JP2012037252A - Quantitative method of phosphate ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a quantitative method by which phosphate ions with comparatively high concentration contained in inspection water is quantitated and which is suitable for automation.SOLUTION: A quantitative method of phosphate ions includes: a process 1 of adding a color-producing agent containing sulfuric acid, molybdenum compound of hexaammonium heptamolybdate and one of alkali metal salt of molybdate, antimony compound whose valence of antimony is 3, iron salt capable of generating bivalent or trivalent iron ions and hydroxylamine salt to the inspection water to be heated at temperature from 65°C to boiling temperature of the inspection water; and a process 2 of measuring absorbance of arbitrary wavelength within a range of 600 to 900 nm for the inspection water which passes through the process 1. One embodiment of the color-producing agent to be used here consists of: a first agent consisting of aqueous solution containing sulfuric acid and hydroxylamine salt; and a second agent consisting of aqueous solution containing the molybdenum compound, antimony compound and iron salt, and iron salt capable of generating trivalent iron ion.

Description

  The present invention relates to a method for quantifying phosphate ions, and more particularly to a method for quantifying phosphate ions contained in test water by producing molybdenum blue.

  Since phosphorus is one of the causative substances related to eutrophication, such as ocean water, lake water, river water, and groundwater, there are restrictions on emission from factory wastewater. For this reason, factory effluent and the like require quantitative determination of phosphorus, particularly phosphate ion, before being discharged into the environment.

As an official method for quantifying phosphate ions contained in water, molybdenum blue (ascorbic acid reduction) absorptiometry described in Non-Patent Document 1 is known. In this quantitative method, a heteropoly compound formed by reacting phosphate ions with hexaammonium heptamolybdate and potassium antimonyl tartrate (bis [(+)-tartrate] diantimony (III) dipotassium) is converted to L (+). -A phosphate ion is quantified by measuring the light absorbency of test water colored with molybdenum blue produced by reduction with ascorbic acid. In the basic operation of this quantification method, a predetermined amount of ammonium molybdate-ascorbic acid mixed solution is added to a predetermined amount of test water, shaken, and then allowed to stand at 20 to 40 ° C. for about 15 minutes. Then, the absorbance at a wavelength of about 880 nm is measured for this solution, and the phosphate ion concentration (mgPO ₄ ³⁻ / L) of the test water is calculated based on a calibration curve prepared in advance from the measured value.

  However, since this quantification method has a quantification range of 2.5 to 75 μg as described in Non-Patent Document 1, the test water contains phosphate ions derived from dissolved phosphate ions and organic substances. When quantifying total phosphorus, which is the total amount of acid ions, etc., as a result, the upper limit of quantification is limited to about 1 to 1.5 mg [P] / L, and some test water cannot be used for quantification of total phosphorus. There is a problem that.

  Moreover, since the frequency of quantification of phosphate ions in factory effluent and the like is steadily increasing due to increased environmental conservation, an automatic device for the quantification operation is desired. In this automatic apparatus, it is ideal to store a required quantitative medicine in the apparatus and use it at the time of quantitative measurement. Specifically, an ammonium molybdate-ascorbic acid mixed solution used as a quantification agent in the above-described molybdenum blue absorptiometry is composed of hexamolybdate hexaammonium tetrahydrate and potassium antimonyl tartrate trihydrate (molybdenum blue). An ammonium molybdate solution prepared by further dissolving sulfuric acid and ammonium amidosulfate (a decomposing agent for nitrite ions that interferes with the formation of molybdenum blue), and L (+ ) -Ascorbic acid solution is mixed at a predetermined ratio, and is prepared by mixing ammonium molybdate solution and L (+)-ascorbic acid solution at the time of use. Keep the pre-prepared ammonium molybdate solution and L (+)-ascorbic acid solution. It is preferable to use while.

  Here, the L (+)-ascorbic acid solution is an aqueous solution prepared by dissolving L (+)-ascorbic acid in water, but the deterioration of L (+)-ascorbic acid proceeds rapidly after preparation. Since it changes in quality (changes in appearance to yellow), Non-Patent Document 1 instructs to store the L (+)-ascorbic acid solution in a dark place at 0 to 10 ° C., and uses a colored one. Is prohibited. As described above, the L (+)-ascorbic acid solution has a limited storage environment, and it is necessary to confirm the presence or absence of coloring during use. It is.

