JP2013007604A - Method for quantitating nitrite ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quantitate nitrite ions contained in inspection water to a high concentration region with a simple operation.SOLUTION: A method for quantitating nitrite ions contained in inspection water includes: a process 1 for allowing a diazotized reagent capable of generating diazonium salt by reaction with the nitrite ions with respect to the inspection water to be added to at least one kind of compound, e.g., sodium hypophosphite, selected from a compound group constituted by alcohol compounds, hypophosphite and salt thereof, and reacting them under acidity with the addition of hydrochloric acid, etc.; and a process 2 for measuring the absorbance of coloring with the diazotized reagent concerning the inspection water treated in the process 1. As the diazotized reagent, an aromatic primary amine compound is used, where a ketone group or a nitro group is contained at the ortho position or para position of 1-amino anthraquinone or 2-nitro aniline, etc.

Description

  The present invention relates to a method for quantifying nitrite ions, and more particularly to a method for quantifying nitrite ions contained in test water by measuring absorbance.

  Since nitrogen is one of the causative substances related to eutrophication such as marine water, lake water, river water, and groundwater, there are emission regulations for factory effluent. Prior to discharge, quantification of ionic nitrogen (for example, nitrate ions and nitrite ions) that is a nutrient source for ecosystems is required. However, factory effluents generally contain not only nitrogen in an ionic state but also nitrogen as various nitrogen compounds, and these nitrogen compounds are naturally decomposed after being discharged into the environment, resulting in an ionic state. Generate nitrogen. For this reason, factory wastewater and the like are often required to determine the total amount of nitrogen including ionic nitrogen that can be generated from nitrogen compounds, so-called total nitrogen.

  In one form of quantification of total nitrogen contained in inspection water such as factory effluent, the nitrogen compound contained in inspection water is converted to nitrate ion by oxidative decomposition, and then pretreated to convert it to nitrite ion, Nitrite ions contained in the test water after this pretreatment are quantified.

  As an official method for quantitative determination of nitrite ions contained in test water, a naphthylethylenediamine spectrophotometric method defined in Japanese Industrial Standards (JIS) is known (Non-patent Document 1). This quantification method (hereinafter referred to as JIS method) is a azo compound produced by coupling a diazonium salt produced by reaction of nitrite ions contained in test water with sulfanilamide under acidic conditions with naphthylethylenediamine. Nitrite ions are quantified by measuring the coloration (coloration) of the test water by means of absorptiometry.

However, the JIS method is very sensitive to coloring of the test water by the azo compound produced, and the coloring intensity (molar extinction coefficient) is too high, so it is difficult to accurately quantify high concentration of nitrite ions in the test water. The measurable range of the nitrite ion concentration is limited to 0.06 to 0.6 mg [NO ₂ ⁻ ] / L. Since the nitrite ion concentration in this range is a very small range of about 0.02 to 0.2 mg [N] / L in terms of total nitrogen, the JIS method is difficult to apply to the determination of total nitrogen. .

In Patent Document 1, as a method for quantifying nitrite ion instead of JIS method, a porphyrin compound having an amino group in a porphine nucleus is added to test water, and a diazo group generated by reaction of the porphyrin compound and nitrite ion is added. It describes a method for measuring the absorbance of the porphyrin compound possessed or the fluorescence intensity upon excitation. This method is based on the fact that the sole absorption band of the porphyrin compound decreases due to the formation of a diazo group, and the only reaction required is the reaction between the porphyrin compound and nitrite ion. Nitrite ions can be quantified with a simple operation compared to the JIS method, which requires a two-step reaction with a ring reaction. However, according to the description of Patent Document 1 (particularly, paragraph 0023), this quantification method has a measurable range of nitrite ion concentration of about 0 to 0.018 mg [NO ₂ ⁻ ] / L. Since the ion concentration is only a minute range of about 0 to 0.006 mg [N] / L in terms of total nitrogen, it is difficult to apply to the determination of total nitrogen as in the JIS method. Moreover, according to the description of Patent Document 1 (particularly, paragraph 0023 and FIG. 4), this quantification method is more than twice the molar equivalent of nitrite ions contained in test water in order to produce a porphyrin compound having a diazo group. Since it is necessary to use a large amount of the porphyrin compound, it is uneconomical and it is difficult to reduce the size of the apparatus for realizing an automated apparatus.

Japanese Industrial Standard JIS K 0102, Factory Wastewater Test Method (2008) 43.1.1

Japanese Patent Laid-Open No. 9-89781 (Claims, paragraphs 0012, 0016 and 0023 and FIG. 4 etc.)

  An object of the present invention is to enable quantitative determination of nitrite ions contained in test water up to a high concentration region by a simple operation.

