas are covered with an oxide film or a nitride film of a refractory metal. 2. A cuvette made of graphite,
Further, the surface of the cuvette and the surface of the electrode which are brought into contact with the heated inert gas or the vaporized sample gas are covered with an oxide film or a nitride film of a refractory metal, and a sample injection hole is further provided in the cuvette. The sample introduction device for inductively coupled plasma mass spectrometry according to claim 1, wherein a tube made of a refractory metal is inserted and the surface of the tube is covered with an oxide film or a nitride film of the refractory metal. 3. A heating furnace provided with an electrode made of a good electric conductor and a cylindrical cuvette made of a heat-generating substance having a sample injection hole in the center, and from one end of the cuvette to the inside and the other end thereof. In a sample introduction device composed of a gas control mechanism for flowing an inert gas into the plasma torch part of an inductively coupled plasma mass spectrometer and controlling the flow of the inert gas, a heated inert gas or vaporized gas is introduced. The cuvette surface and the electrode surface, which are contacted with the sample gas, are coated with a two-layer structure coating in which a carbide film of a refractory metal and an oxide film or a nitride film of a refractory metal are laminated in this order. Inductively coupled plasma mass spectrometry sample introduction device. 4. The cuvette is made of graphite,
And, the cuvette surface and the electrode surface which are contacted with the heated inert gas or the vaporized sample gas are laminated with a refractory metal carbide film and a refractory metal oxide film or nitride film in this order. A tube made of refractory metal having a sample injection hole is inserted into the cuvette, and the tube surface is covered with a carbide film of refractory metal and an oxide film or nitride of refractory metal. The sample introduction device for inductively coupled plasma mass spectrometry according to claim 3, characterized in that the sample film and the physical film are covered with a two-layer structure film laminated in this order.