Analytical methods for ammonia nitrogen

Abstract

To provide an analytical method for accurately analyzing ammonia nitrogen in a sample containing relatively large amount of metal ions.SOLUTION: The analytical method of ammonia nitrogen includes processes for: adding chelation agent into the sample to capture metal ions; converting ammonium ions in the sample into gaseous ammonia by shifting the sample pH, after the metal ions capturing, to alkali side; separating the gaseous ammonia using a gas permeable membrane; casing the separated gaseous ammonia to be absorbed in absorbent to be converted into ammonium ions; and quantifying and analysing the ammonium ions absorbed in the absorbent by indophenol blue method.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for analyzing ammonia nitrogen.

Background Art

[0002] Ammonia is harmful to the human body, and the drainage standard regulates ammonia, ammonium compounds, nitrite compounds, and nitrate compounds (the sum of nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen, where the conversion coefficient of ammonia nitrogen is multiplied by 0.4 in consideration of the nitrification mechanism of ammonia nitrogen in the water environment). As a method for analyzing ammonia nitrogen, the indophenol blue method is defined in the assay method related to the drainage standard (for example, Non-Patent Document 1).

[0003] In the indophenol blue method, since metal ions contained in the sample form white precipitates and interfere with the measurement during absorbance detection, a chelating agent solution such as ethylenediaminetetraacetic acid (EDTA) is added to the sample to capture the metal ions (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in samples containing a relatively large amount of metal ions, there is a problem in that even if a chelating agent solution is added to the sample to capture the metal ions and then ammonia nitrogen is analyzed using the indophenol blue method, accurate analysis may not be possible.

[0007] The present invention aims to provide an analytical method for accurately analyzing ammonia nitrogen even in samples containing a relatively large amount of metal ions. [Means for solving the problem]

[0008] To solve the above problems, one embodiment of the present invention includes the following configuration.

[0009] [1] A method for analyzing ammonia nitrogen, comprising the steps of: adding a chelating agent to a sample to capture metal ions; adjusting the pH of the sample after metal ion capture to the alkaline side to convert ammonium ions in the sample into gaseous ammonia; separating the gaseous ammonia using a gas permeable membrane; absorbing the separated gaseous ammonia into an absorption solution to convert it into ammonium ions; and quantifying the ammonium ions absorbed into the absorption solution by the indophenol blue method.

[0010] [2] The analytical method according to [1], wherein the chelating agent is ethylenediaminetetraacetic acid.

[0011] [3] The analytical method according to [1] or [2], wherein the gas permeable membrane is a polytetrafluoroethylene membrane filter.

[0012] [4] The analytical method according to any one of [1] to [3], wherein in the step of converting ammonium ions in the sample into gaseous ammonia by making the pH of the sample alkaline, sodium hydroxide and boric acid are added to make the pH of the sample solution alkaline.

[0013] [5] The analytical method according to any one of [1] to [4], which quantifies ammonium ions in a sample by the salicylic acid indophenol blue method.

[0014] [6] The analytical method according to any one of [1] to [5], which is a flow analysis method.

[0015] [7] The analytical method according to [6], which performs bubble segmentation on a sample introduced into a pipeline and creates a plurality of segments partitioned by bubbles in the pipeline.

Advantages of the Invention

[0016] According to one aspect of the present invention, even in a sample containing a relatively large amount of metal ions, ammonia nitrogen can be accurately analyzed.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing a schematic configuration of an example of an apparatus used in the analytical method according to an embodiment of the present invention. [Figure 2] It is a diagram showing a schematic configuration of an example of an apparatus used in the analytical method according to an embodiment of the present invention. [Figure 3] It is a diagram schematically showing a gas permeation step in the analytical method according to an embodiment of the present invention. [Figure 4] It is a diagram showing the apparatus used in the examples. [Figure 5] It is a diagram showing the results of measuring 1 mg / L of ammonia nitrogen in the examples. [Figure 6] It is a diagram showing the results of measuring 1 mg / L of ammonia nitrogen in the comparative examples.

