JP4797902B2 - Determination of iron - Google Patents

Description

  The present invention relates to a method for quantifying iron, and particularly to a method for quantifying iron contained in sample water.

  Raw water such as tap water used as boiler feed water usually removes deoxygenation and hardness, ie, calcium and magnesium, to remove dissolved oxygen in order to prevent corrosion and scale generation in the boiler. Water softening treatment is applied. Here, the deoxygenation treatment is usually performed by treating raw water using a separation membrane. Moreover, the water softening process is normally implemented by processing raw | natural water using an ion exchange resin.

  By the way, raw water such as tap water often contains iron. This iron may clog the separation membrane used in the deoxygenation treatment and impair the deoxygenation efficiency of the raw water, and may adsorb on the ion exchange resin used in the water softening treatment, preventing the softening of the raw water. There is sex. For this reason, as for the raw water used as boiler feed water, it is usually important to manage the iron concentration at the stage before deoxidation treatment and water softening treatment. In boilers, the amount of iron contained in boiler water is significant as an indicator of the progress of corrosion in the boiler can and the tendency of scale generation, so accurate quantification of iron in boiler water is important. Therefore, in the boiler system, the amount of iron contained in raw water and boiler water is determined.

  In raw water such as raw water and boiler water, iron is present in various states such as ionic, colloidal, and precipitates such as iron oxide and iron hydroxide. For this reason, in order to accurately quantify the total amount of iron contained in water, in the water to be analyzed (sample water), colloidal or precipitated iron is dissolved in water as ions, and iron ions in water Need to be quantified. Here, quantification of iron ions is usually carried out by phenanthroline absorptiometry, flame atomic absorption, electric heating atomic absorption, or ICP emission spectroscopic analysis. Incidentally, when carrying out the phenanthroline spectrophotometry, it is necessary to reduce trivalent iron ions contained in water to divalent iron ions in advance.

  Non-Patent Document 1 defines a pretreatment method for sample water that can be applied in such a method for quantifying iron. In this pretreatment method, one or two kinds of mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid are added to the sample water, boiled, allowed to cool, and diluted with pure water to adjust the amount of sample water. However, such a pretreatment method requires several steps of adding a mineral acid to the sample water, boiling the sample water, and adjusting the amount of the sample water.

  On the other hand, in water analysis, it may be necessary to quickly analyze hundreds to thousands of sample water, so a series of analysis operations such as fractionation, pretreatment and analysis of sample water are performed on an analytical instrument. The continuous flow analysis, which is automatically performed in, is becoming mainstream. However, the quantification of iron in the sample water requires a complicated and long-time pretreatment as described above, so that it is substantially difficult to perform the continuous flow analysis.

Japanese Industrial Standards JIS K0101: 1998, pages 6-8

  An object of the present invention is to enable easy determination of the total amount of iron contained in sample water.

  The method for quantifying iron according to the present invention is a method for quantifying iron contained in sample water, comprising adding three components of sodium metabisulfite, dithionite and copper masking agent to the sample water, And a step of adding a color former to the sample water to which the components are added and quantifying iron in the sample water by absorptiometry. The copper masking agent used here is, for example, one selected from the group consisting of sodium thiosulfate, thiourea and imidazole.

  In this quantification method, the dithionite added to the sample water ionizes and dissolves the colloidal and precipitated iron content contained in the sample water, and the trivalent contained in the sample water. Reduce iron ions to divalent iron ions. For this reason, when a color former is added to sample water to which dithionite is added, the sample water is colored by the reaction of the color former and divalent iron ions. This color intensity increases according to the concentration of divalent iron ions contained in the sample water. Therefore, when the color intensity of the sample water due to the addition of the color former is measured by absorptiometry, the total amount of iron contained in the sample water can be accurately quantified.

