Permanganate index self-matching air pressure detection system and method

Abstract

The invention discloses a permanganate index self-matching air pressure detection system and method, and belongs to the technical field of environmental monitoring, the detection system 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 of a cylindrical structure with a raised bottom, and the digestion bottle comprises a digestion part, a to-be-detected part and a pressure regulating bottle cap. The detection method comprises the following steps: determining an optimal detection wavelength; establishing a calibration reagent curve; establishing a calibration curve of permanganate indexes; and measuring a water sample, and correcting a curve according to the change rate of signals of the spectrophotometer twice, and the like. According to the invention, the accuracy of a colorimetric result can be ensured, errors generated in a colorimetric process are reduced, meanwhile, automation of sample loading, digestion and colorimetric can be realized, and the detection efficiency is improved.

Description

Technical Field

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

[0002] The permanganate index (I Mn ‌) is a key indicator for measuring the pollution degree of organic matter and oxidizable inorganic matter in water quality monitoring. It is defined as the amount of oxygen consumed when oxidizing a water sample with potassium permanganate (KMnO4) under acidic or alkaline conditions, and the unit is milligram per liter (mg / L). The traditional titration method is time-consuming, energy-consuming, and material-consuming, with cumbersome operations, certain requirements for the color sensitivity of operators, and relatively high requirements for the digestion time and temperature of samples. As a simple and stable method, the spectrophotometry method is also applied to the determination of the permanganate index.

[0003] However, the existing spectrophotometry method for determining the permanganate index still has the following problems: 1. The standard method (GB11892-89) uses a water bath temperature of 98 °C and a digestion time of 30 min ± 2 min to oxidize the oxidizable substances in the water sample with potassium permanganate, and the equivalent oxygen consumption is represented by the amount of potassium permanganate consumed. However, its measurement results are related to experimental conditions such as the water bath temperature and digestion time. Changing any experimental condition will cause deviations in the measurement results. For the titration method and the conventional spectrophotometry method, in medium and high altitude areas, due to the low air pressure, it is difficult for the boiling point temperature of water to reach the water bath temperature (98 °C) specified by the national standard method. In response to this situation, the national standard method only requires indicating the boiling point temperature in the result report without giving a specific solution, resulting in a low measured value of the permanganate index and poor data comparability in high altitude areas, causing difficulties in the evaluation of water environment quality.

[0004] 2. The traditional spectrophotometry method requires preparing a standard curve working solution to establish a calibration curve or calibration curve points before each sample analysis. Then, it needs to be heated for 30 min and then colorimetric each time, which is time-consuming, consumes standard solutions, and results in low sample detection efficiency. Moreover, potassium permanganate itself is not stable, and the concentration of the prepared potassium permanganate solution is prone to change. Frequent preparation of the standard curve working solution to establish a calibration curve or calibration curve points is time-consuming and laborious.

[0005] 3. When the spectrophotometer works continuously for a long time, its sensitivity is prone to drift. In the existing detection methods, the experiment of drawing a calibration curve is usually adopted to solve this problem, but the whole process is time-consuming and laborious, with low efficiency.

[0006] 4. In the original method, the colorimetric is carried out after cooling to room temperature and then transferring to the colorimetric cuvette. When the temperature drops, potassium permanganate is still reacting and the digestion process continues, and there is a possibility of contamination during the transfer.

[0007] Meanwhile, refer to the following Chinese patents: CN113125360A - Analytical System and Method for Automatic Monitoring of Permanganate Index, CN110346509A - An On - line Water Quality Permanganate Index Monitor and Detection Method, CN119104676A - A Detection Method and On - line Monitoring Method for Permanganate Index. The above solutions only apply to the traditional spectrophotometric method for determination and cannot effectively solve one or more of the problems listed above.

[0008] Therefore, a detection method for permanganate index that can adapt to different air pressure conditions is needed to improve the detection efficiency while ensuring the accuracy of the detection results. Summary of the Invention

[0009] The purpose of the present invention is to provide a permanganate index self - matching air pressure detection system and method to solve the problems existing in the background technology.

[0010] The purpose of the present invention is achieved through the following technical solutions: A permanganate index self - matching air pressure detection system includes a digestion bottle, a preparation platform, and a detection platform; The preparation platform includes a sample rack, a reagent automatic addition system, and an automatic capping system; The detection platform includes a base, a sample rotation system, and a spectrophotometer; The digestion bottle is a cylindrical structure with a convex bottom, and the digestion bottle includes a digestion part, a part to be measured, and a pressure - regulating bottle cap.

[0011] Further, the sample rotation system includes a rotating table and a rotating motor located below the rotating table. The rotating table is located inside the base. A plurality of placement grooves are circumferentially arranged above the rotating table. The size of the placement grooves is adapted to the size of the digestion part. An opening for the part to be measured to pass through is provided at the bottom of the placement groove. A graphite heating element is provided on the inner wall of the placement groove. A cavity is provided at the position of the rotating table corresponding to the part to be measured, and a magnetic field generator is provided below the rotating table corresponding to each cavity.

