JP4433765B2 - Emission spectroscopic method - Google Patents

Description

The present invention relates to a method for quantitative analysis of an unknown sample in emission spectroscopic analysis in which a sample is evaporated and excited to emit light by discharge, the light is dispersed, and the wavelength and intensity of atomic spectral lines are measured.

In recent years, the analysis method has become important when the ban on the use of harmful substances contained in plastics and resins is enforced. Particularly in Europe, the Cd regulation value varies from country to country, and there is an allowable range of 10 to 100 μg / g. In many cases, the wet analysis method is designated as the analysis method, and BSEN 1122.2001 shown in Non-Patent Document 1 is often used as a typical analysis method.

In the analysis method of BSEN1122.2001, the sample is decomposed with sulfuric acid, nitric acid, and hydrogen peroxide, and insoluble components are removed by filtration, and then heavy metals contained in the filtrate are analyzed by ICP emission spectroscopy or isotope analysis. Analyze by law. Thus, since it is necessary to decompose the sample as a pretreatment for analysis, there is a problem that it takes a very long time to decompose the sample.
In addition, as other wet analysis methods, there are a sulfuric acid ashing method, a high temperature / high pressure acid dissolution method by microwave irradiation, etc., all of which require a sample to be in solution, and this solution processing takes time.

As a rapid nondestructive quantitative method for analyzing a sample in a solid state, fluorescent X-ray analysis is generally used. However, the detection sensitivity of Cd is 1 to 10 μg / g, which is not always sufficient. Quantitative accuracy (accuracy) is not a problem if the standard sample and the unknown sample are similar in density, thickness, and coexisting elements. However, in the case of substances with significantly different constituent elements and coexisting elements, such as organic substances. In many cases, various correction methods cannot be used.

Another method for analyzing a sample in a solid state is solid-state emission spectroscopy. Solid-state emission spectroscopy has been widely used as an analysis method that can analyze metals and oxides quickly and easily because arc discharge or spark discharge is used as an excitation source and a solid sample can be directly measured. Arc discharge and spark discharge are used separately in terms of sensitivity. Generally, arc discharge is ultra-trace analysis, and sensitivity is <10 μg / g and spark discharge is> 10 μg / g. In addition, the spark discharge needs to impart conductivity to the sample, but the arc discharge is an excitation source that can directly analyze a non-conductive sample such as an oxide.

However, the biggest difficulty of solid-state emission spectrometry is that the quantitative accuracy is low. Therefore, ICP emission spectroscopy, ICP mass spectrometry, and X-ray fluorescence analysis, which can directly measure solid samples, are the current mainstream analysis methods. Spectroscopic analysis is a technique that is used only for some of the precious metal samples that are difficult to dissolve and nuclear fuels that have established quantitative methods.
In solid-state emission spectrometry for organic substances such as plastics and resins, it is generally measured by ashing and oxidization or in solution, and there is a drawback that it takes a lot of time for pretreatment. It was.

In order to improve the quantitative accuracy of solid-state emission spectrometry, in Patent Document 1, before performing the discharge for analysis, a discharge in which the polarity of the counter electrode and the sample is reversed is performed, and the emission intensity due to this discharge starts to increase. An emission spectroscopic analysis method has been proposed in which the polarity is inverted and switched to the analysis discharge.
Further, in Patent Document 2, the sample surface is discharged substantially parallel to the light collection axis of the spectrometer, and thereby the spectral lines that are not affected by the light of the sample itself or the vapor cloud are collected by the spectrometer. A method has been proposed for enhancing the above.
Further, in Patent Document 3, in order to correct the influence of overlapping of adjacent spectral lines, an emission spectroscopic analysis method that simultaneously measures a correction coefficient calculation sample for each measurement and calculates a correction coefficient each time to correct an error due to a coexisting element. Has been proposed.
However, regardless of which analysis method is used, it is difficult to improve the quantitative accuracy of the constituent elements contained in an unknown sample whose density and constituent elements are not similar to those of the standard sample.
BSEN 1122.2001 ("Plastics-Determinationof cadmium-Wet decomposition method" BRITISH STANDARD 2001) JP-A-5-264455 JP-A-8-50097 Japanese Patent Laid-Open No. 5-45287

Accordingly, an object of the present invention is to provide a rapid and simple emission spectroscopic analysis method capable of improving the accuracy of quantification and analyzing organic substances such as plastics and resins that have been difficult to analyze as a measurement object.