  Here, when copper is contained in the sample water, this copper reacts with sulfur derived from dithionite to produce copper sulfide, which may change the color intensity of the sample water by the color former. . Such fluctuations in the color intensity cause the reliability of the quantitative results to be impaired. However, in this quantification method, since a copper masking agent is added to the sample water, this masking agent acts on copper in the sample water to form a complex, thereby preventing the formation of copper sulfide. Therefore, the color intensity of the sample water is stabilized, and the reliability of the quantitative result can be improved.

  In particular, in the quantification method of the present invention, sodium metabisulfite is added to the sample water together with the above dithionite and copper masking agent. The measurement of the color intensity is not easily affected by the pH of the sample water, and an accurate quantitative result is easily obtained.

  In this quantitative method, it is usually preferable to add dithionite and a masking agent after adding sodium metabisulfite to the sample water.

  Further, in this quantification method, it is preferable to adjust the pH of the sample water to 4.2 or less and then add the three components of the sodium metabisulfite, dithionite and copper masking agents. In this case, the reaction rate between the colloidal and precipitate-like iron contained in the sample water and dithionite is increased, and it is possible to determine iron more rapidly.

  In the quantification method of the present invention, usually, after setting the pH of the sample water to which the three components of sodium metabisulfite, dithionite and copper masking agent are added within a range where the color former can develop color, Add color former to water.

  In the method for determining iron according to the present invention, the three components of sodium metabisulfite, dithionite and copper are added to the sample water, and then the color former is added to the sample water. Since the amount of iron in the sample water is quantified, the total amount of iron contained in the sample water can be easily quantified.

In the iron determination method according to the present invention, first, three components of sodium metabisulfite, dithionite and copper masking agent (hereinafter referred to as “copper masking agent”) are added to the sample water.
The sample water is the water to be analyzed and is not particularly limited, and various waters such as tap water, industrial water, ground water, river water, lake water, boiler water, and condensate from thermal equipment such as boilers. It is water.

  The dithionite used here is usually a salt of dithionite and an alkali metal, alkaline earth metal, ammonium, zinc, cadmium or the like, and is water-soluble. The dithionite may be an anhydride or a hydrate. Among these, in this invention, since it is generally marketed and it is easy to obtain, it is preferable to use the anhydrous salt of sodium dithionite which is 1 type of the alkali metal salt of dithionite.

  The amount of dithionite added to the sample water is usually set to a sufficient amount with respect to the amount of iron contained in the sample water, which is predicted from an empirical rule corresponding to the type of sample water. In particular, the total amount of colloidal iron contained in the sample water and precipitated iron such as iron hydroxide and iron oxide can be dissolved in the sample water, and the three existing in the sample water after the dissolution of these iron contents. It is preferable to set it to an amount sufficient to reduce the valent iron ion to the divalent iron ion. Specifically, it is preferable to set the molar ratio to 5 to 500 times equivalent to the iron content expected to be contained in the sample water.

  However, in general, it is sufficient to add at least 30 mg, preferably 100 mg or more of dithionite to 10 ml of sample water.

  On the other hand, the copper masking agent used here is capable of forming a complex by acting on copper that may be contained in sample water, particularly copper ions, and is, for example, sodium thiosulfate, thiourea, or imidazole. Two or more of these copper masking agents may be used in combination.

  The amount of the copper masking agent added to the sample water is usually set to a sufficient amount with respect to the amount of copper contained in the sample water, which is predicted from an empirical rule according to the type of sample water. Specifically, it is preferably set to 500 to 1,000 times mol, more preferably 600 to 800 times mol, with respect to the predicted amount of copper. However, in general, it is sufficient to add at least 60 mg, usually 80 to 120 mg of copper masking agent to 10 ml of sample water.

  Furthermore, sodium metabisulfite is turbid (especially white turbidity) in the sample water due to the addition of dithionite and copper masking agent, or sulfur derived from dithionite is contained in the sample water. It is added to the sample water in order to suppress the formation of copper sulfide that reacts with potential copper and causes the color development intensity described later to fluctuate. It is preferable to set the molar ratio to at least 2-fold equivalent, and more preferably 3-fold equivalent or more, relative to the amount of dithionite added.

