JP7200887B2 - Methods for preparing analytical samples and methods for quantifying liquid samples - Google Patents

Description

The present invention relates to a method of preparing an analytical sample and a method of quantifying a liquid sample.

Methods for quantifying the concentration of a predetermined element in a liquid sample include, for example, inductively coupled plasma optical emission spectrometry (hereinafter also referred to as “ICP/OES”). When performing quantitative determination by this method, as a pretreatment, the liquid sample to be measured is transferred to a volumetric flask using a volumetric pipette, an appropriate acid is added, and pure water is added to a constant volume. necessary. Since this dilution operation takes about 30 minutes to 1 hour, it becomes a factor of lowering the measurement efficiency.

As a measurement method more rapid than the above-mentioned ICP/OES, there is a fluorescent X-ray analysis method (X-ray fluorescence analysis, hereinafter simply referred to as “XRF”) that requires less time for pretreatment (for example, non-document patent 1). XRF is a method of irradiating a sample with X-rays and using secondary X-rays (fluorescent X-rays) generated from the sample to perform qualitative/quantitative analysis of elements constituting the sample. XRF can obtain analysis results in a short period of time compared to chemical analysis methods, ICP/OES, and the like that involve pretreatment. For this reason, it is widely used as a quality control method for raw materials for the purpose of reducing analysis costs and quickly feeding back analysis results to processes.

When a solid sample is analyzed using XRF, it is easy to set the sample in the device, and measurement in vacuum is possible. For example, Patent Document 1 describes a fluorescent X-ray automatic analysis system equipped with an automatic crushing device, an automatic press device, etc., and from the viewpoint that XRF can be automated and labor-saving, It is known to be suitable as an analytical method.

On the other hand, when analyzing a liquid sample using XRF, measurement in a vacuum system is difficult because the liquid volatilizes. Therefore, in the case of a liquid sample, the measurement is performed under a helium atmosphere. When measurements are performed in the atmosphere, air absorbs the long-wavelength X-rays generated from light elements in the liquid sample, making accurate measurements difficult. Therefore, helium, which is expensive but does not easily absorb X-rays, is used. It will be.

However, when XRF is used to measure a liquid sample, the liquid sample may be heated by the X-ray irradiation and air bubbles may be generated, resulting in measurement errors. Also, depending on the acid used to dissolve the sample, the measurement may be adversely affected, resulting in measurement error. When XRF is used to measure a liquid sample in this way, the obtained quantitative values may vary, and the reproducibility of the measurement may be low.

From the viewpoint of maintaining high measurement reproducibility, an internal standard substance containing an internal standard element is added to a liquid sample, and the secondary X-ray (fluorescent X-ray) intensity ratio (intensity ratio ), a method for quantifying the concentration of a predetermined element has been proposed (for example, Patent Document 2 and Non-Patent Document 1).

In addition, from the viewpoint of suppressing the generation of bubbles due to X-ray irradiation and the effects of acid, for example, after dropping the liquid sample on a filter paper and drying it, XRF is applied to the precipitate deposited on the filter paper to quantify the concentration of the predetermined element. A method (so-called filter paper dropping method) has been proposed.

JP-A-01-059043 JP 2017-181309 A

Izumi Nakai, "Actuality of Fluorescent X-ray Analysis", Asakura Shoten, October 20, 2005, 1st edition, 1st printing

However, according to the study of the present inventor, when adding an internal standard element to a liquid sample and quantifying the concentration of the element to be measured by the filter paper dropping method, when the dropped liquid sample is dried, it contains the element to be measured It was confirmed that the salt and the salt containing the internal standard element did not precipitate at the same rate, and one of the salts segregated. In other words, in the precipitate obtained by drying, the ratio between the element to be measured and the internal standard element was sometimes different depending on the location. Therefore, when the precipitate is irradiated with X-rays, the intensity ratio of the fluorescent X-ray intensity fluctuates depending on the irradiation position, and the quantitative results may vary.

SUMMARY OF THE INVENTION The present invention has been made in view of the problems described above, and an object of the present invention is to provide a method for quantifying the concentration of a predetermined component in a liquid sample with high accuracy and high reproducibility.

