JPH09318542A - Method and apparatus for analyzing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for analyzing an element with high sensitivity and high accuracy. SOLUTION: A plasma torch 2 has a conical plasma chamber 2d pointed toward the forward end. In addition, a cold coil 3 for applying high frequency is arranged around the plasma chamber 2d. A plasma 4 is generated in the plasma chamber 2d by applying a high frequency (27.12MHz) voltage from the cold coil 3 while feeding Ar.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an elemental analysis method and an elemental analysis apparatus.

[0002]

2. Description of the Related Art As an analysis of elements contained in a sample,
Flame / emission analysis, atomic absorption analysis, mass spectrometry, etc. are common. Among them, the high frequency inductively coupled plasma mass spectrometry using a high frequency inductively coupled plasma (ICP) torch is
It is widely used because of its characteristics such as high sensitivity and high accuracy. Further, the high frequency inductively coupled plasma mass spectrometry is more sensitive than the high frequency inductively coupled plasma atomic emission spectrometry by three digits or more, and elemental analysis with a concentration of ppt or less is possible.

Further, as a method for increasing the sensitivity of elemental analysis, it is considered that the detection system and the sample introduction system have higher sensitivity. The detection system has been improved by adopting a detection method with higher sensitivity and a detector with high transmittance. Moreover, even in the analysis method using the high frequency inductively coupled plasma torch, by changing the detection method from the spectrometer to the high frequency inductively coupled plasma mass spectrometry employing the highly sensitive mass analyzer, the high frequency inductively coupled plasma is analyzed. It was possible to achieve a sensitivity of ppt that is three orders of magnitude lower than the ppb of emission analysis.

Also in high frequency inductively coupled plasma mass spectrometry, the sensitivity is further improved by adopting a double focusing type mass spectrometer instead of a quadrupole type mass analyzer.
Devices with detection limits of ppq that are three orders of magnitude lower than pt have also become commercially available. On the other hand, regarding the sample introduction system as well, it is known that the efficiency of sample introduction is improved by the development of an ultrasonic nebulizer or a desolvation type nebulizer, and the sensitivity is improved by one to two orders of magnitude over that of a normal nebulizer.

[0005]

However, with the development of high-purity materials such as semiconductor materials, it has become indispensable to develop and improve analytical methods with even higher sensitivity. Under such circumstances, higher sensitivity is required even in the analysis using the above-mentioned high frequency inductively coupled plasma (ICP) torch. Here, the analysis accuracy is greatly influenced by the shape of the plasma flame generated by the torch. And, although the shape of the high temperature flame (plasma flame) is influenced by the control of the sample air flow in the torch, conventionally, the control of the sample air flow simply controls the pressure and the flow rate. Taking high frequency inductively coupled plasma emission spectrometry and high frequency inductively coupled plasma mass spectrometry as examples, currently commercially available devices simply pass pressurized argon gas through the pipes of the device. Of course, pressure control with a pressure reducing valve etc. and flow rate control with a flow meter etc. are performed,
It does not control the sample air flow in the torch itself.

As a result, argon passes through the pipe (torch) in a turbulent state. This turbulence causes pulsation, which causes instability of the plasma flame. When observing the plasma flame, the flame extinguishes momentarily and a flickering fluctuation is observed, which is due to the generation of pulsating flow. This instability of the plasma flame appears as a change in the emission intensity and the ionic intensity, which causes a decrease in accuracy.
Further, in the turbulent flow, the argon gas flow diverges in the torch portion, so that a converged plasma flame does not form. For this reason, in the conventional commercially available device, a method of obtaining a converged plasma flame by using a plasma torch with a triple structure in which the sample airflow is further wrapped by a double gas flow is adopted, but it is sufficiently converged. No plasma flame is obtained. Therefore, conventionally, there has been a problem that element analysis cannot be performed with higher sensitivity and higher accuracy.