  The order of addition of sodium metabisulfite, dithionite, and copper masking agent to the sample water is not particularly limited, but usually, the above-mentioned effects due to sodium metabisulfite are easily obtained. Preferably, sodium metabisulfite is first added and dissolved, and then dithionite and a copper masking agent are added to the sample water.

  The sample water to which the three components of sodium metabisulfite, dithionite and copper masking agent are added is usually left for about 10 to 20 minutes after shaking. As a result, colloidal and precipitated iron contained in the sample water reacts with dithionite, the iron is ionized and dissolved in the sample water, and trivalent iron ions present in the sample water are Reduced to divalent iron ions. That is, the total amount of iron contained in the sample water is dissolved in the sample water in the form of divalent iron ions.

  Moreover, the copper contained in the sample water is masked by the action of the copper masking agent. As a result, in the sample water, the reaction between the sulfur atom derived from dithionite and copper is blocked, and the color developing intensity of the sample water by the color former may be changed in the execution of the absorptiometry described later ( In particular, it is possible to prevent the formation of copper sulfide (which may increase the color intensity and cause the quantification result of iron to vary much). In particular, sulfur atoms derived from dithionite easily react with copper contained in the sample water when the pH of the sample water is 5.5 or more, and easily form copper sulfide, but are added to the sample water. The obtained sodium metabisulfite can suppress the reaction between such sulfur atoms and copper, and can mask the copper in the sample water with a copper masking agent.

  In this process, heating the sample water to which the three components of sodium metabisulfite, dithionite and copper masking agent are added facilitates the reactions described above, and the sample water is more quickly analyzed in the next analysis step. Can be transferred to. The sample water to which the three components of sodium metabisulfite, dithionite and copper masking agent are added may be adjusted in advance so that the pH is 4.2 or less, preferably 3.5 or less. In this case, the sample water can be heated as described above. By adjusting the pH of the sample water in this manner, the reaction between the colloidal and precipitated iron contained in the sample water and dithionite is more easily promoted, and the sample water is more quickly transferred to the next analysis step. Can be migrated. The pH of the sample water is usually preferably adjusted by adding a mineral acid such as hydrochloric acid to the sample water. At this time, the pH of the sample water can be finely adjusted by adding a buffer solution such as an aqueous ammonium acetate solution. When the sample water is heated or the pH of the sample water is adjusted as described above, the sample water is usually allowed to stand for the three components of sodium metabisulfite, dithionite and copper masking agent. Can be shortened to about 3 to 10 minutes.

  Here, the sample water whose pH is adjusted to 4.2 or lower may be turbid due to the influence of dithionite, particularly white turbidity. Such turbidity may interfere with accurate measurement of absorbance in the implementation of absorptiometry described below. However, in this step, since sodium metabisulfite is added and dissolved in the sample water, generation of turbidity as described above in the sample water can be suppressed by this action.

  Next, the sample water treated as described above is subjected to quantitative analysis of iron, that is, divalent iron by absorptiometry. Here, first, a predetermined color former is added to the sample water. The color former used here is not particularly limited as long as it develops color by reacting with divalent iron ions. For example, 1,10-phenanthroline and its hydration which are inexpensive in a wide range of color development pH conditions. 2,4,6-tris (2-pyridyl) -1,3,5-triazine (abbreviation: TPTZ), which has good color development sensitivity and is relatively inexpensive, has a wide color development pH condition and good color development sensitivity 7-Diphenyl-1,10-phenanthroline disulfonic acid (abbreviation: bathophenanthroline sulfonic acid) and its alkali metal salts and 3- (2-pyridyl) -5,6-bis (4- Sulfophenyl) -1,2,4-triazine (abbreviation: PDTS) and alkali metal salts thereof. Of these, 1,10-phenanthroline or its hydrate or TPTZ is preferably used. Usually, the color former is preferably added to the sample water in the form of an aqueous solution or a water-soluble organic solvent solution such as an alcohol solution.