Japanese Industrial Standards JIS K 0102, Factory Wastewater Test Method (2008) 46.1.1

  An object of the present invention is to realize a quantification method that can quantify a relatively high concentration of phosphate ions contained in test water and is suitable for automation.

  The present invention relates to a method for quantifying phosphate ions contained in test water, and this quantification method uses molybdenum of one of sulfuric acid, hexaammonium heptamolybdate and alkali metal salts of molybdic acid for test water. A compound, an antimony compound having an antimony valence of 3, a color former containing an iron salt and a hydroxylamine salt capable of producing a divalent or trivalent iron ion, and a temperature from 65 ° C. to the boiling temperature of the test water And step 2 of measuring absorbance at an arbitrary wavelength in the range of 600 to 900 nm with respect to the inspection water that has passed through step 1.

  The present invention according to another aspect relates to a method for coloring phosphate ions contained in test water, and this color developing method is a method for forming alkali metal salts of sulfuric acid, hexaammonium heptamolybdate and molybdate with respect to test water. One of the molybdenum compounds, an antimony compound having an antimony valence of 3, a color former containing an iron salt capable of producing a divalent or trivalent iron ion and a hydroxylamine salt are added, Heating at a temperature up to the boiling temperature.

  An example of the color former used in the quantification method and color development method of the present invention includes a first agent comprising an aqueous solution containing sulfuric acid and a hydroxylamine salt, and a second agent comprising an aqueous solution containing a molybdenum compound, an antimony compound and an iron salt. Therefore, the iron salt that can generate trivalent iron ions is used.

  The present invention according to still another aspect relates to a color former for coloring phosphate ions contained in test water, the color former comprising a first agent comprising an aqueous solution containing sulfuric acid and a hydroxylamine salt, A second agent comprising an aqueous solution containing one molybdenum compound of hexaammonium heptamolybdate and an alkali metal salt of molybdic acid, an antimony compound having an antimony valence of 3, and an iron salt capable of generating trivalent iron ions It consists of.

  The iron salt used in the quantitative method, color developing method and color former of the present invention was selected from the group consisting of, for example, iron (III) chloride, iron (III) sulfate, iron (III) nitrate and iron (III) acetate. At least one. The hydroxylamine salt is, for example, one of hydroxylamine sulfate and hydroxylamine hydrochloride.

  Since the quantification method of phosphate ions according to the present invention uses a color former containing a specific component, it can quantitate a relatively high concentration of phosphate ions contained in test water, and is suitable for automation. Yes.

  Since the coloring method of phosphate ions according to the present invention uses a color former containing a specific component, the intensity of the phosphate ions contained in the test water to a relatively high concentration range according to the concentration of the phosphate ions. It is possible to make it develop color and is suitable for automation.

  The phosphate ion color former according to the present invention comprises a first agent and a second agent containing specific components, so that the phosphate ion concentration in the test water is relatively high. The color can be developed with an intensity according to the intensity. In addition, since the first agent and the second agent are both stable, this color former can be used while being stored in an apparatus for automating the quantification of phosphate ions.

The figure which shows the relationship between the light absorbency investigated in the comparative example 1, and a phosphate ion concentration. The figure which shows the analytical curve created by Example 1 by the light absorbency of 830 nm. The figure which shows the analytical curve created by Example 1 by the light absorbency of 650 nm. FIG. 6 is a diagram showing a calibration curve created in Example 2. The figure which shows the result of an experiment example.

  The test water capable of quantifying phosphate ions by the method of the present invention is not particularly limited, but in addition to wastewater that is usually provided with phosphorus discharge regulations such as factory wastewater and domestic wastewater, marine water, Natural water such as lake water, river water and groundwater.

  In quantifying the phosphate ion of the inspection water, first, a predetermined amount of inspection water is collected, and a coloring agent is added to the inspection water and heated (step 1).

  Here, when measuring the total phosphorus in the test water, before adding the color former, the organic and inorganic phosphorus compounds that are the source of phosphorus are decomposed to convert the phosphorus element into phosphate ions. As the decomposition method of the phosphorus compound, the potassium peroxodisulfate decomposition method, nitric acid-perchloric acid decomposition method and nitric acid listed in “46.3 Total phosphorus” of Japanese Industrial Standards JIS K0102 “Factory drainage test method (2008)” -A sulfuric acid decomposition method etc. are employable.