The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide an elemental analysis method and an elemental analysis device capable of performing elemental analysis with high sensitivity and accuracy. To aim.

[0008]

According to the elemental analysis method of the present invention, a gas serving as a plasma source is supplied in the elemental analysis method of analyzing a sample using atoms generated by dissociating a sample to be analyzed. Plasma is generated, and the sample air flow obtained by vaporizing the sample using the gas as a carrier or the sample air flow containing the sample components is introduced into the plasma, and the sample air flow or the plasma containing the sample air flows is made into the spiral air flow, and the sample components are dissociated, The sample was analyzed according to the state of atoms generated by the dissociation. As a result of the above, the generated plasma flame becomes more convergent.

Further, the elemental analysis device of the present invention is an elemental analysis device for analyzing a sample to be analyzed by using atoms generated by dissociating the sample to be analyzed, and a coil for applying a high frequency is arranged around the elemental analysis device. A torch having a plasma chamber for generating plasma by the high frequency to dissociate the sample, and the outlet from which the generated plasma is emitted has a shape in which the tip has a smaller diameter at a predetermined throttle angle, and the sample is directed toward the plasma chamber. A sample supply section for discharging a solution, and an auxiliary gas supply section for supplying a supplemental gas serving as a plasma source and for vaporizing the sample solution discharged from the sample supply section from the periphery of the sample supply section toward the plasma chamber. , A main gas supply unit that supplies a main gas that serves as a plasma source and cools the torch wall surface from around the auxiliary gas supply unit toward the plasma chamber. The state of the dissociated sample atoms in the plasma discharged from the torch was set to and a detector for detecting. With the above configuration, the plasma flame generated in the plasma chamber becomes more convergent along the shape of the tip portion of the torch.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a main configuration of a primitive absorption spectrometer using an ICP according to an embodiment of the present invention. As shown in FIG. 1, the sample solution in the sample introduction part 1 is supplied to the sample introduction tube 2a of the plasma torch 2 through the sample tube 1a. This quartz plasma torch 2 has a triple structure, and Ar gas is introduced from the cooling gas system 2b and the auxiliary gas system 2c, and these gases are supplied so as to surround the sample introduction tube 2a. There is.

The plasma chamber 2d of the plasma torch 2
Has a truncated cone shape that is narrowed toward the tip.
In addition, a cold coil 3 for high frequency addition around it
Is arranged. Then, with Ar being supplied, a high frequency (27.12 MHz) is generated by the cold coil 3.
Is applied, plasma 4 is generated in the plasma chamber 2d. Here, Ar supplied from the cooling gas system 2b
Is consumed as a plasma source in the plasma chamber 2d while cooling the outer wall of the plasma torch 2.

On the other hand, Ar supplied from the auxiliary gas system 2c
Is introduced in order to push up the plasma 4 generated in the plasma chamber 2d so that it does not come down to the tip of the sample introduction tube 2a. In addition, since Ar is supplied from around the tip of the sample introduction tube 2a, the sample solution is vaporized and supplied into the plasma chamber 2d from the tip of the sample introduction tube 2a. In this manner, the vaporized sample solution is introduced into the plasma chamber 2d in which the high frequency is applied and the plasma 4 is generated by Ar. And
The sample introduced into plasma 4 is ionized by the plasma and ionized. The outer diameter of the plasma torch 2 is 2
0 mm, the tip diameter d of the plasma torch 2 is 11 m
m, the aperture angle θ of the torch part is 13 degrees. Then, by detecting the emission spectrum or the light absorption spectrum of the sample ionized in the plasma 4 with the detector 5, the sample can be analyzed.

FIG. 2 is a schematic view showing the structure of the main part of a mass spectrometer using the ICP according to the present invention. In the case of this mass spectrometry, the sample ionized in the plasma chamber 2d of the plasma torch 2 and ejected from the plasma torch 2 is subjected to a magnetic field by the separator 6 to bend its direction of flight and reach the detector 7 composed of a Faraday cup or the like. I'm trying to detect. Further, in the case of a mass spectrometer, the outer diameter of the plasma torch 2 is 20 mm and the tip nozzle diameter is 1
6 mm, the aperture angle θ of the tip is 13 degrees.

