JP2005265728A - Quantitative analytical method by colorimetric method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the effect of silica to allow quick and precise measurement, while keeping a system of a measuring object constant, even when a reagent using amount in the actual measurement and an amount of the coloring disturbing silica accompanied to replacement of a using reagent are varied. <P>SOLUTION: The effect of the coexistence silica to a measured value obtained when using a several times of amount in usual measurement of a coloring reagent A coexisting together with the silica affecting coloration, and the effect of the coexistence silica to a measured value obtained in the usual measurement when using the same coloring reagent A are calculated separately as a blank test, before the actual colorimetric analysis, and the effect of the coexistence silica is subtracted from the measured value obtained in the actual analysis to determine quantitatively the silica amount in a sample, using a function calculated by the blank test. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention is one of chemical analyzes for determining the amount of components such as silicon dioxide (commonly referred to as silica, hereinafter referred to as silica (SiO ₂ )) present in a solution, and contains a component to be measured such as silica. Molybdenum blue absorptiometry that quantifies the components to be measured in the sample liquid by measuring the light transmittance or absorbance of the mixed solution after injecting the coloring reagent into the sample liquid to be mixed and reacting for color development. Alternatively, the present invention relates to a quantitative analysis method by a colorimetric method such as molybdenum yellow absorptiometry.

  As a quantitative analysis method for silica and the like, the colorimetric method, in particular, the molybdenum blue absorptiometry method is often adopted because it can be accurately measured to a low concentration and the measurement operation is relatively simple. Yes.

FIG. 1 is a schematic diagram showing the principle of a quantitative analysis method by molybdenum blue absorptiometry (specified in “JIS K 0101: Industrial Water Test Method”), which is a sample solution containing silica (SiO ₂ ) ( Hereinafter, the reagent A mainly composed of a color former composed of sulfuric acid + ammonium molybdate is injected into and mixed with sample S) to produce silicomolybdic acid and yellow. Next, phosphomolybdic acid, which is a component that interferes with the color development reaction, is decomposed by injecting and mixing a reagent B mainly composed of a concealing agent made of oxalic acid and a color development stabilizer for improving color reproducibility. . Subsequently, a reagent C mainly composed of a reducing agent composed of ascorbic acid is injected and mixed to reduce the heteropoly compound produced by the reaction of SiO ₂ with ammonium molybdate, thereby producing molybdenum blue color. In this method, the solution colored in molybdenum blue is transferred to a cell, and the absorbance in the vicinity of a wavelength of 815 nm is measured to quantify the SiO ₂ in the sample S.

  In the quantitative analysis by the colorimetric method such as molybdenum blue absorptiometry as described above, the color developing reagent A injected into the sample S contains a small amount of silica as a measurement target component. Silica present in the reagent A for use becomes an interference component for color development, which greatly affects the measured value and causes measurement errors. Therefore, it is necessary to carry out a blank test in which the degree of influence on the measurement value by such a coloring interference component is detected and the measurement value obtained at the actual measurement is corrected based on the detected degree of influence.

  By the way, in order to detect the influence of the coloring interference component for correcting the actual measurement value as described above, conventionally, a coloring reagent coexisting with the coloring interference component (measurement target component) is used twice as much as the normal measurement. A blank test is performed to calculate the difference between the measured value when measured and the measured value when measured normally using the same coloring reagent, and the difference value calculated by this blank test is the color interference component The difference value is regarded as a correction value (reagent blank value), and the measurement target component such as silica in the sample is quantified by calculating the correction value of the actual measurement value with the reagent blank value. The method was taken.

A method for calculating a reagent blank value by a blank test will be described using a conventionally known silica monitor as an example.
First, when the influence degree for each reagent A to C used in the quantitative analysis method by the colorimetric method such as molybdenum blue absorptiometry described above was confirmed, the result shown in FIG. 2 was obtained. From this result, it is considered that the reagent A is the only reagent that has silica in the reagent and affects the measured value, and there is no problem. This is also clear from the fact that it is consistent with the results described in the conventional silica monitor and JIS.

  Based on this result, in the conventional silica monitor, the difference ΔD (D between the measured value D obtained by the normal measurement and the measured value D ′ obtained by using the usual double amount of the reagent A '-D) was obtained, and the difference value ΔD was used as a reagent blank value used for correction of the measured value in actual measurement.