The present inventors conducted research to solve the above problems. As a result, it was found that the segregation between the salt containing the element to be measured and the salt containing the internal standard element was caused by the difference in the solubility in water of the salt containing each element. Specifically, salts with low water solubility begin to precipitate relatively quickly during drying, while salts with high water solubility start to precipitate later. For this reason, if there is a large difference in solubility between the salt containing the element to be measured and the salt containing the internal standard element, one salt precipitates first and the other salt later. Timing may vary.

Also, when the droplets are dried, the salt is more likely to segregate due to the coffee ring effect. The coffee ring effect indicates that a deposit is deposited in a ring shape when the droplet is dried. In the drying of droplets, drying starts from the central portion of the droplet and gradually progresses toward the outside. In this drying process, the droplets are more concentrated toward the outside, so that the amount of precipitates increases toward the outside of the droplets rather than inside, resulting in the salt being deposited in a ring shape.

Thus, when drying a droplet containing the element to be measured or the internal standard element, the difference in the solubility of the salts formed by each element makes it easy for the highly soluble salt to precipitate at the outer edge of the precipitate. Segregation of the element to be measured and the internal standard element will occur.

From this, the present inventors have found that in order to suppress segregation between the measurement target element and the internal standard element, it is preferable to approximate the solubility of the salt containing each element in water, and the internal standard element should form a salt. It was found that it is preferable to select an element whose solubility is similar to that of the salt of the element to be measured. With such an internal standard element, it is possible to reduce the difference in solubility from the salt of the element to be measured, and reduce the deviation of the timing at which precipitation starts. As a result, the internal standard element and the element to be measured can be precipitated at the same ratio, and segregation of one salt can be suppressed. In addition, in precipitates, it is possible to suppress variations in the ratio between the element to be measured and the internal standard element. According to such a precipitate, when X-rays are irradiated and fluorescent X-rays are measured, a constant intensity ratio can be obtained regardless of the irradiation position of X-rays. In addition, the reproducibility of quantitative results can be improved. The present invention has been made based on the above findings.

That is, the first aspect of the present invention is
A method for preparing an analysis sample for fluorescent X-ray analysis, comprising:
A preparation step of preparing an aqueous solution containing the element to be measured as a liquid sample;
A mixing step of adding an internal standard substance containing an internal standard element to the liquid sample and mixing to form a mixed solution;
a dropping step of dropping the mixed solution onto the sample holder;
By drying the mixed solution that has been dropped onto the sample holder to precipitate a salt containing the element to be measured and a salt containing the internal standard element, the precipitate containing these salts is held on the sample holder. and a drying step to form the analyzed sample,
The internal standard element forms a salt having a solubility in water that is 8 times or less the solubility in water of the salt containing the element to be measured in the drying step. are different elements,
A method for preparing an analytical sample is provided.

A second aspect of the present invention is the method for preparing an analysis sample according to the first aspect,
The element to be measured and the internal standard element are transition metal elements different from each other.

A third aspect of the present invention is the method for preparing an analysis sample according to the first or second aspect,
The element to be measured and the internal standard element are selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn and are different elements.

A fourth aspect of the present invention is the method for preparing an analysis sample according to any one of the first to third aspects,
wherein the liquid sample contains sulfate ions;
Each salt precipitated in the drying step is a sulfate.

A fifth aspect of the present invention is the method for preparing an analysis sample according to any one of the first to fourth aspects,
In the dropping step, the amount of the mixed solution to be dropped is set to 150 μg or less per 1 cm ² of the area of the sample holder.

A sixth aspect of the present invention is the method for preparing an analysis sample according to any one of the first to fifth aspects,
The sample holder is filter paper.

A seventh aspect of the present invention is
A quantification method for quantifying the concentration of a predetermined element contained in a liquid sample,
a preparation step of preparing an aqueous solution containing an element to be measured as the liquid sample;
A mixing step of adding an internal standard substance containing an internal standard element to the liquid sample and mixing to form a mixed solution;
a dropping step of dropping the mixed solution onto the sample holder;
By drying the mixed solution that has been dropped onto the sample holder to precipitate a salt containing the element to be measured and a salt containing the internal standard element, the precipitate containing these salts is held on the sample holder. a drying step to form a filtered analytical sample;
a quantification step of irradiating the precipitate in the analysis sample with X-rays, measuring the X-ray intensities of the element to be measured and the internal standard element, and quantifying the concentration of the element to be measured from the intensity ratio; , has
The internal standard element forms a salt having a solubility in water that is 8 times or less the solubility in water of the salt containing the element to be measured in the drying step. are different elements,
A method for quantifying a liquid sample is provided.

