Detection method and detection device for cod analysis titration end point, and cod automatic 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 device for detecting the titration end point in COD analysis, and to a COD automatic analyzer. [Background technology]

[0002] JIS K 0102 specifies the test method for industrial wastewater, and item 17 states "Oxygen consumption (COD) by potassium permanganate at 100℃" Mn )" is stipulated in JIS K 0102, 17 "Oxygen consumption by potassium permanganate at 100℃ (COD Mn ) is a method in which a silver nitrate solution and sulfuric acid are added to a sample, followed by the addition of a 5 mmol / L potassium permanganate solution and heating in boiling water for 30 minutes; the amount of potassium permanganate consumed is expressed as oxygen equivalents.

[0003] JIS K 0806-1997 contains regulations on automatic measuring instruments for measuring chemical oxygen consumption (COD) in industrial wastewater. The measurement principle of this COD automatic measuring instrument is as follows: JIS K 0102, 17 "Oxygen consumption by potassium permanganate at 100°C (COD Mn ) and the end point of the titration is detected by oxidation-reduction potentiometry or constant current polarization potential difference (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-45187 A Summary of the Invention [Problem to be solved by the invention]

[0005] JIS K 0102, No. 17 "Oxygen consumption by potassium permanganate at 100℃ (COD Mn) specifies that the point at which the solution turns slightly red is the titration endpoint. This method is also known as the official method, but it is a manual analysis method, and the analyst visually checks the titration endpoint, so the judgment of the titration endpoint varies slightly depending on the analyst.

[0006] If the 17 methods of JIS K 0102 were automated and the titration endpoint was detected mechanically, electrically or optically, the individual differences between analysts could be eliminated. However, the endpoint of titration in the automatic COD measuring instruments currently in practical use is detected by the oxidation-reduction potential difference method or constant current polarization potential difference, and no automatic COD measuring instrument has been developed that detects the titration endpoint by detecting a color change.

[0007] The object of the present invention is to obtain the oxygen consumption (COD) of potassium permanganate at 100°C as specified in JIS K 0102, 17. Mn The present invention provides a titration end point detection method and detection device for automatically detecting the titration end point specified in the "COD analysis ... [Means for solving the problem]

[0008] The present invention is based on JIS K 0102, 17 "Oxygen consumption (COD) by potassium permanganate at 100°C" Mn The titration endpoint detection method is defined in the "COD analysis titration endpoint detection method for COD analysis" (hereinafter referred to as "the method for detecting the endpoint of a titration"), characterized in that, during titration, a conical flask containing a solution is irradiated with light having a wavelength of 535 to 545 nm, the light transmitted through the solution and the conical flask is received, and the titration endpoint is detected from the change in the amount of received light having a wavelength of 535 to 545 nm.

[0009] The present invention is based on JIS K 0102, 17 "Oxygen consumption (COD) by potassium permanganate at 100°C" MnThe titration endpoint detection device for COD analysis is characterized in that it comprises: a light irradiating means for irradiating a solution-containing Erlenmeyer flask with light including light having a wavelength of 535 to 545 nm from outside the Erlenmeyer flask; a light receiving means disposed opposite the light irradiating means for receiving light outside the Erlenmeyer flask that has passed through the solution and the Erlenmeyer flask; and a titration endpoint detection means for detecting the titration endpoint from a change in the amount of received light having a wavelength of 535 to 545 nm.

[0010] In the COD analysis titration endpoint detection device of the present invention, the light irradiating means comprises a light emitting element that emits light including light with a wavelength of 535 to 545 nm, and a light diffusing 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 device of the present invention, the Erlenmeyer flask has a stirring bar or stirring blade therein for stirring the solution, and the light irradiation means is characterized in that it irradiates light parallel to the bottom surface of the Erlenmeyer flask.

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

[0013] The present invention provides an automatic COD analyzer comprising an Erlenmeyer flask, a sampling means for sampling a sample, a reagent adding 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 transporting means for transporting the Erlenmeyer flask to a predetermined position, a control means for controlling each device and each means, and the COD analysis titration endpoint detection device. Effect of the Invention

[0014] According to the present invention, the oxygen consumption (COD) of potassium permanganate at 100°C in accordance with JIS K 0102-17 is Mn The present invention provides a titration end point detection method and detection device for automatically detecting the titration end point specified in the "COD analysis titration end point detection method and detection device" and an automatic COD analyzer. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a schematic configuration of a COD analysis titration endpoint detection device 1 according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram for explaining a method for irradiating and receiving light in the COD analysis titration endpoint detection device 1 according to the first embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram for explaining a titration end point detection procedure of the COD analysis titration end point detection device 1 of the first embodiment of the present invention. [Figure 4] FIG. 1 is a diagram illustrating a schematic configuration of a COD automatic analyzer 100 according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Fig. 1 is a diagram showing a schematic configuration of a COD analysis titration endpoint detection device 1 according to a first embodiment of the present invention. Fig. 2 is a diagram for explaining how light is irradiated and received in the COD analysis titration endpoint detection device 1 according to the first embodiment, and Fig. 3 is a diagram for explaining how the titration endpoint detection device 1 according to the first embodiment detects the titration endpoint.

