Method and apparatus for detecting the endpoint of COD analysis titration, and automated COD analyzer.

Abstract

To provide a detection method and detection device for COD analysis titration end point, and a COD automatic analyzer that automatically detect a titration end point that is defined in "oxygen consumption by potassium permanganate at 100°C (CODMn)" in JIS K 0102 17.SOLUTION: A detection method for COD analysis titration end point according to the present invention is a method for detecting a titration end point that is defined in "oxygen consumption by potassium permanganate at 100°C (CODMn)" in JIS K 0102 17, and includes: irradiating an Erlenmeyer flask 115 containing a solution 141 with light with a wavelength of 535-545 nm; receiving light transmitting through the solution 141 and the Erlenmeyer flask 115; and detecting the titration end point from the amount of change in the quantity of received light with a wavelength of 535-545 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for detecting the titration endpoint in COD analysis, as well as an automated COD analyzer. [Background technology]

[0002] JIS K 0102 specifies the testing methods for factory wastewater, and item 17 specifies "the amount of oxygen consumed by potassium permanganate at 100°C (COD)." Mn JIS K 0102, section 17, specifies the amount of oxygen consumed by potassium permanganate at 100°C (COD). Mn The "potassium permanganate" method involves adding silver nitrate solution and sulfuric acid to the sample, then adding 5 mmol / L potassium permanganate solution and heating in boiling water for 30 minutes. The amount of potassium permanganate consumed is expressed as the oxygen equivalent.

[0003] JIS K 0806-1997 contains provisions for automatic measuring instruments for measuring chemical oxygen consumption (COD) in industrial wastewater, etc. The measurement principle of this automatic COD measuring instrument is based on JIS K 0102, section 17, "Oxygen consumption by potassium permanganate at 100°C (COD) Mn In accordance with the "Standard for the Detection of Titration," the redox potential difference method or constant current polarization potential difference method is used to detect the titration endpoint (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-45187 [Overview of the project] [Problems that the invention aims to solve]

[0005] JIS K 0102, Section 17: "Oxygen consumption (COD) due to potassium permanganate at 100°C" MnThe standard method stipulates that the titration endpoint is the point at which the solution turns slightly red. This method is also called the official method, but it is a manual analysis method, and the titration endpoint is confirmed visually by the analyst, so the determination of the titration endpoint can vary slightly depending on the analyst.

[0006] While automating the 17 methods of JIS K 0102 and detecting the titration endpoint mechanically, electrically, or optically can eliminate individual differences among analysts, the detection of the titration endpoint in currently available COD automated meters uses either the oxidation-reduction potential difference method or constant-current polarization potential difference. No COD automated meter has been developed that detects the titration endpoint by detecting a change in color.

[0007] The objective of this invention is to address the issue of "COD consumption by potassium permanganate at 100°C" as specified in JIS K 0102, paragraph 17. Mn The objective is to provide a COD analysis titration endpoint detection method and detection device, as well as an automated COD analyzer, that automatically detects the titration endpoint as defined in "[Regulation No. 2]". [Means for solving the problem]

[0008] This invention relates to JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)." Mn A method for detecting the titration endpoint as defined in ) is a COD analysis titration endpoint detection method characterized by irradiating a conical flask containing a solution with light including light with a wavelength of 535 to 545 nm during titration, receiving the light that has passed through the solution and the conical flask, and detecting the titration endpoint from the change in the amount of light received at a wavelength of 535 to 545 nm.

[0009] This invention relates to JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)." MnA COD analysis titration endpoint detection device that automatically detects the titration endpoint as defined in ")", comprising: a light irradiation means that irradiates a conical flask containing a solution with light including light of a wavelength of 535 to 545 nm from outside the conical flask; a light receiving means positioned opposite to the light irradiation means that receives the light that has passed through the solution and the conical flask outside the conical flask; and a titration endpoint detection means that detects the titration endpoint from the amount of change in the amount of light received at a wavelength of 535 to 545 nm.

[0010] The COD analysis titration endpoint detection apparatus according to the present invention is characterized in that the light irradiation means comprises a light-emitting element that emits light including light with a wavelength of 535 to 545 nm, and a light diffusion means that diffuses the light emitted by the light-emitting element, and the light receiving means comprises a light-collecting means that collects light that has passed through the solution and the Erlenmeyer flask, and a light-receiving element that detects light with a wavelength of 535 to 545 nm from the collected transmitted light.