Modes for Carrying Out the Invention

[0018] The inventors noticed that in samples containing a relatively large amount of metal ions, even after adding a chelating agent solution to the sample to capture the metal ions and then analyzing ammoniacal nitrogen using the indophenol blue method, accurate analysis was sometimes not possible. In their investigation to elucidate this phenomenon, the inventors focused on the fact that, when the amount of ammoniacal nitrogen in a sample is the same, the amount of quantified ammoniacal nitrogen varies depending on the amount of metal ions in the sample. Based on this finding, the inventors investigated and discovered that the chelating agent weakens the color intensity of the indophenol blue method. When a sample contains metal ions, the added chelating agent is consumed for complex formation. Then, depending on the amount of metal ions in the sample, there is a difference in the concentration of chelating agent that has not been consumed for complex formation, i.e., the concentration of chelating agent that weakens the color intensity. As a result, the color intensity of indophenol blue fluctuates, making accurate analysis impossible. Therefore, after adding the chelating agent solution to the sample to capture metal ions, the pH of the suspension containing the metal-captured chelating agent and the sample containing the chelating agent that has not been consumed for complex formation is made alkaline, converting the ammonium ions in the sample into gaseous ammonia. Only the ammonia is separated by a gas permeable membrane, and the separated ammonia is absorbed into the absorption solution to remove ammonium ions (NH4). + By converting the ammonia nitrogen to ammonium ions and quantifying the resulting ammonia nitrogen using the indophenol blue method, we discovered that accurate quantification is possible even when the amount of metal ions in the sample differs, thus completing the invention.

[0019] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and various modifications are possible within the described scope. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. All academic documents and patent documents described in this specification are incorporated herein by reference. Also, unless otherwise specified in this specification, "A~B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0020] [1. Analysis method] The method for analyzing ammonia nitrogen according to an embodiment of the present invention includes a step of adding a chelating agent to a sample to capture metal ions, a step of making the pH of the sample after metal ion capture alkaline to convert ammonium ions in the sample into gaseous ammonia, a step of separating the gaseous ammonia by a gas permeable membrane, a step of absorbing the separated gaseous ammonia into an absorbent to convert it into ammonium ions, and an analysis step of quantifying the ammonium ions absorbed into the absorbent by the indophenol blue method.

[0021] Here, ammonia nitrogen means nitrogen present as ammonium ions (NH4 + ) in an aqueous liquid.

[0022] [[ID=​​​​ The sample to be analyzed can be any aqueous liquid containing ammonia nitrogen, but from the perspective of confirming that the amount of ammonia nitrogen is zero, this method does not exclude samples that do not contain ammonia nitrogen. Furthermore, the analytical method according to the present invention can accurately analyze ammonia nitrogen even in samples containing metal ions, and is therefore effective for samples containing metal ions. Examples of such samples include swamp water, seawater, industrial water, factory wastewater, mine wastewater, river water, groundwater, hot spring water, tap water, raw water, treated water, sewage water, and septic tank water.

[0024] (Gasification process) In this process, the pH of the sample after metal ion capture is made alkaline, thereby converting the ammonium ions in the sample into gaseous ammonia.

[0025] There are no particular limitations on how to adjust the pH of the sample to the alkaline side after metal ion capture, but one possible method is to add an alkali such as sodium hydroxide, potassium hydroxide, calcium carbonate, or calcium hydroxide. By adding an alkali, the ammonium ions in the sample can be gasified into gaseous ammonia. Alternatively, a buffer solution containing boric acid, acetic acid, phosphoric acid, citric acid, tartaric acid, trishydroxymethylaminomethane, etc., to the alkali may be added. By adding a buffer solution, the influence of the sample's pH on the measurement can be reduced.

[0026] In particular, in this process, it is more preferable to make the pH of the sample solution alkaline by adding sodium hydroxide and boric acid to the sample.

[0027] (Gas permeation process) In this process, the ammonia gasified in the gasification process is separated by a gas permeable membrane.

[0028] Figure 3 is a schematic diagram illustrating this process. As shown in Figure 3, when a sample containing gaseous ammonia comes into contact with the gas permeable membrane 11 in the gas permeable section 3, only the gaseous ammonia in the sample permeates through the gas permeable membrane 11, and the remaining portion of the sample is discharged as waste liquid.

[0029] The gas permeable section 3 selectively permeates and separates the gaseous ammonia, thereby removing the chelating agent that weakens the color intensity of the indophenol blue method, and allowing for accurate analysis of the amount of ammonia nitrogen in the sample.

[0030] The gas permeable membrane is not particularly limited as long as it is a membrane capable of selectively separating gases, and may be hydrophobic or hydrophilic, but from the viewpoint of gas permeation efficiency, it is more preferable to be hydrophobic. The material of the gas permeable membrane is also not particularly limited, but examples include polytetrafluoroethylene (hereinafter sometimes referred to as "PTFE"), cellulose, glass fiber, etc.