[0017] The COD analysis titration end point detection device 1 of the first embodiment of the present invention is a device that detects oxygen consumption (COD) of potassium permanganate at 100°C in accordance with JIS K 0102-17. MnThe apparatus is an apparatus for automatically detecting the titration end point defined in the "Titing End Point Detection System for a Titration of a Solution 141" and is provided with a light irradiating means 10 for irradiating a solution 141-containing Erlenmeyer flask 115 with light of a predetermined wavelength from the outside of the Erlenmeyer flask 115, a light receiving means 20 for receiving the light transmitted through the solution 141 and the Erlenmeyer flask 115 outside the Erlenmeyer flask 115, and a titration end point detecting means 40 for detecting the titration end point from the change in the amount of received light of the predetermined wavelength.

[0018] Solution 141 is a sample to be analyzed for COD, and the COD concentration is calculated based on the results of JIS K 0102, 17 "Oxygen consumption by potassium permanganate at 100°C (COD Mn )" and undergoes a specified process, then is titrated with 5 mmol / L potassium permanganate solution.

[0019] Erlenmeyer flask 115 is JIS K 0102 17 "Oxygen consumption by potassium permanganate at 100℃ (COD Mn )". Some commercially available 300 mL Erlenmeyer flasks have the manufacturer's name or logo on the wall 116, but a plain, unbranded Erlenmeyer flask 115 without these is preferable.

[0020] In the COD analysis titration endpoint detection device 1, light is irradiated from the outside of the Erlenmeyer flask 115, the light transmitted through the solution 141 and the Erlenmeyer flask 115 is received outside the Erlenmeyer flask 115, and the titration endpoint is detected from the change in the amount of received light at a specified wavelength. For this reason, the manufacturer's name, logo, etc. on the wall surface 116 of the Erlenmeyer flask 115 are undesirable as they impede the transmission of light.

[0021] A supply pipe 145 for supplying potassium permanganate solution for titration from an upper opening 119 and a stirring blade 142 for stirring the solution 141 are inserted into the Erlenmeyer flask 115. The supply pipe 145 is connected to a supply means (not shown) such as a titration burette, and the potassium permanganate solution is supplied at a constant supply rate via the supply means.

[0022] The light irradiation means 10 includes a light emitting element 12 that emits light of a predetermined wavelength, and a light diffusing 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 may be a surface-mounted green LED as long as it can emit light of a wavelength of 535 to 545 nm with a certain intensity or higher.

[0023] The COD analysis titration endpoint detection device 1 utilizes the change in color of the solution 141 from colorless to red at the titration endpoint, irradiates the solution 141 with green light, which is complementary to red, and detects the titration endpoint from the amount of light transmitted through it. The light emitting element 12 is preferably one that emits only light with a wavelength of 535 to 545 nm, but may be one that has a wavelength of 535 to 545 nm as the main component and also contains light with wavelengths around that wavelength. If the light emitted from the light emitting element 12 contains only a small amount of light with a wavelength of 535 to 545 nm, it is inefficient because it is necessary to increase the overall light amount.

[0024] Since the COD analysis titration endpoint detection device 1 detects the titration endpoint from the change in the amount of received light (transmittance) at a specified wavelength, it is preferable that the change in the amount of transmittance at the specified wavelength is large in order to detect the titration endpoint with high sensitivity. To increase the change in the amount of transmittance, it is preferable to irradiate the solution 141 with light so that the irradiated light transmits a long distance through the solution 141.

[0025] For the above reasons, it is preferable to install the light emitting element 12 so that the irradiated light is parallel to the bottom surface 117 of the Erlenmeyer flask 115 (see FIG. 2(A)). Since the Erlenmeyer flask 115 is usually placed on a horizontal surface, the distance that the light transmits through the solution 141 is increased by irradiating the light parallel to the bottom surface 117 of the Erlenmeyer flask 115. Here, "parallel" includes cases where the light can be regarded as substantially parallel, and cases where the light can be regarded as mostly parallel or substantially parallel.