[0011] In the COD analysis titration endpoint detection apparatus according to the present invention, the Erlenmeyer flask has a stirring bar or stirring blade inside for stirring the solution, and the light irradiation means is characterized by irradiating the bottom surface of the Erlenmeyer flask with light parallel to the bottom surface.

[0012] In the COD analysis titration endpoint detection device according to the present invention, the titration endpoint detection means detects when the change in the amount of light received at a wavelength of 535 to 545 nm exceeds a preset value, and determines the inflection point of the light received amount based on the change in the amount of light received before and after the point in time when the preset value was exceeded, and sets this inflection point as the titration endpoint.

[0013] The present invention is an automated COD analyzer characterized by comprising: an Erlenmeyer flask; a sample collection means for collecting a sample; a reagent addition means for adding a reagent; a water bath for heating the Erlenmeyer flask containing a solution; a stirring means for stirring the solution in the Erlenmeyer flask; a transport means for transporting the Erlenmeyer flask to a predetermined position; a control means for controlling each instrument and each means; and a COD analysis titration endpoint detection device. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a COD analysis titration end point detection method, a detection device, and a COD automatic analyzer that automatically detect the titration end point defined in "Oxygen consumption by potassium permanganate at 100 °C (COD Mn )" of JIS K 0102.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a diagram schematically showing the configuration of a COD analysis titration end point detection device 1 according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the light irradiation and light reception要领 of the COD analysis titration end point detection device 1 according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a diagram for explaining the titration end point detection要领 of the COD analysis titration end point detection device 1 according to the first embodiment of the present invention. [Figure 4] FIG. 22 is a diagram schematically showing the configuration of a COD automatic analyzer 100 according to the second embodiment of the present invention.

Mode for Carrying Out the Invention

[0016] FIG. 1 is a diagram schematically showing the configuration of a COD analysis titration end point detection device 1 according to the first embodiment of the present invention. FIG. 2 is a diagram for explaining the light irradiation and light reception要领 of the COD analysis titration end point detection device 1 according to the first embodiment, and FIG. 3 is a diagram for explaining the titration end point detection要领 of the COD analysis titration end point detection device 1 according to the first embodiment.

[0017] The COD analysis titration end point detection device 1 according to the first embodiment of the present invention is based on "Oxygen consumption by potassium permanganate at 100 °C (COD Mn It should be noted that the term "要领" in the original text seems to be an incorrect or unclear expression. It might be a misspelling or an inappropriate term. In the translation, it is left as it is for the sake of following the translation rules precisely. If this is a specific technical or domain-specific term that has a correct English equivalent, it should be replaced accordingly for a more accurate translation.This device automatically detects the titration endpoint as defined in "[...]", and comprises a light irradiation means 10 that irradiates a conical flask 115 containing solution 141 with light of a predetermined wavelength from the outside of the conical flask 115, a light receiving means 20 that receives light transmitted through the solution 141 and the conical flask 115 on the outside of the conical flask 115, and a titration endpoint detection means 40 that detects the titration endpoint from the change in the amount of light received at a predetermined wavelength.

[0018] Solution 141 is used to analyze the sample subject to COD analysis according to JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)". Mn This is a solution to which the specified drugs have been added and which has undergone a prescribed procedure, and is then titrated with a 5 mmol / L potassium permanganate solution.

[0019] The Erlenmeyer flask 115 conforms to JIS K 0102, item 17, "Oxygen consumption (COD) due to potassium permanganate at 100°C". Mn This is a 300 mL Erlenmeyer flask as specified in the ")" standard. Some commercially available 300 mL Erlenmeyer flasks have the manufacturer's name, logo, etc. on the wall 116, but a plain, unmarked Erlenmeyer flask 115 without these markings is preferred.

[0020] In the COD analysis titration endpoint detection device 1, light is shone from the outside of the Erlenmeyer flask 115, and the light that has passed through the solution 141 and the Erlenmeyer flask 115 is received on the outside of the Erlenmeyer flask 115. The titration endpoint is detected from the change in the amount of light received at a predetermined wavelength. For this reason, manufacturer names, logos, etc. on the wall 116 of the Erlenmeyer flask 115 are undesirable as they interfere with the transmission of light.

[0021] The Erlenmeyer flask 115 has a supply tube 145 inserted through its top opening 119 to supply potassium permanganate solution for titration, and a stirring blade 142 for stirring the solution 141. The supply tube 145 is connected to a supply means (not shown), such as a titration burette, and the potassium permanganate solution is supplied at a constant rate through the supply means.