  The present invention relates to a method for quantifying nitrite ions contained in test water. This quantification method comprises at least one selected from the group consisting of a diazotization reagent capable of producing a diazonium salt by reaction with nitrite ions, alcoholic compounds, hypophosphorous acid and salts thereof with respect to test water. Step 1 in which the compound is added and reacted under acidic conditions, and Step 2 in which the absorbance of the coloring by the diazotizing reagent is measured for the test water that has passed through Step 1. In this quantification method, an aromatic primary amine compound having a ketone group or a nitro group at the ortho or para position is used as the diazotization reagent.

  The aromatic primary amine compounds used here are, for example, 1-aminoanthraquinone, 2-nitroaniline, sodium 4-nitroaniline-2-sulfonate and sodium 1-amino-4-bromoanthraquinone-2-sulfonate Is selected from the group consisting of

  In this quantitative method, it is usually preferable to adjust the pH of the test water that has passed through step 1 to be higher than 7 before step 2.

  The test water to which the quantification method of the present invention is applied is, for example, nitrite ions by further reducing nitrate ions generated by oxidative decomposition of nitrogen compounds contained in the test water for the determination of total nitrogen. This is a preprocess for conversion. In this case, the temperature of the inspection water is usually 60 ° C. or higher and lower than 100 ° C.

  Since the nitrite ion quantification method according to the present invention uses a specific diazotization reagent, nitrite ions can be quantified to a high concentration region by a simple operation that does not require a plurality of reaction steps.

FIG. 3 is a graph showing the result of an absorption spectrum measured in Example 1. FIG. 3 is a diagram showing a calibration curve created in Example 1. FIG. 6 is a graph showing the result of an absorption spectrum measured in Example 2. FIG. 6 is a diagram showing a calibration curve created in Example 2. FIG. 6 is a graph showing the results of absorption spectra measured in Example 3. FIG. 6 is a diagram showing a calibration curve created in Example 3. FIG. 6 is a graph showing the result of an absorption spectrum measured in Example 4. The figure which shows the calibration curve created in Example 4. FIG. FIG. 6 is a graph showing the results of absorption spectra measured in Example 5. FIG. 6 is a diagram showing a calibration curve created in Example 5. FIG. 10 shows the results of absorption spectrum measured in Example 6. FIG. 6 is a diagram showing a calibration curve created in Example 6. The figure which shows the calibration curve created in the comparative example 1. The figure which shows the result of the absorption spectrum measured in Experimental example 1a. The figure which shows the result of the absorption spectrum measured in Experimental example 1b. The figure which shows the result of the absorption spectrum measured in Experimental example 1c. The figure which shows the result of the absorption spectrum measured by Experimental example 1d. The figure which shows the result of the absorption spectrum measured by Experimental example 2a. The figure which shows the result of the absorption spectrum measured in Experimental example 2b. The figure which shows the result of the absorption spectrum measured in Experimental example 2c.

  The test water capable of quantifying nitrite ions by the method of the present invention is not particularly limited, but usually, wastewater that is provided with nitrogen emission regulations such as factory wastewater and domestic wastewater, marine water, Natural water such as lake water, river water and groundwater.

  When quantifying nitrite ions in test water, first, a predetermined amount of test water is collected, and a diazotization reagent and a reducing agent are added to the test water and reacted (step 1). Here, when measuring the total nitrogen of the test water, a pretreatment for decomposing the nitrogen compound contained in the test water and converting the nitrogen element into nitrite ions is performed before adding the diazotization reagent. For example, an oxidizing agent such as potassium peroxodisulfate is added to the test water and heated to oxidatively decompose the nitrogen compound, and the nitrate ions produced thereby are further reduced and converted to nitrite ions. As such a pretreatment method, for example, the pretreatment method described in the copper / cadmium column reduction-naphthylethylenediamine spectrophotometry method described in 45.4 of Japanese Industrial Standards JIS K0102 “Factory Wastewater Test Method (2008)” However, other reduction methods and methods of irradiating ultraviolet rays can also be adopted.

  The diazotization reagent used in this step can generate a diazonium salt by reaction with nitrite ions, and in particular, can be used to color the test water by itself when added to the test water. In the present invention, an aromatic primary amine compound having a ketone group or a nitro group at the ortho position or para position is used as such a diazotization reagent. Examples of such aromatic primary amine compounds include 1-aminoanthraquinone, 2-nitroaniline, sodium 4-nitroaniline-2-sulfonate, and sodium 1-amino-4-bromoanthraquinone-2-sulfonate. P-nitroaniline, 2-amino-3-hydroxyanthraquinone, 2-amino-2′-fluoro-5-bromobenzophenone, 4-aminobenzophenone, 4-fluoro-2-nitroaniline, 5-amino-2-nitro Benzotrifluoride, 4-amino-3-nitrobenzophenone, 2-amino-5-nitrobenzophenone, 4,6-dinitro-o-toluidine, etc., but 1-aminoanthraquinone, 2-nitroaniline, 4-nitroaniline Sodium 2-sulfonate and 1-amino-4- Those selected from the group consisting of Romo sodium anthraquinone-2-sulfonic acid are preferred.