  When TPTZ is used as the color former, it is preferable to add ethanol to the sample water before adding TPTZ. When water containing sodium polyacrylate as a dispersant for preventing scale generation such as boiler water is sample water, suspended matter is generated when TPTZ is added, and this suspended matter is subjected to spectrophotometry. May be a hindrance. When ethanol is added to the sample water, the formation of such suspended matters is suppressed, and the absorptiometry can be carried out stably. Usually, the amount of ethanol added is preferably set to 2 to 5 ml per 10 ml of sample water.

  Next, with respect to the sample water to which the color former is added, the absorbance of the color developed by the color former is measured, and the amount of divalent iron ions contained in the sample water is determined from the measurement result. Here, a calibration curve is prepared by previously examining the relationship between the absorbance at the coloring wavelength according to the type of color former to be used and the amount of divalent iron ions in the sample water, and based on the calibration curve based on the measured absorbance. To determine the amount of divalent iron ions contained in the sample water. At this time, in order to reduce the measurement error due to the turbidity of the sample water, the absorbance of the color development wavelength is determined in advance by adding a blank for the sample water before adding the above three components or after adding the above three components and the color former. It is preferable to measure the blank of the sample water before the addition and correct it using this measured value. Incidentally, the color development wavelengths of the color formers listed above are as follows.

1,10-phenanthroline and its hydrate: 510 nm
TPTZ: 595 nm
Bathophenanthroline sulfonic acid and its alkali metal salt: 535 nm
PDTS and its alkali metal salts: 562 nm

  By the way, the color developing agent has a different pH range for color development for each type. For this reason, it is preferable to adjust the pH of the sample water before adding the color former to the following range according to the type of the color former, if necessary. The pH of the sample water can usually be adjusted by adding an acidic solution such as hydrochloric acid or nitric acid or a buffer solution such as ammonium acetate.

1,10-phenanthroline and its hydrate: pH 2-9
TPTZ: pH 3.0 to 5.8
Bathophenanthroline sulfonic acid and its alkali metal salts: pH 2-9
PDTS and alkali metal salts thereof: pH 3.5 to 4.5

  When water containing ethylenediaminetetraacetic acid and its salt, which is a masking agent for calcium and magnesium, is a sample water, such as boiler water, TPTZ or PDTS or an alkali metal salt thereof as a color former Is used, the divalent iron ion in the sample water reacts with ethylenediaminetetraacetic acid and its salt, and the color intensity may vary. On the other hand, when the pH of the sample water is lowered, the reaction between the divalent iron ions in the sample water and ethylenediaminetetraacetic acid and its salt becomes difficult to proceed, and the divalent iron ions in the sample water react with the color former. It becomes easy. Therefore, when using these color formers, it is preferable to set the pH of the sample water to be close to the lower limit (that is, on the low pH side) of the above-described range where color development is possible before adding the color former. Specifically, when TPTZ is used, the pH of the sample water is preferably set to 3.0 to 3.4, and when PDTS or an alkali metal salt thereof is used, the pH of the sample water is set to 3.5 to 3. It is preferably set to 7. When the pH of the sample water is set in this way, TPTZ, PDTS, and alkali metal salts thereof can obtain stable color intensity even in sample water containing ethylenediaminetetraacetic acid and its salts, and smoothly perform the spectrophotometric method. Can do.

  The method for quantifying iron according to the present invention comprises adding three components of sodium metabisulfite, dithionite and copper masking agent to sample water and leaving it for the required time, and then a color former for sample water. Therefore, the total amount of iron contained in the sample water can be easily quantified in a short time compared to the conventional quantification method requiring complicated pretreatment. Therefore, if this quantification method is employed in an analytical instrument capable of performing absorptiometry, iron in the sample water can be automatically quantitatively analyzed using the analytical instrument, and a continuous flow that is becoming mainstream in water analysis Analysis can be realized.