Incidentally, unlike the present embodiment, even in a normal plasma torch whose tip portion is not narrowed, the introduction ports for the cooling gas and the auxiliary gas are displaced from the center, and the structure has a rotational component to some extent. ing. That is, the conventional torch has a structure in which a swirling flow is generated. However, this alone cannot provide a sufficiently focused plasma flame. Also, simply constricting the outlet of the torch does not result in a converged plasma flame. If the outlet of the torch is simply narrowed in this way, the pressure loss increases and the static pressure cannot be secured, and it becomes difficult for the gas to flow, so that the generated plasma flame is not converged.

On the other hand, in this embodiment, the tip of the plasma torch 2 is squeezed into a predetermined shape (cone shape). When a high frequency is applied, it converges and a stable plasma flame is obtained. Here, the predetermined shape is that the Reynolds number (S _Re ) in the radial direction of the gas flow is −6 or less. Let V _r = f (V _za , θ) be the radial velocity that is a function of the average axial velocity V _za and the torch tip aperture angle θ, and let the kinematic viscosity coefficient be γ _R , then the radial Reynolds is The number is S _Re =
It is represented by V _r R / γ _R. Also, the torch tip diameter d = 2R
It is. It has been clarified that a spiral flow occurs when the Reynolds number is -6 or less. Specifically, when the diameter of the torch tip portion is 0.1 to 100 mm, a spiral airflow is generated in the range of the torch tip end aperture angle θ of 5 to 60 degrees.

FIG. 3 is a graph showing an example of the velocity distribution of the spiral airflow by the torch of the above-described embodiment used to obtain the spiral airflow. In this graph, the horizontal axis represents the ratio of the radial distance r from the central axis of the torch to the nozzle radius R of the torch tip, that is, the relative distance r / R, and the vertical axis represents the axial velocity V _z of the torch and the torch. At the maximum axial velocity V _zmax , that is, the relative velocity V _z / V _{z max} . In FIG. 3, the upward triangle, the circle, the square, and the downward triangle have a ratio z / d of the axial distance z from the nozzle outlet to the nozzle diameter d of 1.25, 2.50, and 3, respectively. .7
The case of 5,5.00 is shown. As is apparent from FIG. 3, in the case of the spiral airflow, the axial velocity Vz is large in the central portion, and the velocity distribution is such that the axial velocity Vz rapidly decreases toward the torch pipe wall. Since it has a stable air flow that is as close to a laminar flow as possible, the plasma flame does not spread and becomes a converged plasma flame.

FIG. 4 shows the difference between the normal swirling flow and the spiral air flow generated by the torch of the above-described embodiment. In FIG. 4, the horizontal axis represents the Reynolds number of the swirling flow and the spiral air flow when the swirl number is 0.3, and the vertical axis represents the half width of the spread of the plasma flame. As is clear from FIG. 4, the half width of the spread of the plasma flame sharply decreases in the vicinity of the Reynolds number of | 6 |, and the spiral flow makes it converge.

As described above, when the supply amount of the sample is constant, the torch for generating the spiral airflow according to the present invention described above has a larger amount of Ar than the conventional torch. Thus, the concentration of impurities other than Ar present in the plasma flame due to, that is, the concentration of the sample element to be detected becomes high. Further, if the diameter of the converged and detectable region is sufficiently smaller than the outer diameter of the plasma flame, the effect is further enhanced. For example, if the diameter of the region where the plasma flame can be detected is ½ of the outer diameter of the plasma flame, the impurity concentration will be four times higher, so the sensitivity will be four times higher, and Diameter is 1 / outer diameter of plasma flame
When the value becomes 3, the impurity concentration becomes 9 times, so the sensitivity becomes 9 times, and the sensitivity is improved by about one digit.