[0031] In addition, by incorporating the gas permeable section 3, the baseline of the measurement chart can be stabilized in the quantitative determination of ammonia nitrogen by the indophenol blue spectrophotometric method using salicylic acid. The indophenol blue method using salicylic acid is preferable to the indophenol blue method using phenol in that there is no release of phenol into the environment. However, analysis by the indophenol blue spectrophotometric method using salicylic acid tends to have an unstable baseline. In particular, a stable baseline is required for samples containing trace amounts of ammonia nitrogen. By performing analysis by the indophenol blue spectrophotometric method using salicylic acid with the apparatus equipped with the gas permeable section 3, the baseline can be stabilized, and therefore, more accurate measurements can be performed even for samples containing trace amounts of nitrogen.

[0032] (Absorption process) In this process, the separated gaseous ammonia is absorbed into an absorption solution and converted into ammonium ions.

[0033] The gaseous ammonia that permeates through the gas permeable membrane 11 is absorbed by the absorption solution and converted back into ammonium ions. The solution containing the ammonium ions absorbed by the absorption solution is subjected to analysis. In Figure 3, to show that the gaseous ammonia permeates through the gas permeable membrane 11, it is labeled as NH3 even after permeating the gas permeable membrane 11, but it is subsequently absorbed by the absorption solution and converted into ammonium ions. The absorption solution is not particularly limited as long as it can absorb gaseous ammonia and convert it into ammonium ions, but for example, acids such as sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid can be used. In addition, a reagent used for detecting ammonium ions may be included along with the acid such as sulfuric acid. For example, reagents such as sodium nitroprusside used in the indophenol blue method can be mentioned. The reagent used in the indophenol blue method may be added after the absorption step and before the analysis step without being included in the absorption solution, or a portion of the reagent may be included in the absorption solution and the remaining reagent may be added after the absorption step and before the analysis step.

[0034] (Analysis process) In this process, the ammonium ions absorbed into the absorption solution are quantified using the indophenol blue method.

[0035] After the absorption step and before the analysis step, reagents used in the indophenol blue method may be added. In the indophenol blue method using salicylic acid, for example, salicylic acid and hypochlorous acid or its salt (e.g., sodium hypochlorite (NaClO), calcium hypochlorite, potassium hypochlorite, etc.) can be added. In this case, salicylic acid and hypochlorous acid or its salt may be added simultaneously or separately, but it is more preferable to add them separately. The order in which salicylic acid and hypochlorous acid or its salt are added does not matter, but it is more preferable to add salicylic acid first, followed by hypochlorous acid or its salt. Furthermore, salicylic acid and hypochlorous acid or its salt may be added in multiple stages. The indophenol blue method using phenol is the same as the indophenol blue method using salicylic acid, except that salicylic acid is replaced by phenol. For example, phenol and hypochlorous acid or its salt are added as reagents. In this case, the method and order of adding phenol and hypochlorous acid or its salt are the same as in the indophenol blue method using salicylic acid.

[0036] In particular, the analytical method according to one embodiment of the present invention is more preferably an analytical method that quantifies ammonium ions in a sample by the salicylic acid indophenol blue method, from the viewpoint of having a low burden on the environment.

[0037] In the analytical process, when employing the indophenol blue method, a spectrophotometer is used for detection. A flow cell type spectrophotometer is more preferable.

[0038] [2. Analysis Method Using Flow Analysis] In the analytical method according to one embodiment of the present invention, flow analysis can be suitably used. Flow analysis is a technique in which multiple samples are sequentially and continuously introduced into a pipeline and delivered as liquid, and after processing such as reaction with reagents in the pipeline, analysis is performed using an analytical instrument. Hereinafter, an analytical method using flow analysis according to one embodiment of the present invention will be described with reference to the drawings.

[0039] [2.1] Continuous flow analysis method Figure 1 shows a schematic configuration of an example of an apparatus used in an analysis method by flow analysis according to one embodiment of the present invention.

[0040] This analytical method includes a sample introduction step of introducing a sample into a conduit 9; a bubble segmentation step of performing bubble segmentation on the sample introduced into the conduit 9 to create multiple segments partitioned by bubbles within the conduit 9; a metal ion capture step of adding a chelating agent to the flow of sample being transported through the conduit 9 to capture metal ions in the sample; a gasification step of making the pH of the sample after metal ion capture being transported through the conduit 9 alkaline, thereby converting ammonium ions in the sample into gaseous ammonia; a gas permeation step of separating the ammonia gasified in the gasification step using a gas permeable membrane; an absorption step of absorbing the separated gaseous ammonia into an absorbent solution being transported through the conduit 9' to convert it into ammonium ions; an analytical reagent addition step of adding a reagent used in the indophenol blue method to the flow of liquid containing the ammonium ions absorbed in the absorbent solution being transported through the conduit 9'; and an analytical step of quantifying the ammonium ions absorbed in the absorbent solution using the indophenol blue method.