[0012] Further, the preparation platform is located on one side of the detection platform. A manipulator for sampling is provided between the preparation platform and the detection platform. The spectrophotometer is located inside the base and on the side away from the preparation platform. The spectrophotometer includes a system body (including a light source, a monochromator, etc.), a light outlet, and a receiver. The system body is slidably connected to the base. The inside of the turntable is a concave structure. The receiver is located below the inside of the turntable and corresponds to the position of the light outlet. The height of the light outlet is the same as the height of the cavity. The cavity is provided with a through hole corresponding to the position of the light outlet. The light emitted from the light outlet passes through the through hole, the cavity, the part to be measured, and is irradiated on the receiver.

[0013] Further, the pressure regulating bottle cap includes a bottle cap body and a temperature control valve. The temperature control valve is fixed in the middle of the bottle cap body and extends into the digestion part.

[0014] A self-matching air pressure detection method for permanganate index 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 100 ml of blank water sample, add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of sulfuric acid solution (1 + 3). Without heating, obtain the absorbance by colorimetry using a spectrophotometer. ; S22: Prepare a fluorescein sodium calibration solution with an absorbance of , and record its solution concentration as ; Prepare a fluorescein sodium calibration solution with an absorbance of , and record its solution concentration as ; is 0.8 - 0.9 times , is 1.1 - 1.2 times . At this time, according to the , two-point calibration reagent curve, obtain , is the absorbance, is the concentration of the calibration reagent, is the slope, is the intercept; S23: Substitute the in 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; S3: Establish a calibration curve for the permanganate index. Step S3 includes sub-steps S31 - S33. S31: Prepare standard solutions with different permanganate index concentrations. Add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L and 5 ml of sulfuric acid solution (1+3), and perform heating digestion. S32: Obtain the absorbances corresponding to different permanganate index concentrations by colorimetry for the digested solution. ; S33: Use the permanganate index concentration as the abscissa and as the ordinate to plot the calibration curve. , is the absorbance of potassium permanganate consumed after digestion of the standard solution, and plot the standard curve. , is the permanganate index, often expressed as , with the unit mg / L; is the absorbance; is the slope; is the intercept; S4: Water sample determination: Step S4 includes sub-steps S41 - S42. S41: Add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L and 5 ml of sulfuric acid solution (1+3) to the water sample for digestion and colorimetry. S42: Obtain the absorbance of the remaining potassium permanganate in the digested water sample by colorimetry. , , is the absorbance of potassium permanganate consumed in the digested water sample. Then, according to the linear equation in step S33 , substitute into to obtain the permanganate index . If > 2, the water sample needs to be diluted before re-determination. The dilution formula is: , where: , is the absorbance of potassium permanganate consumed by the blank sample (pure water), is the absorbance of the remaining potassium permanganate after consumption by the blank sample (pure water), is the dilution factor; S5: Repeat step S4 for multiple groups of water sample determinations.

[0015] Further, for step S5, during continuous water sample determinations without interruption, an interim calibration needs to be performed every 12 h. This interim calibration requires repeating steps S21 - S22, and record the absorbances , , , and obtain a new calibration reagent curve through and ​ , substitute into the new calibration reagent curve to calculate the representative concentration of the calibration solution corresponding to the current potassium permanganate solution . When the ratio of the representative concentration of the potassium permanganate solution 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, the potassium permanganate solution needs to be freshly prepared, and steps S21 - S22 are performed again. After the ratio is within the above - mentioned range, the sample is measured continuously.

[0016] Further, the change rate of the spectrophotometer signals twice , use to correct , that is, use to obtain . According to step S3 and the corresponding to establish a new calibration curve, then measure the sample.

[0017] Further, in step S1, the prepared curves are colorimetric at wavelengths of 475 nm, 500 nm, 525 nm, 550 nm, and 575 nm respectively, and the wavelength with the best sample sensitivity and curve linearity is selected as the working wavelength.

[0018] Further, step S41 includes the following sub - steps: S401: Take 100 ml of water sample into the digestion flask, and add a magnetic stir bar to the digestion flask; S402: Add 5 ml of sulfuric acid solution (1 + 3) and 10 ml of potassium permanganate standard solution for use (0.01 mol / L) through the reagent pipeline respectively, and then stir evenly; S403: Digest at 98 °C for 30 min. If the boiling point of local water is lower than 98 °C, a pressure - regulating component is set at the mouth of the digestion flask; start colorimetry at 29.5 min of digestion. When colorimetric, stop the magnetic stir bar from stirring, continuously colorimetric for 30 s, read the absorbance every 5 s during colorimetry, and the final absorbance value is the average of the last 3 readings. The relative standard deviation (RSD) of the absorbance should not be greater than 1%.

[0019] The beneficial effects of the present invention are: This method is simple through colorimetry and can effectively avoid the problem that in the titration method, when sodium oxalate is added, it is still yellow and it is difficult to judge the end - point color during titration.