[0022] The light irradiation means 10 comprises a light-emitting element 12 that emits light of a predetermined wavelength and a light diffusion means 15 that diffuses the light emitted by the light-emitting element 12. In this embodiment, the predetermined wavelength is 535 to 545 nm, and the light of the predetermined wavelength is green light. The light-emitting element 12 only needs to be able to emit light of a wavelength of 535 to 545 nm with an intensity above a certain level, and a surface-mount type green LED can be used.

[0023] This COD analysis titration endpoint detection device 1 utilizes the fact that solution 141 changes from colorless to red at the titration endpoint. It irradiates solution 141 with green light, which is the complementary color to red, and detects the titration endpoint from the amount of light transmitted. The light-emitting element 12 preferably emits only light with a wavelength of 535 to 545 nm, but it may also contain light with wavelengths before and after 535 to 545 nm as the main component. If the light-emitting element 12 contains little light with a wavelength of 535 to 545 nm, the overall light intensity needs to be increased, resulting in poor efficiency.

[0024] This COD analysis titration endpoint detection device 1 detects the titration endpoint from the change in the amount of light received (transmitted) at a predetermined wavelength. Therefore, to detect the titration endpoint with high sensitivity, it is preferable that the change in the amount of transmittance at the predetermined wavelength is large. To increase the change in transmittance, it is preferable to irradiate the solution 141 with light that penetrates over a long distance.

[0025] Therefore, it is preferable to position the light-emitting element 12 so that the irradiated light is parallel to the bottom surface 117 of the Erlenmeyer flask 115 (see Figure 2(A)). Since the Erlenmeyer flask 115 is usually placed on a horizontal surface, irradiating the light parallel to the bottom surface 117 of the Erlenmeyer flask 115 increases the distance the light travels through the solution 141. Here, "parallel" includes cases where the light can be considered substantially parallel, and cases where the light is mostly parallel or can be considered substantially parallel.

[0026] When irradiating solution 141 with light in a non-contact manner, one possible method is to irradiate the bottom surface 117 of the Erlenmeyer flask 115 at an angle, as shown in Figure 2(C), or to irradiate the bottom surface 117 of the Erlenmeyer flask 115 perpendicularly, as shown in Figure 2(D). However, the transmission distance of the irradiated light through solution 141 is short, which is undesirable.

[0027] Figure 2(B) is a schematic plan view showing what happens when light is shone from the outside of the Erlenmeyer flask 115. As shown in Figure 2(B), the Erlenmeyer flask 115 has a stirring blade 142 for stirring the solution 141, so this part becomes a dead space (shaded area in the figure) through which light cannot pass. Therefore, it is preferable to position the light irradiation means 10 so that light is broadly shone onto the solution 141 inside the Erlenmeyer flask 115 in a plan view.

[0028] In this embodiment, a light-diffusing means 15 is placed between the light-emitting element 12 and the Erlenmeyer flask 115 in order to broadly irradiate the entire solution 141 in the Erlenmeyer flask 115 with light. An example of the light-diffusing means 15 is a frosted glass plate 15.

[0029] If a light-emitting element 12 with a wide light irradiation surface is used, it is possible to irradiate the solution 141 in the Erlenmeyer flask 115 with light over a wide area, but the device becomes large. When the COD analysis titration endpoint detection device 1 is incorporated into the COD automatic analyzer 100 of the second embodiment, it is preferable that the device be as compact as possible. In this COD analysis titration endpoint detection device 1, a light diffusion means 15 is used, so it is possible to use a relatively small light-emitting element 12, and the overall device can be made compact.

[0030] The light-receiving means 20 includes a double-sided convex lens 22, an N / D filter 24, a green filter 26, and a light-receiving element 28, and receives light that has passed through the solution 141 and the Erlenmeyer flask 115.

[0031] The double-sided convex lens 22 is positioned to face the light-emitting element 12, sandwiching the Erlenmeyer flask 115, and focuses the light transmitted through the solution 141 and the Erlenmeyer flask 115. While other devices or means may be used to focus the light transmitted through the solution 141 and the Erlenmeyer flask 115, the double-sided convex lens 22 has the advantage of a wide focusing range and short focal length, even with a relatively small lens diameter, allowing for a more compact device.

[0032] The N / D filter 24 is a neutral density filter that reduces the amount of light that passes through the double-sided convex lens 22. A variable type N / D filter 24 that allows adjustment of the light reduction amount is preferable. If it is not necessary to reduce the amount of light that passes through the double-sided convex lens 22, the N / D filter 24 may be omitted.