[0041] (Sample introduction process) In the sample introduction step, the sample is introduced into the pipeline 9 by the sample introduction unit 7. The sample introduction unit 7 includes, for example, a sampling tube that guides the sample into the pipeline 9 and a sampling pump that applies suction force to the sampling tube. The sampling pump introduces the sample into the pipeline 9 at a predetermined flow rate. The sample is the liquid to be analyzed.

[0042] (Air bubble segmentation process) In the bubble segmentation process, the bubble segmentation unit 8 performs bubble segmentation on the sample introduced into the pipeline 9, creating multiple segments partitioned by bubbles within the pipeline 9. The bubble segmentation unit 8 includes, for example, a gas introduction pipe that guides gas into the pipeline 9 and a gas introduction pump that applies suction force to the gas introduction pipe. By performing bubble segmentation, the vortex flow within the segmented liquid separated by bubbles allows for optimal mixing of reagents such as chelating agents, alkalis, and analytical reagents. Furthermore, since the segmented liquid flows independently within the pipeline 9 after being separated by bubbles, diffusion between samples can be prevented. This method, in which reagents are introduced into a continuous flow within the pipeline, where multiple samples are sequentially and continuously introduced into the pipeline and segmented by bubbles, and then analyzed by a detector installed downstream after the reaction operation, is called continuous flow analysis (CFA). Various gases can be used as the gas for bubble segmentation, including inert gases such as argon and helium; nitrogen; oxygen; and air. These gases may be used individually or in mixtures of two or more types.

[0043] (Metal ion capture process) In the metal ion capture step, a chelating agent is added to the flow of the sample being transported through the pipeline 9 by the chelating agent introduction unit 1. The chelating agent introduction unit 1 comprises a chelating agent introduction tube that guides the chelating agent into the pipeline 9, and a chelating agent introduction pump that applies suction force to the chelating agent introduction tube. By adding the chelating agent, metal ions in the sample can be captured. In the example in Figure 1, the chelating agent introduction unit 1 is located downstream of the bubble segmentation unit 8 and upstream of the alkali introduction unit 2, but the chelating agent introduction unit 1 may also be located downstream of the sample introduction unit 7 and upstream of the bubble segmentation unit 8. In other words, the bubble segmentation step may be performed after the metal ion capture step.

[0044] (Gasification process) In the gasification process, alkali is added to the sample flow by the alkali introduction unit 2 in order to make the pH of the sample being transported through the pipeline 9 after the metal ion capture process alkaline. The alkali introduction unit 2 is located downstream of the chelating agent introduction unit 1 and upstream of the gas permeate unit 3. The alkali introduction unit 2 includes a reagent introduction tube that guides alkali into the pipeline 9 and an alkali introduction pump that applies suction force to the reagent introduction tube. By adding alkali downstream of the chelating agent introduction unit 1 and upstream of the gas permeate unit 3, ammonium ions in the sample can be gasified into gaseous ammonia. Alternatively, a buffer solution containing boric acid or the like added to the alkali such as sodium hydroxide may be added.

[0045] (Gas permeation process) The sample containing gaseous ammonia, which has been transported through the pipeline 9 after the gasification process, is transferred to the gas permeate section 3. As shown in Figures 1 and 3, the gas permeate section 3 is equipped with a gas permeable membrane 11, and the sample containing gaseous ammonia is transported while in contact with the gas permeable membrane 11. When the sample containing gaseous ammonia comes into contact with the gas permeable membrane 11, only the gaseous ammonia in the sample permeates through the gas permeable membrane 11, and the remaining part of the sample continues to be transported through the pipeline 9 and discharged as waste liquid.

[0046] (Absorption process) In the gas permeable section 3, a sample containing gaseous ammonia is transported through conduit 9, and an absorbent solution that absorbs the gaseous ammonia that has permeated through the gas permeable membrane 11 is transported through another conduit, conduit 9'. One side of the gas permeable membrane 11 in the gas permeable section 3 is in contact with the sample containing gaseous ammonia being transported through conduit 9, and the other side is in contact with the absorbent solution being transported through conduit 9'. In the absorption process, the gaseous ammonia that has permeated through the gas permeable membrane 11 is absorbed by the absorbent solution and converted into ammonium ions.