  When the quantification method of the present invention is applied to the continuous flow analysis as described above, it is very laborious and time consuming to measure the blank for all the sample water and correct the absorbance, thereby substantially realizing the continuous flow analysis. Can be difficult. Therefore, when the quantitative method of the present invention is applied in continuous flow analysis, the absorbance can be corrected by a simplified method. Specifically, the absorbance at other than the peak of the color development wavelength corresponding to the type of color former and its tail is used as a correction value, and based on the value obtained by subtracting this correction value from the absorbance at the color development wavelength, Determine the amount. Incidentally, for each of the color formers mentioned above, preferred wavelengths for obtaining the absorbance for correction are as follows.

1,10-phenanthroline and its hydrate: 650 nm
TPTZ: 800nm
Bathophenanthroline sulfonic acid and its alkali metal salt: 700 nm
PDTS and its alkali metal salts: 750 nm

  In the following Examples and Comparative Examples, any of the following sample water was used.

Sample water A
A solution prepared by adding pure water to 0.1 ml of an atomic absorption standard solution (manufactured by Wako Pure Chemical Industries, Ltd.) having an iron ion concentration of 1,000 mg / liter so that the total amount becomes 100 ml.
Sample water B
Sample diluted with 0.1 ml of an atomic absorption standard solution (manufactured by Wako Pure Chemical Industries, Ltd.) having an iron ion concentration of 1,000 mg / liter to a total volume of 100 ml by adding pure water. Prepared separately from water A.
Sample water C
A standard solution for atomic absorption (1000 W / pure) with a copper ion concentration of 1,000 mg / liter, compared to 0.1 ml of an atomic absorption standard solution (Wako Pure Chemical Industries, Ltd.) with an iron ion concentration of 1,000 mg / l. Kogyo Co., Ltd.) Diluted to a total volume of 100 ml by adding 0.5 ml and pure water.
Sample water D
A standard solution for atomic absorption (1000 W / pure) with a copper ion concentration of 1,000 mg / liter, compared to 0.1 ml of an atomic absorption standard solution (Wako Pure Chemical Industries, Ltd.) with an iron ion concentration of 1,000 mg / l. Manufactured by Kogyo Co., Ltd.) 0.5 ml and pure water were added to dilute the total volume to 100 ml, and prepared separately from sample water C.

Comparative Example 1
The amount of iron contained in the sample water A was measured according to the phenanthroline spectrophotometric method specified in JIS K0101: 1998. Specifically, 1 ml of 8 wt% hydrochloric acid aqueous solution and 1 ml of 25 wt% ammonium acetate aqueous solution were added to 10 ml of sample water A, and the pH of sample water A was adjusted to 4.2. Subsequently, 0.4 ml of a 10% by weight hydroxylammonium chloride aqueous solution and 0.5% by weight 1,10-phenanthroline ethanol solution (dissolved 1,10-phenanthroline in a 10% by weight ethanol aqueous solution) ) 0.4 ml was added and left for 10 minutes. As a result, the sample water A showed a red color due to the iron (II) complex. About this sample water A, a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.) was used to measure the absorbance at a wavelength corresponding to red (510 nm), and a correction obtained by subtracting the absorbance at 650 nm from this absorbance. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water A was quantified from this correction value.

Comparative Example 2
In the same manner as in Comparative Example 1, the amount of iron contained in the sample water C was measured.

Comparative Example 3 (Coloring agent: 1,10-phenanthroline)
To 10 ml of sample water, 1 ml of 8 wt% hydrochloric acid aqueous solution and 0.72 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water C to 3.2. Subsequently, 200 mg of sodium metabisulfite powder (special grade manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium dithionite anhydrous salt powder (chemical manufactured by Wako Pure Chemical Industries, Ltd.) Were added in this order, shaken and allowed to stand for 10 minutes. In the sample water C after being allowed to stand, turbidity such as white turbidity was not observed.