[0033] The green filter 26 is a filter that transmits light of a predetermined wavelength from the light that has passed through the N / D filter 24.

[0034] The light-receiving element 28 is an element that receives light transmitted through the green filter 26. The light-receiving element 28 can be any element that can sensitively receive light of a predetermined wavelength.

[0035] As described above, the light emitted from the light-emitting element 12, including light with wavelengths of 535 to 545 nm, is diffused by the light-diffusing means 15 and then incident on the Erlenmeyer flask 115 containing the solution 141. Of this light, the light that passes through the Erlenmeyer flask 115 containing the solution 141 is focused by the double-sided convex lens 22, the light intensity is adjusted by the N / D filter 24, and the light that passes through the green filter 26 is received by the photodetector 28.

[0036] The titration endpoint detection means 40 is a data processing device 40 connected to the light receiving means 20 that detects the titration endpoint from the change in the amount of light received at a predetermined wavelength. In this embodiment, a computer equipped with a program for detecting the titration endpoint is used as the data processing device.

[0037] The data processing device 40 is a known computer equipped with input / output means, storage means, display means, and control / calculation means, and acquires the amount of light of a predetermined wavelength received by the photodetector 28 via the amplifier 30 and A / D converter 35, and detects the titration endpoint according to the installed program.

[0038] This section explains the procedure for detecting the titration endpoint and calculating the volume of 5 mmol / L potassium permanganate solution required for the titration. The titration is initiated by injecting 5 mmol / L potassium permanganate solution into the Erlenmeyer flask 115 through the supply tube 145, and the injection of 5 mmol / L potassium permanganate solution continues until the titration endpoint has been reached.

[0039] From the start of the titration until near the titration endpoint, the solution 141 in the Erlenmeyer flask 115 is almost colorless and transparent. The titration endpoint is determined according to JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)". Mn As specified in the document, the solution 141 should be kept until it shows a slight reddish color.

[0040] Therefore, the amount of light of a predetermined wavelength irradiated from the light irradiation means 10 toward the Erlenmeyer flask 115, transmitted through the Erlenmeyer flask 115 and the solution 141, and received by the light receiving means 20 remains almost constant without significant attenuation from the start of titration to near the titration endpoint, and decreases sharply at the titration endpoint. The data processing device 40 uses this relationship to detect the titration endpoint. The specific detection method will be explained below with reference to Figure 3.

[0041] The data processing device 40 acquires light intensity data of a predetermined wavelength from the photodetector 28 at the start of titration and stores it in the storage means. Thereafter, it acquires light intensity data of a predetermined wavelength from the photodetector 28 at predetermined intervals until after the completion of the titration endpoint, and stores the acquired light intensity data and the elapsed time from the start of titration in the storage means, starting from the titration start time. When the data processing device 40 acquires light intensity data, it compares it with previously acquired light intensity data and calculates the change in light intensity. When it detects that the change in light intensity ΔC exceeds a predetermined set value, it sets that point as the provisional titration endpoint. The set value is, for example, a 10% reduction in light intensity.

[0042] Even if the data processing device 40 detects a provisional titration endpoint, the titration operation continues without termination, and the data processing device 40 acquires light intensity data for a further predetermined time after the detection of the provisional titration endpoint. The titration operation terminates when the further predetermined time has elapsed since the detection of the provisional titration endpoint. This predetermined time is the time required to acquire approximately 3 to 5 light intensity data points.

[0043] Once the data processing device 40 has completed acquiring all the light intensity data, it divides the light intensity data into light intensity data before the detection of the provisional titration endpoint and light intensity data after the detection of the provisional titration endpoint, starting from the point of detection, and obtains relational equations (1) and (2) for each with respect to the elapsed time of the light intensity data. Relational equations (1) and (2) are linear equations.

[0044] The data processing device 40 determines the intersection of two relational equations: equation (1) for the elapsed time of light intensity data before the detection of the provisional titration endpoint, and equation (2) for the elapsed time of light intensity data after the detection of the provisional titration endpoint. This intersection is defined as the titration endpoint. As can be seen from Figure 3, the intersection of the two relational equations is the inflection point of the light intensity. Once the titration endpoint is calculated, the elapsed time θ from the start of the titration is determined. F Since we can see this, this elapsed time θ F The amount of 5 mmol / L potassium permanganate solution required for the titration is calculated from the supply rate of the 5 mmol / L potassium permanganate solution.