According to the present invention, it is possible to quantify the concentration of a predetermined component in a liquid sample with high accuracy and high reproducibility.

FIG. 1 is a diagram for explaining a case of measuring a sample using a fluorescent X-ray measuring device. FIG. 2 is a flow chart of operations when performing fluorescent X-ray analysis of a liquid sample in Example 1. FIG. FIG. 3 is a photograph of a surface analysis result of the analysis sample prepared in Example 1 by an electron probe microanalyzer. FIG. 4 is a photograph of a surface analysis result of an analysis sample prepared in Comparative Example 1 by an electron probe microanalyzer. 5 is a diagram showing a calibration curve used in Example 1. FIG.

<One embodiment of the present invention>
An embodiment of the present invention will be described below. In this embodiment, a case will be described in which the concentration of a predetermined component contained in a liquid sample is quantified by preparing an analysis sample from a liquid sample and then performing fluorescent X-ray analysis on the analysis sample. The liquid sample quantification method of the present embodiment has a preparation process, a mixing process, a dropping process, a drying process, and a quantification process. Each step will be described in detail below.

(Preparation process)
First, a liquid sample, which is a solution to be measured, and an internal standard are prepared.

A liquid sample is an aqueous solution containing the element to be measured. Such a liquid sample is not particularly limited as long as the contained components such as the element to be measured are clear. For example, an aqueous solution obtained by dissolving a metal compound constituting the functional material in an acid solution can be used.

The element to be measured is not particularly limited as long as the measurement intensity measured by X-ray fluorescence analysis (XRF) varies with similar behavior and sufficient measurement sensitivity can be obtained, and practically Na ( Any element having an atomic number of Z=11) or more may be used. In the case of dissolving a metal compound such as a functional material, the element to be measured is a transition metal element. For example, at least one transition metal element selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn.

In addition to the element to be measured, the liquid sample may contain other components (hereinafter also referred to as coexisting components). Such coexisting components include, for example, components derived from the acid component used when dissolving the metal compound. For example, when sulfuric acid is used as the acid component, sulfate ions are included as coexisting components. Nitric acid contains nitrate ions as a coexisting component, and hydrochloric acid contains chloride ions as a coexisting component. Other anions include inorganic ions such as carbonate ions and hydroxide ions. In addition, when an organic acid is used as the acid component, anions derived from the organic acid include, for example, formate ion, acetate ion, oxalate ion and citrate ion.

The internal standard substance contains an internal standard element. The internal standard element is an element that is not contained in the liquid sample, and when the mixed solution is dried, the solubility in water is 8 times or less the solubility in water of the salt containing the element to be measured. It is an element different from the element to be measured, which forms such a salt.

The internal standard substance may be selected, for example, as follows. First, the type of the element to be measured contained in the sample solution, the type of salt (for example, sulfate, nitrate, etc.) generated by drying the mixed solution of the element to be measured, and the solubility thereof are specified. Next, among the salts generated when the mixed solution of the internal standard element is dried, the elements whose solubility is within a predetermined range in terms of the ratio to the salt generated by the element to be measured are extracted, and appropriate Select an element with a similarity as the internal standard element.

Here, salts and their solubility are explained.

The salt in the present embodiment means a precipitate formed by precipitation of each element when the mixed solution is dried. The type of salt is not particularly limited as it varies depending on the components contained in the liquid sample. For example, if the liquid sample contains sulfate ions, the salt will be sulfate.

The solubility of salt in water indicates the amount of salt that can be dissolved in 100 g of pure water at a temperature of 20°C. The solubility of the salt containing the internal standard element is close to the solubility of the salt containing the element to be measured. Just do it. Specifically, where A is the solubility of the salt containing the element to be measured, and B is the solubility of the salt containing the internal standard element, B/A should be 8 or less. Although the lower limit of the solubility ratio is not particularly limited, B/A is preferably 1/8 or more. From the viewpoint of more reliably suppressing salt segregation, the solubility ratio (B/A) is more preferably 1/3 or more and 3 or less.