  The color former added to the inspection water contains sulfuric acid, molybdenum compound, antimony compound, iron salt and hydroxylamine salt.

  The amount of sulfuric acid used is preferably set so that the concentration of sulfuric acid when the color former is added to the test water is usually 0.08 to 0.4M, preferably 0.1 to 0.3M. More preferably.

  As the molybdenum compound, hexaammonium heptamolybdate or an alkali metal salt of molybdic acid is used. Examples of alkali metal salts of molybdate include sodium molybdate, potassium molybdate and lithium molybdate.

  The amount of the molybdenum compound used is usually 0.3 to 3.0 g / L when the color developing agent is added to the test water. Is preferably set to be 0.5 to 2.0 g / L, and more preferably set to 0.5 to 2.0 g / L.

  As the antimony compound, an antimony compound having an antimony valence of 3 is used. Examples of the antimony compound having an antimony valence of 3 include potassium antimonyl tartrate, antimony trioxide (that is, antimony (III) oxide), and a halide salt of antimony. As the halide salt of antimony, it is preferable to use antimony trichloride (that is, antimony (III) chloride) that hardly generates harmful substances by hydrolysis.

  An antimony compound having an antimony valence of 5 can also be used as the antimony compound. Since this antimony compound is naturally converted into an antimony compound having an antimony valence of 3 in an aqueous solution, it can be used as a source of the antimony compound having an antimony valence of 3. Examples of the antimony compound having an antimony valence of 5 usable here include antimony pentoxide (that is, antimony (V) oxide) and an antimony halide salt having a valence of 5. As the halide salt of antimony having a valence of 5, it is preferable to use antimony pentachloride (that is, antimony chloride (V)) that does not easily generate harmful substances by hydrolysis.

  The amount of the antimony compound used is usually 0.01 to 0.24 g / L of the concentration of the antimony compound when the color former is added to the test water (concentration converted excluding water molecules when a hydrate is used). Is preferably set to be 0.02 to 0.13 g / L. However, in the test water, the concentration ratio (A: B) between the antimony compound (A) and the molybdenum compound (B) is preferably set to 1: 8 to 100, and set to 1:10 to 50. More preferably.

  As the iron salt, one that can generate divalent or trivalent iron ions by dissociation in water is used. Examples of iron salts that can generate divalent iron ions include iron (II) chloride, iron (II) sulfate, iron (II) nitrate, and iron (II) acetate. Examples of iron salts capable of generating trivalent iron ions include iron (III) chloride, iron (III) sulfate, iron (III) nitrate, and iron (III) acetate. Two or more types of iron salts can be used in combination. Preferred iron salts are selected from iron salts capable of generating trivalent iron ions, particularly iron (III) chloride, iron (III) sulfate, iron (III) nitrate and iron (III) acetate. At least one thing.

  Usually, the amount of iron salt used is preferably set so that the concentration of divalent or trivalent iron ions is 0.1 to 25 mg / L when the color former is added to the test water. It is more preferable to set to 15 mg / L. In addition, when the concentration of the iron salt in the test water is excessive, especially when the concentration of the trivalent iron ion is 30 mg / L or more, the molybdenum blue, which will be described later, fades due to the influence of the iron ion. There is a possibility of losing the quantitative accuracy.

  The hydroxylamine salt is not particularly limited as long as it can reduce trivalent iron ions to divalent iron ions in the test water. For example, hydroxylamine sulfate (also called hydroxylammonium sulfate), Hydroxylamine hydrochloride, methylhydroxylamines, ethylhydroxylamines and the like are used. Of these, hydroxylamine sulfate or hydroxylamine hydrochloride is preferably used.

  Usually, the amount of the hydroxylamine salt used is preferably set so that the concentration of hydroxylamine when the color former is added to the test water is 0.5 to 5 g / L, and preferably 1 to 3 g / L. It is more preferable to set.

  The color former is usually added to the inspection water as an aqueous solution in which required components are dissolved in purified water such as pure water, distilled water or ion exchange water. Here, the color former should be added to the test water by separately adding to the test water an aqueous solution prepared separately for each component of sulfuric acid, molybdenum compound, antimony compound, iron salt and hydroxylamine salt. Can do. Moreover, it can also add with respect to test water as mixed aqueous solution prepared by mixing the aqueous solution of each component just before the addition to test water. Since the aqueous solutions of the respective components used in these addition methods are all stable at room temperature or in a wide temperature environment of about 3 to 60 ° C., they can be prepared and stored in advance and used as appropriate.

