JPH0721973A - Quantitative method of metal element in acid solution - Google Patents

Abstract

PURPOSE:To obtain a quantitative method of metal element in acid solution which is carried out accurately and rapidly, and with an excellent repeatability. CONSTITUTION:A quantitative method of a metal element in a acid solution which quantifies a metal element dissolved in an acid solution by using the ICP mass spectrometry is a quantification method in which the temperature of a solution atomizing chamber in an ICP mass specrometry device is controlled within 23+ or -3 deg.C. The density of an acid led in the Ar plasma is reduced, the corrosion of a sampling cone can be prevented, and a stable measuring result can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a metal element in an acid solution, and more particularly to a method for determining a metal element in a solution containing an acid such as sulfuric acid or phosphoric acid by ICP mass spectrometry. It relates to a metal element determination method.

[0002]

2. Description of the Related Art Ceramic materials such as silicon carbide and alumina used in the manufacturing process of semiconductor devices contain as little metal impurities as possible so as not to deteriorate the characteristics of semiconductor devices such as LSI to be manufactured. Is required. In order to meet this demand, attempts have been made to produce ceramics containing extremely small amounts of metal impurities, but analytical techniques for analyzing how much impurities were actually produced were completely established. Therefore, establishment of a method for analyzing trace impurities in ppm or less is desired.

As a method of analyzing trace metal impurities in ceramics, a sample is decomposed with an acid to form a solution,
The method of applying inductively coupled plasma (ICP) emission spectrometry is generally used, but as a method of acid-decomposing hardly soluble ceramics recently, sulfuric acid or nitric acid / hydrofluoric acid /
A pressurized acid decomposition method in which a mixed acid of sulfuric acid is used as a decomposing acid, and a fluororesin or the like is used as an inner cylindrical container and heated in a closed container has come to be applied (Naoyuki Hirate analysis 506).
Pp. 513 (1990), Yoshinori Kamio et al. Analytical Chemistry 41
T151-T155 (1992)).

As another more sensitive analysis method,
Flameless atomic absorption spectrometry and ICP mass spectrometry have also been applied.

[0005]

However, in the above ICP emission analysis method, it is difficult to measure an accurate value because the sensitivity is insufficient for the determination of metal impurities of ppm or less. Also,
Although flameless atomic absorption spectrometry has high sensitivity, it can analyze only one element in one measurement, so if you want to analyze many elements or many samples, take a long time to complete the analysis. There was a problem of cost.

On the other hand, ICP mass spectrometry is a very effective method for analyzing trace metal impurities in ceramics, since it is highly sensitive and capable of simultaneously analyzing multiple elements. However, since it is difficult to easily remove the sulfuric acid and the like used for decomposing the sample, the analysis is usually performed with the sulfuric acid and the like remaining in the analysis sample. in this case,
It has been reported that when this solution containing sulfuric acid or the like is introduced into an ICP mass spectrometer, the measurement intensity decreases with the measurement time (Teruo Okano, Taiji Matsumura Iron and Steel 77 1
951-1958 (1991)).

Actually, the metal was dissolved in sulfuric acid to prepare ICP.
When mass spectrometry is performed, the following results are obtained.
5 and 6 show a 3 v / v% solution of sulfuric acid containing about 100 μg / liter of Cu and about 100 μg / liter of Ni (concentrated sulfuric acid 3 ml with a concentration of 98 wt% is 3 ml).
Relationship between the measurement time and the strength ratio (ratio of strength at the time of measurement to strength at the start of measurement) when continuously introduced into an ICP mass spectrometer in a solution in which is dissolved in pure water to make 100 ml, and so on. It is a graph showing.

[0008] In the ICP mass spectrometry, ⁴⁰ Ar ¹⁶ O in which the Ar gas for generating oxygen plasma in the water vapor generated upon spraying an acidic aqueous solution in the plasma is generated by the reaction, ⁵⁶ Since it interferes with Fe, the solution spray chamber (hereinafter referred to as the spray chamber) is usually cooled in order to suppress the generation of water vapor as much as possible.
Even when performing the above measurement, keep the temperature of the spray chamber at -4 ° C.
The sampling cone, which is a jig for extracting ions from plasma, is made of Ni which is usually used.