The internal standard element may be appropriately changed according to the type of the element to be measured, and is not particularly limited. When the element to be measured is selected from the group consisting of transition metal elements, specifically Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, the internal standard element is the element to be measured It is preferable to select from different types of transition metal elements. By selecting in this way, the internal standard element can be selected from elements having an atomic weight close to that of the element to be measured. By using an internal standard element whose atomic weight is close to that of the element to be measured, it is possible to approximate the influence of absorption and excitation by other coexisting components when the internal standard substance is added to the liquid sample and dried. As a result, when the finally obtained sample is measured by XRF, the X-ray intensity ratio obtained from the X-ray intensities of the element to be measured and the internal standard element can be made more stable.

(Mixing process)
Subsequently, an internal standard substance is added to the liquid sample and mixed to form a mixed solution. The resulting mixed solution contains, for example, the element to be measured, the internal standard element, and the coexisting component.

The internal standard substance may be dissolved in pure water in advance, and then added as a solution containing the internal standard element (internal standard solution). For example, an internal standard solution having a predetermined concentration may be added to a liquid sample by accurately weighing a predetermined amount of an internal standard substance and then adding and dissolving it in a predetermined weight of pure water.

(Dripping process)
Subsequently, for example, filter paper is prepared as a sample holder. The mixed solution is dripped onto the filter paper to impregnate it. The sample holder is not limited to filter paper, and is not particularly limited as long as it can hold precipitates that precipitate when the mixed solution is dried. For example, filter paper, a glass member, or the like can be used. However, when measuring with XRF, a glass member or the like may generate fluorescent X-rays derived from the glass and reduce the measurement accuracy, so filter paper is preferable from the viewpoint of maintaining high measurement accuracy.

In the dropping step, the amount of the liquid sample dropped onto the filter paper is preferably 150 μg/cm ² or less. Dropping the liquid sample in this amount not only reduces the concentration gradient of the element to be measured and the internal standard element in the vertical direction (thickness direction) of the sample holder, but also reduces the concentration gradient in the horizontal direction (planar direction). It can be evenly distributed. Thereby, the quantification accuracy can be further improved.

(Drying process)
Subsequently, the sample holder onto which the mixed solution has been dropped is dried. As a result, the solvent (for example, moisture) in the mixed solution is volatilized, and the salt containing the element to be measured and the salt containing the internal standard element are precipitated. As a result, an analytical sample for XRF is obtained in which precipitates containing these salts are held on the sample holder. This analysis sample is in a state in which precipitates containing salts of each element are attached to the region where the mixed solution is dropped.

In this embodiment, the internal standard element forms a salt whose solubility in water is 8 times or less the solubility in water of the salt containing the element to be measured when the mixed solution is dried. , an element different from the element to be measured is selected. Therefore, when the mixed solution is dried, the salt containing the element to be measured and the salt containing the internal standard element can be precipitated at approximately the same ratio. As a result, in the precipitate obtained by drying the mixed solution, the element to be measured and the internal standard element can be precipitated so as to be uniformly dispersed in the plane.

The drying temperature of the mixed solution is not particularly limited as long as the temperature does not deform the sample holder. In the case of filter paper, the drying temperature is preferably 80° C. or lower. On the other hand, from the viewpoint of shortening the drying time, it is preferable to increase the drying temperature, preferably 50° C. or higher.

As a drying method, natural drying, drying using a dryer, or the like can be used, but drying using a dryer is preferable from the viewpoint of performing rapid and uniform drying.

(Quantification process)
Subsequently, the obtained analysis sample is introduced into a fluorescent X-ray measuring device and subjected to fluorescent X-ray analysis. Here, a case where an analysis sample is introduced into a fluorescent X-ray measuring apparatus and measurement is performed will be described with reference to FIG. FIG. 1 is a diagram for explaining the case of measuring an analysis sample using a fluorescent X-ray measuring device.

