A permanganate index self-matching air pressure detection system and method

Abstract

The application discloses a permanganate index self-matching air pressure detection system and method, belongs to the technical field of environmental monitoring, and comprises a digestion bottle, a preparation platform and a detection platform. The preparation platform comprises a sample rack, an automatic reagent adding system and an automatic cap screwing system. The detection platform comprises a base, a sample rotating system and a spectrophotometer. The digestion bottle is a bottom-protruding cylindrical structure, and comprises a digestion part, a to-be-detected part and a pressure regulating bottle cap. The detection method comprises determining an optimal detection wavelength, establishing a calibration reagent curve, establishing a calibration curve of the permanganate index, water sample determination, correcting the curve through the change rate of the spectrophotometer signal twice and the like. The application can guarantee the accuracy of the colorimetric result, reduce the error generated in the colorimetric process, realize the automation of sample loading, digestion and colorimetry, and improve the detection efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental monitoring, and particularly relates to a permanganate index self-matching air pressure detection system and method. BACKGROUND

[0002] The permanganate index (I Mn ) is a key index for measuring the pollution degree of organic matter and oxidizable inorganic matter in water quality monitoring, is defined as the oxygen consumption when a water sample is oxidized by potassium permanganate (KMnO4) as an oxidizing agent under acidic or alkaline conditions, and is expressed in milligrams per liter (mg / L). The traditional titration method is time-consuming, energy-consuming, material-consuming, and complicated to operate, has certain requirements for the color sensitivity of the operator, and has high requirements for the sample digestion time and temperature. The spectrophotometric method, as a simple and stable method, is also applied to the determination of the permanganate index.

[0003] However, the existing spectrophotometric method for determining the permanganate index still has the following problems:

[0004] 1. The standard method (GB11892-89) is to use potassium permanganate to oxidize the oxidizable substances in the water sample at a water bath temperature of 98℃ and a digestion time of 30 min±2 min, and the equivalent oxygen consumption is represented by the amount of potassium permanganate consumed. However, the determination result is related to experimental conditions such as water bath temperature and digestion time, and changing any experimental condition will cause deviation in the determination result. For the titration method and the conventional spectrophotometric method, in the medium and high altitude areas, due to the low air pressure, the boiling point temperature of water is difficult to reach the water bath temperature (98℃) specified in the national standard method, and in view of this situation, the national standard method only requires to indicate the boiling point temperature in the result report, and does not give a specific solution, which leads to low determination value of the permanganate index in the high altitude area, poor data comparability, and difficulty in water environment quality evaluation.

[0005] 2. The traditional spectrophotometric method needs to prepare a standard curve use liquid to establish a calibration curve or a calibration curve point before each sample analysis, and then colorimetric after heating for 30 min, which is time-consuming, consumes standard liquid, and causes low sample detection efficiency. Moreover, potassium permanganate itself is not stable, and the concentration of the prepared potassium permanganate solution is prone to change, and the preparation of the standard curve use liquid to establish the calibration curve or the calibration curve point is time-consuming and labor-consuming.

[0006] 3. When the spectrophotometer works continuously for a long time, its sensitivity is prone to drift, and the existing detection method usually uses the experiment of drawing a calibration curve to solve this problem, but the whole process is time-consuming and labor-consuming, and the efficiency is low.

[0007] 4. The original method is colorimetric, which is air-dried to room temperature, and then transferred to the colorimetric cup for colorimetric analysis. When the temperature drops, potassium permanganate is still in reaction, and the digestion process continues. The transfer may cause the possibility of contamination.

[0008] Meanwhile, refer to the following Chinese patents, CN113125360A-Analysis system and method for automatic monitoring of permanganate index, CN110346509A-Water quality online permanganate index monitor and detection method, CN119104676A-Detection method and online monitoring method for permanganate index, the above-mentioned solutions are only applicable to traditional spectrophotometric determination, and cannot effectively solve one or more of the problems listed above.

[0009] Therefore, a permanganate index detection method that can adapt to different air pressure conditions is needed, which can ensure the accuracy of the detection results while improving the detection efficiency. SUMMARY

[0010] The purpose of the present application is to provide a permanganate index self-matching air pressure detection system and method to solve the problems in the background art.

[0011] The purpose of the present application is achieved by the following technical solutions:

[0012] A permanganate index self-matching air pressure detection system, comprising a digestion bottle, a preparation platform and a detection platform;

[0013] The preparation platform comprises a sample holder, an automatic reagent adding system and an automatic cap twisting system;

[0014] The detection platform comprises a base, a sample rotation system and a spectrophotometer;

[0015] The digestion bottle is a cylindrical structure with a protruding bottom, and comprises a digestion part, a to-be-measured part and a pressure regulating bottle cap.

[0016] Further, the sample rotation system comprises a rotating table and a rotating motor located below the rotating table. The rotating table is located in the base below, and a plurality of placement grooves are arranged in the circumferential direction above the rotating table. The size of the placement groove is matched with the size of the digestion part. The bottom of the placement groove is provided with an opening for the to-be-measured part to pass through. The inner wall of the placement groove is provided with a graphite heating element. The rotating table is provided with cavities corresponding to the positions of the to-be-measured parts. The rotating table is provided with a magnetic field generator below each cavity.