As is clear from the results shown in FIGS. 5 and 6,
Despite introducing a solution having the same Cu concentration or Ni concentration into the ICP mass spectrometer, its relative intensity ratio is largely fluctuating, and Cu tends to have a lower relative intensity ratio, and Ni is The relative intensity ratio tends to increase. It is considered that this is because the acid contained in the sprayed droplets corroded and dissolved the sampling cone, which introduced Ni in the sampling cone into the mass spectrometer.

As a method of preventing such corrosion of the sampling cone, a method of using acid-resistant platinum for the sampling cone can be considered.

As another method, there is a method of preparing a sample solution containing no acid in the solution. For that purpose, sulfuric acid and phosphoric acid, which are difficult to volatilize by simply heating, are heated to dryness and volatilized. Alternatively, it must be separated and removed by ion exchange.

However, the platinum sampling cone is very expensive, while the method of removing the acid by heating to dryness or ion exchange requires a long time, and contamination occurs during the operation, resulting in inaccurate analytical values. There was a problem that it was easy to become.

The present invention has been invented in view of the above problems, and is a rapid, accurate, and stable measurement result in a method for quantifying metal elements in an acid solution containing an acid such as sulfuric acid or phosphoric acid by ICP mass spectrometry. It is an object of the present invention to provide a method for quantifying a metal element in an acid solution capable of obtaining

[0014]

In order to achieve the above object, the metal element quantification method in an acid solution according to the present invention is a method for quantifying a metal element dissolved in an acid solution using ICP mass spectrometry. In the method for quantifying a metal element in an acid solution, the temperature of the solution spray chamber in the ICP mass spectrometer is controlled to 23 ± 3 ° C.

As the acid solution to which the analysis method of the present invention can be applied, for example, sulfuric acid, phosphoric acid and the like have high viscosity,
An acid solution that has a relatively high boiling point and is difficult to scatter,
Analysis is possible when the concentration of these acids is about 10 v / v% or less.

As the material to which the analysis method of the present invention can be applied, for example, in addition to ceramic materials such as alumina and silicon carbide, iron and steel materials having a small amount of inclusions, rocks and the like, and sulfuric acid and phosphoric acid as decomposing acids are used. Examples of the metal element that can be used as the material and that can be actually analyzed include Si, P, K, and Ca that interfere with the molecular peak, and other metal elements other than Ni that is the material of the sampling cone.

The concentration range in which the metal can be analyzed varies depending on the type of the metal, so it cannot be generally stated.
For example, most can be analyzed in the concentration range of about 0.1 μg / liter to 1 mg / liter.

[0018]

The operation of the analysis method of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows an ICP using an ICP mass spectrometer.
It is the conceptual diagram which showed typically the method of quantifying the metal impurity in a solution by a mass spectrometry, In the figure, 11 has shown the sample solution.

A sample solution 11 containing a trace amount of a metal element and an acid such as sulfuric acid or phosphoric acid prepared by subjecting a sample of silicon carbide or the like to acid decomposition under pressure is sucked by a constant flow pump 12, and a nebulizer 13 is supplied. Is sprayed into the spray chamber 14.

The periphery of the spray chamber 14 has a double structure, and the inside thereof is a cooling water flow chamber 17. A thermometer 15 is installed in the spray chamber 14, and a temperature controller 16 connected to the thermometer 15 is used to cool the cooling water 1 flowing through the cooling water flow chamber 17.
By controlling the temperature of No. 8, the temperature of the spray chamber 14 is controlled.

The fine droplets thus formed by being sprayed in the spray chamber 14 controlled to have a predetermined temperature generate water vapor, and the liquid droplets and part of the water vapor are
The analysis element is ionized by being introduced into the Ar plasma 19, and the generated ion is introduced into the mass spectrometer 21 through the sampling cone 20 and the amount thereof is measured.