[0047] Furthermore, the absorbent liquid is introduced into the pipeline 9' by the absorbent liquid introduction unit 4. The absorbent liquid introduction unit 4 includes, for example, a sampling tube that guides the absorbent liquid into the pipeline 9' and a sampling pump that applies suction force to the sampling tube.

[0048] The gas permeable section 3 can be constructed, for example, by stacking two instruments, each having grooves formed as flow paths (pipes 9 and 9'), so that their grooves face each other, for example, with the gas permeable membrane 11 sandwiched between them. In this structure, because the grooves of the two instruments are aligned, the sample flows through one groove (pipe 9) and the absorption liquid flows through the other groove (pipe 9'), with the gas permeable membrane 11 in between.

[0049] The absorbent liquid may be supplied segmented by bubbles. Alternatively, the liquid containing ammonium ions after the absorption process may be segmented by bubbles. The gas used for bubble segmentation is as described in the description of the (bubble segmentation process).

[0050] (Analytical reagent introduction process) In the analytical reagent introduction step, the reagent used for the analysis of ammonia nitrogen by the indophenol blue method, as described above, is added to the flow of ammonium ion-containing liquid being transported through the pipeline 9' after the absorption step, via the analytical reagent introduction section 6.

[0051] In the example shown in Figure 1, the analytical reagent introduction section 6 is located downstream of the gas permeate section 3 and upstream of the analysis section 5. However, the analytical reagent introduction section 6 may also be located downstream of the absorption solution introduction section 4 and upstream of the gas permeate section 3. Alternatively, it may be located in both locations. Alternatively, at least a portion of the analytical reagent may be introduced into the conduit 9' by the absorption solution introduction section 4 while already mixed with the absorption solution.

[0052] The analytical reagent introduction section 6 includes a reagent introduction tube that guides the analytical reagent into the conduit 9, and a reagent introduction pump that applies suction force to the reagent introduction tube. For example, in the indophenol blue method using salicylic acid, salicylic acid and hypochlorous acid or its salt may be added from one analytical reagent introduction section 6, but it is more preferable to have two analytical reagent introduction sections downstream of the gas permeate section 3 and upstream of the analysis section 5, and to add the reagents separately from these two analytical reagent introduction sections 6. In this case, the order in which salicylic acid and hypochlorous acid or its salt are added does not matter, but it is more preferable to add salicylic acid from the upstream analytical reagent introduction section first, and then add hypochlorous acid or its salt from the downstream analytical reagent introduction section.

[0053] (Analysis process) In the analysis step, the analysis unit 5 quantifies the ammonium ions in the liquid being transported through the pipeline 9'. In one embodiment of the present invention, since the indophenol blue method is used as the analysis method, the analysis unit 5 is, for example, a spectrophotometer. A flow cell type spectrophotometer is more preferable as the spectrophotometer.

[0054] (Other aspects) In the example shown in Figure 1, the flow analyzer is equipped with three types of reagent introduction sections: a chelating agent introduction section 1, an alkali introduction section 2, and an analytical reagent introduction section 6. However, further reagent introduction sections may be provided as needed. The reagents introduced through these reagent introduction sections are not limited to those listed above, but examples include acids such as nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, phosphoric acid, hydrogen peroxide, and hydrofluoric acid; and alkalis such as sodium peroxide, calcium carbonate, and sodium carbonate. By adding these reagents, the pH of the sample can be adjusted.

[0055] Although not shown in the example in Figure 1, the apparatus used in the analytical method according to this embodiment may further include a mixing coil for mixing the reagent added in the reagent introduction section, such as the chelating agent introduction section 1, the alkali introduction section 2, and the analytical reagent introduction section 6, with the sample or liquid flowing through the conduit. The mixing coil is a conduit formed in a coil shape, and when the sample or liquid passes through the mixing coil, the reagent or liquid and the sample flowing through the conduit are mixed. The mixing coil may be located after the reagent introduction section, such as the chelating agent introduction section 1, the alkali introduction section 2, and / or the analytical reagent introduction section 6.

[0056] Although not shown in the example in Figure 1, the apparatus used in the analytical method according to this embodiment may include a heating tank for heat treatment of the sample being transported through the pipeline. The heating tank may be a constant temperature bath equipped with a heater. However, the configuration of the heating tank is not limited to this, and may also be an ultrasonic decomposition device, a microwave, an autoclave decomposition device, etc. Furthermore, within the heating tank, the pipeline forms a coil or a helix. In one embodiment of the present invention, the heating tank is provided downstream of the analytical reagent introduction section 6 or downstream of the mixing coil provided downstream of the analytical reagent introduction section 6. By heating the liquid containing ammonium ions to which the analytical reagent has been added, the reaction with the reagent can be promoted.