[0020] By using a stir bar to stir during digestion, the generation of minute particles ( ) is avoided, effectively solving the problem that the generation of abnormal colors during sample digestion affects the accuracy of colorimetry. At the same time, the highest concentration of the curve is set at 2 mg / L, and by dilution, the water sample contains less organic or inorganic substances, and the permanganate ( The reduction reaction of () is more complete and will be reduced to which is soluble in water, rather than being reduced to During colorimetry, the water sample is clear and does not affect the colorimetric result.

[0021] By setting the pressure regulating component, the air pressure in the digestion bottle is maintained at a fixed value, and the boiling point temperature is maintained at 98 °C, which can be applied to different altitude areas.

[0022] The sample loading, digestion, and colorimetry are automated through the detection system, which improves the detection efficiency. At the same time, it can automatically perform in-process calibration and establish a calibration curve in a timely manner.

[0023] Using sodium fluorescein for the calculation of the concentration change rate of potassium permanganate solution and the correction of the sensitivity drift of the spectrophotometer, it can be repeatedly used for subsequent calibration after being prepared in the early stage. Using the sodium fluorescein solution, no pretreatment such as heating is required, and it can be directly colorimetric, with short time consumption and small dosage, which is beneficial to improving the detection efficiency; since there is no need to repeatedly prepare the calibration curve use solution, it is also beneficial to simplify the experimental steps and reduce the consumption of material costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a top view of a permanganate index self-matching air pressure detection system of the present invention; Figure 2 It is a side view of the detection platform in the present invention; Figure 3 It is a partial cross-sectional view of the rotating table in the present invention; Figure 4 It is a schematic diagram of the digestion bottle in the present invention; In the figure, 1 - detection platform, 11 - base, 2 - preparation platform, 21 - sample rack, 22 - automatic capping system, 3 - digestion bottle, 31 - digestion part, 32 - part to be measured, 33 - pressure regulating bottle cap, 34 - temperature control valve, 4 - manipulator, 5 - spectrophotometer, 51 - system body, 52 - light outlet, 53 - receiver, 6 - sample rotation system, 61 - placement groove, 62 - rotating table, 63 - rotating motor, 64 - cavity, 65 - graphite heating element, 66 - through hole, 67 - magnetic field generator, 68 - magnetic stirrer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present invention.

[0026] This application uses spectrophotometry to determine the permanganate index. The specific experimental principle is as follows: Under acidic conditions, an excessive amount of potassium permanganate is used to oxidize the reducing substances in the water body. According to the property that potassium permanganate has good sensitivity during colorimetry, the amount of the remaining potassium permanganate is measured by colorimetry, and a calibration curve between the permanganate index and the absorbance of the consumed potassium permanganate is established. The permanganate index of the water sample is directly calculated through the curve. Example

[0027] A permanganate index self-matching air pressure detection system As Figures 1 - 4 shown, this system includes a digestion bottle 3, a preparation platform 2, and a detection platform 1; The preparation platform 2 includes a sample rack 21, a reagent automatic addition system, and an automatic capping system 22; The detection platform 1 includes a base 11, a sample rotation system 6, and a spectrophotometer 5; The digestion bottle 3 is a cylindrical structure with a convex bottom. The digestion bottle 3 includes a digestion part 31, a part to be measured 32, and a pressure-regulating bottle cap 33.

[0028] Through the above technical solution, both the sample rack 21 and the turntable 62 are provided with placement grooves 61 of the same size specification. Among them, the digestion bottle 3 containing the water sample is placed on the sample rack 21. A sulfuric acid solution, a potassium permanganate working solution, and a magnetic stirrer 68 are added into the digestion bottle 3 through the reagent automatic addition system. The magnetic stirrer 68 can be manually placed or picked up by a manipulator. The prepared water sample is placed on the sample rack 21 and waits for the manipulator 4 to pick up the prepared digestion bottle 3 and place it on the turntable 62. The reagent automatic addition system (automatic sample loading machine) is a mature technology in the art and is not shown in the figure. When the boiling point of local water ≥ 98 °C, there is no need to install the pressure-regulating bottle cap 33 on the digestion bottle 3.

[0029] Furthermore, both the potassium permanganate solution and the calibration solution are filled in the digestion bottle 3 and placed at the fixed position in the upper right corner of the sample rack 21. Preferably, both the potassium permanganate solution in step S21 and the low-concentration fluorescein sodium calibration solution and the high-concentration fluorescein sodium calibration solution prepared in step S22 in the permanganate index self-matching air pressure detection method are filled in the digestion bottle 3 and placed at the fixed position in the upper right corner of the sample rack 21.

[0030] Furthermore, as Figures 1 - 3As shown, the sample rotation system 6 includes a rotating table 62 and a rotating motor 63 located below the rotating table 62. The lower part of the rotating table 62 is located within the base 11. A plurality of placement grooves 61 are circumferentially arrayed above the rotating table 62. The size of the placement grooves 61 is adapted to the size of the digestion part 31. An opening for the part to be measured 32 to pass through is provided at the bottom of the placement groove 61. A graphite heating element 65 is provided on the inner wall of the placement groove 61. A cavity 64 is provided at the position of the rotating table 62 corresponding to the part to be measured 32. A magnetic field generator 67 is provided below the rotating table 62 corresponding to each cavity 64.