  The diazotizing reagent is usually preferably added to test water as a solution dissolved in a solvent. Examples of the solvent used for dissolving the diazotizing reagent include pure water obtained by membrane treatment with a reverse osmosis membrane or the like, purified water such as distilled water and ion-exchanged water, dimethyl sulfoxide, N, N-dimethyl Examples include formamide, acetone, and alcohols such as methanol, ethanol, propanol, butanol, polyethylene glycol, and glycerin.

The amount of diazotizing reagent added to the test water must be set to an amount sufficient to produce a diazonium salt by reaction with the total amount of nitrite ions contained in the test water. It is necessary to set at least equimolar to the assumed nitrite ion. In this regard, in consideration of nitrite ions derived from compounds contained in test water, the concentration of nitrite ions contained in test water is generally assumed to be in the range of about 0 to 35 mg [NO ₂ ⁻ ] / L. Therefore, for example, when the amount of test water is 2.0 mL, it is usually preferable to set the addition amount of the diazotization reagent to be 1.5 μmol or more. However, if the nitrite ion concentration in the test water is found to be significantly lower than 35 mg [NO ₂ ⁻ ] / L or is assumed, the diazotization reagent should be added in consideration of it. The amount can also be set to less than 1.5 μmol.

The reducing agent used in this step can reduce the diazonium group (—N ₂ ⁺ ) of the diazonium ion to a hydrogen atom (—H) with respect to the diazonium salt produced by the reaction of the nitrite ion and the diazotizing reagent. Usually, it is at least one compound selected from the group consisting of alcohol compounds and hypophosphorous acid and salts thereof. Examples of alcohol compounds that can be used include ethanol, methanol, propanol, butanol, polyethylene glycol, and glycerin. Examples of hypophosphites include sodium hypophosphite, potassium hypophosphite and calcium hypophosphite, and hydrates of these hypophosphites.

  In general, the reducing agent is preferably added to the inspection water as a solution dissolved in a solvent. Examples of the solvent used for dissolving the reducing agent include pure water obtained by membrane treatment with a reverse osmosis membrane or the like, purified water such as distilled water and ion-exchanged water, and dimethyl sulfoxide. Moreover, a reducing agent can also be added to test water as a solution of an acid used for setting test water acidic or an aqueous solution thereof as described later.

  The amount of reducing agent added to the test water must be set to an amount sufficient to reduce the total amount of diazonium ions of the diazonium salt produced by the reaction in this process. It is preferable to set at least equimolar with the reagent amount.

  In addition, when adding a diazotization reagent as a solution which melt | dissolved in alcohol to test water, alcohol used as a solvent can be used as a reducing agent.

  In this step, the reaction between the diazotizing reagent and nitrite ion, that is, the formation reaction of the diazonium salt proceeds under acidic conditions. Specifically, the test water is adjusted to acidity by adding to the test water an acid that does not contain nitrogen elements that may affect the quantitative results and does not inhibit the reaction between the diazotization reagent and nitrite ions, The reaction proceeds in that environment. Examples of the acid include inorganic acids such as hydrochloric acid and sulfuric acid, organic acids such as acetic acid, benzenesulfonic acid, citric acid and succinic acid, and aqueous solutions thereof, but it is usually preferable to use aqueous hydrochloric acid. The acid may be added to the test water before the diazotizing reagent and the reducing agent are added, or after the diazotizing reagent and the reducing agent are added. Further, as described above, the acid can be added to the inspection water as a solvent for the reducing agent.

  The amount of acid added to the test water must be set so that the test water can be adjusted to acidity so that the reaction between the nitrite ions contained in the test water and the diazotization reagent proceeds stably. It is preferable to set so that the pH of water is 6.0 or less, and it is particularly preferable to set it to be 0 to 4.0.

  The reaction in this step can usually proceed at room temperature of about 5 to 40 ° C. The time required for the reaction varies depending on the temperature, but is usually about 1 to 10 minutes. In addition, in order to shorten reaction time, test water can also be heated suitably. In this case, the heating temperature is preferably set to 40 to 100 ° C. Moreover, when the pretreatment for converting the nitrogen compound into nitrite ions is applied to the inspection water, the inspection water is usually heated to 60 ° C. or more and less than 100 ° C. in the pretreatment step. Therefore, the reaction in this step can be performed while maintaining the heating state.

  In this step, the test water is colored by the added diazotizing reagent itself. Further, nitrite ions contained in the test water react with the diazotization reagent under acidity adjusted with an acid to produce a diazonium salt. As a result, the test water colored with the diazotizing reagent is discolored by the diazotizing reagent itself as the diazotizing reagent is consumed by reaction with nitrite ions.