  However, in the conventional quantitative analysis method based on the colorimetric method for quantifying the measurement target component by correcting the actual measurement value using the reagent blank value obtained in the blank test as described above, (a) the reagent at the time of actual analysis When the amount used is changed, the pH of the sample is different from that at the time of normal measurement using a normal amount of reagent, so that a calibration curve completely different from that at the time of normal measurement is obtained. (B) In addition to the coloring reagent during actual analysis, as described above, another reagent for concealing the coloring reaction hindering component or stabilizing the color reproducibility (see FIG. 1). B, C) are often used in combination, and the quantitative balance between these different reagents and the coloring reagent is different between the case of normal measurement and the case where the amount of reagent used is changed. As a result, the effect on the measured value obtained during the actual analysis will be greater than the effect during the blank test. As a result, there is a problem that the error of the actual measurement value becomes so large that it exceeds the allowable range.

  An improved method for solving such a problem is also known. This improved method will be described using a silica monitor as an example. The problem (a) is caused by the fact that the color developing reagent A used in the conventional silica monitor is a mixed solution of sulfuric acid and ammonium molybdate. Instead of using such a mixed solution, as shown in JIS, separate solutions of sulfuric acid and ammonium molybdate and ammonium molybdate at the time of reagent blank value measurement (blank test) In this method, only a double amount of the solution is injected, and the injection amounts of the other reagents B and C are changed in accordance with the change of the injection amount.

  However, in the case of this improved method, although the error in the measured value due to the change in pH can be eliminated, an ammonium molybdate solution different from the sulfuric acid solution forms a recrystallized product in the solution within a short time. Since the concealing effect of the reagent B on the reagent A differs depending on the concentration of silica in the sample solution, when the measurement is continuously performed, the injection amount of the reagent B is also adjusted and changed in accordance with the change in the concentration of the measurement target component. Therefore, there are many problems such as necessity. Therefore, in general, the former method, that is, measurement using a measurement value obtained by a normal measurement and a usual double amount of reagent (mixed solution) A is used. As a result, a blank test was performed in which a difference value from the measured value obtained as the reagent blank value was used as a reagent blank value. As a result, the above-described problem occurred.

  The present invention has been made in view of the various circumstances as described above, and its purpose is that when the amount of reagent used is changed during actual measurement, or when the amount of the coloring interference component is changed due to replacement of the reagent used. In any case, the colorimetric method can be used for quantitative analysis by colorimetric method, which can correct the degree of influence of the coloring interference component appropriately and quickly and accurately obtain measurement values while maintaining the measurement target system constant. Is to propose.

In order to achieve the above object, the colorimetric quantitative analysis method according to the present invention is a method in which a coloring reagent is injected into a sample solution containing a component to be measured and mixed to cause a coloring reaction. A colorimetric quantitative analysis method for quantifying a measurement target component in a sample solution by measuring light transmittance or absorbance,
Prior to the actual analysis, the measurement target component or the measurement target component and the color interference component with respect to the measurement value obtained by measurement using a color developing reagent in which a measurement target component that affects color development exists several times the normal measurement And the degree of influence of the measurement target component or the measurement target component and the coloring interference component with respect to the measurement value obtained by normal measurement using the same color-developing reagent. Based on, a blank test to calculate a function with both measured values as variables,
Using the function calculated in this blank test, it is possible to quantify the measurement target component in the sample liquid by subtracting the measurement target component or the measurement target component and the influence of the coloring interference component from the measurement value obtained during the actual analysis. It is a feature.

  Here, as the colorimetric method in the method of the present invention, either molybdenum blue absorptiometry or molybdenum yellow absorptiometry may be employed.

  In addition to the coloring reagent, the reagent that is injected into and mixed with the sample solution conceals the coloring reaction between the coloring reagent and the measurement target component in the sample, and improves the stability of the coloring reaction. May be injected and mixed.

