JPH05180772A - Laser gasifying/inductively coupled plasma analysis and plasma torch - Google Patents

Abstract

PURPOSE:To perform accurate analysis using a solution standard sample by using a plasma torch having a quadruplex structure and guiding a solvent to plasma. CONSTITUTION:A solid substance is irradiated with laser beam to be gasified and a sample is collected using argon gas of high purity as a carrier. The collected sample is introduced into a plasma torch and, at this time, a solvent is together introduced to excite plasma to analyze the sample by an analyser. In this case, since sensitivity coincides with that in the case of a solution sample even in the laser gasified collected sample when the solvent is allowed to present, the solution sample is used as a standard sample by introducing the solvent into the plasma to enable highly accurate analysis. Therefore, the plasma torch is formed into a concentric circular quadruplex pipe consisting of a sample passage 1, a plasma gas passage 3, a cooling gas passage 4 and the solvent passage 2 provided so as to be adjacent to the passage 1 inside the passage 3 to introduce the solvent such as an acid solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct analysis technique for solid substances regardless of conductors and insulators, and more particularly to analysis of a sample in which an appropriate standard sample is difficult to obtain.

[0002]

2. Description of the Related Art In the materials industry, there is a strong demand for a rapid analysis that can quickly obtain results when maintaining and improving the product quality, or a local analysis that can grasp the variation of the components inside the material when developing the material. Laser vaporization / inductively coupled plasma analysis is being researched as a technique to meet this demand.

According to this method, first, a solid substance is irradiated with a laser beam having high-density energy to melt or scatter a target portion of a sample, and a sample is taken with an inert gas as a carrier (hereinafter, laser vaporization). Called the law). Next, the collected sample is introduced into plasma and excited (including ionization) at high temperature, and finally the element species and the amount thereof are measured. Although various methods are used for this measurement, typical methods include spectroscopy and mass spectrometry.

In the spectroscopic method, a spectrum emitted from an element excited by plasma is measured and analyzed. In mass spectrometry, the ions ionized in plasma are measured and analyzed. In the analysis, from the measurement information, the component in the solid substance for each component element,
The concentration is calculated, and a calibration curve is used for this. This calibration curve is obtained from a standard sample whose components and concentrations are known and measured values. As the standard sample, it is customary to use a plurality of solid samples which are composed of the same kind of components as the solid substance and have different concentrations.

Therefore, the preparation of this standard sample is the most important technical element, and its success or failure has a significant influence on the quantitative result. Therefore, it takes a lot of time and effort to create it. Furthermore, a standard sample may not exist for a new material or a natural product, and even if there is a standard sample, if the component concentration range is deviated, a good calibration curve may not be obtained and the analysis accuracy may deteriorate. A solution sample can be prepared with fine components and concentrations, and if the solution sample can be used as a standard sample, the above problems can be solved.

From this viewpoint, there is an attempt to use an aqueous solution sample instead of the solid sample. "Relative Elemental Response
s for Laser Ablation-Indudtively Coupled Plasma Ma
ss Spectrometry ”Anal. Chem. 1989, 61, p1243-1248,
In order to correct the selective sampling of the laser vaporization method, we have reported a method of correcting the concentration deviation between the collected sample and the solid sample by using the heat of vaporization of the constituent elements and the heat conduction of the solid substance.

[0007]

However, although the above-mentioned correction method can be used to correct the error associated with sampling, it is not possible to eliminate the error when excited by plasma. Solution samples contain solvent, while harvested samples contain no solvent. The presence or absence of this solvent changes the excitation state in the plasma and gives a difference in the measured value. This is an error when a solution sample is used as a standard sample, and it has been left as an issue to eliminate this error.

The present invention has been made in order to solve this problem, and aims to provide an accurate analysis technique using a solution standard sample by considering the presence or absence of a solvent at the time of plasma excitation. ..

[0009]

Means for achieving this object is to use a solution sample as a standard sample for introducing a sample obtained by irradiating a solid material with laser light into inductively coupled plasma for analysis. A laser vaporization / inductively coupled plasma analysis method in which a solvent is introduced into plasma at the time of measurement, and a concentric quadruple tube structure plasma torch that enables introduction of the solvent.

[0010]

FIG. 4 shows an example of a commonly used inductively coupled plasma torch. The plasma torch is a concentric triple tube, and the sample to be collected is carried by the carrier and introduced from the sample passage 1. Argon gas is introduced into the plasma gas passage 3 and cooling gas is introduced into the cooling gas passage 4. There is a high frequency coil 5 at the exit of the triple tube, and a plasma flame 6 is generated.

In the conventional analytical method using the solution standard sample,
First, the solution standard sample is introduced into the sample passage 1, and the relationship between the measured values at various concentrations and the amounts of components contained in the solution standard sample is obtained. This is the calibration curve. Next, instead of the solution standard sample, a laser vaporization sampling sample from a solid substance is used as the sample passage 1.
Introduce to measure the components. The measured value is converted into the content by correcting the conversion amount obtained by the previously obtained calibration curve with heat of vaporization and heat conduction.

According to the research conducted by the inventors, even if the same amount of the component is introduced into the plasma, the difference appears in the sensitivity between the laser vaporization sample and the solution sample. However, it was found that even in the case of the laser vaporization sample, the sensitivity was in agreement with that of the solution sample in the presence of the solvent. this is,
It is considered that the electron density and temperature of the plasma flame differ depending on the presence or absence of the solvent, which affects the measurement sensitivity.