[0031] Through the above technical solution, a cavity 64 is correspondingly provided below each placement groove 61, and an independent magnetic field generator 67 is provided below each cavity 64. At the same time, an independent graphite heating element 65 for controlling the temperature is provided in each placement groove 61. The digestion bottle 3 is placed in the placement groove 61 on the rotating table 62 by the manipulator 4. At this time, the part to be measured 32 passes through the opening below the placement groove 61 and extends into the cavity 64. The solution in the digestion bottle 3 can be heated by the graphite heating element 65. At the same time, the magnetic stirrer 68 in the bottle is kept rotating by the magnetic field generator 67 below, fully stirring the solution.

[0032] In this embodiment, the digestion part 31 of the digestion bottle 3 is a cylindrical structure with a diameter of 5 cm. The digestion part 31 is used for digestion reaction, while the part to be measured 32 is a cylindrical structure or a cubic structure with a diameter of 1 cm. The part to be measured is equivalent to a cuvette for colorimetry. The length of the magnetic stirrer 68 is greater than 2 cm to prevent the magnetic stirrer 68 from falling into the part to be measured 32 and unable to stir normally. The top of the digestion bottle 3 extends out of the placement groove 61, facilitating the taking and placing of the digestion bottle 3 from the placement groove 61.

[0033] During the rotation of the rotating table 62, the digestion bottle 3 is always in a heated state and kept stirred by the magnetic generator until the digestion bottle 3 is about to move to the spectrophotometer 5, then the stirring stops.

[0034] Further, the preparation platform 2 is located on one side of the detection platform 1. A manipulator 4 for sampling is provided between the preparation platform 2 and the detection platform 1. The spectrophotometer 5 is located inside the base 11 and on the side far from the preparation platform 2. The spectrophotometer 5 includes a system body 51, a light outlet 52, and a receiver 53. The system body 51 includes a housing, a light source, a monochromator, etc. The system body 51 is slidably connected to the base 11. Since the system body 51 is slidably connected to the base 11, and the light outlet 52 is located at the front end of the system body 51, while the receiver 53 is fixed on the base, the distance between the light outlet 52 and the part to be measured 32 can be conveniently adjusted through the sliding structure to ensure the distance of the optical path and thus ensure the accuracy of the measurement. The light emitted by the light source is irradiated onto the part to be measured 32 through the light outlet 52. The part to be measured 32 is equivalent to a cuvette in conventional colorimetry. The light source passes through the part to be measured 32 and shines on the receiver 53. The receiver 53 detects the light, converts it into an electrical signal using the photoelectric effect, and then transmits the electrical signal back to the system body 51 for analysis and recording, thereby obtaining the absorbance.

[0035] The spectrophotometer 5 is a commonly used instrument in the detection field, and the detection principle will not be elaborated here.

[0036] The interior of the rotating table 62 is a concave structure. The receiver 53 is located below the interior 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. A through hole 66 is provided at the position of the cavity 64 corresponding to the light outlet 52.

[0037] Through the above technical solution, since the lower part of the rotating table 62 is located inside the base 11, the space below the rotating table 62 is in a sealed and lightless environment. At the same time, the spectrophotometer 5 is also located inside the base 11. It is convenient to perform subsequent colorimetry under the darkroom conditions of the spectrophotometer 5.

[0038] A position sensor is provided at the position of the through hole 66 of the cavity 64 corresponding to the light outlet 52 of the spectrophotometer 5. When the through hole 66 rotates to the position of the light outlet 52, it stops. At this time, the spectrophotometer 5 is started, and 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 irradiate on the receiver 53. At this time, the sample in the part to be measured 32 can be colorimetrically analyzed by the spectrophotometer 5.

[0039] After the colorimetry is completed, the digestion bottle 3 stops heating. The tested digestion bottle 3 is moved to one side of the manipulator 4 through the rotating table 62 and taken out by the manipulator 4.

[0040] Further, as Figure 4 shown, the pressure regulating bottle cap 33 includes a 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.

[0041] The temperature control valve is a mature technology. For reference, see CN109027403B - A Passive Temperature Control Valve and CN208417719U - Automatic Temperature Control Valve. The core of both is to detect the temperature through a temperature control element. When the temperature of the temperature - variable substance (heat - expandable material) is greater than the preset temperature, it generates a thrust to push the piston head to drive the connecting rod and the valve to move, so that the valve opens the valve hole; when the temperature is less than or equal to the preset temperature, based on the elastic restoring force of the elastic component, the valve is controlled to seal the valve hole.

[0042] In this solution, a temperature control valve is provided on the temperature - adjustable bottle cap. The temperature element of the temperature control valve extends into the digestion bottle, and the valve hole is controlled according to the temperature in the digestion bottle, and then the air is exhausted. When the temperature is less than or equal to the preset temperature, the valve hole closes, enabling the sample in the digestion bottle to continue to heat up.