[0026] When irradiating the solution 141 with light in a non-contact manner, a method in which the light irradiation means is irradiated at an angle to the bottom surface 117 of the Erlenmeyer flask 115 as shown in FIG. 2(C) or a method in which the light irradiation means is irradiated perpendicularly to the bottom surface 117 of the Erlenmeyer flask 115 as shown in FIG. 2(D) can be considered. However, these methods are not preferable because the transmission distance of the irradiated light in the solution 141 is short.

[0027] Fig. 2(B) is a plan view that shows a schematic view of the Erlenmeyer flask 115 when light is irradiated from the outside. As shown in Fig. 2(B), the Erlenmeyer flask 115 has stirring blades 142 for stirring the solution 141, and this portion becomes a dead space (shaded portion in the figure) through which light cannot pass. Therefore, it is preferable to arrange the light irradiating means 10 so that the solution 141 in the Erlenmeyer flask 115 is irradiated with light over a wide area in a plan view.

[0028] In this embodiment, in order to widely irradiate the entire solution 141 in the Erlenmeyer flask 115 with light, a light diffusion means 15 is provided between the light emitting element 12 and the Erlenmeyer flask 115. As the light diffusion means 15, a ground glass plate 15 is exemplified.

[0029] If a light emitting element 12 having a wide light irradiation surface is used, it is possible to widely irradiate the solution 141 in the Erlenmeyer flask 115 with light, but the device will become 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 the COD analysis titration endpoint detection device 1, the light diffusing means 15 is used, which makes it possible to use a relatively small light emitting element 12, and the device as a whole 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 transmitted through the solution 141 and the Erlenmeyer flask 115 .

[0031] The double-convex lens 22 is disposed facing the light-emitting element 12 across the Erlenmeyer flask 115, and focuses the light that has passed through the solution 141 and the Erlenmeyer flask 115. The device or means for focusing the light that has passed through the solution 141 and the Erlenmeyer flask 115 may be something other than the double-convex lens 22, but the double-convex lens 22 has the advantage that the focusing range is wide even with a relatively small lens diameter, and the focal length is short, allowing the device to be made compact.

[0032] The N / D filter 24 is a light-reducing filter that reduces the amount of light that has passed through the double-convex lens 22. The N / D filter 24 is preferably a variable type that can adjust the amount of light reduction. When there is no need to reduce the amount of light that has passed through the double-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 out of the light that has passed through the N / D filter 24 .

[0034] The light receiving element 28 is an element that receives light that has passed through the green filter 26. The light receiving element 28 may be any element that can receive light of a predetermined wavelength with good sensitivity.

[0035] As described above, the light containing light of wavelengths of 535 to 545 nm irradiated from the light-emitting element 12 is diffused by the light diffusion means 15 and then enters 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 concentrated by the double-sided convex lens 22, the amount of light is adjusted by the N / D filter 24, and the light that passes through the green filter 26 is received by the light-receiving element 28.

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

[0037] The data processing device 40 is a known computer equipped with input / output means, memory means, display means, and control / calculation devices, and inputs the amount of light of a specified wavelength received by the light receiving element 28 via the amplifier 30 and A / D converter 35, and detects the titration end point according to the installed program.

[0038] The following describes how to detect the titration end point and how to calculate the amount of 5 mmol / L potassium permanganate solution required for the titration. The titration is started by injecting 5 mmol / L potassium permanganate solution into the Erlenmeyer flask 115 through the supply pipe 145, and the injection of the 5 mmol / L potassium permanganate solution is continued until the titration end point is reached.

[0039] The solution 141 in the Erlenmeyer flask 115 is almost colorless and transparent from the start of the titration to near the end point of the titration. The end point of the titration is determined by the measurement of the oxygen consumption (COD) of potassium permanganate at 100°C in accordance with JIS K 0102-17. Mn ) until the solution 141 takes on a slight red color.

[0040] Therefore, the amount of light of a predetermined wavelength that is irradiated from the light irradiating means 10 toward the Erlenmeyer flask 115, passes through the Erlenmeyer flask 115 and the solution 141, and is received by the light receiving means 20 is substantially constant without significant attenuation from the start of titration to near the titration end point, and then significantly decreases at the titration end point. The data processing device 40 detects the titration end point using this relationship. A specific detection method will be described below with reference to FIG. 3.