The diazonium salt produced here produces a compound in which the diazonium group of the diazonium ion forming it is easily decomposed and converted to a hydroxyl group (—OH) (hereinafter sometimes referred to as a conversion compound). Tend to. For example, when 1-aminoanthraquinone is used as a diazotization reagent, the diazonium group of the diazonium ion is converted to a hydroxyl group, and 1-hydroxyanthraquinone is generated as a conversion compound. The hydroxyl group of the resulting conversion compound has a lone pair like the amino group (—NH ₂ ) of the diazotization reagent, and thus forms a conjugated system with the aromatic structure moiety to which it is bonded. For this reason, the conversion compound colors test water as another dye having a maximum absorption wavelength at a wavelength close to the maximum absorption wavelength of the diazotizing reagent, and may affect the absorbance measured in Step 2 described later. For example, in the absorption spectrum of coloring due to 1-aminoanthraquinone, the maximum absorption wavelength is around 480 nm, whereas in the absorption spectrum of coloring due to 1-hydroxyanthraquinone which is a conversion compound, the maximum absorption wavelength is around 400 nm. For this reason, when measuring the absorbance using a light source such as a light-emitting diode in step 2, light having a wavelength width is emitted from the light source. Coloring of inspection water tends to be an obstacle. This is when the temperature of the test water to which this process is applied is high, for example, when the test water is at a high temperature for pretreatment for quantifying total nitrogen or when the reaction in this process is performed under heating However, the formation of the conversion compound is likely to proceed.

  In contrast, in this process, since a reducing agent is added to the test water together with the diazotization reagent, the diazonium ion of the generated diazonium salt is converted by the rapid reduction of the diazonium group to a hydrogen atom. Converted to a compound different from the compound. For example, when the diazotizing reagent is 1-aminoanthraquinone, in this step, the production of 1-hydroxyanthraquinone is suppressed, and anthraquinone is produced instead. This other compound is less likely to color the test water because the hydrogen atom resulting from the reduction of the diazonio group is not involved in the conjugated system of the aromatic structure portion, and is less likely to affect the absorbance measurement in step 2.

  Next, the absorbance of the test water after the reaction of the diazotizing reagent is measured (step 2). The absorbance measured here is the colored absorbance imparted to the test water by the diazotizing reagent itself, that is, the colored absorbance imparted to the test water by the diazotizing reagent remaining in the test water.

  The coloring of the test water by the diazotizing reagent decreases in strength as the diazotizing reagent is consumed in the reaction with nitrite ions in the test water. For this reason, the absorbance measured here has a correlation with the diazotizing reagent concentration and the nitrite ion concentration in the test water. The absorbance measurement wavelength is the maximum absorption wavelength of the color imparted to the test water by the diazotization reagent or a wavelength in the vicinity thereof, and is not specified because it varies depending on the type of diazotization reagent used. It is in the range of 600 nm. In addition, since the production | generation of a conversion compound is suppressed, the test | inspection water can measure the light absorbency of coloring by a diazotization reagent stably.

In this step, the amount of nitrite ions in the test water is determined from the measured value of absorbance based on a calibration curve prepared by examining the relationship between absorbance and nitrite ion concentration in advance. The calibration curve created here has a good linear relationship between the nitrite ion concentration and absorbance up to the relatively high nitrite ion concentration range. The possible range is 0 to 53 mg / [NO ₂ ⁻ ] / L (0 to 16 mg [N] / L in terms of total nitrogen), which is wider than the range possible with the conventional method such as JIS method. Therefore, this quantification method is applied to test water having a high content of nitrite ions, for example, test water in which nitrogen compounds are converted into nitrite ions by the above-described pretreatment for the determination of total nitrogen. Useful in cases. In particular, the test water subjected to such pretreatment has a high temperature of 60 to 100 ° C. due to heating in the pretreatment, and is an environment in which a conversion compound is easily generated.

  In the quantification method of the present invention, it is preferable to adjust the pH of the test water that has passed through step 1 to be higher than 7 before step 2. The absorbance measured in step 2 may cause some error in the quantitation result of nitrite ions because the numerical value may vary depending on the pH value when the pH of the test water is 7 or less. If the adjustment is made properly, the measurement error due to the influence of pH is reduced, and the quantitative accuracy of the nitrite ion concentration can be further increased.

  The pH of the test water can usually be adjusted by adding an alkali compound such as an alkali metal hydroxide, carbonate or bicarbonate or an aqueous solution thereof to the test water after completion of step 1. Is preferably adjusted by adding an aqueous sodium hydroxide solution.