Furthermore, since the spiral airflow is an airflow which is as close as possible to a laminar flow, there is almost no pulsating flow, and since the directivity is strong, a stable plasma flame with almost no fluctuation can be obtained. Therefore, the impurity distribution and the plasma distribution can be obtained with good reproducibility, and the emission spectrum intensity and the amount of ions obtained from this can also be obtained with good reproducibility, so that the repeatability and the like are improved.

Here, the plasma states obtained by the plasma torch according to the present invention and the conventional plasma torch are shown in FIGS. 5 and 6, respectively. At this time, a high frequency of 27.12 MHz was output to the torch plasma chamber at 1 k
The sample air flow that applies and supplies W is 0.55 (l / min)
And In addition, as a cooling gas, Ar was set at 15 (l / mi)
n) is supplied and Ar is used as an auxiliary gas at 0.5 (l / mi)
n) Supplied. As shown in FIG. 6, the plasma flame is not converged in the conventional plasma torch, but as shown in FIG. 5, the plasma flame is converged in the plasma torch according to the present invention.

From the above, in the elemental analysis apparatus of the present invention and the elemental analysis method using the apparatus shown in FIGS. 1 and 2, since the sample airflow becomes a spiral airflow in the plasma torch, the converged plasma is generated. A flame is obtained. As a result, firstly, the trace amount of elements contained in the sample can be analyzed with high sensitivity. Further, in the spiral-flow plasma flame, since the flow velocity at the central portion is high, interaction with the tube wall of the torch hardly occurs, and the plasma flame does not directly touch the tube wall of the torch as shown in FIG. Therefore, the torch is not melted, and the analytical sensitivity and accuracy are not hindered by the contamination due to the chemical reaction between the torch and the sample components.

Further, according to the present invention, a stable plasma flame with almost no fluctuation can be obtained, and therefore, the elemental analysis can be performed with high accuracy. For example, the frequency 27.12
High frequency output of 1.4MHz, cooling gas flow rate of 1
2.0 (l / min), auxiliary gas flow rate 0.5 (l / m)
in), the sample gas flow rate is 1.0 (l / mi
When the 10 ppb lanthanum solution of n) was subjected to mass spectrometry using a conventional plasma torch, the intensity of ¹³⁹ La was 7.4 × 10 ¹⁰ counts in Faraday cup (detector) measurement.

On the other hand, when the plasma torch of the present invention is used and analyzed by the mass spectrometer shown in FIG. 2 under the same conditions, the intensity of ¹³⁹ La measured by the detector 7 is 1.6.
It was x10 ¹¹ counts, and the sensitivity could be improved about twice as much as the conventional one. Further, regarding the accuracy of repetition in 10 measurements, the relative standard deviation is 4.04% in the analysis using the conventional plasma torch, whereas the relative standard deviation is in the analysis using the plasma torch of the present invention. It was 1.04%, which is a marked improvement in accuracy. Further, since the plasma flame is enclosed by the tip of the torch, the sensitivity and accuracy are prevented from being deteriorated due to the interference of air components.

An example of phosphorus analysis will be shown below. FIG. 7 shows the results of phosphorus analysis by a conventional mass spectrometer using a torch, and FIG. 8 shows the results of phosphorus analysis by a mass spectrometer using a torch according to the present invention. The concentration of phosphorus to be analyzed is 10 ppb, and the analysis resolution at this time is 300
It was set to 0 or more. As shown in FIG. 7, ICP was used.
^{In 31} P mass spectrometry, ¹⁵ N ¹⁶ O and ¹⁴ N ¹⁶ O ¹ H are interfering ions. As shown in FIG. 8, when the torch of the present invention is used, the ³¹ P detection peak height is approximately doubled. However, interfering ions such as ¹⁵ N ¹⁶ O and ¹⁴ N ¹⁶ O ¹ H
There is no change in the height of the detected peak. That is, it can be seen that the use of the torch of the present invention relatively reduces the influence of interfering ions by half.

