JP2011013053A - Method for measuring nitrate nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate an automation using equipment by improving measurement sensitivity in measuring nitrate nitrogen of inspection water.SOLUTION: A method for measuring the nitrate nitrogen of the inspection water is provided, which includes: the step of adding one of coloring agents being 2,3-dihydroxy naphthalene and 6,7-dihydroxy naphthalene-2-sulfonic acid alkali metal salt to the inspection water; the step of adding sulfuric acid to the inspection water added by the coloring agent, thereby preparing the inspection water so as to be made acid; and the step of measuring an absorbance of optional wavelengths in the range of 350-450 nm for the acid-preparation processed inspection water.

Description

  The present invention relates to a method for measuring nitrate nitrogen, and more particularly to a method for measuring nitrate nitrogen in test water.

  Since nitrogen is one of the causative substances related to eutrophication, such as marine water, lake water, river water, and groundwater, emission regulations for factory effluent are established. For this reason, factory wastewater and the like are required to measure nitrogen before being discharged into the environment. Nitrogen contained in industrial wastewater and the like exists as various forms of nitrogen compounds such as nitrate nitrogen, but nitrogen compounds in forms other than nitrate nitrogen can be converted to nitrate nitrogen by oxidative decomposition. For this reason, factory wastewater etc. can measure substantially all nitrogen, if nitrate nitrogen is measured after converting into nitrate nitrogen by oxidizing and decomposing a nitrogen compound by required pretreatment.

As an official method for measuring a small amount of nitrate nitrogen contained in water, the dimethylphenol method and the chromotropic acid method described in Non-Patent Document 1 are known. In the dimethylphenol method, first, an alkaline potassium peroxodisulfate solution is added to test water collected from factory effluent, etc., and heated at a predetermined temperature for a predetermined time to perform a pretreatment for oxidizing and decomposing nitrogen compounds in the test water. All nitrogen compounds contained in the nitrate are ionized. Then, after adding sodium sulfite powder to the pretreated test water, a 2,6-dimethylphenol solution is added under strong acidity with sulfuric acid and phosphoric acid. As a result, the added 2,6-dimethylphenol is nitrated by nitronium ions (NO ₂ ⁺ ) derived from nitrate ions to be induced to 4-nitro-2,6-dimethylphenol, depending on the concentration. Therefore, when the absorbance at 330 nm is measured, the test water can determine the nitrate ion concentration based on the level of the absorbance.

  On the other hand, in the chromotropic acid method, chromotropic acid powder is added to the test water pretreated in the same manner as in the dimethylphenol method under strong acidity. Thereby, since the nitrate ion contained in the test water exhibits a yellow color due to the reaction with chromotropic acid, the test water can determine the nitrate ion concentration based on the level of the absorbance when measuring the absorbance at 410 nm. .

  However, in these measurement methods, the detection lower limit concentration of nitrate ions is set to 1 mg N / liter in the dimethylphenol method and 0.5 mg N / liter in the chromotropic acid method from the viewpoint of measurement sensitivity, There is a limit to the purpose of measuring very small amounts of nitrate ions in test water. In addition, since the dimethylphenol method measures absorbance at a wavelength as low as 330 nm, it is necessary to use a high-accuracy spectrophotometer, so that it is difficult to automate with an instrument. On the other hand, the chromotropic acid method may require refrigerated storage of chromotropic acid, and chromotropic acid is likely to lose its stability when used as an aqueous solution. Have difficulty.

2002 Ministry of the Environment contract work result report, water quality analysis method study (nitrogen and phosphorus simple measuring instrument and semi-automatic measuring method of water pollution load measurement method manual), March 2003, Ministry of the Environment Environment Management Bureau water environment Part, page 5 and page 8

  An object of the present invention is to increase measurement sensitivity and facilitate automation by an instrument in the measurement of nitrate nitrogen in test water.

  The present invention relates to a method for measuring nitrate nitrogen of test water, and this measurement method is based on 2,3-dihydroxynaphthalene and 6,7-dihydroxynaphthalene-2-sulfonic acid alkali for test water. The step of adding one coloring reagent of the metal salt, the step of adjusting the test water to which the coloring reagent is added to acid, and the absorbance of an arbitrary wavelength in the range of 350 to 450 nm for the test water adjusted to be acidic Measuring.

  In one form of this measuring method, a dimethyl sulfoxide solution of 2,3-dihydroxynaphthalene is used as a coloring reagent. In another embodiment of this measuring method, an aqueous solution of 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt is used as a coloring reagent.