[0017] Further, the preparation platform is located on one side of the detection platform, a mechanical hand for sampling is arranged between the preparation platform and the detection platform, the spectrophotometer is located on one side of the base away from the preparation platform, the spectrophotometer comprises a system body (including a light source, a monochromator and the like), a light outlet and a receiver, the system body is in sliding connection with the base, the interior of the rotating table is in a concave structure, the receiver is located below the interior of the rotating table and corresponds to the position of the light outlet, the height of the light outlet is the same as the height of the cavity, a through hole is arranged at the position corresponding to the light outlet in the cavity, light emitted from the light outlet passes through the through hole, the cavity, the to-be-detected part and is irradiated on the receiver.

[0018] Further, the pressure regulating bottle cap comprises a cap body and a temperature control valve, the temperature control valve is fixed in the middle of the cap body and extends into the digestion part.

[0019] A permanganate index self-matching gas pressure detection method, comprising the following steps:

[0020] S1: determining an optimal detection wavelength;

[0021] S2: establishing a calibration reagent curve, step S2 comprises sub-steps S21-S23,

[0022] S21: taking 100 ml of a blank water sample, adding 10 ml of a potassium permanganate solution with a concentration of 0.01 mol / L and 5 ml of a sulfuric acid solution (1+3), and obtaining an absorbance by colorimetry through a spectrophotometer without heating ;

[0023] S22: preparing a fluorescein sodium calibration solution with an absorbance of , and recording the solution concentration as ; preparing a fluorescein sodium calibration solution with an absorbance of , and recording the solution concentration as ; 0.8~0.9 times , 1.1~1.2 times , at this time, a calibration reagent curve is established according to the two points , , the , is an absorbance, is a concentration of a calibration reagent, is a slope, is an intercept;

[0024] S23: substituting the in step S21 into the linear equation in step S22, to obtain an initial characterization concentration of the potassium permanganate solution corresponding to the calibration solution ;

[0025] S3: Establishing calibration curve of permanganate index, step S3 includes sub-steps S31-S33,

[0026] S31: Preparing standard solution with different permanganate index concentration, adding 10ml of 0.01mol / L potassium permanganate solution and 5ml of sulfuric acid solution (1+3) for heating digestion;

[0027] S32: Getting absorbance corresponding to different permanganate index concentration by colorimetry after digestion of the solution ;

[0028] S33: Drawing calibration curve with permanganate index concentration as abscissa and as ordinate, , absorbance of potassium permanganate consumed after digestion of standard solution, drawing standard curve , permanganate index, often represented by , unit: mg / L; absorbance; slope; intercept;

[0029] S4: Water sample determination: step S4 includes sub-steps S41-S42,

[0030] S41: Water sample adding 10ml of 0.01mol / L potassium permanganate solution and 5ml of sulfuric acid solution (1+3) for digestion and colorimetry;

[0031] S42: Getting absorbance of residual potassium permanganate after digestion of water sample by colorimetry , , absorbance of potassium permanganate consumed after digestion of water sample, then according to linear equation in step S33 , substituting into , permanganate index is obtained, if >2, water sample needs to be diluted before determination, dilution formula is: , in which: , absorbance of potassium permanganate consumed by blank sample (pure water), absorbance of residual potassium permanganate after consumption by blank sample (pure water), dilution multiple;

[0032] S5: Repeating step S4 for determination of multiple groups of water samples.

[0033] Further, for step S5, in the uninterrupted continuous water sample determination, a periodical calibration is needed every 12h, which needs to repeat steps S21-S22, respectively record the absorbance 、 、 , get a new calibration reagent curve and , , , , if the ratio of the KMnO4 solution characterization concentration to the calibration solution characterization concentration is in the range of 0.95-1.05, it indicates that the current KMnO4 solution can continue to be used; if the ratio is not in this range, the KMnO4 solution needs to be prepared again, and steps S21-S22 are performed again to make the ratio in the above range before continuing to determine the sample.

[0034] Further, the rate of change of the two spectrophotometer signals , , , i.e. , , according to steps S3 and the corresponding , a new calibration curve is established, and then the sample is determined.

[0035] Further, in step S1, the prepared curve is respectively colorimetric at wavelengths of 475nm, 500nm, 525nm, 550nm and 575nm, and the wavelength with the best sample sensitivity and curve linearity is selected as the working wavelength.

[0036] Further, step S41 includes the following sub-steps:

[0037] S401: take 100ml water sample in a digestion bottle, and add a magnetic stirrer in the digestion bottle;

[0038] S402: add 5ml sulfuric acid solution (1+3) and 10ml potassium permanganate standard solution (0.01 mol / L) through the reagent pipeline respectively, and stir uniformly;

[0039] S403: digest at 98℃ for 30min, if the boiling point of the local water is lower than 98℃, set a pressure regulating component on the bottle mouth of the digestion bottle; when the digestion is to 29.5min, start colorimetry, stop the magnetic stirrer stirring during colorimetry, continuously colorimetry for 30s, read the absorbance every 5s during colorimetry, and the final absorbance value is the average of the last 3 readings, and the relative standard deviation (RSD) of the absorbance should be not more than 1%.

[0040] ​The beneficial effects of the present application are:

[0041] The method is simple by colorimetry, and can effectively avoid the problem that the color is difficult to determine the endpoint during titration when sodium oxalate is added and still yellow.

[0042] By stirring with a stirrer during digestion, the generation of small particles ( ) is avoided, effectively solving the problem of color accuracy affected by the generation of different colors during sample digestion. At the same time, the highest concentration of the curve is set at 2 mg / L, so that the water sample contains less organic or inorganic matter, and the reduction reaction of permanganate ( ) is more complete, which will be reduced to water-soluble , rather than , so that the water sample is clear during colorimetry, which does not affect the colorimetry result.