In order to achieve the above object, the invention according to claim 1 is an emission spectroscopic analysis method for measuring the wavelength and intensity of a spectral line obtained by evaporating and exciting emission of a sample by discharge and spectroscopically analyzing the light. A standard sample with a known element content is excited to emit light, a calibration curve is obtained from the relationship between the content of a predetermined component element of the standard sample and the intensity of the spectral line, and the unknown sample is excited to emit light, A step of measuring the intensity of a spectral line in the same component element as that of the component element, and a step of correcting the intensity of the spectral line obtained from the unknown sample by using an evaporated weight ratio of the standard sample and the unknown sample And a step of obtaining the content of the component elements of the unknown sample based on the corrected intensity of the spectral line and the calibration curve.

In general, the quantification method of solid-state emission spectrometry is a standard curve (a sample whose constituent element content is known) is measured, and a calibration curve method is used to obtain the relationship between the content ratio and the intensity of the atomic spectral line of each element. Used. Then, the unknown sample is excited to emit light, the intensity of the spectral line in the same component element as the standard sample is measured, and the content (concentration) of the component element in the unknown sample is obtained based on the intensity of the spectral line and the calibration curve.
However, when quantifying constituent elements contained in an unknown sample, if there is a difference in constituent elements between the standard sample and the unknown sample, a difference in density occurs, which causes fluctuations in the intensity of the spectral line. Therefore, accurate quantitative analysis cannot be performed even if samples having the same form and volume are evaporated and excited to emit light and the spectrum intensity is measured.
In the present invention, attention is paid to the weight ratio between the evaporated unknown sample and the standard sample. That is, if the intensity of the spectral line of the unknown sample is corrected using the weight ratio, and the content rate is obtained using the corrected spectral intensity and the calibration curve, the constituent elements and density between the standard sample and the unknown sample are calculated. Even if there is a difference, it is possible to reduce the error of the content rate or concentration finally obtained, and it is possible to perform quantitative analysis with higher accuracy.

The discharge in the present invention may be any discharge as long as it is a discharge that evaporates and excites a sample, such as arc discharge or spark discharge.
In addition, there is a method in which the sample is excited to emit light while being solid, but the sample can be powdered and accommodated in a recess provided in the electrode to emit light.
When the sample is excited to emit light while being solid, only a part of the sample is evaporated, so the weight ratio of the evaporated sample can be obtained by measuring the weight of the sample before and after the excitation light emission. . On the other hand, when evaporating / exciting light emission of a powdery sample, the weight of the sample filled in the concave portion of the electrode is measured in advance, and if the entire amount of the filled powder sample is evaporated, the sample is excited after emission of light. The weight ratio can be obtained without measuring the weight. However, also in the case of a powder sample, the weight ratio of the evaporated sample may be obtained by measuring the weight of the sample before and after excitation light emission.
Samples that can be analyzed according to the present invention include all kinds of metals, oxides, organic substances including trace elements.

In claim 1, after correcting the intensity of the spectrum line measured for a predetermined component element of the unknown sample by the weight ratio, the content of the element element of the unknown sample is corrected based on the intensity of the spectrum line and the calibration curve after the correction. Although the rate was determined, the intensity of the spectral line in the predetermined component element of the unknown sample was measured as in claim 2, and based on the measured spectral line intensity and the calibration curve, the component element of the unknown sample After obtaining the content ratio, the content ratio of the component elements of the unknown sample may be corrected using the weight ratio of the evaporated sample to the standard sample.
In this case as well, the content or concentration of the elemental component contained in the unknown sample can be analyzed with high accuracy, as in the first aspect.

In the solid-state emission spectroscopic analysis method of the present invention, as in claim 3, if the spectral line intensity is corrected by dividing the spectral line intensity SIR of the unknown sample measured by the weight ratio J, the type of the sample is obtained. It can be quantified regardless.
J = evaporation weight of unknown sample / evaporation weight of standard sample (1)
Intensity of corrected spectral line = SIR / J (2)
That is, in the case of an unknown sample having a large weight, the intensity of the spectrum line is also large, and by dividing this by the weight ratio J, the intensity of the spectrum line can be adjusted to the intensity of the spectrum line of the standard sample. The error can be reduced.