[0025]

As described above, in the present invention, a torch having a shape in which the exit from which the generated plasma is emitted has a smaller diameter toward the tip at a predetermined throttle angle is used.
With such a configuration, in the region where the plasma flame of the torch is generated, the sample air flow becomes a spiral air flow and the plasma flame is converged. As a result, according to the present invention, element analysis can be performed with high sensitivity, and a stable flame with almost no fluctuation can be obtained. Therefore, element analysis can be performed with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of a primitive absorption spectrometer using ICP according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a main configuration of a mass spectrometer using an ICP according to an embodiment of the present invention.

FIG. 3 is a graph showing an example of a velocity distribution of a spiral airflow by the torch of the present invention.

FIG. 4 is a characteristic diagram showing a difference between a normal swirling flow and a spiral air flow generated by the torch of the present invention.

FIG. 5 is a photograph showing a state of plasma generation by the plasma torch according to the present invention.

FIG. 6 is a photograph showing a state of plasma generation by a conventional plasma torch.

FIG. 7 is a characteristic diagram showing results of phosphorus analysis by a conventional mass spectrometer using a torch.

FIG. 8 is a characteristic diagram showing the results of phosphorus analysis by a mass spectrometer using a torch according to the present invention.

[Explanation of symbols]

1 ... Sample introduction part, 1a ... Sample tube, 2 ... Plasma torch,
2a ... Sample introduction pipe, 2b Cooling gas system ... 2c ... Auxiliary gas system, 3 ... Cold coil, 4 ... Plasma, 5 ... Detector,
6 ... Separator, 7 ... Detector.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoyuki Horii 5-8-5-15, Kameguro, Meguro-ku, Tokyo

Claims (5)

[Claims] 1. In an elemental analysis method for analyzing a sample by using atoms generated by dissociating a sample to be analyzed, a torch having a shape in which plasma supplied by a gas serving as a plasma source has a smaller diameter toward the tip. Generated in the, the gas is used as a carrier to guide the sample gas stream vaporized the sample or a sample gas stream containing the components of the sample to the plasma, the sample gas stream or the plasma containing the sample gas stream into a spiral gas stream, An elemental analysis method, characterized in that a component is dissociated, and the sample is analyzed according to the state of atoms generated by the dissociation. 2. An element analyzer for analyzing a sample using atoms generated by dissociating a sample to be analyzed, wherein a coil for applying a high frequency is arranged around the element, and plasma is generated by the high frequency. A torch having a plasma chamber for dissociating the sample by means of which the generated plasma is discharged, and the outlet has a shape in which the tip has a smaller diameter at a predetermined throttle angle, and the sample solution is discharged toward the plasma chamber. A sample supply unit, a plasma source, and an auxiliary gas supply unit that supplies an auxiliary gas for vaporizing the sample solution discharged from the sample supply unit toward the plasma chamber from around the sample supply unit, and a plasma source And a main gas supply unit that supplies the main gas for cooling the torch wall surface from the periphery of the auxiliary gas supply unit toward the plasma chamber, Elemental analysis apparatus characterized by comprising a detector for detecting the state of the dissociated atoms of the sample in discharged from serial torch plasma. 3. The elemental analysis device according to claim 2, wherein the aperture angle is an angle at which the Reynolds number at the tip of the torch is -6 or less. 4. The elemental analysis device according to claim 2 or 3, wherein the detector is composed of a photo-detecting means for detecting optical characteristics of atoms in plasma emitted from the torch. Element analysis device. 5. The elemental analysis device according to claim 2, wherein the detection unit includes a separator disposed in the torch where the plasma is emitted, and a separator which is emitted from the torch and passes through the separator. An element analysis device comprising an ion detector for detecting atoms.