First, as shown in FIG. 1, the analysis sample 26 is placed on the sample holder 20 . The sample holder 20 includes a cylindrical frame 21 that accommodates an analysis sample 26, and a support portion 22 that is provided at the bottom of the frame 21 and supports the analysis sample 26. The support portion 22 includes: A hole 23 for exposing an analysis sample 26 is formed in its central portion. An analysis sample 26 is placed on the support portion 22 of the frame 21 of the sample holder 20 via a ring-shaped mask 24 having a mask hole 25 . The analysis sample 26 is placed on the sample holder 20 such that its peripheral portion is supported by the support portion 22 and is partially exposed from the hole portion 23 . At this time, the analysis sample 26 is arranged so that the region where the mixed solution in the analysis sample 26 is dripped and the precipitate is attached is exposed from the hole portion 23 . The ring-shaped mask 24 functions as a washer, and the mask 24 may be omitted by providing the support portion 22 with a washer structure.

Next, a weight 28 is placed on the mounted analysis sample 26 to apply a uniform load to the analysis sample 26 . By sandwiching the analysis sample 26 between the mask 24 and the weight 28, deformation and displacement of the analysis sample 26 during measurement can be suppressed. Moreover, when the analysis sample 26 is filter paper, its smoothness can be ensured.

The weight 28 is not particularly limited as long as it does not contain the element to be measured and the internal standard element and does not generate fluorescent X-rays of wavelengths that interfere with the detection of the fluorescent X-rays generated by these elements. As such a weight 28, for example, a member made of a fluororesin such as PTFE, PFA, PCTFE, PVDF, PVF, ETFE, ECTFE, or the like can be used.

Subsequently, the analysis sample 26 is irradiated with _primary X-rays X1 generated by the X-ray tube 10 . Specifically, a partial region of the analysis sample 26 exposed from the sample holder 20 is irradiated with _primary X-rays X1. Due to this irradiation, the elements contained in the precipitates adhering to the analysis sample 26 each generate their own unique fluorescent X _- rays X2. Then, the generated fluorescent X _- rays X2 are detected by the X-ray detector 30, and the X _- ray intensity of the fluorescent X-rays X2 peculiar to each of the element to be measured and the internal standard element is measured. Also, the intensity ratio of these is obtained.

Subsequently, using a previously prepared calibration curve showing the correlation between the concentration ratio and the X-ray intensity ratio for the element to be measured and the internal standard element, the measurement contained in the liquid sample is determined from the obtained X-ray intensity ratio. Quantify the concentration of the target element.

A calibration curve may be prepared, for example, as follows. Specifically, a solution containing the element to be measured at a predetermined concentration is mixed with an internal standard material, and the X-ray intensity ratio between the element to be measured and the internal standard element is obtained. It is preferable to prepare a calibration curve showing the correlation between the concentration ratio and the X-ray intensity ratio for the element to be measured and the internal standard element by repeatedly changing the amount and obtaining the X-ray intensity ratio at each sampling amount. .

As described above, the concentration of the element to be measured contained in the precipitate in the liquid sample can be measured based on the internal standard element, and the concentration of the element to be measured contained in the liquid sample can be quantified.

<Effects of this embodiment>
According to this embodiment, one or more of the following effects can be obtained.

When using as an internal standard substance a compound containing an element that forms a salt with a solubility that is greatly different from the solubility in water of the salt containing the element to be measured, the mixed solution is dried to evaporate the solvent. Sometimes salts with low water solubility start to precipitate first, and salts with high water solubility start to precipitate later. As a result, the higher the water solubility of the salt, the more the salt is deposited outside the central portion in the area where the mixed solution is dropped. Thus, the salt containing the element to be measured and the salt containing the internal standard element precipitate differently due to the difference in water solubility, and one of the salts segregates. If one salt is precipitated, the ratio of the element to be measured and the internal standard element varies depending on the part of the precipitate that is irradiated with X-rays, and the concentration of the element to be measured can be quantified with high accuracy and high reproducibility. Can not do it.

On the other hand, in the present embodiment, the internal standard substance is salt water containing the element to be measured, which is different from the element to be measured and has a solubility in water when mixed with a liquid sample and dried. A compound containing an element that forms a salt that is 8 times or less than the solubility in water is used. This makes it possible to approximate the solubility of the salt containing the element to be measured and the salt containing the internal standard element. can be precipitated. As a result, the ratio between the element to be measured and the internal standard element can be made uniform in the region where the precipitate containing the salt of each element adheres. According to the sample in which the element to be measured and the internal standard element are uniformly precipitated in the region in this way, the intensity ratio between the element to be measured and the internal standard element can be kept constant regardless of the X-ray irradiation position. Therefore, the concentration of the element to be measured can be quantified with high accuracy and high reproducibility.