As in claim 4, the method of the present invention is suitable when the standard sample and the unknown sample are organic substances containing inorganic elements.
Organic substances such as plastics and resins are used for many purposes, and their properties are modified according to their functions, and many additives (for example, pigments, fillers, flame retardants, etc.) are added. Since the organic substance to which these are added is about twice as large as the density of the organic substance alone, it is difficult to make the constituents of the standard sample and the unknown sample similar, making quantitative analysis difficult.
When quantifying an inorganic element contained in a sample made of such an organic substance, even if a standard sample and an unknown sample having a constant volume are prepared, a difference in the weight is generated, and the intensity of the spectral line is changed. For this reason, solid-state emission spectroscopy has been considered unsuitable for analysis of inorganic elements contained in organic substances.
In the present invention, the intensity of the spectral line or the content rate of the component elements of the unknown sample is corrected using the weight ratio, so that even with an inorganic element contained in an organic substance, a highly accurate quantitative analysis is possible.

6. A concave portion is formed in one electrode of an electrode pair for discharging as in claim 5, and a standard sample and an unknown sample, which are each in powder form, are accommodated in the concave portion, and the standard sample is accommodated in the concave portion. It is preferable that the unknown sample is evaporated and excited by arc discharge.
If the sample is powdered, it can be easily evaporated and excited by arc discharge. Arc discharge has a high sensitivity of less than 10 μg / g and is suitable for ultra-trace analysis. In addition, there is an advantage that non-conductive samples such as organic substances and oxides can be directly analyzed without forming a solution.

By using the invention according to claim 1, by correcting the weight ratio between the unknown sample and the standard sample based on the calibration curve of the standard sample prepared from a specific standard substance, the coexisting elements and the configuration It is possible to quantify unknown samples with different elements. Thereby, a complicated pretreatment such as solutionization is not required, and a quantitative analysis method that is quicker than other analysis methods (fluorescent X-ray analysis method, wet chemical analysis method) can be provided with a small amount of sample.

Embodiments of the present invention will be described below with reference to examples.

FIG. 1 shows an example of an analyzer for carrying out an emission spectroscopic analysis method according to the present invention.
Reference numeral 1 denotes a discharge generator for generating a DC arc discharge, which is composed of a DC power supply 2 and a pair of electrodes 3 and 4 connected to the power supply 2. The cathode side electrode 3 is formed in a cone shape, the anode side electrode 4 is formed in a cup shape, and a recess 4 a for filling the powder sample W is provided at the tip of the anode side electrode 4. The electrodes 3 and 4 are made of graphite, for example. By applying a DC voltage between the electrodes 3 and 4, arc discharge is generated, and the sample W filled in the recess 4a of the electrode 4 is evaporated and excited to emit light.
The excited light passes through the entrance slit 5, is reflected by the concave mirror 6, is split by the prism 7, and is then decomposed into eigenspectral lines by the diffraction grating 8. A spectral line corresponding to a predetermined component element is reflected by the concave mirror 9 and detected by a detector 10 such as a semiconductor detector.
Although a single spectral line detection method is illustrated here, a plurality of spectral lines can be detected simultaneously by providing a plurality of detectors 10.
The excitation emission of the sample may be performed in air, it may be carried out in Ar + O ₂ atmosphere.
FIG. 1 merely shows an example of a DC arc excitation emission spectroscopic analysis apparatus, and the apparatus for performing the analysis method of the present invention is not limited to FIG.

Next, a specific example of the emission spectroscopic analysis method according to the present invention will be described.
First, using the reference materials shown in Table 1 (European Commission Certified Reference Material BCR-680,681) and polyethylene as diluent (POLYETHYLENE low density made by SCIENTIIFIC POLYMER PRODUCTS, INC.), The composition shown in Table 2 was blended and freeze-ground. Thus, powdery standard samples STD1 to STD7 were prepared. In addition to the freeze pulverization, normal pulverization may be performed. If the sample is a solid that can fit in the recess 4a of the electrode 4, it can be analyzed as it is without being crushed.

Table 3 shows the measurement conditions for creating a calibration curve from the standard samples STD1 to STD7 using the analyzer shown in FIG. 1, and STD in FIG. 2 shows the calibration curve created under the measurement conditions.