[0045] As described above, by using the COD analysis titration endpoint detection device 1 of this embodiment, the COD analysis titration endpoint detection device can be performed according to JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)". Mn The titration endpoint specified in ) can be automatically detected.

[0046] Regarding the COD analysis titration endpoint detection device 1 of this embodiment, a prototype COD analysis titration endpoint detection device consisting of the same configuration has been fabricated, and COD analysis has been performed using actual samples to confirm that the titration endpoint can be automatically detected with good reproducibility.

[0047] One method for detecting the titration endpoint in COD analysis is to use a potentiometer. However, this method requires time for the potential to stabilize. This COD analysis titration endpoint detection device 1 detects the titration endpoint based on the color change of solution 141, resulting in a highly responsive system that allows for rapid detection of the titration endpoint.

[0048] As described above, this COD analysis titration endpoint detection device 1 incorporates features to efficiently irradiate the Erlenmeyer flask 115 and the solution 141 with light, and to efficiently receive the light that has passed through the Erlenmeyer flask 115 and the solution 141, thus allowing the COD analysis titration endpoint detection device 1 to be made compact.

[0049] Furthermore, since this COD analysis titration endpoint detection device 1 is non-contact with the Erlenmeyer flask 115 and the solution 141, maintenance is easy and the maintenance cycle can be extended. In addition, since this COD analysis titration endpoint detection device 1 does not require the placement of optical fiber or other light irradiation means and light receiving means for receiving transmitted light inside the Erlenmeyer flask 115, the device configuration is simple, and the replacement of the Erlenmeyer flask 115 is also easy. Therefore, the COD analysis time, including preparation time, can be shortened.

[0050] Figure 4 is a schematic diagram showing the configuration of the COD automatic analyzer 100 according to the second embodiment of the present invention. Components identical to those in the COD analysis titration endpoint detection device 1 of the first embodiment shown in Figure 1 are denoted by the same reference numerals and their descriptions are omitted.

[0051] The COD automatic analyzer 100 is based on JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)". Mn This device automatically analyzes COD based on the method specified in ) and incorporates the COD analysis titration endpoint detection device 1 of the first embodiment.

[0052] The COD automatic analyzer 100 includes a sample preparation unit 110, a heating unit 130, a COD measurement unit 140, a drainage unit 150, a washing unit 160, a moving actuator 170 for moving the Erlenmeyer flask 115, and a control PLC 180 for controlling the movement of the entire device.

[0053] The sample preparation unit 110 includes means for collecting a sample, and JIS K 0102 17 "Oxygen consumption by potassium permanganate at 100°C (COD) Mn The system is equipped with means for adding and mixing a predetermined amount of the drug specified in "[ ]" to prepare a sample.

[0054] Specifically, the sample preparation unit 110 takes an appropriate amount of sample into a 300 mL Erlenmeyer flask 115 via a preparative burette 125, adds water to make a total volume of 100 mL, adds 10 mL of sulfuric acid (1+2), adds 5 mL of silver nitrate solution (200 g / L) while stirring, and then adds 10 mL of 5 mmol / L potassium permanganate solution and stirs to prepare the sample for analysis.

[0055] The heating unit 130 is equipped with a boiling water bath 135, and the sample prepared in the sample preparation unit 110 is heated in the boiling water bath 135 for 30 minutes.

[0056] The COD measurement unit 140 is equipped with a COD analysis titration endpoint detection device 1, a stirrer 143, and a titration burette 147 for supplying a 5 mmol / L potassium permanganate solution, and performs COD analysis of the sample (solution 141). The Erlenmeyer flask 115 containing the solution 141 heated in the heating unit 130 is placed at an intermediate point on the line connecting the light irradiation means 10 and the light receiving means 20 that constitute the COD analysis titration endpoint detection device 1.

[0057] Subsequently, in the COD measurement unit 140, a stirring blade 142 is inserted into the Erlenmeyer flask 115, 10 mL of sodium oxalate solution (12.5 mmol / L) is added, and the mixture is reacted while stirring. Then, a 5 mmol / L potassium permanganate solution is supplied via the titration burette 147, and the titration endpoint is detected via the COD analysis titration endpoint detection device 1.

[0058] The drainage section 150 is equipped with a drainage pump 152 and a drainage tank 154, and recovers the solution 141 after titration as drainage.

[0059] The washing unit 160 is equipped with a pure water pump 162 and a pure water tank 164, and washes the Erlenmeyer flask 115 from which the solution 141 has been collected with pure water. After washing, the Erlenmeyer flask 115 is sent to the sample preparation unit 110.