[0057] Furthermore, although not provided in the example in Figure 1, the apparatus used in the analysis method according to this embodiment may include a debubble section between the chelating agent introduction section 1 and the gas permeation section 3. This prevents fine bubbles from flowing into the gas permeation section 3 when they are generated in the pipeline, thereby reducing disturbances in the peak shape obtained in the analysis section. It is preferable that the debubble section be provided immediately before or near the gas permeation section 3. In other words, it is preferable that the analysis method according to this embodiment includes a debubble section between the metal ion capture step and the gas permeation step, more preferably between the metal ion capture step and the gasification step. Additionally, a bubble segmentation section that introduces new gas into the pipeline may be provided downstream of the debubble section.

[0058] Furthermore, in the apparatus used in the analytical method according to this embodiment, an autosampler can be used as the sample introduction unit 7. In addition, before sampling, an ultrasonic homogenizer or stirrer may be provided to grind and / or stir the sample.

[0059] Alternatively, the apparatus used in the analytical method according to this embodiment may be further equipped with a dilution device in the middle of the pipeline 9. This allows for automatic dilution within the flow analyzer when dilution is required according to the concentration of the sample. A commercially available automatic dilution device can be suitably used as such a dilution device.

[0060] Furthermore, the apparatus used in the analysis method according to this embodiment may be an apparatus that incorporates an apparatus for pre-treating non-liquid samples such as solids to prepare liquid samples into the sample introduction section 7, or an apparatus that incorporates such an apparatus upstream of the sample introduction section 7. A flow analyzer is an apparatus that analyzes liquid samples using the flow analysis method, and non-liquid samples such as solids cannot be measured directly. Therefore, by incorporating an apparatus for pre-treating non-liquid samples such as solids to prepare liquid samples, it is possible to perform the entire process from pre-treatment to analysis of non-liquid samples such as solids in a consistent manner.

[0061] [2.2] Flow injection analysis method Figure 2 shows a schematic configuration of an example of an apparatus used in a flow analysis method according to another embodiment of the present invention. For the sake of convenience of explanation, components having the same function as those described in "[2.1] Continuous Flow Analysis Method" are denoted by the same reference numerals, and their descriptions are not repeated.

[0062] The apparatus used in the analytical method according to this embodiment is a flow injection analysis (FIA) method in which a reagent is introduced into the flow of a sample that is not segmented by bubbles in a pipeline, a reaction operation is performed, and then the analysis is performed with a detector installed downstream.

[0063] This analytical method includes a carrier introduction step of introducing a carrier into a pipeline 9, a sample introduction step of introducing a sample into the pipeline 9, a metal ion capture step of adding a chelating agent to the flow of the sample being transported through the pipeline 9 to capture metal ions in the sample, a gasification step of making the pH of the sample after metal ion capture being transported through the pipeline 9 alkaline to convert ammonium ions in the sample into gaseous ammonia, a gas permeation step of separating the ammonia gasified in the gasification step using a gas permeable membrane, an absorption step of absorbing the separated gaseous ammonia into an absorbent liquid being transported through the pipeline 9 to convert it into ammonium, an analytical reagent addition step of adding a reagent used in the indophenol blue spectrophotometric method to the flow containing ammonium ions absorbed in the absorbent liquid being transported through the pipeline 9', and an analytical step of quantifying the ammonium ions being transported through the pipeline 9' by the indophenol blue method.

[0064] The analysis method according to this embodiment has the same configuration as the continuous flow analysis method described above, except that a carrier introduction step is performed to introduce a carrier into the pipeline 9 before a sample introduction step to introduce a sample into the pipeline 9, and it does not include a bubble segmentation step.

[0065] The flow analysis method according to this embodiment is a flow injection analysis (FIA) method, in which a carrier is introduced into the pipeline 9 by the carrier introduction unit 10, and a sample is introduced into the flow in the pipeline 9 through the sample introduction unit 7.

[0066] The carrier is not particularly limited as long as it is a liquid that does not have an undesirable effect on the analysis of the sample, and examples include water, surfactants, acidic solutions, and alkaline solutions.