In the case of the analyzer shown in FIG. 1 and Table 3, the function of the calibration curve can be approximated by the following equation.
SIR = A ₀ + (A ₁ × C) ⁿ + (A ₂ × C) ²ⁿ (3)
Where SIR: spectral line intensity, A ₀ : offset, A ₁ : gain coefficient, A ₂ : curve coefficient, C: concentration, n: best fit coefficient.
Since the parameters A ₀ , A ₁ , A ₂ , n are values determined by the analyzer and measurement conditions, the concentration C can be obtained by calculation by measuring the intensity SIR of the spectral line.
Equation (3) is a calculation formula of the analyzer under the measurement conditions as shown in Table 3. In the case of analyzers having different measurement conditions and configurations, the calculation formulas are also different.

Next, four types of substances shown in Table 4 (PPS resin, epoxy resin, PPO resin, PVC resin) were prepared. Of these materials, the PPS resin contains 190 ppm of Cd, while the other resins each have a Cd content of less than 1 ppm. For quantification of these substances, a solution was prepared using a μ-Wave acid dissolution method, and an ICP-AES analysis method or an ICP-MS analysis method was used.

Next, four types of substances shown in Table 4 were used and blended as shown in Table 5 to prepare 15 types of examination samples having different Cd contents (concentrations). Here, a powder sample was prepared by freeze pulverization, but not only freeze pulverization but also normal pulverization may be performed.
Table 5-1 shows five samples (Epo-1 to Epo-5) having different Cd concentrations by blending an epoxy resin with a PPS resin, and Table 5-2 shows a PPS resin with a PPS resin. 5 types of samples (PPO-1 to PPO-5) having different Cd concentrations were prepared, and Table 5-3 shows the same 5 types as the standard sample STD by adding BCR to PVC resin. Samples (PVC-1 to PVC-5) were prepared.

In FIG. 2, in addition to the calibration curve STD, the spectral intensity of Cd was measured for the above-mentioned examination samples under the same conditions as in Table 3, and the relationship between the intensity and the Cd concentration was plotted. Here, the wavelength of the spectral line of Cd is 228.8 nm.
As is clear from FIG. 2, the test sample using PVC resin approximates the calibration curve STD, but the test sample using epoxy resin and the test sample using PPO resin have spectral line intensities. It can be seen that this is far from the calibration curve STD.
In this way, when quantifying inorganic elements contained in organic substances such as resins, even if the intensity of the spectral line is measured, the relationship between the spectral intensity and concentration may be far from the calibration curve. The concentration cannot be accurately determined from the spectral line intensity and the calibration curve.

Therefore, in the present invention, the spectral intensity of the unknown sample is corrected using the weight ratio of the sample filled in the concave portion 4a of the electrode 4 with a constant volume.
The weight ratio J is obtained by the ratio between the weight of the unknown sample filled in the concave portion 4a of the electrode 4 and the weight of the standard sample STD as shown in the following equation.
J = weight of unknown sample / weight of standard sample (1)
And correction | amendment like following Formula is performed with respect to the spectral intensity SIR of an unknown sample by weight ratio J. SIR ′ is the corrected spectral intensity.
SIR ′ = SIR / J (2)
An equation for calculating the concentration C of the unknown sample using the correction equation and the above-described calibration curve (3) is as follows.
SIR / J = A ₀ + (A ₁ × C) ⁿ + (A ₂ × C) ²ⁿ (4)

Table 6 shows an example of the weight ratio. Here, the weight ratio of the examination sample made of epoxy resin is larger than that of the examination sample made of PPO resin or PVC resin. In addition, this weight ratio changes with the component elements contained in each resin, and its density | concentration.

FIG. 3 shows the relationship between the spectral intensity and Cd concentration of the test sample corrected using the weight ratio J in Table 6 and the calibration curve STD.
As is apparent from FIG. 3, it can be seen that the STD and the sample to be examined are in good agreement up to around 30 ppm, which is a low Cd concentration range.

Table 7 shows the result of quantifying the Cd of the sample to be examined from the corrected spectral line intensity in comparison with the chemical analysis method. Similarly to Table 4, chemical analysis is a solution using the μ-Wave acid dissolution method and quantified using the ICP-AES analysis method or ICP-MS analysis method, and is a highly accurate analysis method. .
Here, it can be seen that the method of the present invention and the chemical analysis method tend to coincide with each other up to around 30 ppm, which is a low concentration region of Cd, and the quantitative accuracy of the method of the present invention is improved.