Reagents and spectrophotometers The reagents and spectrophotometers used in the following examples and the like are as follows.
Nitrite nitrogen standard solution (for ion chromatograph): Wako Pure Chemical Industries, Ltd. Code 147-06341
10% by weight hydrochloric acid: Wako Pure Chemical Industries, Ltd. Code 085-07535
1 mol / L hydrochloric acid: Wako Pure Chemical Industries, Ltd. Code 083-01095
Ethanol: Wako Pure Chemical Industries, Ltd. Code 052-00467
Sodium hypophosphite monohydrate: Wako Pure Chemical Industries, Ltd. Code 193-02225
1 mol / L sodium hydroxide solution: Wako Pure Chemical Industries, Ltd. Code 192-02175
10 w / v% sodium hydroxide solution: Wako Pure Chemical Industries, Ltd. Code 191-1555
1-propanol: Wako Pure Chemical Industries, Ltd. Code 162-04816
Dimethyl sulfoxide (reagent special grade): Wako Pure Chemical Industries, Ltd. Code 043-07216
1-aminoanthraquinone: Tokyo Chemical Industry Co., Ltd. Code A0590
2-Nitroaniline: Tokyo Chemical Industry Co., Ltd. Code N0118
Sodium 4-nitroaniline-2-sulfonate: Tokyo Chemical Industry Co., Ltd. Code A0375
Sodium 1-amino-4-bromoanthraquinone-2-sulfonate: Tokyo Chemical Industry Co., Ltd. Code A0279
p-Nitroaniline: Tokyo Chemical Industry Co., Ltd. Code N0119
Naphthylethylenediamine (for nitrogen oxide measurement): Wako Pure Chemical Industries, Ltd. Code 147-04141
Spectrophotometer: Shimadzu Corporation trade name “UV-1600PC”

Example 1
(Preparation of nitrite ion solution)
Four types of nitrite ion solutions having nitrite ion concentrations of 0.0, 4.0, 8.0, and 12.0 mg [N] / L were prepared. Nitrite ion solution with a nitrite ion concentration of 0 mg [N] / L uses distilled water as it is, and other nitrite ion solutions dilute a nitrite nitrogen standard solution with distilled water. Adjusted.

(Create a calibration curve)
Add 1.0 mL of 1-aminoanthraquinone ethanol solution (concentration 0.5 g / L) to 2.5 mL of each of the four types of prepared nitrite ion solutions, and then add 1.0 mL of 10 wt% hydrochloric acid. The pH was set to 0.2. After this nitrite ion solution was allowed to react at 70 ° C. for 15 minutes, an absorption spectrum at 330 to 600 nm of the reaction solution was measured. The results are shown in FIG.

  Next, the absorbance at 480 nm, which is the color development wavelength of 1-aminoanthraquinone, was extracted from the measured absorbance spectrum, and a calibration curve for determining the nitrite ion concentration was created from this absorbance. The results are shown in FIG. According to FIG. 2, the prepared calibration curve shows high linearity at least in the range of nitrite ion concentration of 0 to 12.0 mg [N] / L.

Example 2
(Preparation of nitrite ion solution)
Seven kinds of nitrite ion solutions having nitrite ion concentrations of 0.0, 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0 mg [N] / L Prepared in a similar manner.

(Create a calibration curve)
Add 2.0 mL of 1-propanol solution of 1-aminoanthraquinone (concentration 0.2 g / L) to 2.0 mL of each of the seven types of prepared nitrite ion solutions, and further add 0.5 mL of 10 wt% hydrochloric acid. The pH was set to 0.6 by addition. After this nitrite ion solution was allowed to react at 25 ° C. for 15 minutes, an absorption spectrum at 330 to 600 nm of the reaction solution was measured. The results are shown in FIG.

  Next, the absorbance at 480 nm, which is the color development wavelength of 1-aminoanthraquinone, was extracted from the measured absorbance spectrum, and a calibration curve for determining the nitrite ion concentration was created from this absorbance. The results are shown in FIG. According to FIG. 4, the prepared calibration curve shows high linearity at least in the range of nitrite ion concentration of 0 to 12.0 mg [N] / L.

Example 3
After the nitrite ion solution adjusted to pH 0.6 was allowed to react at 25 ° C. for 15 minutes, 0.6 mL of 10 w / v% sodium hydroxide solution was further added to the reaction solution to adjust the pH to 12.4. A calibration curve was prepared in the same manner as in Example 2 except that the absorption spectrum was measured after adjustment. The measurement result of the absorption spectrum is shown in FIG. 5, and the calibration curve is shown in FIG. According to FIG. 6, the prepared calibration curve shows high linearity at least in the range of nitrite ion concentration of 0 to 12.0 mg [N] / L.

Example 4
(Preparation of nitrite ion solution)
Four types of nitrite ion solutions having nitrite ion concentrations of 0.0, 2.0, 4.0, and 6.0 mg [N] / L were prepared in the same manner as in Example 1.