[0067] Other configurations of the analysis method according to this embodiment are as described in "[2.1] Continuous Flow Analysis Method," so their explanation will be omitted here. [Examples]

[0068] The present invention will be described more specifically by the following embodiments, but the present invention is not limited to these embodiments, and embodiments obtained by appropriately combining the technical means disclosed in each embodiment are also included in the scope of the present invention.

[0069] [reagent] The preparation methods for the reagents used in the examples are shown below.

[0070] (1) EDTA reagent Dissolve 7.5g of disodium ethylenediaminetetraacetate (EDTA-2Na) in approximately 600ml of pure water, and adjust the pH to 10 by adding 80g / L sodium hydroxide aqueous solution. Add pure water to the resulting solution to make a total volume of 1000mL.

[0071] (2) Alkaline reagents Approximately 800 mL of pure water was used to dissolve 30 g of boric acid and 30 g of sodium hydroxide. Pure water was then added to the resulting solution to make a total volume of 1000 mL.

[0072] (3) Sulfuric acid reagent 4 mL of concentrated sulfuric acid was dissolved in approximately 800 mL of pure water, and pure water was added to the resulting solution to make a total volume of 1000 mL. 2 mL of 50% Triton X-100 was added to the resulting solution and gently stirred.

[0073] (4) Salicylic acid reagent 0.5 g of sodium hexametaphosphate and 3.0 g of trisodium phosphate dodecahydrate were dissolved in approximately 400 mL of pure water. Then, 50 g of sodium salicylate and 0.25 g of sodium pentacyanonitrosylferrate(III) were dissolved in the solution. Pure water was added to the resulting solution to make 500 mL. Subsequently, 36 g of sodium hydroxide and 36 g of boric acid were dissolved in the resulting solution.

[0074] (5) Hypochlorite reagent 5 mL of sodium hypochlorite (commercially available product with approximately 10% available chlorine) and 5 g of sodium hydroxide were dissolved in approximately 400 mL of pure water. Pure water was added to the resulting solution to make a total volume of 500 mL.

[0075] [Example 1] [Device] A continuous flow analyzer (CFA) as shown in Figure 4 was used. The flow analyzer includes a sample introduction unit for introducing the sample into a conduit 9, a bubble segmentation unit for segmenting the sample introduced into the conduit 9 using air, a chelating agent introduction unit for adding EDTA reagent to the flow of the sample being transported through the conduit 9, a mixing coil 12 for mixing the sample and the added EDTA reagent in each segment segmented by air bubbles, a debubble unit for removing bubbles from the sample being transported through the conduit 9, a bubble segmentation unit for newly segmenting the sample using air from which bubbles have been removed, an alkali introduction unit for adding an alkaline reagent to the flow of the sample being transported through the conduit 9, a mixing coil 12 for mixing the sample and the alkaline reagent in each segment segmented by air bubbles, and a permeable unit for gaseous ammonia generated by the addition of the alkaline reagent. The apparatus included a gas permeation section 3 that allows the permeated gaseous ammonia to be absorbed by a sulfuric acid reagent, which is an absorbent liquid being transported through a pipeline 9'; a bubble segmentation section that performs bubble segmentation with air on the liquid that has absorbed the gaseous ammonia; a first analytical reagent introduction section that introduces salicylic acid reagent into the flow of liquid being transported through the pipeline 9'; a mixing coil 12 that mixes the liquid and the added salicylic acid reagent in each segment segmented by air bubbles; a second analytical reagent introduction section that further introduces hypochlorous acid reagent into the liquid being transported through the pipeline 9'; a mixing coil 12 that mixes the liquid and the added hypochlorous acid reagent in each segment segmented by air bubbles; a heating tank 13 that reacts ammonium ions in the liquid with salicylic acid and hypochlorous acid; and an analysis section 14 that analyzes ammonium ions in the liquid. A flow cell type spectrophotometer (SCIC3000, manufactured by BLTECH Co., Ltd.) was used in the analysis section. The flow cell 14 has a cell length of 50 mm, and measurements were taken at a wavelength of 660 nm. The gas permeable section 3 is equipped with a PTFE membrane filter as the gas permeable film.

[0076] The heating tank 13 has a mixing coil placed inside, and the temperature inside the heating tank 13 is set to 45°C.

[0077] [Measurement of 1 mg / L of ammonia nitrogen] Using the above apparatus, the ammonia nitrogen content of a sample containing 1 mg / L was measured under conditions where the sample contained metal ions and under conditions where it did not contain metal ions.