[0043] By setting the pressure regulating assembly, the gas pressure in the digestion bottle is a fixed value, and the boiling point temperature is maintained at 98℃, which can be applied to different altitudes.

[0044] The detection system realizes automatic loading, digestion and colorimetry, improves the detection efficiency, and can automatically realize periodical calibration and timely establish calibration curve.

[0045] The use of fluorescein sodium for the calculation of the concentration change rate of potassium permanganate solution and the correction of the sensitivity drift of the spectrophotometer only needs to be prepared in advance, and can be repeatedly used in subsequent calibration. Using fluorescein sodium solution, no heating pretreatment is needed, and colorimetry can be directly performed, which is time-saving, less dosage, and conducive to improving the detection efficiency; without the need to repeatedly prepare the use liquid for calibration curve, it is also conducive to simplifying the experimental steps and reducing the consumption of materials. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a top view of a permanganate index self-matching gas pressure detection system of the present application;

[0047] Figure 2 It is a side view of the detection platform in the present application;

[0048] Figure 3 It is a partial sectional view of the rotating table in the present application;

[0049] Figure 4 It is a schematic view of the digestion bottle in the present application;

[0050] In the figure, 1 is a detection platform, 11 is a base, 2 is a preparation platform, 21 is a sample rack, 22 is an automatic cap screwing system, 3 is a digestion bottle, 31 is a digestion part, 32 is a to-be-detected part, 33 is a pressure regulating bottle cap, 34 is a temperature control valve, 4 is a mechanical hand, 5 is a spectrophotometer, 51 is a system body, 52 is a light outlet, 53 is a receiver, 6 is a sample rotation system, 61 is a placing groove, 62 is a rotating table, 63 is a rotating motor, 64 is a cavity, 65 is a graphite heating element, 66 is a through hole, 67 is a magnetic field generator, and 68 is a magnetic stirring rod. DETAILED DESCRIPTION

[0051] The technical solutions of the present application will be described clearly and completely below in combination with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort fall within the protection scope of the present application.

[0052] The present application uses a spectrophotometric method to determine the permanganate index. The specific experimental principle is as follows: under acidic conditions, excessive potassium permanganate is used to oxidize the reducing substances in the water body. According to the good sensitivity of potassium permanganate in colorimetry, the amount of residual potassium permanganate is determined by colorimetry. A calibration curve of the permanganate index and the absorbance of the consumed potassium permanganate is established, and the permanganate index of the water sample is directly calculated through the curve. EMBODIMENT

[0053] A permanganate index self-matching air pressure detection system,

[0054] As shown in the figure, the system includes a digestion bottle 3, a preparation platform 2 and a detection platform 1. Figures 1-4

[0055] The preparation platform 2 includes a sample rack 21, a reagent automatic adding system and an automatic cap screwing system 22.

[0056] The detection platform 1 includes a base 11, a sample rotation system 6 and a spectrophotometer 5.

[0057] The digestion bottle 3 is a cylindrical structure with a protruding bottom. The digestion bottle 3 includes a digestion part 31, a to-be-detected part 32 and a pressure regulating bottle cap 33.

[0058] ​Through the technical scheme, the sample rack 21 and the rotating table 62 are both provided with placing grooves 61 of the same size, the sample rack 21 is provided with the digestion bottle 3 containing the water sample, the reagent automatic adding system is used for adding the sulfuric acid solution, the potassium permanganate solution and the magnetic stirring rod 68 into the digestion bottle 3, the magnetic stirring rod 68 can be manually put or grabbed by the mechanical arm. The prepared water sample is placed on the sample rack 21 and waits for the mechanical arm 4 to grab the prepared digestion bottle 3 to the rotating table 62. The reagent automatic adding system (automatic sample feeding machine) is a mature technology in the field, and is not shown in the figure. When the local water boiling point is greater than or equal to 98 DEG C, the digestion bottle 3 does not need to be provided with the pressure regulating bottle cap 33.

[0059] Further, the potassium permanganate solution and the calibration solution are both contained in the digestion bottle 3 and placed in the fixed position at the upper right corner of the sample rack 21. Preferably, the potassium permanganate solution in step S21 of the self-matching air pressure detection method of the permanganate index, and the low-concentration sodium fluorescein calibration solution and the high-concentration sodium fluorescein calibration solution prepared in step S22 are all contained in the digestion bottle 3 and placed in the fixed position at the upper right corner of the sample rack 21.

[0060] Further, as shown in Figures 1-3 The sample rotating system 6 includes the rotating table 62 and the rotating motor 63 located below the rotating table 62, the rotating table 62 is located in the base 11, a plurality of placing grooves 61 are arranged in the circumferential direction above the rotating table 62, the size of the placing groove 61 is matched with the size of the digestion part 31, the bottom of the placing groove 61 is provided with an opening for the to-be-tested part 32 to pass through, the inner wall of the placing groove 61 is provided with a graphite heating element 65, the rotating table 62 is provided with a cavity 64 corresponding to the position of the to-be-tested part 32, and the rotating table 62 is provided with a magnetic field generator 67 below each cavity 64.

[0061] Through the technical scheme, each placing groove 61 is correspondingly provided with a cavity 64 below, each cavity 64 is provided with an independent magnetic field generator 67 below, and each placing groove 61 is provided with an independent graphite heating element 65 for controlling the temperature. The mechanical arm 4 is used for placing the digestion bottle 3 into the placing groove 61 on the rotating table 62, at this time, the to-be-tested part 32 passes through the opening below the placing groove 61 and extends into the cavity 64, the graphite heating element 65 can heat the solution in the digestion bottle 3, and the magnetic field generator 67 below makes the magnetic stirring rod 68 in the bottle rotate to fully stir the solution.