  Next, 0.4 ml of 0.5 wt% 1,10-phenanthroline ethanol solution (dissolved 1,10-phenanthroline in 10 wt% ethanol aqueous solution) is added to the sample water C after standing. Left for a minute. As a result, the sample water C showed a red color due to the iron (II) complex. About this sample water C, using a spectrophotometer ("U-2010" manufactured by Hitachi, Ltd.), the absorbance at a wavelength corresponding to red (510 nm) is measured, and the absorbance obtained by subtracting the absorbance at 650 nm from this absorbance is corrected. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water C was quantified from this correction value.

Example 1 (Coloring agent: 1,10-phenanthroline)
Compared to sample water C, except that sodium metabisulfite powder and sodium dithionite anhydrous salt powder were added, and then 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was further added. In the same manner as in Example 3, the iron contained in the sample water C was quantified.

Comparative Example 4 (Coloring agent: TPTZ)
To 10 ml of sample water, 1 ml of 8 wt% hydrochloric acid aqueous solution and 0.72 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water C to 3.2. Subsequently, 200 mg of sodium metabisulfite powder (special grade manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium dithionite anhydrous salt powder (chemical manufactured by Wako Pure Chemical Industries, Ltd.) Were added in this order, shaken and allowed to stand for 10 minutes. In the sample water C after being allowed to stand, turbidity such as white turbidity was not observed.

  Next, 0.4 ml of 0.5 wt% TPTZ solution (TPTZ dissolved in 1.0 wt% hydrochloric acid) was added to the sample water C after standing, and left for 5 minutes. As a result, the sample water C exhibited a bluish purple color due to the iron (II) complex. For this sample water C, the absorbance at a wavelength corresponding to blue-violet (595 nm) is measured using a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.), and correction is performed by subtracting the absorbance at 800 nm from this absorbance. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water C was quantified from this correction value.

Comparative Example 5 (Coloring agent: TPTZ)
Included in sample water C in the same manner as in Comparative Example 4 except that the amount of 25 wt% ammonium acetate aqueous solution added to sample water C was changed to 1 milliliter and the pH of sample water C was adjusted to 4.2. The amount of iron to be quantified. In this comparative example, suspended matters were confirmed in the sample water C at the time of measuring the absorbance.

Example 2 (Coloring agent: TPTZ)
To 10 ml of sample water, 1 ml of 8 wt% hydrochloric acid aqueous solution and 0.72 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water C to 3.2. Subsequently, for this sample water C, sodium metabisulfite powder (special grade made by Wako Pure Chemical Industries, Ltd.) 200 mg, sodium dithionite anhydrous salt powder (chemicals made by Wako Pure Chemical Industries, Ltd.) 100 mg, and 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added in this order, shaken, and allowed to stand for 10 minutes. In the sample water C after being allowed to stand, turbidity such as white turbidity was not observed.

  Next, 5 ml of ethanol and 0.4 ml of 0.5 wt% TPTZ solution (TPTZ dissolved in 1.0 wt% hydrochloric acid) were added to the sample water C after standing, and left for 5 minutes. . As a result, the sample water C exhibited a bluish purple color due to the iron (II) complex. For this sample water C, the absorbance at a wavelength corresponding to blue-violet (595 nm) is measured using a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.), and correction is performed by subtracting the absorbance at 800 nm from this absorbance. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water C was quantified from this correction value.

Example 3 (Coloring agent: TPTZ)
Included in sample water C in the same manner as in Example 2 except that the amount of 25 wt% ammonium acetate aqueous solution added to sample water C was changed to 1 milliliter and the pH of sample water C was adjusted to 4.2. The amount of iron to be quantified. In this example, no suspended matter was confirmed in the sample water C at the time of absorbance measurement.