[0078] In measurements under conditions containing metal ions, a sample containing 1 mg / L of ammonia nitrogen, along with a total of 60 mg / L of zinc and copper ions, was used.

[0079] The results are shown in Figure 5. In Figure 5, (a) shows the measurement results for a sample containing 1 mg / L of ammonia nitrogen, zinc ions, and copper ions, and (b) shows the measurement results for a sample containing 1 mg / L of ammonia nitrogen but no metal ions. The peak height of the absorbance in the measurement results for (a) was 85.78%, and the peak height of the absorbance in the measurement results for (b) was 84.11%, showing similar peak heights regardless of the presence or absence of metal ions. In other words, according to the analytical method of one embodiment of the present invention, accurate quantification can be performed regardless of the presence or absence of metal ions and the degree of consumption of the chelating agent.

[0080] Furthermore, in this example, comparisons were made in the presence and absence of zinc and copper ions. However, since chelating agents such as EDTA are used to capture various other metals, it is believed that accurate quantification can be performed similarly even when metal ions other than zinc and copper are present.

[0081] [Comparative Example 1] [Device] The same apparatus as in Example 1 was used, except that it lacked an alkali introduction section, a mixing coil 12 for mixing the sample and the alkaline reagent within each segment segmented by air bubbles, and a gas permeation section 3 for allowing gaseous ammonia generated by the addition of the alkaline reagent to permeate and for absorbing the permeated gaseous ammonia into the absorption solution. That is, the sample mixed with the EDTA reagent in the same flow as in Example 1 was mixed with the analytical reagent in the same flow as in Example 1, mixed and heated, and the ammonium ions in the sample were analyzed.

[0082] [Measurement of 1 mg / L of ammonia nitrogen] Using the above apparatus, the ammonia nitrogen content of a sample containing 1 mg / L was measured under the same conditions as in Example 1, both under conditions containing metal ions and under conditions not containing metal ions.

[0083] The results are shown in Figure 6. In Figure 6, (a) shows the measurement results for a sample containing 1 mg / L of ammonia nitrogen, zinc ions, and copper ions, and (b) shows the measurement results for a sample containing 1 mg / L of ammonia nitrogen but no metal ions. The peak height of the absorbance in the measurement results for (a) is 85.28%, and the peak height of the absorbance in the measurement results for (b) is 55.79%. This shows that in the presence of metal ions, the chelating agent is consumed to capture the metal and does not contribute to color development, resulting in a higher apparent peak compared to conditions without metal ions. [Industrial applicability]

[0084] This invention enables accurate analysis of ammonia nitrogen even in samples containing relatively high levels of metal ions. Conventional analytical methods, such as those specified in JIS K 0102, require distillation for samples containing inhibitory substances, resulting in excessive heat energy loss, a complicated analytical procedure, and poor accuracy due to the open-system analysis. Therefore, this invention has extremely high industrial value in all technical fields involving the analysis of ammonia nitrogen. [Explanation of symbols]

[0085] 1. Chelating agent introduction section 2. Alkali introduction section 3. Gas permeable section 4. Absorbent liquid introduction section 5 Analysis Department 6. Analytical reagent introduction section 7. Sample introduction section 8. Bubble segment 9, 9' conduit 10. Carrier Introduction Section 11 Gas permeable membrane 12 Mixing coil 13 Heating tank 14 Flow Cells

Claims

1. A step of adding a chelating agent to the sample to capture metal ions, The process involves adjusting the pH of the sample to the alkaline side after metal ion capture, thereby converting ammonium ions in the sample into gaseous ammonia. A process of separating gaseous ammonia using a gas permeable membrane, The process involves absorbing the separated gaseous ammonia into an absorbent solution to convert it into ammonium ions, The process includes an analytical step of quantifying ammonium ions absorbed into an absorption solution using the indophenol blue method, It is a flow analysis method, A method for analyzing ammonia nitrogen, which involves introducing a sample into a pipeline and performing bubble segmentation to create multiple segments within the pipeline, each partitioned by bubbles.

2. The analytical method according to claim 1, wherein the chelating agent is ethylenediaminetetraacetic acid.

3. The analytical method according to claim 1, wherein the gas permeable membrane is a polytetrafluoroethylene membrane filter.

4. The analytical method according to claim 1, wherein in the step of converting ammonium ions in the sample into gaseous ammonia by making the pH of the sample alkaline, sodium hydroxide and boric acid are added to make the pH of the sample solution alkaline.

5. The analytical method according to claim 1, wherein the ammonium ions in a sample are quantified by the salicylic acid indophenol blue method.

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