  In addition, the color former can be added to the test water by preparing two agents, the first agent and the second agent, and adding each agent to the test water. In this case, the two agents may be added individually to the test water, or may be mixed and added immediately before addition to the test water.

  Examples of the color former composed of the two agents include the following forms 1 and 2. The first agent and the second agent in each form of color former are both prepared and stored in advance because they can maintain stability over a long period of time at room temperature or in a wide temperature environment of about 3 to 60 ° C. be able to. In particular, Form 1 color former has high stability and is suitable for storage. In addition, those composed of two agents other than the following forms 1 and 2, or those composed of an aqueous solution containing all the necessary components, the molybdenum compound or the antimony compound is altered or the hydroxylamine salt is naturally disappeared. It is not suitable for storage.

<Form 1>
What consists of the 1st agent consisting of the aqueous solution containing a sulfuric acid and hydroxylamine salt, and the 2nd agent consisting of the aqueous solution containing a molybdenum compound, an antimony compound, and an iron salt.
<Form 2>
What consists of the 1st agent consisting of the aqueous solution containing a hydroxylamine salt and the 2nd agent consisting of the aqueous solution containing a sulfuric acid, a molybdenum compound, an antimony compound, and an iron salt.

  The iron salt used in the color formers of Form 1 and Form 2 is trivalent because it can easily react with other components and alter itself or other components when it can generate divalent iron ions. It is necessary to select one that can generate iron ions.

  The concentration of each component in various aqueous solutions for preparing the color former and the amount of the color former added to the test water are within the ranges described above when the color former is added to the test water. It is preferable to make adjustments.

  In this step, when the inspection water to which the color former is added is heated, it is preferable to stir the inspection water as appropriate. The heating temperature is set to a range from 65 ° C. to the boiling temperature of the inspection water. Moreover, it is usually preferable to set the heating time to 2 to 60 minutes.

The phosphate ions in the heated test water react with the color formers molybdenum compound and antimony compound to form a heteropoly compound. In addition, when an iron salt capable of generating trivalent iron ions is used, trivalent iron ions (that is, Fe ³⁺ ) are generated by dissociation of the iron salt in an aqueous solution containing the iron salt or in inspection water. The trivalent iron ions are reduced to divalent iron ions (ie, Fe ²⁺ ) by the action of the hydroxylamine salt. The produced heteropoly compound is reduced by divalent iron ions in an acidic environment with sulfuric acid, and this reduction produces molybdenum blue (coloration of phosphate ions). Thereby, the inspection water is colored (discolored). At this time, the generated divalent iron ion is oxidized to a trivalent iron ion during the reduction of the heteropoly compound. This trivalent iron ion is converted into a divalent iron ion by the action of a hydroxylamine salt. Since it is reduced, it functions as a reducing agent for the heteropoly compound.

  On the other hand, when an iron salt capable of generating divalent iron ions is used, divalent iron ions are generated by dissociation of the iron salt in an aqueous solution containing the iron salt or in test water. The ion functions as a reducing agent for generating molybdenum blue from the heteropoly compound. At this time, the divalent iron ion is oxidized to the trivalent iron ion as described above, but this trivalent iron ion is reduced to the divalent iron ion by the action of the hydroxylamine salt. Therefore, it functions as a reducing agent for heteropoly compounds.

  Thus, the hydroxylamine salt functions as a reducing agent that reduces trivalent iron ions to divalent iron ions, and can stably reduce the heteropoly compound with divalent iron ions. However, since it does not show a reducing action on heteropoly compounds, it can function as a selective reducing agent for trivalent iron ions.

  Next, the absorbance at an arbitrary wavelength in the range of 600 to 900 nm is measured for the test water discolored by molybdenum blue (step 2). Then, based on the calibration curve prepared by examining the relationship between the absorbance and the phosphate ion concentration in advance, the phosphate ion amount of the test water is determined from the measured absorbance value.

  The method for quantifying phosphate ions according to the present invention is suitable for automation because a color developing agent comprising an aqueous solution that can be stably stored can be used. In the method for quantifying phosphate ions according to the present invention, when a calibration curve is prepared, the linear relationship between the phosphate ion concentration and the absorbance at an arbitrary wavelength in the range of 600 to 900 nm is relatively high. Therefore, the upper limit of quantification of phosphate ions contained in the test water is expanded to a range of 3 mg [P] / L or more. For this reason, this quantification method is particularly effective when quantifying the total phosphorus of test water.