Both the element to be measured and the internal standard element are preferably transition metals, are selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, and are different elements. is more preferred. Even if the element to be measured is a transition metal element, it can be quantified with high accuracy by selecting a transition metal element whose solubility in salt water is close to that of salt as an internal standard element.

The amount of the mixed solution dropped onto the sample holder is preferably 150 μg or less per 1 cm ² of area of the sample holder. As a result, in the precipitates of the analysis sample, the concentration gradient of the element to be measured and the internal standard element can be reduced in the thickness direction, and can be uniformly dispersed in the planar direction. As a result, it is possible to further improve the quantification accuracy.

Filter paper is preferably used as the sample holder. Unlike glass, for example, filter paper does not interfere with the detection of fluorescent X-rays generated from the element to be measured or the internal standard element, so it is possible to quantify the concentration of the element to be measured with higher accuracy.

<Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be modified in various ways without departing from the gist of the present invention.

For example, in the mixing step, a mixed solution may be prepared using a gravimetric method. Specifically, it is preferable to add an accurately weighed internal standard substance to a liquid sample that has been accurately weighed, and to mix the mixture by stirring. According to the gravimetric method, it is not necessary to measure the liquid volume by simply weighing the liquid weight in the process of forming the mixed solution, so the measurement accuracy can be improved and the time required for quantitative analysis can be shortened. be able to.

Specifically, in an operation to aliquot a certain volume of a liquid sample, if the operator's skill in operating a push-button microvolume meter for liquids (so-called micropipette) is inexperienced, aliquoting may be difficult. The error increases, and as a result, accurate measurement may not be possible. On the other hand, in the operation of weighing the weight of a liquid, the error is small and a more precise measurement operation can be easily performed even if the operator is unskilled in the operation.

Moreover, according to the gravimetric method, the ratio between the element to be measured and the internal standard source contained in the liquid sample can be strictly determined at the stage of forming the mixed solution. As a result, when a fixed volume of the mixed solution is dropped onto the sample holder, the ratio between the predetermined element and the internal standard element is maintained even if the liquid volume is measured with an inexperienced operating skill. Therefore, the mixed solution can be handled by the liquid volume measurement operation method without lowering the measurement accuracy, even if the operator is unskilled in operation.

The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

(Example 1)
In Example 1, in order to quantify the Ni concentration contained in nickel (II) sulfate, which is a solid sample, nickel (II) sulfate was dissolved to prepare a liquid sample according to the flow shown in FIG. An analytical sample was prepared for analysis.

Specifically, first, nickel (II) sulfate is dissolved in water in advance to prepare a constant Ni concentration in the range of 50 to 130 g / L, liquid sample 1 (nickel sulfate (II) solution) was prepared. Next, 1 mL of the liquid sample was accurately weighed to the order of 0.1 mg into a polystyrene test tube using a precision balance. Next, Mn is selected as an internal standard element, and 3 mL of an internal standard solution (manganese (II) sulfate solution) with a Mn concentration of 40 g / L is added to a polystyrene test tube using a precision balance to the order of 0.1 mg. Weighed accurately. Then, the polystyrene test tube was sealed and stirred to obtain a mixed solution 1-1. This operation was repeated nine times to prepare a total of ten mixed solutions 1-1 to 1-10.

20 μL of each of the prepared mixed solutions 1-1 to 1-10 was dispensed using a micropipette and dropped onto the center of a circular filter paper (No. 5C) having an outer diameter of 50 mm. After dripping and leaving for 30 seconds or more, the circular filter paper impregnated with the mixed solution is loaded into a natural convection type constant temperature dryer with the temperature inside the chamber set at 50 ° C. and dried by heating for 60 minutes. , 10 analytical samples 1-1 to 1-10 according to Example 1 were obtained.

Analytical samples 1-1 to 1-10 were placed in sample holders (frames with an inner diameter of 52 mm). Then, PTFE having a diameter of 50 mm and a thickness of 40 mm was placed as a weight on the side of the analysis sample not facing the X-ray tube.