FIG. 2 shows that the temperature of the spray chamber 14 is changed, and a solution having a sulfuric acid concentration of 3 v / v% solution is sprayed into the spray chamber 14 at different temperatures, and a part thereof is sampled. 3 is a graph showing the relationship between the temperature of s and the concentration of sulfate ions. In addition,
Sulfate ion was quantified by ion chromatography.

As is apparent from FIG. 2, as the temperature of the spray chamber 14 rises, the concentration of sulfate ions gradually decreases. This is because the water vapor from the droplets formed by spraying the acid solution increases the amount of water vapor introduced into the Ar plasma 19 as the temperature of the spray chamber 14 rises, and the concentration of sulfuric acid relatively decreases. it is conceivable that. In particular, when the temperature of the spray chamber 14 is 20 ° C. or higher, the acid concentration is reduced to about ¼ or less as compared with the case where the temperature of the spray chamber 14 is −5 ° C.

Based on the above-mentioned examination results, if quantitative analysis is carried out at various acid concentrations and metal ion concentrations and the analysis is carried out within the temperature range of 23 ± 3 ° C. in the spray chamber 14, a long time is obtained. It is possible to obtain stable analysis values,
It was also found to be excellent in reproducibility.

This is because by setting the temperature condition of the spray chamber 14 to the above condition, the concentration of the acid introduced into the Ar plasma 19 is greatly reduced, so that the corrosion of the sampling cone 20 can be prevented, and the sampling cone 20 can be prevented. It is considered that there is no metal contamination from 20. When the temperature of the spray chamber 14 exceeds 26 ° C., the content of water vapor becomes too high, so that the temperature of the Ar plasma 19 decreases and the sensitivity decreases.

As described above, according to the metal element quantification method in the acid solution having the above-mentioned constitution, the metal element quantification method in the acid solution for quantifying the metal element dissolved in the acid solution using the ICP mass spectrometry. In the above, since the temperature of the spray chamber 14 in the ICP mass spectrometer is controlled to 23 ± 3 ° C., the concentration of the acid introduced into the Ar plasma 19 becomes low and the sampling cone does not corrode, so that stable measurement results can be obtained. Therefore, a method for quantitatively determining a metal element in an acid solution which is accurate, rapid, and excellent in reproducibility can be realized.

[0028]

EXAMPLES Examples of the metal element quantification method in an acid solution according to the present invention will be described below.

FIGS. 3 and 4 show the measurement time and intensity ratio (measurement) when measuring the metal concentration of a 3 v / v% sulfuric acid solution containing Cu of about 100 μg / liter and Ni of about 100 μg / liter, respectively. It is the graph which showed an example of the relationship with the ratio of the intensity | strength at the time of measurement with respect to the intensity | strength at the time of starting. The temperature of the spray chamber 14 is 25 ° C.
Set to.

As is apparent from FIGS. 3 and 4, even if the 100-minute analysis was continuously performed, both Cu concentration and Ni concentration were
It was confirmed that their relative intensity ratios hardly changed.

Further, 3 v / v% containing Cu and Ni
The same measurement is performed on the phosphoric acid solution (3 ml of concentrated phosphoric acid having a concentration of 85 wt% in pure water to 100 ml), and the relative intensity ratio does not change even if the measurement is continued for about 2 hours. I was able to confirm.

Therefore, the concentration of a 3 v / v% sulfuric acid solution containing Al, Cr, and Cu was analyzed by the calibration curve method, and the results are shown in Table 1 below.

[0033]

[Table 1]

Here, the relative standard deviation is the standard deviation of the analysis values for 5 samples divided by the analysis value and expressed as a percentage.

From the results shown in FIGS. 3 and 4 and Table 1, the metal element quantification method in the acid solution according to the example is capable of accurately quantifying the metal element in the acid solution with little variation due to measurement. Recognize.

In addition, 3 containing the above Al, Cr, Cu
When the detection limit value of the v / v% sulfuric acid solution was calculated,
0.05 μg / liter for Cr and 0.03 μg / liter for Cr
It was found that even minute amounts of metals such as 0.04 μg / liter can be measured for liters and Cu. The detection limit value was determined as 3 times the standard deviation of the analytical value of the blank test solution.