[0062] The digestion part 31 of the digestion bottle 3 in the embodiment is a cylindrical structure with a diameter of 5 cm, and is used for digestion reaction; the detection part 32 is a cylindrical structure or a cubic structure with a diameter of 1 cm, and is equivalent to a cuvette used for colorimetry. The magnetic stirring rod 68 has a length greater than 2 cm, so as to avoid the magnetic stirring rod 68 from falling into the detection part 32 and failing to be normally stirred. The top of the digestion bottle 3 extends out of the placement groove 61, so as to facilitate taking and placing the digestion bottle 3 from and in the placement groove 61.

[0063] During the rotation of the rotating table 62, the digestion bottle 3 is always in a heating state and is kept stirring by the magnetic force generator, until the digestion bottle 3 is about to move to the spectrophotometer 5, and then the stirring is stopped.

[0064] Further, the preparation platform 2 is located on one side of the detection platform 1, a mechanical hand 4 for sampling is arranged between the preparation platform 2 and the detection platform 1, the spectrophotometer 5 is located in the base 11 and away from one side of the preparation platform 2, and the spectrophotometer 5 comprises a system body 51, a light outlet 52 and a receiver 53. The system body 51 comprises a shell, a light source, a monochromator and the like, and is in sliding connection with the base 11. Since the system body 51 is in sliding connection with the base 11, the light outlet 52 is located at the front end of the system body 51, and the receiver 53 is fixed on the base, so that the distance between the light outlet 52 and the detection part 32 can be conveniently adjusted through the sliding structure, so as to ensure the distance of the optical path and the accuracy of measurement. The light emitted by the light source is irradiated onto the detection part 32 through the light outlet 52, the detection part 32 is equivalent to a cuvette in a conventional colorimetry, the light source passes through the detection part 32 and is irradiated onto the receiver 53, the receiver 53 detects the light, converts the light into an electric signal by using a photoelectric effect, and then transmits the electric signal back to the system body 51 for analysis and recording, so as to obtain the absorbance.

[0065] The spectrophotometer 5 is a commonly used instrument in the detection field, and the detection principle will not be described herein.

[0066] The inside of the rotating table 62 is a concave structure, the receiver 53 is located below the inside of the rotating table 62 and corresponds to the position of the light outlet 52, the height of the light outlet 52 is the same as the height of the cavity 64, and the cavity 64 is provided with a through hole 66 corresponding to the position of the light outlet 52.

[0067] Through the above technical solution, since the lower part of the rotating table 62 is located in the base 11, the lower part of the rotating table 62 is in a closed and light-free environment, and the spectrophotometer 5 is also located in the base 11, so that the spectrophotometer 5 is in a darkroom condition and is convenient for subsequent colorimetry.

[0068] A position sensor is provided at the position of the through hole 66 of the cavity 64 corresponding to the position of the light outlet 52 of the spectrophotometer 5. When the through hole 66 rotates to the position of the light outlet 52, it stops and the spectrophotometer 5 is started. The light emitted from the light outlet 52 can pass through the through hole 66, the cavity 64, the part to be measured 32, and illuminate the receiver 53. At this time, the spectrophotometer 5 can perform colorimetry on the sample in the part to be measured 32.

[0069] After the colorimetry is completed, the heating of the digestion bottle 3 stops, and the digestion bottle 3 after the test is moved to the side of the robot 4 through the rotating platform 62 and is taken out by the robot 4.

[0070] Furthermore, if Figure 4 As shown, the pressure regulating bottle cap 33 includes a bottle cap body and a temperature control valve 34. The temperature control valve 34 is provided with a temperature control element and a mechanical structure for regulating the opening and closing of the valve port.

[0071] Temperature control valves are a mature technology. Please refer to CN109027403B - a passive temperature control valve, and CN208417719U - an automatic temperature control valve. The core of both technologies is to detect temperature through a temperature control element. When the temperature of the temperature-variable object (heat-expanding material) is greater than the preset temperature, it generates thrust to push the piston head to drive the connecting rod and valve movement, so that the valve opens the valve hole. When the temperature is less than or equal to the preset temperature, the elastic recovery force of the elastic component controls the valve to seal the valve hole.

[0072] In this solution, a temperature control valve is provided on the thermos bottle cap. The temperature element of the temperature control valve extends into the digestion bottle. The valve hole is controlled according to the temperature inside the digestion bottle to exhaust air. When the temperature is less than or equal to the preset temperature, the valve hole is closed, so that the sample in the digestion bottle can continue to heat up.

[0073] Specifically, when the boiling point of local water is lower than 98° C., the digestion bottle 3 is capped with a pressure regulating bottle cap 33 by the automatic capping system 22 at the preparation platform 2 ;

[0074] When the digestion bottle 3 is placed on the rotating table 62 and begins to be heated, the temperature in the digestion bottle has not yet reached the critical temperature at which the temperature-variable material (heat-expanding material) in the temperature control valve expands and opens the valve hole. At this time, the valve hole of the temperature control valve is in a closed state, and the digestion bottle 3 is kept sealed by the pressure-regulating bottle cap 33. As the heating proceeds, the pressure in the digestion bottle 3 gradually increases, making it convenient to continuously raise the solution in the digestion bottle 3 to a suitable temperature for digestion.