[0043] Specifically, when the boiling point of local water is lower than 98 °C, the digestion bottle 3 is covered with a pressure - regulating bottle cap 33 at the preparation platform 2 through the automatic capping system 22; When the digestion bottle 3 is placed on the rotating table 62 and starts to be heated, at this time, since the temperature in the digestion bottle has not reached the critical temperature at which the temperature - variable substance (heat - expandable material) in the temperature control valve expands to open the valve hole, the valve hole of the temperature control valve is in a closed state at this time, and the digestion bottle 3 is kept sealed through the pressure - regulating bottle cap 33. As the heating progresses, the pressure in the digestion bottle 3 gradually increases at this time, which is convenient to continuously raise the solution in the digestion bottle 3 to a suitable temperature for digestion.

[0044] When the temperature reaches the set value, the volume of the temperature - variable substance (heat - expandable material) expands beyond the critical value, and the expansion pushes the mechanical structure to act, and then opens the valve hole. For example, when the critical temperature is set to 95.5 °C, when it reaches 95.5 °C, the volume of the temperature - variable substance (heat - expandable material) in the temperature control valve expands beyond the critical value. The heat - expandable material can be selected from graphite, high - expansion alloy, etc. After the heat - expandable material expands, it generates a thrust to push the piston head to drive the connecting rod and the valve to move, so that the valve opens the valve hole, and the gas in the digestion bottle is discharged to avoid excessive pressure in the digestion bottle; when the temperature is getting higher and higher, it will make the heat - expandable material expand faster, the valve hole opens wider, and the gas discharge flow rate is larger. Through the above components, it is ensured that the boiling point of the sample in the digestion bottle is 98 °C.

[0045] The pressure - regulating bottle cap 33 is used to control the pressure in the pressure - regulating bottle. During heating, the digestion bottle 3 is kept sealed through the pressure - regulating bottle cap 33, so that the air pressure in the digestion bottle 3 is higher than the local atmospheric pressure, increasing the boiling point temperature; when the sample in the digestion bottle 3 is higher than 98 °C, it exhausts air through the temperature control valve 34 to reduce the air pressure in the bottle, thereby reducing the boiling point of the sample to 98 °C, so as to ensure a constant air pressure in the bottle during digestion. By setting the pressure - regulating bottle cap 33, it can be applied to the detection of permanganate index in different altitude areas to ensure accurate detection results.

[0046] The basic working principle of this system is as follows: A digestion bottle 3 filled with water sample is placed on the sample rack 21 of the preparation platform 2. A sulfuric acid solution, a potassium permanganate working solution, and a magnetic stir bar 68 are added into the digestion bottle 3 through the reagent automatic addition system. Then, wait for the manipulator 4 to grab the prepared digestion bottle 3 onto the rotating table 62; The manipulator 4 places the digestion bottle 3 into the placement groove 61 on the rotating table 62. At this time, the part to be measured 32 passes through the opening below the placement groove 61 and extends into the cavity 64. The solution in the digestion bottle 3 can be heated by the graphite heating element 65. At the same time, the magnetic field generator 67 below makes the magnetic stir bar 68 in the bottle keep rotating to fully stir the solution; During the rotation of the rotating table 62, the digestion bottle 3 is always in the heating state and keeps stirring through the magnetic generator until the digestion bottle 3 is about to move to the spectrophotometer 5, then the stirring stops; The light emitted by the light source is irradiated onto the part to be measured 32 through the light outlet 52. The part to be measured 32 is equivalent to the colorimetric cuvette in conventional colorimetry. The light source passes through the part to be measured 32 and shines on the receiver 53. The receiver 53 detects the light, converts it into an electrical signal using the photoelectric effect, and then transmits the electrical signal back to the system body 51 for analysis and recording, thereby obtaining the absorbance. At this time, the sample in the part to be measured 32 can be colorimetrically analyzed by the spectrophotometer 5, and then the amount of the remaining 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.

[0047] Through this system, the processes of sample loading, digestion, and colorimetry are automated, improving the detection efficiency. At the same time, it can be applied to the permanganate index self-matching air pressure detection method and is suitable for the detection of the permanganate index in different altitude areas to ensure the accuracy of the detection results. Also, when in-situ calibration is required, the prepared potassium permanganate solution and calibration solution placed on the sample rack 21 can be taken by the manipulator 4, rotated by the rotating table 62, and moved to the position of the spectrophotometer 5 for measurement without heating. After the measurement and the establishment of the calibration curve, the subsequent samples are grabbed by the manipulator 4 for colorimetry. The whole process does not require manual operation, improving the detection efficiency. Embodiment

[0048] A permanganate index self-matching air pressure detection method includes the following steps: S1: Determine the optimal detection wavelength; Specifically, the prepared curves are colorimetrically analyzed at wavelengths of 475 nm, 500 nm, 525 nm, 550 nm, and 575 nm respectively, and the wavelength with the best sample sensitivity and curve linearity is selected as the working wavelength. Preferably, at a wavelength of 525 nm, the curve linearity is the best. It should be noted that step S1 is generally only performed once during the initial installation and commissioning of the instrument and will not be changed subsequently.

[0049] It is known that before step S1, there is a preparation of a potassium permanganate standard solution. The preparation method is a conventional technique and will not be elaborated here. Commercially available potassium permanganate standard solution with a concentration of 0.01 mol / L can also be directly used.