Comparative Example 6 (coloring agent: bathophenanthroline sulfonic acid)
To 10 ml of sample water, 1 ml of 8 wt% hydrochloric acid aqueous solution and 0.72 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water C to 3.2. Subsequently, 200 mg of sodium metabisulfite powder (special grade manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium dithionite anhydrous salt powder (chemical manufactured by Wako Pure Chemical Industries, Ltd.) Were added in this order, shaken and allowed to stand for 10 minutes. In the sample water C after being allowed to stand, turbidity such as white turbidity was not observed.

  Next, 1 ml of a 0.5 wt% aqueous bathophenanthrolinesulfonic acid solution was added to the sample water C after standing, and left for 5 minutes. As a result, the sample water C exhibited a red color due to the iron (II) complex. For this sample water C, the absorbance at a wavelength corresponding to red (535 nm) is measured using a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.), and a correction value obtained by subtracting the absorbance at 700 nm from this absorbance. Asked. Based on a calibration curve prepared in advance, iron contained in the sample water C was quantified from this correction value.

Example 4 (Coloring agent: bathophenanthroline sulfonic acid)
Compared to sample water C, except that sodium metabisulfite powder and sodium dithionite anhydrous salt powder were added, and then 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was further added. In the same manner as in Example 6, iron contained in the sample water C was quantified.

Comparative Example 7 (Coloring agent: PDTS)
To 10 ml of sample water C, 1 ml of 8 wt% hydrochloric acid aqueous solution and 1 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water C to 4.2. Subsequently, for this sample water C, sodium metabisulfite powder (special grade made by Wako Pure Chemical Industries, Ltd.) 1,000 mg and sodium dithionite anhydrous salt powder (for chemicals made by Wako Pure Chemical Industries, Ltd.) 100 mg was added in this order, shaken, and allowed to stand for 10 minutes. In the sample water C after being allowed to stand, turbidity such as white turbidity was not observed.

  Next, 0.3 ml of a 0.5 wt% PDTS aqueous solution was added to the sample water C after standing, and left for 5 minutes. As a result, the sample water C exhibited a reddish purple color due to the iron (II) complex. For this sample water C, the absorbance at a wavelength corresponding to reddish purple (562 nm) was measured using a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.), and correction was performed by subtracting the absorbance at 750 nm from this absorbance. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water C was quantified from this correction value.

Example 5 (Coloring agent: PDTS)
Compared to sample water C, except that sodium metabisulfite powder and sodium dithionite anhydrous salt powder were added, and then 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was further added. In the same manner as in Example 7, iron contained in the sample water C was quantified.

Evaluation 1
The quantitative results of Examples 1 to 5 and Comparative Examples 1 to 7 are shown in Table 1. Table 1 also shows the relative value (%) when the quantitative result of Comparative Example 1 is used as a reference value. According to Table 1, in Examples 1 to 5, a result almost equal to that of Comparative Example 1 is obtained, and it can be seen that the reliability is high.

Comparative Example 8
In the same manner as in Comparative Example 1, the amount of iron contained in the sample water B was measured.

Example 6 (Coloring agent: 1,10-phenanthroline)
To 10 ml of sample water D, 1 ml of 8 wt% hydrochloric acid aqueous solution and 1 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water D to 4.2. Subsequently, 200 mg of sodium metabisulfite powder (special grade made by Wako Pure Chemical Industries, Ltd.), 100 mg of sodium dithionite anhydrous salt powder (chemical use, manufactured by Wako Pure Chemical Industries, Ltd.) 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added in this order, shaken, and allowed to stand for 10 minutes. Turbidity such as white turbidity was not observed in the sample water D after being allowed to stand.

  Next, 0.4 ml of 0.5 wt% 1,10-phenanthroline ethanol solution (1,10-phenanthroline dissolved in 10 wt% ethanol aqueous solution) is added to the sample water D after standing. Left for a minute. As a result, the sample water D showed a red color due to the iron (II) complex. About this sample water D, the absorbance at a wavelength corresponding to red (510 nm) was measured using a spectrophotometer (“U-2010” manufactured by Hitachi, Ltd.), and correction was performed by subtracting the absorbance at 650 nm from this absorbance. The value was determined. Based on a calibration curve prepared in advance, iron contained in the sample water D was quantified from this correction value.