[0075] When the temperature reaches the set value, the temperature change object (heat-expandable material) expands to a volume exceeding a critical value, and the expansion pushes the mechanical structure to move, thereby opening the valve hole. For example, the critical temperature is set to 95.5°C, and when it reaches 95.5°C, the temperature change object (heat-expandable material) in the temperature control valve expands to a volume exceeding a critical value. The heat-expandable material can be selected from graphite, high-expansion alloy, etc. After the heat-expandable material expands, a pushing force is generated to push the piston head to move the connecting rod and the valve, so as to open the valve hole and discharge the gas in the digestion bottle to avoid excessive pressure in the digestion bottle. When the temperature is higher and higher, the heat-expandable material expands faster, the valve hole opens larger, and the gas discharge flow is larger. Through the above components, it is ensured that the boiling point of the sample in the digestion bottle is 98°C.

[0076] The pressure regulating bottle cap 33 is used to control the pressure in the pressure regulating bottle. When heating, the digestion bottle 3 is kept sealed through the pressure regulating bottle cap 33, so that the gas pressure in the digestion bottle 3 is higher than the local atmospheric pressure, and the boiling point temperature is increased. When the sample in the digestion bottle 3 is higher than 98°C, the gas is discharged through the temperature control valve 34 to reduce the gas pressure in the bottle, so as to reduce the boiling point of the sample to 98°C, thereby ensuring that the gas pressure in the bottle is constant during digestion. By setting the pressure regulating bottle cap 33, the permanganate index detection can be applied to different altitudes, and the detection result is ensured to be accurate.

[0077] The basic working principle of the system is that the digestion bottle 3 containing water sample is placed on the sample holder 21 of the preparation platform 2, and the reagent automatic adding system adds sulfuric acid solution, potassium permanganate solution and magnetic stirrer 68 into the digestion bottle 3, and then the mechanical hand 4 grabs the prepared digestion bottle 3 to the rotating table 62.

[0078] The digestion bottle 3 is placed in the placing groove 61 on the rotating table 62 by the mechanical hand 4. At this time, the to-be-measured part 32 penetrates through the opening below the placing groove 61 and extends into the cavity 64. The solution in the digestion bottle 3 can be heated by the graphite heating element 65, and the magnetic field generator 67 below keeps the magnetic stirrer 68 in the bottle rotating to fully stir the solution.

[0079] During the rotation of the rotating table 62, the digestion bottle 3 is always in a heated state and is stirred by the magnetic field generator until the digestion bottle 3 is about to move to the spectrophotometer 5, and the stirring is stopped.

[0080] The light emitted by the light source is irradiated onto the to-be-detected part 32 through the light outlet 52, the to-be-detected part 32 corresponds to a cuvette in a conventional colorimetry, the light source passes through the to-be-detected part 32 to reach the receiver 53, the receiver 53 detects the light, converts the light into an electric signal by using a photoelectric effect, and then transmits the electric signal back to the system body 51 for analysis and recording, and then the absorbance is obtained. At this time, the sample in the to-be-detected part 32 can be subjected to colorimetry by the spectrophotometer 5, then the amount of residual potassium permanganate is determined by colorimetry, a calibration curve of permanganate index and absorbance of consumed potassium permanganate is established, and the permanganate index of the water sample is directly calculated through the curve.

[0081] Through the system, the sample loading, digestion and colorimetry are automated, the detection efficiency is improved, the system can be applied to a permanganate index self-matching air pressure detection method, is suitable for permanganate index detection in different altitudes, and ensures the accuracy of the detection result. Meanwhile, when periodical calibration is needed, the prepared potassium permanganate solution and the calibration solution placed on the sample rack 21 can be taken by the mechanical hand 4, are rotated by the rotating table 62, and are moved to the spectrophotometer 5 position for determination without heating. After the determination and the establishment of the calibration curve, the subsequent sample is grabbed by the mechanical hand 4 for colorimetry. The whole process does not need manual operation, and the detection efficiency is improved. EMBODIMENT

[0082] A permanganate index self-matching air pressure detection method, comprising the following steps:

[0083] S1: determining an optimal detection wavelength;

[0084] Specifically, the prepared curve is subjected to colorimetry at wavelengths of 475 nm, 500 nm, 525 nm, 550 nm and 575 nm, and the wavelength with the best sample sensitivity and the best curve linearity is selected as the working wavelength. Preferably, the curve linearity is the best at the wavelength of 525 nm. It can be known that step S1 is generally performed only once at the initial stage of instrument installation and debugging, and is not changed subsequently.

[0085] It can be known that the preparation of the potassium permanganate standard solution is performed before step S1, and the preparation method is a conventional technique and will not be repeated here. A commercially available potassium permanganate standard solution with a concentration of 0.01 mol / L can also be directly used.

[0086] S2: establishing a calibration reagent curve, and step S2 comprises sub-steps S21-S23,

[0087] S21: taking 100 ml of a blank water sample, adding 10 ml of a potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of a sulfuric acid solution (1+3), and obtaining the absorbance by colorimetry of the spectrophotometer without heating ;

[0088] The sulfuric acid solution (1+3) refers to a mixed solution of 1 volume of concentrated sulfuric acid and 3 volumes of distilled water.