As is clear from FIG. 3 and Table 7, correction by weight ratio improves the quantitative accuracy, but it cannot be said to have sufficient accuracy compared to chemical analysis.
In order to improve this, for example, in addition to the weight ratio J, the accuracy can be further improved by using a standard sample in consideration of the light emission behavior for each Cd compound and the carrier effect (coexisting element).
Further, in the equation (2), the corrected spectral intensity SIR ′ is obtained by dividing the measured spectral intensity SIR by the weight ratio J, but a correction equation other than the equation (2) can also be used.

In the above embodiment, the concave portion of one electrode is filled with a powder sample, and an arc discharge is generated between the electrode and the opposite electrode so that the sample is excited and emitted, but a solid sample is used. An arc discharge or a spark discharge may be applied to cause excitation light emission.

Moreover, in the said Example, after correcting spectral intensity SIR by weight ratio J like (2) Formula, based on the corrected spectral line intensity | strength SIR 'and a calibration curve, the content rate of the component element of an unknown sample Although the method for obtaining (concentration) has been described, the content (concentration) of the component elements of the unknown sample is obtained based on the intensity of the spectral line obtained from the unknown sample and the calibration curve, and this content is then weighted. Correction may be performed using the ratio J.
The correction formula in this case is not limited to dividing the content ratio by the weight ratio J, and other correction formulas can be used.

It is the schematic of an example of the emission-spectral-analysis apparatus with which the emission-spectral-analysis method concerning this invention is used. It is a figure which shows the relationship between the Cd spectrum intensity | strength of the examination sample before correction | amendment, and Cd density | concentration, and a calibration curve. It is a figure which shows the relationship between the Cd spectrum intensity | strength of the examination sample after correction | amendment, and Cd density | concentration, and a calibration curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Arc discharge generator 3, 4 Electrode 4a Recessed part 8 Diffraction grating 10 Detector W Sample

Claims (5)

In an emission spectroscopic analysis method for measuring the wavelength and intensity of a spectral line obtained by evaporating and exciting emission of a sample by electric discharge and dispersing the light,
A step of exciting and emitting a standard sample whose component element content is known, and obtaining a calibration curve from the relationship between the content of the predetermined component element of the standard sample and the intensity of the spectral line;
A step of exciting an unknown sample to emit light and measuring the intensity of a spectral line in the same component element as that of the standard sample;
Correcting the intensity of the spectral line obtained from the unknown sample using the evaporated weight ratio of the unknown sample and the standard sample;
Determining the content of the component element of the unknown sample based on the corrected intensity of the spectral line and the calibration curve. In an emission spectroscopic analysis method for measuring the wavelength and intensity of a spectral line obtained by evaporating and exciting emission of a sample by electric discharge and dispersing the light,
A step of exciting and emitting a standard sample whose component element content is known, and obtaining a calibration curve from the relationship between the content of the predetermined component element of the standard sample and the intensity of the spectral line;
A step of exciting an unknown sample to emit light and measuring the intensity of a spectral line in the same component element as that of the standard sample;
Based on the intensity of the spectral line obtained from the unknown sample and the calibration curve, determining the content of component elements of the unknown sample;
Correcting the content of the component elements of the unknown sample by using the evaporated weight ratio of the unknown sample and the standard sample. The emission spectroscopic analysis method according to claim 1, wherein the intensity SIR of the spectral line obtained from the unknown sample is corrected by the following equation using the weight ratio J.
J = evaporation weight of unknown sample / evaporation weight of standard sample (1)
Intensity of corrected spectral line = SIR / J (2) The emission spectroscopic analysis method according to any one of claims 1 to 3, wherein the standard sample and the unknown sample are organic substances containing an inorganic element. A concave portion is formed in one electrode of the electrode pair for performing the discharge, and a standard sample and an unknown sample which are in powder form are accommodated in the concave portion, respectively, and the standard sample and the unknown sample accommodated in the concave portion are arc-discharged. 5. The emission spectroscopic analysis method according to claim 1, wherein the light is evaporated and excited to emit light.

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