[0060] The moving actuator 170 has a gripping device 175 for gripping the Erlenmeyer flask 115, and transports and places the Erlenmeyer flask 115 to a predetermined position based on commands from the control PLC 180.

[0061] The control PLC 180 is a programmable logic controller that controls the overall operation of the COD automatic analyzer 100, and controls each device and means to operate according to predetermined procedures.

[0062] The COD automatic analyzer 100 of the second embodiment, consisting of the above, has a control PLC 180 that controls the amount of oxygen consumed by potassium permanganate at 100°C (COD). Mn Each instrument and means is controlled in accordance with the method specified in JIS K 0102, and the COD analysis titration endpoint detection device 1 automatically detects the titration endpoint. Therefore, by using the COD automatic analyzer 100, the method specified in JIS K 0102, item 17, "Oxygen consumption by potassium permanganate at 100°C (COD)" is performed. Mn It is possible to automate COD analysis in accordance with the method specified in )."

[0063] The COD analysis titration endpoint detection method and detection device and the COD automatic analyzer according to the present invention have been described above using the COD analysis titration endpoint detection device 1 of the first embodiment and the COD automatic analyzer 100 of the second embodiment. However, the COD analysis titration endpoint detection method and detection device and the COD automatic analyzer according to the present invention are not limited to the above embodiments and can be modified without changing the gist of the invention. [Explanation of symbols]

[0064] 1. COD analysis titration endpoint detection device 10 Light irradiation means 12 Light-emitting elements 15 Light Diffusion Means 20 Light receiving means 28. Photodetector 40. Titration endpoint detection means 100 COD automatic analyzer 110 Sample Creation Department 115 Erlenmeyer flasks 130 Heating section 140 COD measurement section 141 Solution 142 Agitator blades 150 Drainage section 160 Cleaning section 170 Mobile Actuator 180 Control PLCs

Claims

1. JIS K 0102-17 "Oxygen consumption (COD) due to potassium permanganate at 100°C" Ｍｎ A method for detecting the titration endpoint as specified in ) A method for detecting the endpoint of a COD analysis titration, characterized by irradiating a conical flask containing a solution with light including light with a wavelength of 535 to 545 nm during titration, receiving the light that has passed through the solution and the conical flask, and detecting the titration endpoint from the change in the amount of light received at a wavelength of 535 to 545 nm.

2. JIS K 0102-17 "Oxygen consumption (COD) due to potassium permanganate at 100°C" Ｍｎ A device for automatically detecting the titration endpoint as defined in ) A light irradiation means that irradiates a conical flask containing a solution with light containing light with a wavelength of 535 to 545 nm from outside the conical flask, A light receiving means, positioned opposite the light irradiation means, receives light transmitted through the solution and the Erlenmeyer flask outside the Erlenmeyer flask. A titration endpoint detection means for detecting the titration endpoint from the change in the amount of light received at wavelengths of 535 to 545 nm, A COD analysis titration endpoint detection device characterized by comprising the following features.

3. The light irradiation means comprises a light-emitting element that emits light including light with a wavelength of 535 to 545 nm, and a light diffusion means that diffuses the light emitted by the light-emitting element. The light-receiving means includes a light-collecting means for collecting light that has passed through the solution and the Erlenmeyer flask, and a light-receiving element for detecting light with a wavelength of 535 to 545 nm from the collected transmitted light. The COD analysis titration endpoint detection device according to claim 2, characterized by comprising the above.

4. The aforementioned Erlenmeyer flask has a stirring bar or blade inside for stirring the solution, The COD analysis titration endpoint detection apparatus according to claim 2, characterized in that the light irradiation means irradiates light onto the bottom surface of the Erlenmeyer flask parallel to the surface.

5. The titration endpoint detection device according to claim 2, characterized in that when the titration endpoint detection means detects that the change in the amount of light received at a wavelength of 535 to 545 nm exceeds a preset value, it determines the inflection point of the light received amount based on the change in the amount of light received before and after the point in time when the preset value was exceeded, and sets this inflection point as the titration endpoint.

6. A triangular flask and A sampling means for collecting a sample, A reagent addition means for adding reagents, A water bath for heating the Erlenmeyer flask containing the solution, A stirring means for stirring the solution in the Erlenmeyer flask, A conveying means for transporting the aforementioned Erlenmeyer flask to a predetermined position, Control means for controlling each device and each means, The COD analysis titration endpoint detection device according to claim 2, An automated COD analyzer characterized by having the following features.

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