[0089] S22: Prepare a fluorescein sodium calibration solution with an absorbance of 0.8-0.9, record the solution concentration as 0.65 mmol / L-0.95 mmol / L; prepare a fluorescein sodium calibration solution with an absorbance of 1.1-1.2, record the solution concentration as 1.1 mmol / L-1.2 mmol / L. ; The fluorescein sodium concentration is 0.8-0.9 times the concentration of the calibration solution. , The fluorescein sodium concentration is 1.1-1.2 times the concentration of the calibration solution. At this time, two points are used to calibrate the reagent curve, and the concentration of the calibration solution is obtained. , The absorbance is the absorbance, the concentration of the calibration reagent is the concentration of the calibration reagent, the slope is the slope, and the intercept is the intercept. ,

[0090] S23: Substitute the value of step S21 into the linear equation in step S22 to obtain the initial characterization concentration of the potassium permanganate solution corresponding to the calibration solution. The characterization concentration refers to a numerical value rather than the true concentration.

[0091] Through step S2, it can be known that the traditional spectrophotometric method needs to prepare a standard curve using liquid to establish a calibration curve or calibration curve point before each analysis. If the traditional calibration method is used for calibration, then this method needs to be heated for 30 min before colorimetry each time, which consumes a lot of time.

[0092] Now introduce fluorescein sodium, which is stable and can be stored for a long time. At the same time, it also has stable and sensitive absorption to light with a wavelength of about 525 nm. Fluorescein sodium is used for the calculation of the concentration change rate of potassium permanganate solution and the correction of the sensitivity drift of the spectrophotometer. It only needs to be prepared in advance and can be repeatedly used in subsequent calibration. Using fluorescein sodium solution, there is no need for heating and other pretreatment, and it can be directly colorimetric, which saves time and reduces the amount of use, and is conducive to improving the detection efficiency; without the need to prepare calibration curve using liquid repeatedly, it is also conducive to simplifying the experimental steps and reducing the cost of materials.

[0093] Preferably, the concentration of fluorescein sodium is between 0.65 mmol / L and 0.95 mmol / L.

[0094] Further, in the uninterrupted continuous determination of water samples, a periodical calibration is needed every 12 hours, which needs to repeat steps S21-S22, and record the absorbance ,​​​​​​​​​ 、 ,pass and Get a new calibration reagent curve ,Will Substitute the new calibration reagent curve to calculate the characteristic concentration of the calibration solution corresponding to the current potassium permanganate solution , when the concentration ratio of potassium permanganate solution is If the value is within the range of 0.95 to 1.05, there is no need to re-establish the calibration curve through experiments.

[0095] Through the above steps, when the potassium permanganate solution characterizes the concentration ratio If the ratio is within the range of 0.95 to 1.05, it indicates that the concentration of the potassium permanganate solution is within the appropriate range, indicating that the current potassium permanganate solution can continue to be used. If the ratio is not within this range, it is necessary to re-prepare the potassium permanganate solution and perform steps S21-S22 again. After the ratio is within the above range, continue to measure the sample. Avoid large changes in the concentration of the potassium permanganate solution that may affect the accuracy of the test results.

[0096] S3: Establish a calibration curve for the permanganate index. Step S3 includes sub-steps S31-S33.

[0097] S31: Prepare standard solutions with different permanganate index concentrations, add 10 ml of 0.01 mol / L potassium permanganate solution and 5 ml of sulfuric acid solution (1+3), and heat to digest;

[0098] S32: The digested solution is subjected to colorimetry to obtain absorbance A corresponding to different permanganate index concentrations;

[0099] S33: With the concentration of permanganate index as the horizontal axis, Draw the calibration curve for the ordinate, , Draw a standard curve based on the absorbance of potassium permanganate consumed after digestion of the standard solution , Is the permanganate index, often expressed as It is expressed in mg / L; is absorbance; is the slope; is the intercept.

[0100] S4: Water sample determination: Step S4 includes sub-steps S41-S42,

[0101] S41: Add 10 ml of 0.01 mol / L potassium permanganate solution and 5 ml of sulfuric acid solution (1+3) to the water sample for digestion and colorimetry;

[0102] The specific step S41 comprises the following sub-steps:

[0103] S401: take 100 ml water sample in a digestion bottle, and add a magnetic stirring bar in the digestion bottle;

[0104] S402: add 5 ml sulfuric acid solution (1+3) and 10 ml potassium permanganate standard solution (0.01 mol / L) through a reagent pipeline respectively, and then stir uniformly;

[0105] By stirring with the stirring bar during digestion, the generation of precipitate is avoided, and the influence of color difference on the accuracy of colorimetry is effectively solved.

[0106] S403: digest at 98℃ for 30 min, if the boiling point of local water is lower than 98℃, set a pressure regulating component on the bottle mouth of the digestion bottle; start colorimetry when the digestion reaches 29.5 min, stop the magnetic stirring bar during colorimetry, continuously colorimetry for 30 s, read the absorbance every 5 s during colorimetry, the final absorbance value is the average of the last three readings, and the relative standard deviation (RSD) of absorbance should be not greater than 1%.

[0107] If the RSD is greater than 1%, the data needs to be reselected, since the final absorbance value is the average of the last three readings, one value with large deviation can be removed, and the last fourth reading is introduced to calculate the RSD again, if the RSD is still greater than 1%, repeat the above steps to remove the value with large deviation and introduce a new reading.

[0108] When the boiling point of local water is lower than 98℃, a pressure regulating component is set on the bottle mouth of the digestion bottle, the pressure regulating component is used to control the pressure in the pressure regulating bottle, and the digestion bottle is kept sealed by the pressure regulating component during heating, so that the gas pressure in the digestion bottle is higher than the local atmospheric pressure, and the boiling point temperature is increased; when the sample in the digestion bottle is higher than 98℃, the gas is discharged through the pressure regulating component to reduce the gas pressure in the bottle, so that the boiling point of the sample is reduced to 98℃, so as to ensure that the gas pressure in the bottle is constant during digestion. By setting the pressure regulating component, the detection method of the application can be applied to different altitudes.