Example 7 (Coloring agent: 1,10-phenanthroline)
Example 6 and Example 6 except that 1 ml of 8 wt% hydrochloric acid aqueous solution and 2.5 ml of 25 wt% aqueous ammonium acetate solution were added to 10 ml of sample water D, and the pH of sample water D was adjusted to 5.1. The same operation was performed to determine the amount of iron contained in the sample water D.

Example 8 (Coloring agent: 1,10-phenanthroline)
Adjust the pH of sample water D to 6.2 by adding 1 ml of 8 wt% hydrochloric acid aqueous solution, 1 ml of 25 wt% ammonium acetate aqueous solution and 0.3 ml of 30 wt% sodium hydroxide aqueous solution to 10 ml of sample water D. Except for the points described above, the iron contained in the sample water D was quantified in the same manner as in Example 6.

Comparative Example 9
To 10 ml of sample water D, 1 ml of 8 wt% hydrochloric acid aqueous solution and 1 ml of 25 wt% ammonium acetate aqueous solution were added to adjust the pH of sample water D to 4.2. Subsequently, 100 mg of anhydrous sodium dithionite powder (for chemical use manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) were added to the sample water D. They were added in this order, shaken and left for 10 minutes. Then, the iron contained in the sample water D was quantified by operating in the same manner as in Example 6.

Comparative Example 10
To 10 ml of sample water D, 1 ml of 8 wt% aqueous hydrochloric acid solution and 2.5 ml of 25 wt% aqueous ammonium acetate solution were added to adjust the pH of sample water D to 5.1. Subsequently, 100 mg of anhydrous sodium dithionite powder (for chemical use manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) were added to the sample water D. They were added in this order, shaken and left for 10 minutes. Then, the iron contained in the sample water D was quantified by operating in the same manner as in Example 6.

Comparative Example 11
Adjust the pH of sample water D to 6.2 by adding 1 ml of 8 wt% hydrochloric acid aqueous solution, 1 ml of 25 wt% ammonium acetate aqueous solution and 0.3 ml of 30 wt% sodium hydroxide aqueous solution to 10 ml of sample water D. did. Subsequently, 100 mg of anhydrous sodium dithionite powder (for chemical use manufactured by Wako Pure Chemical Industries, Ltd.) and 100 mg of sodium thiosulfate powder (first grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) were added to the sample water D. They were added in this order, shaken and left for 10 minutes. Then, the iron contained in the sample water D was quantified by operating in the same manner as in Example 6.

Evaluation 2
The quantitative results of Examples 6 to 8 and Comparative Examples 8 to 11 are shown in Table 2. Table 2 also shows the relative value (%) when the quantitative result of Comparative Example 8 is used as a reference value. According to Table 2, the results of Examples 6 to 8 are almost the same as those of Comparative Example 8, and it can be seen that the reliability is high.

Claims (5)

A method for quantifying iron contained in sample water,
Adding three components of sodium metabisulfite, dithionite and copper masking agent to the sample water;
Adding a color former to the sample water to which the three components have been added, and quantifying iron in the sample water by absorptiometry;
Method for the determination of iron containing iron.   The method for quantifying iron according to claim 1, wherein the masking agent is one selected from the group consisting of sodium thiosulfate, thiourea and imidazole.   The method for quantifying iron according to claim 1 or 2, wherein the dithionite and the masking agent are added to the sample water after the sodium metabisulfite is added.   The method for quantifying iron according to any one of claims 1 to 3, wherein the three components are added after the pH of the sample water is adjusted to 4.2 or lower.   5. The color developer is added to the sample water after the pH of the sample water to which the three components are added is set in a range in which the color developer can develop color. 6. Method for the determination of iron.