  Since the method for measuring nitrate nitrogen according to the present invention uses a specific coloring reagent, it is possible to stably measure a very small amount of nitrate nitrogen contained in test water with high sensitivity, and automation by equipment. Is also easy.

The figure which shows the absorption spectrum at the time of using 1, 2- dihydroxy naphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the absorption spectrum at the time of using 1, 3- dihydroxy naphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the light absorption spectrum at the time of using 1, 5- dihydroxy naphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the light absorption spectrum at the time of using 2, 6- dihydroxy naphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the absorption spectrum at the time of using 2,7- dihydroxynaphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the light absorption spectrum at the time of using 2, 3- dihydroxy naphthalene as a coloring reagent in Experimental example 1. FIG. The figure which shows the light absorption spectrum at the time of using the sodium 7, 7- dihydroxy naphthalene-2-sulfonate as a coloring reagent in Experimental example 1. FIG. The graph which shows the relationship between the nitrate ion density | concentration of the test water in Experimental example 2, and the light absorbency in 395 nm. The graph which shows the relationship between the nitrate ion density | concentration of test water in Example 3, and a light absorbency. The graph which shows the relationship between the nitrate ion density | concentration of the test water in Experimental example 4, and the light absorbency in 380 nm.

  The test water capable of quantifying nitrate nitrogen by the method of the present invention is not particularly limited, but usually, wastewater in which nitrogen emission regulations such as factory wastewater and domestic wastewater are provided, marine water, Water such as lake water, river water and groundwater.

  When quantifying nitrate nitrogen in test water, a predetermined amount of test water is collected, and a coloring reagent is added to the test water. Here, when total nitrogen of test water is measured by measuring nitrate nitrogen of test water, nitrogen compounds other than nitrate nitrogen contained in test water are oxidatively decomposed and converted to nitrate nitrogen. As a method for oxidative decomposition of a nitrogen compound, a method similar to the method described in Non-Patent Document 1, that is, a powder or solution of alkaline potassium peroxodisulfate is added to test water and heated at 100 to 160 ° C. for 10 to 60 minutes. The method can be adopted.

  The coloring reagent added to the test water is a 2,3-dihydroxynaphthalene or 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt represented by the following structural formulas (1) and (2), respectively. One. In the structural formula (2), M represents an alkali metal. This alkali metal is usually potassium or sodium, but sodium is preferred because sodium salts are widely available on the market and are easily available.

  Here, since 2,3-dihydroxynaphthalene is a compound that is difficult to dissolve in water, it is usually preferable to use it as a solution dissolved in a water-soluble organic solvent such as dimethyl sulfoxide in order to uniformly dissolve in test water. On the other hand, since 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt is a compound that is easily dissolved in water, it is usually preferable to use it as an aqueous solution that is easily dissolved uniformly in test water. A dimethyl sulfoxide solution or an aqueous solution of these coloring reagents is stable and can be stored for a long time.

  The amount of coloring reagent added to the test water is usually set to 0.1 to 10 mg in terms of 2,3-dihydroxynaphthalene or 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt per milliliter of test water. Is preferable, and is more preferably set to 0.5 to 5 mg. When this addition amount is less than 0.1 mg, the measurement sensitivity of nitrate nitrogen may be lowered.

Next, in order to change nitrate nitrogen (nitrate ions) contained in the test water to nitronium ions (NO ₂ ⁺ ), the test water is adjusted to be acidic, and is usually left after that. Nitronium ions generated in the test water in this step undergo a substitution reaction with the color reagent to nitrate the color reagent. As a result, the coloring reagent develops color and colors the test water.

  In this step, it is usually preferable to add sulfuric acid to the test water and adjust the test water to be acidic. In particular, the acidity of the test water is preferably adjusted to a strong acidity of 50% by weight or more in terms of sulfuric acid concentration. . In addition, when adding sulfuric acid, it is preferable to vigorously stir the test water in order to promote nitronium ionization of nitrate ions and nitration of the coloring reagent.

  Next, the absorbance at an arbitrary wavelength in the range of 350 to 450 nm is measured for the test water colored by nitration of the coloring reagent. Then, based on a calibration curve prepared by examining the relationship between the absorbance and the nitrate nitrogen concentration in advance, the nitrate nitrogen concentration of the test water is determined from the measured absorbance value.

  Absorbance at wavelengths in the above range can be measured using a spectrophotometer. However, the absorbance in the above-mentioned range of wavelengths can be measured using a general-purpose light-emitting diode (emission wavelength is about 350 to 450 nm) that is currently on the market, so measure without using a complicated and expensive spectrophotometer. You can also.