[0109] S42: obtain the absorbance of residual potassium permanganate after colorimetry of the water sample after digestion , , is the absorbance of consumed potassium permanganate after digestion of the water sample, then according to the linear equation in step S33 , is substituted into , the permanganate index is obtained, if >2, the water sample needs to be diluted and then measured, and the dilution formula is: , in the formula: , is the absorbance of potassium permanganate consumed by the blank sample (pure water), is the absorbance of potassium permanganate remaining after the blank sample (pure water) is consumed, is the dilution multiple.

[0110] Two laboratory blank samples should be prepared for each batch of sample testing. The testing steps are the same as the actual sample steps, and heating digestion is required. The laboratory blank absorbance , its purpose is to eliminate the influence of reagent background and laboratory pure water.

[0111] Through the above technical solution, the highest concentration of the curve is set at 2 mg / L. By diluting the water sample to contain less organic or inorganic matter, potassium permanganate will be reduced more slowly, and the water sample will be clear during colorimetry, which will not affect the colorimetric results.

[0112] At the same time, the drift of the spectrophotometer sensitivity can be corrected by introducing sodium fluorescein. Specifically, the change rate of the spectrophotometer signal between the two ,use Correction , ready to use ,get , according to step S3 and the corresponding After establishing a new calibration curve, measure the samples again.

[0113] S5: Repeat step S4 to perform multiple water sample measurements.

[0114] Through the above technical solution, the method is simple by colorimetry and can effectively avoid the problem that the sample changes color after the sample is digested with a high permanganate index concentration in the titration method, remains yellow after the addition of sodium oxalate, and the end point is difficult to determine by color during titration.

[0115] The detection method provided in this embodiment preferably uses the detection system provided in Example 1. The potassium permanganate solution in step S21 and the low-concentration sodium fluorescein calibration solution and high-concentration sodium fluorescein calibration solution prepared in step S22 are all placed in a digestion bottle 3 and placed in a fixed position in the upper right corner of the sample rack 21. The digestion bottle 3 containing the water sample is placed on the sample rack 21. The sulfuric acid solution, potassium permanganate working solution, and magnetic stirrer 68 are added to the digestion bottle 3 by the automatic reagent addition system. Referring to steps S401 and S402, the prepared water sample is placed on the sample rack 21 and waits for the robot 4 to grab the prepared digestion bottle 3 and place it on the rotating table 62. Then, the subsequent heating digestion and colorimetric steps are performed.

[0116] When the calibration is needed in the uninterrupted continuous water sample determination, the potassium permanganate solution, low concentration fluorescein sodium calibration solution and high concentration fluorescein sodium calibration solution prepared on the sample rack 21 can be taken by the mechanical hand 4, rotated by the rotating table 62 and moved to the spectrophotometer 5 position for determination without heating, and after the determination and the establishment of the calibration curve, the subsequent sample is grabbed by the mechanical hand 4 for colorimetry. The whole process does not need manual operation, and the detection efficiency is improved.

[0117] The above description is only the preferred embodiment of the present application, and it should be understood that the present application is not limited to the form disclosed herein, and should not be considered as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein by the above teaching or related art or knowledge. Any modification and change made by the person skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the appended claims of the present application.

Claims

1. A permanganate index self-matching air pressure detection method, characterized in that: The permanganate index self-matching air pressure detection method adopts a permanganate index self-matching air pressure detection system, wherein the permanganate index self-matching air pressure detection system comprises a digestion bottle (3), a preparation platform (2) and a detection platform (1); The preparation platform (2) includes a sample rack (21), an automatic reagent adding system and an automatic capping system (22); The detection platform (1) comprises a base (11), a sample rotation system (6) and a spectrophotometer (5); The digestion bottle (3) is a cylindrical structure with a raised bottom, and comprises a digestion portion (31), a portion to be tested (32) and a pressure regulating bottle cap (33); The permanganate index self-matching air pressure detection method includes the following steps: S1: Determine the optimal detection wavelength; S2: Establish a calibration reagent curve. Step S2 includes sub-steps S21-S23. S21: Take 100ml of blank water sample, add 10ml of 0.01mol / L potassium permanganate solution and 5ml of sulfuric acid solution, and obtain the absorbance by spectrophotometry without heating. , the sulfuric acid solution is a mixed solution of 1 volume of concentrated sulfuric acid and 3 volumes of distilled water; S22: Prepare absorbance Sodium fluorescein calibration solution, record its solution concentration as ; Prepare absorbance Sodium fluorescein calibration solution, record its solution concentration as ; 0.8~0.9 times , 1.1~1.2 times , at this time according to 、 Two-point calibration reagent curve, obtained , is the absorbance, is the concentration of the calibration reagent, is the slope, is the intercept; S23: The Substitute into the linear equation in step S22 , get the initial characterization concentration of potassium permanganate solution corresponding to the calibration solution ; S3: Establish a calibration curve for the permanganate index. Step S3 includes sub-steps S31-S33. S31: preparing standard solutions of different permanganate index concentrations, adding 10 ml of 0.01 mol / L potassium permanganate solution and 5 ml of sulfuric acid solution, and heating to digest, wherein the sulfuric acid solution is a mixed solution of 1 volume of concentrated sulfuric acid and 3 volumes of distilled water; S32: The digested solution is subjected to colorimetry to obtain the absorbance corresponding to different permanganate index concentrations. ; S33: With the concentration of permanganate index as the horizontal axis, Draw the calibration curve for the ordinate, , Draw a standard curve based on the absorbance of potassium permanganate consumed after digestion of the standard solution , Is the permanganate index, often expressed as It is expressed in mg / L; is absorbance; is the slope; is the intercept; S4: Water sample determination: Step S4 includes sub-steps S41-S42, S41: The water sample is digested by adding 10 ml of 0.01 mol / L potassium permanganate solution and 5 ml of sulfuric acid solution, and the colorimetry is performed. The sulfuric acid solution is a mixed solution of 1 volume of concentrated sulfuric acid and 3 volumes of distilled water; S42: Colorimetrically obtain the absorbance of potassium permanganate remaining after water sample digestion , , is the absorbance of potassium permanganate consumed after the water sample is digested, and then according to the linear equation in step S33 ,Will Substitution , the permanganate index is obtained ,like >2, the water sample needs to be diluted before measurement. The dilution formula is: , where: , is the absorbance of potassium permanganate consumed by the blank sample pure water, is the absorbance of potassium permanganate remaining after the pure water of the blank sample is consumed, is the dilution multiple; S5: Repeat step S4 to perform multiple water sample measurements.