  Step 1 in the quantification method of the present invention can be used as a method for coloring phosphate ions in test water containing phosphate ions. For example, when it is necessary to simply determine whether or not the test water contains phosphate ions, this determination can be easily performed in a short time by using this coloring method. Specifically, this coloring method is applied to test water, and when the coloration of phosphate ions is observed in test water, it can be determined that the test water contains phosphate ions, When color development of phosphate ions is not observed in the inspection water, it can be determined that the inspection water does not contain phosphate ions.

Reagents Reagents and spectrophotometers used in the following examples and the like are as follows.
Phosphorus standard solution (for water quality test): Wako Pure Chemical Industries, Ltd. Code 160-19241
Sulfuric acid (special grade reagent): Wako Pure Chemical Industries, Ltd. Code 192-04696
Molybdenum (VI) disodium dihydrate (reagent special grade): Wako Pure Chemical Industries, Ltd. Code 190-02475
Hexammonium hexamolybdate tetrahydrate (special reagent grade): Wako Pure Chemical Industries, Ltd. Code 018-06901
Potassium antimony tartrate trihydrate (special grade reagent): Wako Pure Chemical Industries, Ltd. Code 020-12832
Antimony (III) chloride (reagent special grade): Wako Pure Chemical Industries, Ltd. Code 011-0492
Iron (III) chloride hexahydrate (reagent special grade): Wako Pure Chemical Industries, Ltd. Code 095-00875
Iron (III) sulfate n hydrate (special grade reagent): Wako Pure Chemical Industries, Ltd. Code 090-01062
Hydroxylamine sulfate: Wako Special Code 086-01502 from Wako Pure Chemical Industries, Ltd.
Ascorbic acid (special grade reagent): Wako Pure Chemical Industries, Ltd. Code 014-04801
Spectrophotometer: Shimadzu Corporation trade name “UV-1600PC”

Test water The test water used in the following examples and the like is as follows.
Five types of test water having phosphate ion concentrations of 0, 0.5, 1.0, 2.0, and 3.0 mg [P] / L were prepared. The unit of mg [P] / L indicates the number of mg of phosphorus contained in 1 L of test water. Distilled water was used as it was for the test water having a phosphate ion concentration of 0 mg [P] / L, and the phosphate ion concentration was adjusted by diluting the phosphorus standard solution with distilled water.

Comparative Example 1
In accordance with the molybdenum blue (ascorbic acid reduction) spectrophotometric method specified in Japanese Industrial Standards JIS K 0102, Factory Wastewater Test Method (2008) 46.1.1 (Non-patent Document 1), each of the five types of test water 2.5 mL The absorbance at 890 nm was measured, and the relationship between the absorbance and the phosphate ion concentration was examined. The results are shown in FIG. According to FIG. 1, the absorbance of the test water having a phosphate ion concentration of 2 mg [P] / L does not double the absorbance of the test water having a phosphate ion concentration of 1 mg [P] / L, and the phosphate ion can be quantified. It can be seen that the concentration is limited to a low concentration range of up to 1.5 mg [P] / L.

Example 1
A first agent comprising an aqueous solution containing 3M sulfuric acid and 100 g / L of hydroxylamine sulfate, 16 g / L of disodium molybdate (VI) dihydrate, 0.5 g / L of antimony potassium tartrate trihydrate And a second agent comprising an aqueous solution containing 60 mg / L of iron (III) chloride hexahydrate.

  About 2.5 mL of each of the five types of test water, after preheating for 3 minutes using a block heater heated to 95 ° C., add 0.2 mL of the first agent and 0.4 mL of the second agent, and at 95 ° C. for 12 minutes Heated. Immediately after the heating, the absorbance at 830 nm and the absorbance at 650 nm of each test water was measured using a spectrophotometer, and a calibration curve of phosphate ion concentration based on the absorbance at each wavelength was prepared. The results are shown in FIG. 2 (calibration curve based on absorbance at 830 nm) and FIG. 3 (calibration curve based on absorbance at 650 nm). According to FIG. 2 and FIG. 3, these calibration curves show high linearity at least in the range where the phosphate ion concentration is 0 to 3 mg [P] / L.