  When applied to test water that does not contain nitrate nitrogen, the measurement method of the present invention does not substantially color the test water, and the absorbance in the wavelength range of 350 to 450 nm of the test water is high. It becomes virtually zero. On the other hand, when the measurement method of the present invention is applied to test water containing a small amount of nitrate nitrogen, the absorbance peak of the test water is easily observed clearly in the wavelength range of 350 to 450 nm. For this reason, the measurement method of the present invention can measure nitrate nitrogen with high accuracy even for test water containing nitrate nitrogen at a concentration of less than 0.5 mg N / L, which has been difficult with the conventional measurement methods. it can. In particular, when 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt is used as a luminescent reagent, even in test water containing nitrate nitrogen at a low concentration of about 0.2 mg N / L, nitrate nitrogen is increased. It can be measured with accuracy.

  In addition, the measurement method of the present invention uses a luminescent reagent having high storage stability, and a commercially available general-purpose light-emitting diode can be used in the measurement of absorbance. It is.

Experimental example 1
A nitrate ion solution (a nitrate nitrogen standard solution (code 144-06351) from Wako Pure Chemical Industries, Ltd.) was diluted with distilled water to prepare test water having a nitrate ion concentration of 3 mg / liter. In addition, the color reagent was dissolved in dimethyl sulfoxide (special grade reagent of Wako Pure Chemical Industries, Ltd .: Code 043-0726) to prepare a color reagent solution having a color reagent concentration of 20 g / liter. Here, 1,2-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd .: Code D2299), 1,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd .: Code D0588), 1,5-dihydroxynaphthalene (Tokyo Chemical Co., Ltd.) Company: Code D0590), 2,6-dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd .: Code D0956), 2,7-dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd .: Code D0594), 2,3-dihydroxynaphthalene (Tokyo Chemical Industry) Seven kinds of coloring reagent solutions using one of the following: Code D0593) and sodium 6,7-dihydroxynaphthalene-2-sulfonate (Tokyo Chemical Industry Co., Ltd .: Code D0597) were prepared.

  One milliliter of a coloring reagent solution was added to 2 milliliters of test water, and 2 milliliters of sulfuric acid (special grade from Wako Pure Chemical Industries, Ltd.) was further added while vigorously stirring the test water. The test water was allowed to stand for 15 minutes, then placed in a 10 mm cell, and the absorption spectrum was measured using a spectrophotometer (UV-1600PC manufactured by Shimadzu Corporation). The results are shown in FIGS. In addition, in FIG. 1 to FIG. 7, the result when distilled water is used as a blank instead of the inspection water is also shown.

  According to FIGS. 1 to 7, when 2,3-dihydroxynaphthalene or sodium 6,7-dihydroxynaphthalene-2-sulfonate is used as a coloring reagent, the absorbance is substantially not observed in the case of a blank in a wavelength range of about 360 nm or more. On the other hand, a clear peak is observed in the vicinity of 370 to 380 nm for the test water, whereas the peak is zero. According to this, when 2,3-dihydroxynaphthalene or sodium 6,7-dihydroxynaphthalene-2-sulfonate is used as a coloring reagent, nitric acid is highly sensitive even when the nitrate ion concentration in the test water is low. Quantification of ions is possible.

Experimental example 2
A nitrate ion solution (nitrate nitrogen standard solution (code 144-06351) from Wako Pure Chemical Industries, Ltd.) is diluted with distilled water, and the nitrate ion concentration is 0.01 mg / liter, 0.02 mg / liter, 0.05 mg / liter. Six types of test water were prepared: five types of test water adjusted to liters, 0.1 mg / liter and 0.2 mg / liter, respectively, and test water consisting only of distilled water.

  0.1 ml of a mixed solution of 0.1 g of chromotropic acid and 25 ml of sulfuric acid is added to 2 ml of each test water, and further dimethyl sulfoxide (reagent special grade of Wako Pure Chemical Industries, Ltd .: Code 043-0726) 0.1 ml was added. Each test water was allowed to stand for 15 minutes and then placed in a 10 mm cell, and the absorbance of transmitted light at 395 nm was measured using a spectrophotometer (UV-1600PC manufactured by Shimadzu Corporation).

  FIG. 8 shows the relationship between the nitrate ion concentration of the test water and the absorbance at 395 nm. According to FIG. 8, the absorbance at 0.5 mg / liter, which is the detection lower limit concentration of nitrate ion concentration when chromotropic acid is used, is approximately 0.05 A.n. U. become.