[0050] S2: Establish a calibration reagent curve. Step S2 includes sub-steps S21 - S23. S21: Take 100 ml of blank water sample, add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of sulfuric acid solution (1 + 3). Without heating, obtain the absorbance through colorimetry with a spectrophotometer. ; Among them, the sulfuric acid solution (1 + 3) refers to the solution after mixing 1 volume of concentrated sulfuric acid and 3 volumes of distilled water.

[0051] S22: Prepare fluorescein sodium calibration solutions with absorbances of and record their solution concentrations as ; Prepare fluorescein sodium calibration solutions with absorbances of and record their solution concentrations as ; is 0.8 - 0.9 times , is 1.1 - 1.2 times . At this time, according to the two-point calibration reagent curve of and , obtain , is the absorbance, is the concentration of the calibration reagent, is the slope, is the intercept; S23: Substitute in step S21 into the linear equation in step S22 to obtain the initial characterization concentration of the calibration solution corresponding to the potassium permanganate solution; where the characterization concentration refers to a numerical value rather than the true concentration.

[0052] Through step S2, it can be known that the traditional spectrophotometry method requires preparing the standard curve working solution before each analysis to establish the calibration curve or calibration curve points. If calibrated with the traditional calibration method, then this method requires heating for 30 minutes each time before colorimetry, consuming a large amount of time.

[0053] Fluorescein sodium is now introduced. This reagent has stable properties and can be stably stored for a long time. At the same time, it also has stable and sensitive absorption of light with a wavelength of about 525 nm. Using fluorescein sodium for the calculation of the concentration change rate of potassium permanganate solution and the correction of the sensitivity drift of the spectrophotometer, it can be repeatedly used for subsequent calibrations after being prepared in the early stage. When using the fluorescein sodium solution, there is no need for pretreatment such as heating, and it can be directly colorimetric, which takes a short time and uses less amount, thus being beneficial to improving the detection efficiency; since there is no need to repeatedly prepare the calibration curve use solution, it is also beneficial to simplify the experimental steps and reduce the consumption of material costs.

[0054] Preferably, the concentration of fluorescein sodium is between 0.65 mmol / L and 0.95 mmol / L.

[0055] Furthermore, during the continuous measurement of water samples without interruption, an interim calibration needs to be carried out every 12 h. This interim calibration requires repeating steps S21 - S22, and the absorbances are recorded respectively 、 、 . Through and a new calibration reagent curve is obtained . Substitute into the new calibration reagent curve to calculate the representative concentration of the calibration solution corresponding to the current potassium permanganate solution . When the ratio of the representative concentration of the potassium permanganate solution is within the range of 0.95 - 1.05, there is no need to re - establish the calibration curve through experiments.

[0056] Through the above steps, when the ratio of the representative concentration of the potassium permanganate solution is within the range of 0.95 - 1.05, it indicates that the concentration of the potassium permanganate solution is within the appropriate range, which means the current potassium permanganate solution can continue to be used. If the ratio is not within this range, the potassium permanganate solution needs to be re - prepared, and steps S21 - S22 are carried out again. After the ratio is within the above - mentioned range, the sample determination can be continued. This can avoid the large change in the concentration of the potassium permanganate solution affecting the accuracy of the detection results.

[0057] S3: Establish a calibration curve for the permanganate index. Step S3 includes sub - steps S31 - S33. S31: Prepare standard solutions with different permanganate index concentrations, add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of sulfuric acid solution (1 + 3), and carry out heating digestion. S32: Obtain the absorbance A corresponding to different permanganate index concentrations by colorimetry of the digested solution. S33: Using the permanganate index concentration as the abscissa and as the ordinate, draw a calibration curve. , is the absorbance of potassium permanganate consumed after digestion of the standard solution, and a standard curve is plotted , is the permanganate index, often expressed as , with the unit of mg / L; is the absorbance; is the slope; is the intercept.

[0058] S4: Water sample determination: Step S4 includes sub-steps S41 - S42, S41: Add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L and 5 ml of sulfuric acid solution (1 + 3) to the water sample for digestion and colorimetry; The specific step S41 includes the following sub-steps: S401: Take 100 ml of water sample in a digestion flask, and add a magnetic stir bar to the digestion flask; S402: Add 5 ml of sulfuric acid solution (1 + 3) and 10 ml of potassium permanganate standard working solution (0.01 mol / L) respectively through the reagent pipeline and then stir evenly; By using a stir bar to stir during digestion, precipitation is avoided, effectively solving the problem that the color of the sample during digestion affects the accuracy of colorimetry.

[0059] S403: Digest at 98 °C for 30 min. If the boiling point of the local water is lower than 98 °C, a pressure regulating component is set at the mouth of the digestion flask; start colorimetry at 29.5 min of digestion. Stop the magnetic stir bar during colorimetry, continuously colorimetric for 30 s, read the absorbance every 5 s during colorimetry, and the final absorbance value is the average of the last 3 readings. The relative standard deviation (RSD) of the absorbance should not be greater than 1%.