FIG. 1 shows a comparison of the sensitivities in these cases. This is an examination of a steel standard sample. The horizontal axis of the figure is the sensitivity when this standard sample is dissolved in an acid to form a solution sample (hereinafter referred to as the solution method), and the vertical axis is the sensitivity when sampled by the laser vaporization method. When the sample was collected by the laser vaporization method, as in the conventional case, the case where the solvent did not exist and the case where the solvent existed using the quadruple tube described later were examined. The case where the solvent does not exist is indicated by a circle, and the case where the solvent exists is indicated by a triangle. Even if the shape of the sample introduced into the plasma is changed, if the sensitivity is the same, the sensitivity curve becomes a straight line of 45 °.

The results of the investigation are Mn, Ni, Cu, Cr,
In the components such as V, the circles are distributed apart from the 45 ° straight line, while the triangles are distributed on the straight line or extremely close to each other. Although there is a difference in sensitivity between the laser vaporization method in which no solvent is present and the solution method, this difference is clearly resolved by the presence of the solvent.

That is, in the inductively coupled plasma analysis in which the sample is collected by the laser vaporization method, the solvent sample is introduced into the plasma, so that the solution sample can be used as a standard sample and highly accurate analysis can be performed.

In order to introduce the solvent, it is difficult to use a plasma torch with a triple tube, and a quadruple tube structure is preferable. This structure is shown in FIG. The concentric quadruple tube is provided with a solvent passage 2 in addition to the sample passage 1, the plasma gas passage 3, and the cooling gas passage 4. The solvent passage 2 is adjacent to the sample passage 1 and inside the plasma gas passage 3. The sample passage 1 and the solvent passage 2 may be replaced with each other.

When preparing the calibration curve, only the carrier gas is introduced into the sample passage 1 and the solution standard sample is introduced into the solvent passage 2. Any solvent can be used as long as it can dissolve the standard components. For example, an organic solvent,
Water, an acid aqueous solution, an alkaline aqueous solution and the like, and a solvent closer to the solution sample solvent is more preferable.

Further, the internal standard method is generally used as a method for correcting the fluctuation of the apparatus and the sample introduction amount, but this measures the ratio of the measured value of the target component and the measured value of the main component which are simultaneously measured. It is a method of analyzing as strength, and is also effective in the present invention. Furthermore, when information such as thermal conductivity is obtained for a solid substance, corrections by thermal conductivity and heat of vaporization may be used together.

[0019]

[Examples] The solid substances of low alloy steel, aluminum alloy, titanium alloy and silicon nitride were analyzed, and their accuracy was examined by comparing with the chemical analysis values.

The apparatus used for the measurement is shown in FIG. The solid substance 10 is irradiated with a laser beam emitted from a laser oscillator 11 to perform laser vaporization, and an Alcon gas cylinder 12
The high-purity argon gas stored in the sample was used as a carrier for sampling. The collected sample was introduced into the plasma torch 13, excited by plasma, and identified and quantified by the analyzer 14.

A ruby laser with a Q switch is used as the laser oscillator 11, and the plasma torch 13 is shown in FIG.
It is the quadruple tube structure shown in. As the analyzer 14, a spectroscopic analyzer was used for analysis of low alloy steel and aluminum alloy, and a mass analyzer was used for titanium alloy and silicon nitride.

The solution standard sample 15 used for preparing the calibration curve and calibrating the apparatus is an aqueous solution sample prepared by mixing pure metals with an acid. As the solvent introduced at the time of measurement, the same acid solution as the standard sample was used in the analysis of low alloy steel and titanium alloy, and distilled water was used in the analysis of aluminum alloy and silicon nitride.

The investigation was also carried out by the conventional method and compared with the embodiment of the present invention. The results of the investigations targeting low alloy steel, aluminum alloy, titanium alloy and ceramics are shown in Table 1, Table 2, Table 3 and Table 4, respectively.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

In the embodiment of the present invention, the deviation from the true value is
-12% to 15%, whereas in the conventional method, the deviation was -89% to 82%, which was six times larger.

[0029]

As described above, according to the present invention,
Introducing a solvent into the plasma made it possible to perform accurate analysis using a solution standard sample in laser vaporization / inductively coupled plasma analysis. This technique greatly contributes to the direct analysis in the material manufacturing process and the analysis of a new material or the like for which a solid standard sample is hard to be obtained, and its effect is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an improvement in sensitivity for explaining the principle of the present invention.

FIG. 2 is a diagram showing an outline of a plasma torch having a quadruple tube structure.

FIG. 3 is a diagram showing an outline of an analyzer used in Examples.

FIG. 4 is a diagram showing an outline of a conventional plasma torch having a triple-tube structure.

[Explanation of symbols]

 1 Sample Passage 2 Solvent Passage 3 Plasma Gas Passage 4 Cooling Gas Passage 10 Solid Material 13 Plasma Torch 14 Analyzer

Claims (2)

[Claims] 1. A calibration curve is prepared by using a solution sample as a standard sample when introducing a sample obtained by irradiating a solid substance with laser light into an inductively coupled plasma for analysis.
A laser vaporization / inductively coupled plasma analysis method, which comprises introducing a solvent into plasma during measurement. 2. A plasma torch, wherein the torch used for laser vaporization / inductively coupled plasma analysis has a concentric quadruple tube structure.