According to the quantitative analysis method by the colorimetric method of the present invention having the above-described characteristics, it is possible to perform the measurement using a coloring reagent several times the amount of normal measurement and the normal measurement by a blank test performed before actual analysis. A function having both measured values as variables is calculated based on the degree of influence of the measurement target component and the coloring interference component on both measured values obtained at the time of measurement. For example, when a double amount of reagent is used, the measured value when using the double amount of reagent is D ′, the measured value at the time of normal measurement is D, the degree of influence by the measurement target component is β, and the primary coefficient is α When
f (x) = α (D′−D) −β
The degree of influence on the measured value that can be expressed by the function is calculated. In the actual analysis, the function calculated by the blank test is used to subtract the influence of the measurement target component or the measurement target component and the coloring interference component from the measurement value obtained in the actual analysis, so that the reagent Regardless of how much the amount of color-blocking components changes due to the amount used or the reagent used, the system to be measured is kept constant without requiring complicated control operations such as adjusting the amount of other reagents to be injected. Thus, it is possible to quickly obtain an accurate measurement value while maintaining the above. Therefore, there is an effect that the analysis efficiency can be increased and the accuracy of repeated analysis can be improved without the need for correction using a standard solution for each actual measurement.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a functional block diagram of a silica monitor that employs a molybdenum blue absorptiometric method used in the implementation of a quantitative analysis method by a colorimetric method according to the present invention. This silica monitor is a sample containing silica (SiO ₂ ). A sampling unit 1 for extracting S, a sample (sample) heating unit 2 for heating the extracted sample S so as to promote a color reaction with a reagent, and a sample S heated by the heating unit 2 are illustrated in FIG. Reagent A (mainly composed of a color former composed of sulfuric acid + ammonium molybdate), reagent B (mainly composed of a hiding agent composed of oxalic acid and a color stabilizer) and reagent C (ascorbic acid) And a reaction part 4 for injecting a coloring agent through a reagent pump 3 and a solution colored in molybdenum blue by the coloring reaction in a cell. It includes a measurement unit 5 equipped with temperature control device (not omitted) measuring absorbance near a wavelength 815nm transferred, and a waste-water outlet 6 for discharging the solution after the measurement. The reaction unit 4 is provided with a measuring unit 7 that measures the sample S and the reagents A to B and overflows the surplus.

  When the silica monitor having the functional configuration as described above is used to perform a predetermined analysis for quantitatively determining silica by measuring the silica concentration actually contained in the sample S, the sample S extracted by the sampling unit 1 is used. After heating in the heating unit 2, the heated sample S is introduced into the reaction unit 4, and the reagents A to C are supplied to the reaction unit 4 via the reagent pump 3 to mix them. Along with the formation of silicomolybdic acid (colored in yellow) → Decomposition of phosphomolybdic acid, a component that interferes with the coloring reaction → Molybdenum through the reduction action of the heteropoly compound produced by the reaction of silica and ammonium molybdate It is colored blue. Then, the solution colored in molybdenum blue is guided to the measuring unit 5, where it is transferred to the cell, and the silica in the sample S is quantified by measuring the absorbance near the wavelength of 815 nm.

  Before performing such a predetermined analysis, the degree of color development for each of the reagents A to C is confirmed, and as a result (see FIG. 2), it is confirmed that a small amount of silica that affects color development exists. With respect to the reagent A, a blank test is performed to detect the degree of influence of the silica. In this blank test, only the reagent A is supplied to the reaction unit 3 via the reagent pump 3, the reagent solution colored in molybdenum blue is guided to the measurement unit 5 and the absorbance is measured, and corrected during the actual analysis described above. The reagent blank value for performing the calculation is calculated.

  The reagent blank value is calculated from the correlation between the measurement value in the normal measurement and the measurement value when the reagent A is used in double amount, and hereinafter, in order to calculate the correlation, etc. The calculation processing flow will be described.

1. First, when performing a normal measurement, a known concentration of silica is added to the reagent A, and the silica concentration in the reagent A is changed to check the degree of influence of the silica present in the reagent A on multiple points (inspect) ).
2. Also, when measuring with reagent A twice the amount of normal measurement, the concentration of silica added in reagent A is changed, and the influence of the silica present in reagent A on the measured value is confirmed at multiple points. Do (examine).
Above 1. And 2. When the normality measurement time is expressed as a and the double amount measurement time as 2a, it is as shown in Table 1 below, and can be actually confirmed with a silica monitor as shown in FIG. The value is an indication value of the monitor, which is as shown in FIG.

From this result, the first-order coefficient of the correlation function indicating the degree of influence of the reagent and the measured value at the time of normal measurement and double measurement is
Normal measurement a: 0.9052, double amount measurement 2a: 2.2725
The formula for the estimated influence on the measured value during normal measurement is
y = 0.09052x + 0.6461 (1)
It becomes.

3. The above equation (1) includes an unknown constant in the zeroth order coefficient, but the other higher order coefficients correctly indicate the degree of influence on the measurement value by the silica in the reagent A. Assuming that there is no influence of pH change or hiding effect fluctuation at the time of double volume measurement, the first order coefficient at the time of double volume measurement is only the difference in the amount of reagent A to be injected.
0.9052 × 2 = 1.8104
It becomes. Expressing this as a ratio to the degree of influence when measuring twice the amount,
1.8104 / 2.2725 = 0.796656
It becomes.

  4). Therefore, using the coefficient of the correlation function described above, 3. When the difference between the measurement value estimated from the measurement value 2a obtained at the time of double amount measurement in the case of the assumption (hereinafter referred to as 2a ′) and the measurement value a obtained at the normal measurement is obtained, Table 2 below.