[0060] If the RSD is greater than 1%, data needs to be reselected. Since the final absorbance value is the average of the last 3 readings, a value with a large deviation can be excluded, and the reading of the fourth from the bottom is introduced to re - calculate the RSD. If the RSD is still greater than 1%, repeat the above steps to exclude data with large deviations and introduce new readings.

[0061] When the boiling point of the local water is lower than 98 °C, a pressure regulating component is set at the mouth of the digestion flask. The pressure regulating component is used to control the pressure in the pressure regulating flask. During heating, the digestion flask is kept sealed through the pressure regulating component, so that the air pressure in the digestion flask is higher than the local atmospheric pressure, increasing the boiling point temperature; when the sample in the digestion flask is higher than 98 °C, exhaust through the pressure regulating component to reduce the air pressure in the flask, thereby reducing the boiling point of the sample to 98 °C, ensuring that the air pressure in the flask is constant during digestion. By setting the pressure regulating component, the detection method of this application can be applied to different altitude areas.

[0062] S42: Obtain the absorbance of the remaining potassium permanganate in the water sample after digestion by colorimetry , , is the absorbance of the consumed potassium permanganate in the water sample after digestion. Then, according to the linear equation in step S33 , substitute into to obtain the permanganate index . If > 2, the water sample needs to be diluted before re - determination. The dilution formula is: , where: , is the absorbance of the consumed potassium permanganate in the blank sample (pure water), is the absorbance of the remaining potassium permanganate after consumption in the blank sample (pure water), is the dilution factor.

[0063] Two laboratory blank samples should be prepared for each batch of sample detection. The detection steps are the same as those of the actual samples and require heating and digestion. The absorbance of the laboratory blank , and its purpose is to eliminate the influence of reagent background and laboratory pure water.

[0064] Through the above technical solution, the highest concentration of the curve is set at 2 mg / L. By dilution, the water sample contains less organic or inorganic substances, and potassium permanganate will be reduced more slowly. The water sample is clear during colorimetry and does not affect the colorimetric result.

[0065] At the same time, by introducing sodium fluorescein, the drift of the spectrophotometer sensitivity can be corrected. Specifically, the change rate of the two spectrophotometer signals , use to correct , that is, use to obtain . After establishing a new calibration curve according to step S3 and the corresponding , then determine the sample.

[0066] S5: Repeat step S4 for multiple groups of water sample determinations.

[0067] Through the above technical solution, this method is simple by colorimetry and can effectively avoid the problems of the titration method, such as the sample changing color after digestion of high - concentration permanganate index samples, remaining yellow after adding sodium oxalate, and being difficult to judge the end - point color during titration.

[0068] The detection method provided in this embodiment preferably uses the detection system provided in Embodiment 1. The potassium permanganate solution in step S21 and the low-concentration fluorescein sodium calibration solution and high-concentration fluorescein sodium calibration solution prepared in step S22 are all contained in the digestion flask 3, and are placed at the fixed position in the upper right corner of the sample rack 21. Among them, the digestion flask 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 into the digestion flask 3 through the reagent automatic addition system. Referring to steps S401 and S402, the prepared water sample is placed on the sample rack 21 and waits for the manipulator 4 to grab the prepared digestion flask 3 onto the turntable 62, and then the subsequent heating digestion and colorimetric steps are carried out.

[0069] Among them, when in-situ calibration is required during the continuous measurement of water samples without interruption, the potassium permanganate solution, low-concentration fluorescein sodium calibration solution and high-concentration fluorescein sodium calibration solution prepared and placed on the sample rack 21 can be taken by the manipulator 4, rotated by the turntable 62 and moved to the position of the spectrophotometer 5 for measurement without heating. After the measurement and the calibration curve is established, the manipulator 4 grabs the subsequent samples for colorimetry. The whole process does not require manual operation, improving the detection efficiency.

[0070] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in related fields. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A permanganate index self-matching air pressure detection system, characterized in that: It includes a digestion flask (3), a preparation platform (2) and a detection platform (1); The preparation platform (2) includes a sample rack (21), a reagent automatic addition system and an automatic capping system (22); The detection platform (1) includes a base (11), a sample rotation system (6) and a spectrophotometer (5); The digestion flask (3) is a cylindrical structure with a convex bottom, and the digestion flask (3) includes a digestion part (31), a part to be measured (32) and a pressure-regulating bottle cap (33).

2. The permanganate index self-matching air pressure detection system according to claim 1, wherein: The sample rotation system (6) includes a rotating table (62) and a rotating motor (63) located below the rotating table (62). The lower part of the rotating table (62) is located inside the base (11). A plurality of placement grooves (61) are circumferentially arranged above the rotating table (62). The size of the placement grooves (61) is adapted to the size of the digestion part (31). An opening for the part to be measured (32) to pass through is provided at the bottom of the placement grooves (61). A graphite heating element (65) is provided on the inner wall of the placement grooves (61). A cavity (64) is provided at the position of the rotating table (62) corresponding to the part to be measured (32). A magnetic field generator (67) is provided below each cavity (64) corresponding to the rotating table (62).