Next, a method of applying the present invention to the analysis of impurity elements in silicon carbide will be described.

First, about 0.5 g of silicon carbide was accurately weighed and put into a mixed acid of 3 ml of sulfuric acid, 10 ml of hydrofluoric acid and 5 ml of nitric acid, and heated and pressurized to decompose in an autoclave having an inner cylinder container made of fluororesin. Then, after taking out, it is further heated to volatilize Si, which is a decomposition product of the main component, and hydrofluoric acid and nitric acid used for decomposition. At this time, the high boiling sulfuric acid remains in the solution. This solution is diluted to 100 ml with water, and the concentration of each metal is measured by the ICP mass spectrometry method of the present invention.

The detection limit values shown in Table 2 below were obtained by applying the above-mentioned method for measuring the concentration of metal impurities in silicon carbide. For comparison, Table 2 below also shows the detection limit values when the same pretreatment was carried out and then the analysis was carried out by ICP emission spectrometry.

[0040]

[Table 2]

As is clear from Table 2 above, the metal element quantification method in the acid solution according to the embodiment enables very sensitive analysis as compared with the conventional ICP emission analysis method.
It is possible to analyze metal impurities having a pb-order concentration quickly and accurately.

Of course, when performing these ppb-order analyzes, contamination from the environment has a great influence on the accuracy of the analysis. Therefore, not only control of impurities such as sampling containers and reagents, but also the environment in which the analysis is performed. Extreme care should be taken to prevent pollution from the environment.

[0043]

As described in detail above, in the method for quantifying metal elements in an acid solution according to the present invention, an acid solution for quantifying the metal elements dissolved in the acid solution using ICP mass spectrometry is used. In the metal element determination method, the temperature of the solution spray chamber in the ICP mass spectrometer is controlled to 23 ± 3 ° C, so the concentration of the acid introduced into the Ar plasma becomes low, and the corrosion of the sampling cone is prevented. Therefore, stable measurement results can be obtained. Therefore, it is possible to provide an accurate, rapid, and reproducible method for quantifying a metal element in an acid solution.

[Brief description of drawings]

FIG. 1 is a conceptual diagram schematically showing a method for quantifying metal impurities in a solution by ICP mass spectrometry using an ICP mass spectrometer.

[Fig. 2] Changing the temperature of the spray chamber to 3 v / v
It is the graph which showed the relationship between the temperature of a spray chamber, and the density | concentration of a sulfate ion at the time of spraying the solution which has the sulfuric acid concentration of a% solution in the spray chamber of different temperature, and sampling some of it.

FIG. 3 shows the relationship between the measurement time and the strength ratio (ratio of strength at the time of measurement to strength at the start of measurement) at the time of measuring the metal concentration in a 3 v / v% sulfuric acid solution containing Cu in Examples. It is a graph which showed an example of a relation.

FIG. 4 shows the relationship between the measurement time and the strength ratio (ratio of strength at the time of measurement to strength at the start of measurement) at the time of measuring the metal concentration in a 3 v / v% sulfuric acid solution containing Ni in Examples. It is a graph which showed an example of a relation.

FIG. 5: Measurement time and strength ratio when measuring the metal concentration of a 3 v / v% sulfuric acid solution containing Cu by the conventional method (ratio of strength at the time of measurement to strength at the start of measurement)
It is a graph which showed an example of the relation with.

FIG. 6: Measurement time and strength ratio when measuring the metal concentration of a 3 v / v% sulfuric acid solution containing Ni by a conventional method (ratio of strength at the time of measurement to strength at the start of measurement)
It is a graph which showed an example of the relation with.

[Explanation of symbols]

 14 Spray chamber (solution spray chamber)

Claims (1)

[Claims] 1. A metal element quantification method in an acid solution for quantifying a metal element dissolved in an acid solution using ICP mass spectrometry, wherein a solution spray chamber in an ICP mass spectrometer is set to 23.
A method for determining a metal element in an acid solution, characterized by controlling the temperature to ± 3 ° C.