(Create a calibration curve)
0.5 mL of dimethyl sulfoxide solution (concentration 0.3 g / L) of 2-nitroaniline is added to 2.0 mL of each of the four prepared nitrite ion solutions, and hypophosphorous acid is added to a 1 mol / L hydrochloric acid aqueous solution. 0.2 mL of a solution in which sodium acid was dissolved to a concentration of 10 g / L was added to set the pH to 1.2. After this nitrite ion solution was allowed to react at 25 ° C. for 10 minutes, an absorption spectrum of 315 to 530 nm of the reaction solution was measured. The results are shown in FIG.

  Next, the absorbance at 415 nm, which is the color development wavelength by 2-nitroaniline, was extracted from the measured absorption spectrum, and a calibration curve for determining the nitrite ion concentration was created from this absorbance. The results are shown in FIG. According to FIG. 8, the prepared calibration curve shows high linearity at least in the range of 0 to 6.0 mg [N] / L.

Example 5
(Preparation of nitrite ion solution)
Five types of nitrite ion solutions having nitrite ion concentrations of 0.0, 0.5, 1.0, 1.5, and 2.0 mg [N] / L were prepared in the same manner as in Example 1.

(Create a calibration curve)
0.15 mL of an aqueous solution (concentration 0.6 g / L) of sodium 4-nitroaniline-2-sulfonate is added to 2.0 mL of each of the five types of prepared nitrite ion solutions, and a 1 mol / L hydrochloric acid aqueous solution is further added. Then, 0.2 mL of a solution in which sodium hypophosphite was dissolved to a concentration of 10 g / L was added to adjust the pH to 1.1. After this nitrite ion solution was allowed to react at 25 ° C. for 10 minutes, an absorption spectrum at 270 to 440 nm of the reaction solution was measured. The results are shown in FIG.

  Next, the absorbance at 370 nm, which is the color development wavelength by sodium 4-nitroaniline-2-sulfonate, was extracted from the measured absorbance spectrum, and a calibration curve for determining the nitrite ion concentration was created from this absorbance. The results are shown in FIG. According to FIG. 10, the prepared calibration curve shows high linearity at least in the range of 0 to 2.0 mg [N] / L.

Example 6
(Preparation of nitrite ion solution)
Four types of nitrite ion solutions having nitrite ion concentrations of 0.0, 4.0, 8.0, and 12.0 mg [N] / L were prepared in the same manner as in Example 1.

(Create a calibration curve)
1.0 mL of an aqueous solution (concentration 1.0 g / L) of sodium 1-amino-4-bromoanthraquinone-2-sulfonate was added to 2.5 mL of each of the four types of prepared nitrite ion solutions. The pH was set to 0.5 by adding 0.5 mL of a solution of sodium hypophosphite dissolved in a weight% aqueous hydrochloric acid solution to a concentration of 10 g / L. After this nitrite ion solution was allowed to react at 60 ° C. for 10 minutes, an absorption spectrum at 330 to 600 nm of the reaction solution was measured. The results are shown in FIG.

  Next, the absorbance at 480 nm, which is the color development wavelength of sodium 1-amino-4-bromoanthraquinone-2-sulfonate, is extracted from the measured absorbance spectrum, and a calibration curve for determining the nitrite ion concentration is created from this absorbance did. The results are shown in FIG. According to FIG. 12, the prepared calibration curve shows high linearity at least in the range of nitrite ion concentration of 0 to 12.0 mg [N] / L.

Comparative Example 1
Nitrite ion concentrations of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mg [N ] 11 types of nitrite ion solutions were prepared in the same manner as in Example 1. And the naphthylethylenediamine absorptiometric method prescribed | regulated to Japanese Industrial Standard JISK0102, factory wastewater test method (2008) 43.1.1 (nonpatent literature 1) is applied with respect to each nitrite ion solution, and 540 nm The relationship between absorbance and nitrite ion concentration was investigated. The results are shown in FIG.

  According to FIG. 13, the quantifiable range of the nitrite ion concentration is limited to the range of 0 to 0.3 mg [N] / L, and it is understood that high concentration nitrite ions cannot be quantified by this method.

Experimental example 1
(Experimental example 1a)
A nitrite ion solution having a nitrite ion concentration of 12.0 mg [N] / L was prepared in the same manner as in Example 1. The prepared nitrite ion solution is put into 2.5 mL of each of three test tubes A, B and C, and 1-aminoanthraquinone dimethyl sulfoxide solution (concentration 0.5 g / L) is added to the nitrite ion solution of each test tube. ) 1.0 mL was added. Moreover, 10% by weight hydrochloric acid was added in 0.5 mL portions, and the pH was set to 0.5. And after heating each test tube on the following conditions using a block heater, the absorption spectrum of 360-600 nm was measured. The results are shown in FIG. FIG. 14 also shows the result of measuring the same absorption spectrum (blank) immediately after the addition of the dimethyl sulfoxide solution of 1-aminoanthraquinone for test tube A and before heating.