3. The permanganate index self-matching air pressure detection system according to claim 1, characterized in that: The preparation platform (2) is located on one side of the detection platform (1). A manipulator (4) for sampling is provided between the preparation platform (2) and the detection platform (1). The spectrophotometer (5) is located inside the base (11) and on the side far from the preparation platform (2). The spectrophotometer (5) includes a system body (51), a light outlet (52) and a receiver (53). The system body (51) is slidably connected to the base (11). 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). A through hole (66) is provided at the position of the cavity (64) corresponding to the light outlet (52). The light emitted from the light outlet (52) passes through the through hole (66), the cavity (64), the part to be measured (32), and irradiates on the receiver (53).

4. The permanganate index self-matching air pressure detection system according to claim 1, wherein: The pressure-regulating bottle cap (33) includes a bottle cap body and a temperature control valve (34). The temperature control valve (34) is fixed in the middle of the bottle cap body and extends into the digestion part (31).

5. A permanganate index self-matching air pressure detection method, which is implemented by using the permanganate index self-matching air pressure detection system described in any one of claims 1-4, and is characterized in that: It 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 100 ml of blank water sample, add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of sulfuric acid solution (1+3). Without heating, obtain the absorbance by colorimetry using a spectrophotometer ; S22: Prepare a fluorescein sodium calibration solution with an absorbance of , record its solution concentration as ; prepare a fluorescein sodium calibration solution with an absorbance of , record its solution concentration as ; is 0.8 - 0.9 times , is 1.1 - 1.2 times . At this time, according to the two-point calibration reagent curve of and , obtain , where is the absorbance, is the concentration of the calibration reagent, is the slope, and is the intercept; S23: Substitute the in 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 ; S3: Establish a calibration curve for the permanganate index. Step S3 includes sub-steps S31 - S33, S31: Prepare standard solutions with different permanganate index concentrations, add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of sulfuric acid solution (1 + 3), and perform heating digestion; S32: Obtain the absorbance corresponding to different permanganate index concentrations by colorimetry of the digested solution ; S33: With the permanganate index concentration as the abscissa, as the ordinate, plot the calibration curve, , is the absorbance of potassium permanganate consumed after digestion of the standard solution, and plot the standard curve , is the permanganate index, often represented by , with the unit of mg / L; is the absorbance; is the slope; is the intercept; S4: Water sample determination: Step S4 includes sub-steps S41 - S42, S41: Add 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L and 5 ml of sulfuric acid solution (1 + 3) to the water sample for digestion and colorimetry; S42: Obtain the absorbance of the remaining potassium permanganate in the water sample after digestion by colorimetry , , is the absorbance of the potassium permanganate consumed in the water sample after digestion. Then, according to the linear equation in step S33 , substitute into to obtain the permanganate index . If > 2, the water sample needs to be diluted and then measured. The dilution formula is: . In the formula: , is the absorbance of the potassium permanganate consumed by the blank sample (pure water), is the absorbance of the remaining potassium permanganate after consumption by the blank sample (pure water), is the dilution factor; S5: Repeat step S4 for multiple groups of water sample measurements.

6. The permanganate index self-matching air pressure detection method according to claim 5, wherein: For step S5, during continuous water sample measurement without interruption, an interim calibration shall be performed every 12 hours. This interim calibration shall repeat steps S21 - S22, and the absorbance shall be recorded respectively. , , , and through and , a new calibration reagent curve is obtained. Substitute into the new calibration reagent curve to calculate the representative concentration of the calibration solution corresponding to the current potassium permanganate solution. When the ratio of the representative concentration of the potassium permanganate solution 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, the potassium permanganate solution needs to be re-prepared, and steps S21 - S22 shall be performed again. After the ratio is within the above range, the sample measurement can continue.

7. The permanganate index self-matching air pressure detection method according to claim 6, characterized in that: The change rate of the spectrophotometer signal twice , using to correct , that is, using , to obtain , according to step S3 and the corresponding After establishing a new calibration curve, measure the sample again.

8. The permanganate index self-matching air pressure detection method according to claim 5, wherein: In step S1, the prepared curves are colorimetrically measured at wavelengths of 475 nm, 500 nm, 525 nm, 550 nm, and 575 nm respectively, and the wavelength with the best sample sensitivity and curve linearity is selected as the working wavelength.

9. The permanganate index self-matching air pressure detection method according to claim 5, characterized in that: Step S41 includes the following sub-steps: S401: Take 100 ml of water sample in a digestion flask and add a magnetic stir bar to the digestion flask. S402: Add 5 ml of sulfuric acid solution (1+3) and 10 ml of potassium permanganate standard working solution (0.01 mol / L) through the reagent pipeline respectively and stir evenly. Digest at 98 °C for 30 min. If the boiling point of local water is lower than 98 °C, a pressure regulating component is set at the mouth of the digestion flask. Start colorimetric measurement at 29.5 min of digestion. Stop the magnetic stir bar during colorimetric measurement. Conduct continuous colorimetric measurement for 30 s. Read the absorbance every 5 s during colorimetric measurement. The final absorbance value is the average of the last 3 readings. The relative standard deviation (RSD) of the absorbance should not be greater than 1%.

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