  5). 1 above. ~ 4. The values of a and 2a ′ obtained so far are the effects of the silica concentration obtained by adding silica intentionally added to Reagent A in order to confirm the influence of silica present in Reagent A. Therefore, the degree of influence on the measurement value during the normal measurement due to the change in the concentration of silica present in the reagent A is equal to the difference between (2a′−a) and (a). This is shown in Table 3 below, and the average value is equal to 0.13002, and the average value is the zeroth order coefficient of the function for calculating the reagent blank influence value.

6). And the reagent blank value in consideration of (2a-a) as the value obtained by the actual silica monitor and the influence due to the silica concentration in the reagent A is as shown in the following Table 4 and FIG. Therefore, the reagent blank value is
Reagent blank value = 0.6641 × (2a−a) −0.4025 (2)

  By correcting the measurement value obtained during the actual analysis using the reagent blank value obtained by performing the blank test as described above, it becomes possible to subtract the influence due to the silica coexisting in the reagent A. Regardless of how the amount of reagent A used changes during the analysis of the sample, and the amount of coloring interference component changes as the reagents A to C are changed, the system to be measured in the silica monitor A highly accurate measurement value can be obtained by keeping the minimum error while maintaining a constant value. Therefore, the analysis efficiency can be increased and the accuracy of repeated analysis can be improved without the need for correction using a standard solution for each actual measurement.

  Even when the degree of influence by the measurement target component such as silica in the reagent A has a higher-order correlation other than the first-order, the first-order or higher-order coefficient can be calculated in the same arithmetic processing flow as described above. It is possible to calculate the zeroth order coefficient.

  In the above embodiment, the description is applied to the silica monitor adopting the molybdenum blue absorptiometry. However, the present invention may be applied to a silica monitor adopting the molybdenum yellow absorptiometry, and a measurement object other than silica. The present invention can also be applied to a method of quantitatively analyzing components by a similar colorimetric method.

  Furthermore, in the above embodiment, when calculating the reagent blank value at the time of the blank test, the reagent is determined from the correlation between the measured value when measured using a reagent twice the amount of the normal measurement and the measured value when measured normally. Although what calculated a blank value was demonstrated, the reagent blank value was calculated from the correlation between the measured value when measured using a reagent such as 3 times or 4 times the amount of normal measurement and the measured value when measured normally. Of course, it may be calculated.

1 is a schematic diagram showing the principle of a quantitative analysis method by a molybdenum blue absorptiometry, which is one of the quantitative analysis methods by a colorimetric method according to the present invention. FIG. It is a graph which shows the influence confirmation result for each reagent used with the quantitative analysis method by colorimetric methods, such as a molybdenum blue absorptiometry same as the above. It is a functional block diagram of the silica monitor which employ | adopted the molybdenum blue absorptiometry used for implementation of the quantitative analysis method by the colorimetric method which concerns on this invention. In the blank test for the reagent that coexists with silica that affects color development, the silica monitor indicates the measured value when measured using twice the amount of normal measurement and the degree of influence of silica on the measured value when measured normally It is a graph shown as a value. It is a graph which shows the correlation with the difference of the measured value when measured using twice the amount of normal measurement, and the measured value when measured normally, and a blank influence value.

Explanation of symbols

A Reagent for color development B Reagent for concealment and color stabilization C Reagent for reduction S Sample (sample solution)

Claims (3)

Quantify the measurement target component in the sample solution by injecting the coloring reagent into the sample solution containing the measurement target component and mixing and reacting to develop a color reaction to measure the light transmittance or absorbance of the mixed solution. A quantitative analysis method by a colorimetric method,
Prior to the actual analysis, the measurement target component or the measurement target component and the color interference component with respect to the measurement value obtained by measurement using a color developing reagent in which a measurement target component that affects color development exists several times the normal measurement And the degree of influence of the measurement target component or the measurement target component and the coloring interference component with respect to the measurement value obtained by normal measurement using the same color-developing reagent. Based on, a blank test to calculate a function with both measured values as variables,
Using the function calculated in this blank test, it is possible to quantify the measurement target component in the sample liquid by subtracting the measurement target component or the measurement target component and the influence of the coloring interference component from the measurement value obtained during the actual analysis. Quantitative analysis method by colorimetric method.   The quantitative analysis method by a colorimetric method according to claim 1, wherein molybdenum blue absorptiometry or molybdenum yellow absorptiometry is used as the colorimetric method. 2. In addition to the coloring reagent, a reagent for hiding the coloring reaction between the coloring reagent and a measurement target component in the sample and for improving the stability of the coloring reaction are injected and mixed. Or a quantitative analysis method by a colorimetric method according to 2.

Images