Test tube A: 10 minutes at 95 ° C. Test tube B: 30 minutes at 95 ° C. Test tube C: 10 minutes at 85 ° C.

  According to FIG. 14, the absorption spectra of the test tubes A to C after the heating are inconsistent in the vicinity of 440 to 470 nm, which is close to 480 nm, which is the coloring wavelength by 1-aminoanthraquinone (within the one-dot chain line in FIG. 14). . This is because heating temperature and heating time are measured when the absorbance of 1-aminoanthraquinone coloring is measured using a light emitting diode having a broad emission wavelength centered around 480 nm or a phototransistor having a similar sensitivity wavelength. This means that the measurement result of the absorbance fluctuates due to the fluctuation of the nitrite, and the quantitative result of nitrite ion may be inaccurate.

(Experimental example 1b)
Except that the dimethyl sulfoxide solution of 1-aminoanthraquinone was changed to a 1-propanol solution of 1-aminoanthraquinone (concentration 0.5 g / L), the same operation as in Example 1a was performed, and an absorption spectrum at 360 to 600 nm was measured. did. The results are shown in FIG. FIG. 15 also shows the result of measuring the same absorption spectrum (blank) immediately after adding the 1-propanol solution of 1-aminoanthraquinone for test tube A and before heating.

  According to FIG. 15, the absorption spectra for the test tubes A to C after heating are substantially the same in the vicinity of 440 to 470 nm, which is close to 480 nm, which is the coloring wavelength by 1-aminoanthraquinone (inside the one-dot chain line frame in FIG. 15). ). Even if it is intended to measure the absorbance of coloring due to 1-aminoanthraquinone using a light-emitting diode having a broad emission wavelength centered around 480 nm or a phototransistor having a similar sensitivity wavelength, the heating temperature or This means that the absorbance measurement result does not substantially change due to fluctuations in the heating time, indicating that a highly reliable quantitative result of nitrite ions can be obtained.

(Experimental Example 1c)
Four types of nitrite ion solutions having nitrite ion concentrations of 0.0, 4.0, 8.0, and 12.0 mg [N] / L were prepared in the same manner as in Example 1. The prepared four types of nitrite ion solutions (2.0 mL) were placed in individual test tubes, and each test tube was attached to a 90 ° C. block heater. Then, 0.8 mL of an aqueous solution (concentration 1.0 g / L) of sodium 1-amino-4-bromoanthraquinone-2-sulfonate and 0.5 mL of 10 wt% hydrochloric acid aqueous solution and 0.5 mL of distilled water were added to each test tube. And the pH was set to 0.5. After changing the heating temperature of the nitrite ion solution with a block heater to 95 ° C. and reacting for 15 minutes, the absorption spectrum of 360 to 600 nm of the reaction solution was measured. The results are shown in FIG.

  According to FIG. 16, the maximum absorption wavelength in the range of 420 to 540 nm fluctuates due to the different concentrations of the nitrite ion solution. This is because, in the measured absorption spectrum, a colored absorption spectrum by sodium 1-amino-4-bromoanthraquinone-2-sulfonate and a sodium 1-amino-4-bromoanthraquinone-2-sulfonate via a diazonium salt This is probably because the absorption spectrum of the hydroxy form (sodium 1-hydroxy-4-bromoanthraquinone-2-sulfonate) produced in this manner appears in a fused state. In particular, the reason why the maximum absorption wavelength shifts to the lower wavelength side as the nitrite ion concentration is higher is considered to be because the production amount of the hydroxy compound is relatively increased due to the higher nitrite ion concentration.

(Experimental example 1d)
The reaction solution was 360 to 600 nm in the same manner as in Experimental Example 1c except that 0.5 mL of sodium hypophosphite aqueous solution with a concentration of 10 g / L was added to the test tube instead of 0.5 mL of distilled water. The absorption spectrum of was measured. The results are shown in FIG.