Experimental example 3
2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd .: Code D0593) is dissolved in dimethyl sulfoxide (special grade of Wako Pure Chemical Industries, Ltd .: Code 043-0726), and the concentration of 2,3-dihydroxynaphthalene is 20 g / liter. A coloring reagent solution was prepared. A nitrate ion solution (nitrate nitrogen standard solution (code 144-06351) from Wako Pure Chemical Industries, Ltd.) was diluted with distilled water, and the nitrate ion concentrations were 0.01 mg / liter, 0.02 mg / liter, 0.005. Six types of test water were prepared: five types of test water adjusted to 05 mg / liter, 0.1 mg / liter, and 0.2 mg / liter, respectively, and test water consisting of distilled water only.

  For each 2 ml of test water, 0.1 ml of a coloring reagent solution was added, and then 2 ml of sulfuric acid (special grade of Wako Pure Chemical Industries, Ltd.) was further added while stirring the test water vigorously. Each test water was allowed to stand for 15 minutes and then placed in a 10 mm cell, and the absorbance at 375 nm was measured using a spectrophotometer (UV-1600PC manufactured by Shimadzu Corporation).

  FIG. 9 shows the relationship between the nitrate ion concentration of the test water and the absorbance. According to FIG. 9, even in a low concentration test water having a nitrate ion concentration of less than 0.5 mg / liter, the absorbance is 0.05 A.m. U. The part exceeding is recognized. According to this, when 2,3-dihydroxynaphthalene is used as a coloring reagent, the nitrate ion concentration of test water can be measured even below the lower limit of measurement by the chromotropic acid method.

Experimental Example 4
Sodium 6,7-dihydroxynaphthalene-2-sulfonate (manufactured by Tokyo Chemical Industry Co., Ltd .: code D0597) was dissolved in dimethyl sulfoxide (special grade of Wako Pure Chemical Industries, Ltd. code: code 043-0726), and 6,7-dihydroxy A coloring reagent solution having a sodium naphthalene-2-sulfonate concentration of 25 g / liter was prepared. A nitrate ion solution (nitrate nitrogen standard solution (code 144-06351) from Wako Pure Chemical Industries, Ltd.) was diluted with distilled water, and the nitrate ion concentrations were 0.01 mg / liter, 0.02 mg / liter, 0.005. Six types of test water were prepared: five types of test water adjusted to 05 mg / liter, 0.1 mg / liter, and 0.2 mg / liter, respectively, and test water consisting of distilled water only.

  For each 2 ml of test water, 0.1 ml of a coloring reagent solution was added, and then 2 ml of sulfuric acid (special grade of Wako Pure Chemical Industries, Ltd.) was further added while stirring the test water vigorously. Each test water was allowed to stand for 15 minutes, then placed in a 10 mm cell, and absorbance at 380 nm and 660 nm was measured using a spectrophotometer (UV-1600PC manufactured by Shimadzu Corporation). The absorbance at 660 nm was measured for turbidity correction, and the value obtained by subtracting the absorbance at 660 nm from the absorbance at 380 nm was defined as the absorbance at 380 nm.

  FIG. 10 shows the relationship between the nitrate ion concentration of the test water and the absorbance at 380 nm. According to FIG. 10, even in a low concentration test water having a nitrate ion concentration of less than 0.5 mg / liter, the absorbance is 0.05 A.m. U. The part exceeding is recognized. In particular, even in test water having a nitrate ion concentration of about 0.2 mg / liter, the absorbance is 0.05 A.m. U. Is over. According to this, when sodium 6,7-dihydroxynaphthalene-2-sulfonate is used as a coloring reagent, the nitrate ion concentration of test water can be measured even below the lower limit of measurement by the chromotropic acid method.

Claims (3)

A method for measuring nitrate nitrogen in test water,
Adding one coloring reagent of 2,3-dihydroxynaphthalene and 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt to the test water;
Adjusting the test water to which the coloring reagent has been added to acidity;
Measuring the absorbance of any wavelength in the range of 350 to 450 nm for the test water adjusted to be acidic; and
Method for measuring nitrate nitrogen containing oxygen.   The method for measuring nitrate nitrogen according to claim 1, wherein the dimethyl sulfoxide solution of 2,3-dihydroxynaphthalene is used as the coloring reagent.   The method for measuring nitrate nitrogen according to claim 1, wherein an aqueous solution of the 6,7-dihydroxynaphthalene-2-sulfonic acid alkali metal salt is used as the coloring reagent.

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