A sample holder on which analysis samples 1-1 to 1-10 were placed and a PTFE weight was placed was loaded into the XRF measurement device. Then, the fluorescent X-ray intensities of 10 Ni and Mn in analytical samples 1-1 to 1-10 were measured, the X-ray intensity ratio between Ni and Mn was calculated, and the Ni concentration in the mixed solution was quantified. . Then, the relative standard deviation (RSD) was obtained as the XRF repeated measurement accuracy from the Ni concentration measured for each of the 10 analytical samples. As a result, the relative standard deviation (RSD) was 0.15%, and it was confirmed that Example 1 had excellent XRF repeatability.

Incidentally, the Ni concentration was calculated using the calibration curve shown in FIG. Based on the flow in FIG. 2, this calibration curve was obtained by changing the amount of nickel (II) sulfate solution with a known concentration in the Ni concentration range of 50 to 130 g / L, and the Ni and Mn It was created by obtaining the X-ray intensity ratio with When the correlation coefficient of the calibration curve was calculated, it was 1.000, and it was confirmed that the linearity of the calibration curve was very good.

(Comparative example 1)
In Comparative Example 1, Fe was selected as the internal standard element, and an analysis sample 2 was prepared in the same manner as in Example 1 except that an internal standard solution (iron (III) sulfate solution) having a Fe concentration of 40 g / L was used. -1 to 2-10 were prepared, and the X-ray intensity ratio between Ni and Fe was calculated by measuring the fluorescent X-ray intensity of Ni and Fe for this analysis sample, and the Ni concentration in the mixed solution was obtained. . Then, in the same manner as in Example 1, the relative standard deviation (RSD) was obtained from the Ni concentration measured for each of the analytical samples 2-1 to 2-10 as the XRF repeated measurement accuracy. As a result, in Comparative Example 1, the RSD was 0.60%, and compared with Example 1, it was confirmed that the quantitative values obtained by repeated XRF measurements varied greatly.

In order to examine the difference in repeated measurement accuracy by XRF between Example 1 and Comparative Example 1, the analytical samples prepared in Example 1 and Comparative Example 1 were measured with an electron probe microanalyzer (EPMA). FIG. 3 shows a photograph of the surface analysis result of the analysis sample prepared in Example 1 by an electron probe microanalyzer, and FIG. 4 shows a photograph of the surface analysis result of the analysis sample prepared in Comparative Example 1 by an electron probe microanalyzer. each shown.

As shown in FIG. 4, when the internal standard element is Fe, Fe and S derived from the salt containing the internal standard element (iron (III) sulfate) are present in the peripheral area ( It was confirmed that it was concentrated and segregated in the central peripheral part of the filter paper). That is, Fe and S derived from iron (III) sulfate and Ni and S derived from the salt containing the element to be measured (nickel (II) sulfate) are present at the same time in the portion of the analysis sample to which the mixed solution is dropped. It was found that they were not evenly distributed.

In Comparative Example 1, the segregation of the salts occurred due to the solubility in water of nickel (II) sulfate, which is the salt containing the element to be measured, and the solubility in water of iron (III) sulfate, which is the salt containing the internal standard element. This is presumed to be due to the large divergence between Specifically, as shown in Table 1 below, the solubility of nickel (II) sulfate in water at a temperature of 20°C is 44.4 g, and the solubility of iron (III) sulfate in water at a temperature of 20°C is , 440 g, and the solubility ratio of these salts is about 9.9. That is, Fe, which was selected as the internal standard element in Comparative Example 1, has higher solubility than Ni, which is the element to be measured, and forms a salt that is less likely to volatilize water and precipitate during drying. When the mixed solution containing Ni and Fe having such solubility is dried to volatilize the solvent (moisture), the salt containing Ni is likely to precipitate, whereas the salt containing Fe is difficult to precipitate. Fe is concentrated and tends to precipitate outside the region where the mixed solution is dropped. As a result, in the region where the mixed solution was dropped, Ni and Fe were not precipitated at the same ratio, so the X-ray intensity ratio (Ni / Fe) was not constant depending on the X-ray irradiation position, and repeated measurements by XRF It is considered that the dispersion of each quantitative value increased when the

On the other hand, in Example 1, as shown in FIG. 3, when the internal standard element is Mn, Mn and S derived from a salt containing the internal standard element (manganese (II) sulfate) It was confirmed that Ni and S derived from the salt (nickel (II) sulfate) containing Ni and S are uniformly distributed without segregation in the dropping portion of the mixed solution on the filter paper.