  According to FIG. 17, even when the nitrite ion concentration is different, the maximum absorption wavelength in the range of 420 to 540 nm is substantially constant except when the nitrite ion concentration is 12.0 mg [N] / L. Yes. This is because the use of an aqueous sodium hypophosphite solution suppresses the formation of a hydroxy compound as in Experimental Example 1c, and a stable absorption spectrum of colored by sodium 1-amino-4-bromoanthraquinone-2-sulfonate is obtained. It is thought that it was because

Experimental example 2
(Experimental example 2a)
Four diazotization reagent aqueous solutions prepared by adding 0.15 mL of a dimethyl sulfoxide solution (concentration 0.3 g / L) of p-nitroaniline as a diazotization reagent to 2.5 mL of distilled water were prepared. Three types of solutions with hydrogen ion concentrations adjusted to 0.011 mol / L, 0.022 mol / L and 0.033 mol / L by adding 0.03 mL, 0.06 mL and 0.09 mL of 1 mol / L hydrochloric acid to Prepared. After these solutions were allowed to stand at 25 ° C. for 5 minutes, an absorption spectrum at 290 to 480 nm was measured. The results are shown in FIG. FIG. 18 also shows the result of measuring the same absorption spectrum for only the diazotizing reagent aqueous solution to which 1 mol / L hydrochloric acid was not added.

(Experimental example 2b)
Four diazotizing reagent aqueous solutions similar to those prepared in Experimental Example 2a are prepared, and 0.03 mL, 0.06 mL, and 1 mol / L sodium hydroxide solution are used instead of 1 mol / L hydrochloric acid, respectively. Three kinds of solutions whose pH was adjusted to 7 or more by adding 0.09 mL were prepared. These solutions were allowed to stand under the same conditions as in Experimental Example 2a, and then the absorption spectrum was measured. The results are shown in FIG. In FIG. 19, the result of having measured the same absorption spectrum only about the diazotization reagent aqueous solution which has not added 1 mol / L sodium hydroxide solution is shown collectively.

(Experimental example 2c)
Three types of solutions with adjusted hydrogen ion concentrations were prepared in the same manner as in Experimental Example 2a, and these solutions were left at 25 ° C. for 5 minutes. Thereafter, 0.15 mL of a 1 mol / L sodium hydroxide solution was added to each solution to prepare three types of solutions with pH adjusted to 12.6, 12.5, and 12.3, respectively. About these solutions, the result of having measured the absorption spectrum similarly to Experimental example 2a is shown in FIG. FIG. 20 shows the same absorption spectrum of a solution adjusted to pH 12.7 by adding only 0.15 mL of 1 mol / L sodium hydroxide solution to the same diazotizing reagent aqueous solution prepared in Experimental Example 2a. The results of measuring are also shown.

(Explanation of Experimental Examples 2a to 2c)
FIG. 18 relating to Experimental Example 2a shows that the absorbance at the maximum absorption wavelength is different even when the concentration of p-nitroaniline, which is a diazotization reagent, is the same because the hydrogen ion concentration of the solution from which the absorption spectrum was measured is different. ing. More specifically, each time the hydrogen ion concentration of the solution increases by 0.011 mol / L, the absorbance at the maximum absorption wavelength decreases by about 5%. On the other hand, FIG. 19 relating to Experimental Example 2b shows the maximum absorption wavelength in a solution having the same p-nitroaniline concentration when a 1 mol / L sodium hydroxide solution is added to a diazotizing reagent aqueous solution and the pH is set to 7 or more. It shows that there is no significant change in the absorbance. FIG. 20 relating to Experimental Example 2c shows that the solution in which the hydrogen ion concentration is increased by adding 1 mol / L hydrochloric acid is adjusted to pH 7 or higher by adding 1 mol / L sodium hydroxide solution, and then the absorption spectrum is obtained. Measurement shows that there is almost no change in absorbance at the maximum absorption wavelength.

  From the above results, when quantifying nitrite ions in the test water, it is considered preferable to measure the absorbance after adjusting the pH of the test water after the reaction of the diazotization reagent to 7 or more.

Claims (5)

A method for quantifying nitrite ions contained in test water,
A diazotization reagent capable of generating a diazonium salt by reaction with the nitrite ion with respect to the test water; and at least one compound selected from the group consisting of alcohol compounds and hypophosphorous acid and salts thereof; And reacting under acidic conditions,
Measuring the color absorbance of the diazotizing reagent with respect to the test water that has undergone step 1, and
As the diazotizing reagent, an aromatic primary amine compound having a ketone group or a nitro group at the ortho-position or para-position is used,
Quantitative method of nitrite ion.   The aromatic primary amine compound is selected from the group consisting of 1-aminoanthraquinone, 2-nitroaniline, sodium 4-nitroaniline-2-sulfonate and sodium 1-amino-4-bromoanthraquinone-2-sulfonate The method for quantifying nitrite ions according to claim 1, wherein   The method for quantifying nitrite ions according to claim 1 or 2, wherein the pH of the test water having undergone step 1 is adjusted to be greater than 7 before step 2.   The test water is pretreated to convert nitrate ions generated by oxidative decomposition of nitrogen compounds contained in the test water into nitrite ions for the determination of total nitrogen. The method for quantifying nitrite ions according to any one of claims 1 to 3.   The method for quantifying nitrite ions according to claim 4, wherein the temperature of the inspection water is 60 ° C or higher and lower than 100 ° C.

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