[0041] The data processing device 40 acquires light intensity data of a predetermined wavelength from the light receiving element 28 at the same time as the titration starts, and stores it in the storage means. Thereafter, light intensity data of a predetermined wavelength is acquired from the light receiving element 28 at predetermined intervals until the titration end point is reached, and starting from the titration start time, the acquired light intensity data is linked to the elapsed time from the titration start and stored in the storage means. When the data processing device 40 acquires light intensity data, it compares it with the light intensity data acquired previously to calculate the amount of change in the amount of light. When it detects that the amount of change in the amount of light, ΔC, exceeds a predetermined set value, it sets that time as the tentative titration end point. The set value is, for example, a 10% decrease in the amount of light.

[0042] Even if the data processing device 40 detects the tentative titration end point, the titration operation continues without ending, and the data processing device 40 acquires light intensity data for a further preset time from the detection of the tentative titration end point. The titration operation ends when a further preset time has elapsed from the detection of the tentative titration end point. This preset time is the time required to acquire about 3 to 5 pieces of light intensity data.

[0043] When the data processing device 40 has acquired all the light intensity data, it divides the light intensity data into the light intensity data before the tentative titration end point detection and the light intensity data after the tentative titration end point detection, and obtains the relational expressions (1) and (2) of the light intensity data with respect to the elapsed time for each of them. The relational expressions (1) and (2) are linear expressions.

[0044] The data processing device 40 obtains an intersection point between the two relational expressions (1) for the elapsed time of the light intensity data before the detection of the tentative titration end point and (2) for the elapsed time of the light intensity data after the detection of the tentative titration end point, and determines this intersection point as the titration end point. As can be seen from FIG. 3, the intersection point of the two relational expressions is the bending point of the amount of received light. When the titration end point is calculated, the elapsed time θ F Since we know the elapsed time θ F Calculate the amount of 5 mmol / L potassium permanganate solution required for titration from the above and the supply rate of the 5 mmol / L potassium permanganate solution.

[0045] As described above, by using the COD analysis titration end point detection device 1 of this embodiment, the COD analysis titration end point detection device 1 can be used to detect the amount of oxygen consumed by potassium permanganate at 100° C. (COD Mn ) 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 having the same configuration has been manufactured, and COD analysis has been performed using actual samples, and it has been confirmed that the titration endpoint can be automatically detected with good reproducibility.

[0047] As a method for detecting the titration end point in COD analysis, there is a method for detecting the end point using a potential difference. In the method for detecting the titration end point using a potential difference, it takes time for the potential to stabilize, but the titration end point detection device 1 for COD analysis detects the titration end point based on the color change of the solution 141, so it has good responsiveness and can quickly detect the titration end point.

[0048] As described above, in the present COD analysis titration endpoint detection device 1, the device is devised to efficiently irradiate light onto the Erlenmeyer flask 115 and the solution 141, and to efficiently receive light that has passed through the Erlenmeyer flask 115 and the solution 141, so that the COD analysis titration endpoint detection device 1 can be made compact.

[0049] Furthermore, since the present COD analysis titration endpoint detection device 1 does not come into contact with the Erlenmeyer flask 115 and the solution 141, maintenance is easy and the maintenance interval can be extended. Furthermore, since the present COD analysis titration endpoint detection device 1 does not require the placement of a light irradiating means such as an optical fiber or a light receiving means for receiving transmitted light inside the Erlenmeyer flask 115, the device configuration is simplified and it is also easy to replace the Erlenmeyer flask 115. Therefore, the COD analysis time, including preparation time, can be shortened.

[0050] 4 is a diagram showing a schematic configuration of a COD automatic analyzer 100 according to a second embodiment of the present invention. The same components as those in the COD analysis titration endpoint detection device 1 according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals and will not be described.

[0051] The COD automatic analyzer 100 complies with JIS K 0102, 17 "Oxygen consumption by potassium permanganate at 100°C (COD Mn ) and incorporates the COD analysis titration endpoint detection device 1 of the first embodiment.

[0052] The COD automatic analyzer 100 comprises a sample preparation section 110, a heating section 130, a COD measurement section 140, a drainage section 150, a washing section 160, a movement actuator 170 that moves the Erlenmeyer flask 115, and a control PLC 180 that controls the movement of the entire apparatus.

[0053] The sample preparation unit 110 is a means for collecting samples, and is a measuring device for measuring the oxygen consumption (COD) of potassium permanganate at 100° C. according to JIS K 0102-17. Mn ) and a means for adding and mixing a specified amount of a chemical specified in the "Preparation of Samples for Use in Testing" is provided to prepare samples.

[0054] Specifically, the sample preparation unit 110 collects an appropriate amount of sample into a 300 mL Erlenmeyer flask 115 via a dispensing burette 125, adds water to make 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 a specimen for analysis.