This is because in Example 1, Mn, which has a solubility close to that of a salt containing Ni (nickel sulfate (II)), which is the element to be measured, is used as the internal standard element when a salt is formed. guessed. Specifically, as shown in Table 1 below, the solubility of nickel (II) sulfate in water at a temperature of 20°C is 44.4 g, and the solubility of manganese (II) sulfate in water at a temperature of 20°C is , 62.9 g, and the solubility ratio of these salts is about 1.4. That is, since Mn selected as the internal standard element in Example 1 and Ni, which is the element to be measured, have the same degree of solubility, the difference in the timing of starting to precipitate as a salt is small. Therefore, when the mixed solution containing Ni and Mn is dried to volatilize the solvent (moisture), Ni and Mn can start to precipitate at the same time. It can be uniformly deposited. As a result, the X-ray intensity ratio (Ni/Mn) can be kept constant regardless of the X-ray irradiation position, so that the variation in each quantitative value can be reduced when XRF is repeatedly measured. .

In Table 1, the solubility of each substance indicates the amount [g] of each substance dissolved in 100 g of pure water at a temperature of 20°C.

As described above, the mixed solution containing the element to be measured and the internal standard element is dried by selecting, as the internal standard element, an element having a solubility close to that of the salt containing the element to be measured when a salt is formed. Occasionally, it is possible to suppress the segregation of one salt and form an analysis sample for fluorescent X-ray analysis in which the ratio of each element is uniform in the plane. According to such an analysis sample, a constant X-ray intensity ratio of each element can be obtained regardless of the X-ray irradiation position, so that the concentration of the predetermined element can be quantified with high accuracy and good reproducibility.

10: X-ray tube 20: Sample holder 21: Frame 22: Support 23: Hole 24: Mask 25: Mask hole 26: Analysis sample (filter paper)
28: Weight 30: X-ray detector X1: _Primary X-ray X2: Fluorescent X _- ray

Claims (7)

A method for preparing an analysis sample for fluorescent X-ray analysis, comprising:
A preparation step of preparing an aqueous solution containing the element to be measured as a liquid sample;
A mixing step of adding an internal standard substance containing an internal standard element to the liquid sample and mixing to form a mixed solution;
a dropping step of dropping the mixed solution onto the sample holder;
By drying the mixed solution that has been dropped onto the sample holder to precipitate a salt containing the element to be measured and a salt containing the internal standard element, the precipitate containing these salts is held on the sample holder. and a drying step to form the analyzed sample,
The internal standard element forms a salt having a solubility in water that is 8 times or less the solubility in water of the salt containing the element to be measured in the drying step. are different elements,
A method for preparing an analytical sample. The element to be measured and the internal standard element are transition metal elements different from each other,
The method for preparing an analysis sample according to claim 1. The element to be measured and the internal standard element are selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn and are different elements.
The method for preparing an analysis sample according to claim 1 or 2. wherein the liquid sample contains sulfate ions;
Each salt precipitated in the drying step is a sulfate,
A method for preparing an analysis sample according to any one of claims 1 to 3. In the dropping step, the amount of the mixed solution to be dropped is set to 150 μg or less per 1 cm ² of the area of the sample holder.
A method for preparing an analysis sample according to any one of claims 1 to 4. wherein the sample holder is filter paper;
A method for preparing an analysis sample according to any one of claims 1 to 5. A quantification method for quantifying the concentration of a predetermined element contained in a liquid sample,
a preparation step of preparing an aqueous solution containing an element to be measured as the liquid sample;
A mixing step of adding an internal standard substance containing an internal standard element to the liquid sample and mixing to form a mixed solution;
a dropping step of dropping the mixed solution onto the sample holder;
By drying the mixed solution that has been dropped onto the sample holder to precipitate a salt containing the element to be measured and a salt containing the internal standard element, the precipitate containing these salts is held on the sample holder. a drying step to form a filtered analytical sample;
a quantification step of irradiating the precipitate in the analysis sample with X-rays, measuring the X-ray intensities of the element to be measured and the internal standard element, and quantifying the concentration of the element to be measured from the intensity ratio; , has
The internal standard element forms a salt having a solubility in water that is 8 times or less the solubility in water of the salt containing the element to be measured in the drying step. are different elements,
A quantitative method for liquid samples.

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