2. The permanganate index self-matching air pressure detection method according to claim 1, characterized in that: The sample rotation system (6) includes a rotating table (62) and a rotating motor (63) located below the rotating table (62). The bottom of the rotating table (62) is located in the base (11). A plurality of placement slots (61) are arranged in a circular array above the rotating table (62). The size of the placement slots (61) is adapted to the size of the digestion part (31). The bottom of the placement slot (61) is provided with an opening for the part to be tested (32) to pass through. The inner wall of the placement slot (61) is provided with a graphite heating element (65). The rotating table (62) is provided with a cavity (64) corresponding to the position of the part to be tested (32). A magnetic field generator (67) is provided below each cavity (64) of the rotating table (62).

3. The permanganate index self-matching air pressure detection method according to claim 2, characterized in that: The preparation platform (2) is located on one side of the detection platform (1), and a manipulator (4) for sampling is provided between the preparation platform (2) and the detection platform (1). The spectrophotometer (5) is located in the base (11) and away from the preparation platform (2). The spectrophotometer (5) comprises a system body (51), a light outlet (52) and a receiver (53). The system body (51) is slidably connected to the base (11). The interior of the rotating platform (62) is a concave structure. The receiver (53) is located below the interior of the rotating platform (62) and corresponds to the position of the light outlet (52). The height of the light outlet (52) is the same as the height of the cavity (64). A through hole (66) is provided in the cavity (64) at a position corresponding to the light outlet (52). Light emitted from the light outlet (52) passes through the through hole (66), the cavity (64), the part to be measured (32), and is irradiated on the receiver (53).

4. The permanganate index self-matching air pressure detection method according to claim 1, characterized in that: The pressure-regulating bottle cap (33) comprises a bottle cap body and a temperature-controlled valve (34). The temperature-controlled valve (34) is fixed in the middle of the bottle cap body and extends into the digestion portion (31).

5. The permanganate index self-matching air pressure detection method according to claim 1, characterized in that: For step S5, during the uninterrupted continuous water sample measurement, a period calibration is required every 12 hours. During the period calibration, steps S21-S22 are repeated to record the absorbance respectively. 、 、 ,pass and Get a new calibration reagent curve ,Will Substitute the new calibration reagent curve to calculate the characteristic concentration of the calibration solution corresponding to the current potassium permanganate solution , when the concentration ratio of potassium permanganate solution is If the ratio is within the range of 0.95~1.05, it indicates that the current potassium permanganate solution can continue to be used; if the ratio is not within this range, it is necessary to re-prepare the potassium permanganate solution and perform steps S21-S22 again to make the ratio within the above range before continuing to measure the sample.

6. The permanganate index self-matching air pressure detection method according to claim 5, characterized in that: The rate of change of two spectrophotometer signals ,use Correction , ready to use ,get , according to step S3 and the corresponding After establishing a new calibration curve, measure the samples again.

7. The permanganate index self-matching air pressure detection method according to claim 1, characterized in that: In step S1, the prepared curve is colorimetrically compared at wavelengths of 475 nm, 500 nm, 525 nm, 550 nm, and 575 nm, and the wavelength with the best sample sensitivity and curve linearity is selected as the working wavelength.

8. The permanganate index self-matching air pressure detection method according to claim 1, characterized in that: Step S41 includes the following sub-steps: S401: Take 100 ml of water sample into a digestion bottle and add a magnetic stirrer into the digestion bottle; S402: Add 5 ml of sulfuric acid solution and 10 ml of potassium permanganate standard working solution through the reagent line and stir evenly. The sulfuric acid solution is a mixed solution of 1 volume of concentrated sulfuric acid and 3 volumes of distilled water. The concentration of the potassium permanganate standard working solution is 0.01 mol / L. S403: Digest at 98°C for 30 minutes. If the boiling point of local water is lower than 98°C, install a pressure regulating assembly at the mouth of the digestion bottle. Start colorimetry at 29.5 minutes of digestion. Stop stirring with the magnetic stirrer during colorimetry. Continue colorimetry for 30 seconds. Read the absorbance every 5 seconds during colorimetry. The final absorbance value is the average of the last three readings. The relative standard deviation (RSD) of the absorbance should not be greater than 1%.

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