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

[0056] The COD measurement section 140 includes the COD analysis titration end point 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 a sample (solution 141). The Erlenmeyer flask 115 containing the solution 141 heated by the heating section 130 is placed at the midpoint on the line connecting the light irradiating means 10 and the light receiving means 20 that constitute the COD analysis titration end point detection device 1.

[0057] Then, in the COD measurement section 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 being stirred. Then, a 5 mmol / L potassium permanganate solution is supplied via a titration burette 147, and the titration end point is detected via the COD analysis titration end point detection device 1.

[0058] The drainage unit 150 includes a drainage pump 152 and a drainage tank 154, and recovers the solution 141 after the titration as drainage.

[0059] The cleaning unit 160 includes a pure water pump 162 and a pure water tank 164, and uses pure water to clean the inside of the Erlenmeyer flask 115 in which the solution 141 has been collected. The Erlenmeyer flask 115 after cleaning is sent to the sample preparation unit 110.

[0060] The movement actuator 170 has a gripper 175 for gripping the Erlenmeyer flask 115 , and transports and places the Erlenmeyer flask 115 at 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 unit to operate in accordance with a predetermined procedure.

[0062] The COD automatic analyzer 100 of the second embodiment described above is configured such that the control PLC 180 measures the oxygen consumption (COD) of potassium permanganate at 100° C. according to JIS K 0102-17. Mn Each device and means is controlled to follow the method specified in "JIS K 0102:17:2001" and the COD analysis titration end point detection device 1 automatically detects the titration end point. Therefore, by using the COD automatic analyzer 100, the oxygen consumption by potassium permanganate at 100°C (COD Mn ) can be used to automate COD analysis.

[0063] The above describes the COD analysis titration endpoint detection method and detection device, as well as the COD automatic analyzer of the present invention, 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, as well as the COD automatic analyzer of the present invention are not limited to the above embodiments and can be modified within the scope that does not change the gist of the invention. [Explanation of symbols]

[0064] 1. COD analysis titration end point detector 10 Light irradiation means 12 Light emitting element 15 Light diffusion means 20 Light receiving means 28 Photodetector 40 Titration end point detection means 100 COD automatic analyzer 110 Sample Creation Department 115 Erlenmeyer Flask 130 Heating section 140 COD measurement section 141 Solution 142 Mixing blade 150 Drainage section 160 Cleaning section 170 Movement Actuator 180 Control PLC

Claims

1. JIS K 0102-17 "Oxygen consumption by potassium permanganate at 100°C (COD Ｍｎ A method for detecting the titration end point as defined in the "Titration End Point Detection Method for the Titration of a 2000-25000 Hz" A method for detecting an end point of titration in COD analysis, comprising the steps of: irradiating an Erlenmeyer flask containing a solution with light including light having a wavelength of 535 to 545 nm during titration; receiving light that has passed through the solution and the Erlenmeyer flask; and detecting the end point of titration from a change in the amount of light received at a wavelength of 535 to 545 nm.

2. JIS K 0102-17 "Oxygen consumption by potassium permanganate at 100°C (COD Ｍｎ An apparatus for automatically detecting the titration end point as defined in the "Titration End Point Test" A light irradiation means for irradiating the Erlenmeyer flask containing the solution with light having a wavelength of 535 to 545 nm from outside the Erlenmeyer flask; a light receiving means disposed opposite to the light irradiating means and configured to receive light transmitted through the solution and the Erlenmeyer flask outside the Erlenmeyer flask; a titration end point detection means for detecting the end point of the titration based on a change in the amount of received light having a wavelength of 535 to 545 nm; A COD analysis titration endpoint detection device comprising:

3. the light irradiating means includes a light emitting element that emits light including light with a wavelength of 535 to 545 nm, and a light diffusing means that diffuses the light emitted by the light emitting element; The light receiving means includes a light collecting means for collecting light transmitted through the solution and the Erlenmeyer flask, and a light receiving element for detecting light having a wavelength of 535 to 545 nm from the collected transmitted light.

3. The COD analysis titration endpoint detection device according to claim 2, further comprising:

4. The Erlenmeyer flask has a stirring bar or stirring blade therein for stirring the solution, 3. The COD analysis titration endpoint detection device according to claim 2, wherein said light irradiating means irradiates light parallel to the bottom surface of said Erlenmeyer flask.

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

6. An Erlenmeyer flask, A sampling means for collecting a sample; A reagent adding means for adding a reagent; 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 conveying the Erlenmeyer flask to a predetermined position; A control means for controlling each device and each means; The COD analysis titration endpoint detection device according to claim 2 ; A COD automatic analyzer comprising:

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