  The first agent and the second agent used at the time of preparing the calibration curve were both stored for 14 days in an environment of 50 ° C. after the preparation, and a highly linear calibration curve could be created. Therefore, the storage stability is good.

Example 2
A first agent comprising an aqueous solution containing 6 M sulfuric acid and 200 g / L hydroxylamine sulfate, 15 g / L hexamolybdenum hexamolybdate tetrahydrate, 0.6 g / L antimony chloride and iron (III) sulfate n water A second agent consisting of an aqueous solution containing 0.5 g / L of a Japanese product was prepared.

  About 2.5 mL of each of the five types of test water, after preheating for 3 minutes using a block heater heated to 95 ° C., add 0.1 mL of the first agent and 0.2 mL of the second agent, and at 95 ° C. for 12 minutes Heated. Immediately after the completion of heating, the absorbance at 830 nm of each test water was measured using a spectrophotometer, and a calibration curve of phosphate ion concentration based on the absorbance at the wavelength was prepared. The results are shown in FIG. According to FIG. 4, this calibration curve shows high linearity at least in the range where the phosphate ion concentration is 0 to 3 mg [P] / L.

  The first agent and the second agent used at the time of preparing the calibration curve were both stored for 14 days in an environment of 50 ° C. after the preparation, and a highly linear calibration curve could be created. Therefore, the storage stability is good.

Experimental Example A storage test was conducted on the 72 g / L ascorbic acid solution used in the molybdenum blue (ascorbic acid reduction) spectrophotometric method of Comparative Example 1.

  Here, the ascorbic acid solution was placed in a brown bottle and placed in an incubator at 50 ° C. And about the ascorbic acid solution, the absorption spectrum after 24 hours, 48 hours, and 96 hours after preparation was measured, and these absorption spectra were compared with the absorption spectrum immediately after preparation. The results are shown in FIG.

  According to FIG. 5, the ascorbic acid solution shows a change in absorption spectrum as early as 24 hours after preparation, so that the deterioration is progressing at an early stage after preparation, and stable storage is difficult. .

Claims (7)

A method for quantifying phosphate ions contained in test water,
One molybdenum compound of sulfuric acid, hexaammonium heptamolybdate, and alkali metal salts of molybdic acid, antimony compound with antimony valence of 3, divalent or trivalent iron ions can be generated for the test water Adding a color former containing an iron salt and a hydroxylamine salt, and heating at a temperature from 65 ° C. to the boiling temperature of the test water;
Step 2 of measuring the absorbance of an arbitrary wavelength in the range of 600 to 900 nm for the test water that has undergone Step 1;
For quantifying phosphate ions containing   The color former comprises a first agent comprising an aqueous solution containing the sulfuric acid and the hydroxylamine salt, and a second agent comprising an aqueous solution containing the molybdenum compound, the antimony compound and the iron salt, and the iron salt. The method for quantifying phosphate ions according to claim 1, wherein is capable of generating trivalent iron ions.   The phosphoric acid according to claim 1 or 2, wherein the iron salt is at least one selected from the group consisting of iron (III) chloride, iron (III) sulfate, iron (III) nitrate and iron (III) acetate. Ion quantification method.   The method for quantifying phosphate ions according to claim 1, wherein the hydroxylamine salt is one of hydroxylamine sulfate and hydroxylamine hydrochloride. A method for coloring phosphate ions contained in test water,
One molybdenum compound of sulfuric acid, hexaammonium heptamolybdate, and alkali metal salts of molybdic acid, antimony compound with antimony valence of 3, divalent or trivalent iron ions can be generated for the test water Adding a color former containing an iron salt and a hydroxylamine salt, and heating at a temperature from 65 ° C. to the boiling temperature of the test water,
Method for coloring phosphate ions.   The color former comprises a first agent comprising an aqueous solution containing the sulfuric acid and the hydroxylamine salt, and a second agent comprising an aqueous solution containing the molybdenum compound, the antimony compound and the iron salt, and the iron salt. The method for coloring phosphate ions according to claim 5, wherein is capable of generating trivalent iron ions. A color former for coloring phosphate ions contained in test water,
A first agent comprising an aqueous solution containing sulfuric acid and a hydroxylamine salt;
A second agent comprising an aqueous solution containing one molybdenum compound of hexaammonium heptamolybdate and an alkali metal salt of molybdic acid, an antimony compound having an antimony valence of 3, and an iron salt capable of generating trivalent iron ions When,
A phosphate ion color former comprising:

Images