CN114942299B - Titration endpoint analysis method and system based on permanganate index automatic analyzer - Google Patents
Titration endpoint analysis method and system based on permanganate index automatic analyzer Download PDFInfo
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- 238000004448 titration Methods 0.000 title claims abstract description 177
- 238000004458 analytical method Methods 0.000 title claims abstract description 23
- 230000029087 digestion Effects 0.000 claims abstract description 79
- 239000012286 potassium permanganate Substances 0.000 claims abstract description 74
- 238000006243 chemical reaction Methods 0.000 claims abstract description 37
- 238000000034 method Methods 0.000 claims abstract description 35
- 238000000954 titration curve Methods 0.000 claims abstract description 28
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 25
- 239000007788 liquid Substances 0.000 claims abstract description 25
- 230000008569 process Effects 0.000 claims abstract description 22
- 238000003756 stirring Methods 0.000 claims abstract description 16
- 230000004044 response Effects 0.000 claims abstract description 15
- 239000000243 solution Substances 0.000 claims description 49
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 12
- 239000011259 mixed solution Substances 0.000 claims description 10
- 230000003647 oxidation Effects 0.000 claims description 8
- 238000007254 oxidation reaction Methods 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 5
- 238000002360 preparation method Methods 0.000 claims description 3
- 241000208479 Anagallis arvensis Species 0.000 claims 2
- 230000007613 environmental effect Effects 0.000 abstract description 2
- ZNCPFRVNHGOPAG-UHFFFAOYSA-L sodium oxalate Chemical compound [Na+].[Na+].[O-]C(=O)C([O-])=O ZNCPFRVNHGOPAG-UHFFFAOYSA-L 0.000 description 6
- 229940039790 sodium oxalate Drugs 0.000 description 6
- 230000001590 oxidative effect Effects 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 239000007800 oxidant agent Substances 0.000 description 3
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 2
- 238000002835 absorbance Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 239000008103 glucose Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000003918 potentiometric titration Methods 0.000 description 2
- 238000003908 quality control method Methods 0.000 description 2
- 238000002798 spectrophotometry method Methods 0.000 description 2
- 239000012086 standard solution Substances 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000003760 magnetic stirring Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000035772 mutation Effects 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 238000012797 qualification Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000002352 surface water Substances 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 238000003221 volumetric titration Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/40—Concentrating samples
- G01N1/4044—Concentrating samples by chemical techniques; Digestion; Chemical decomposition
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/44—Sample treatment involving radiation, e.g. heat
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N35/00—Automatic analysis not limited to methods or materials provided for in any single one of groups G01N1/00 - G01N33/00; Handling materials therefor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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- Y02A20/20—Controlling water pollution; Waste water treatment
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Abstract
The invention relates to a titration endpoint analysis method and a titration endpoint analysis system based on a permanganate index automatic analyzer, wherein the method comprises the following steps: s1, starting titration; s2, in a first titration stage, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process, and judging whether the potential is larger than a potential threshold; if yes, go to step S3; s3, reducing the amount of each drop of potassium permanganate in the titration process, and entering the potassium permanganate titration in the second titration stage; s4, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process in the second titration stage, and establishing a dynamic titration curve corresponding to the potential of the digestion liquid, the response time of an electrode, the titration reaction temperature, the stirring speed of the digestion liquid, the volume of a reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started; s5, judging a titration end point based on the dynamic titration curve. The dynamic titration curve established by the invention considers the influence of titration environmental factors cooperatively, and further improves the judgment precision of the titration endpoint.
Description
Technical Field
The invention belongs to the technical field of analysis and detection, and particularly relates to a titration endpoint analysis method and system based on a permanganate index automatic analyzer.
Background
Permanganate index is one of the important indicators for automatic monitoring of surface water. According to GB 11892-1989 determination of permanganate index of water quality, known amounts of potassium permanganate and sulfuric acid are added into a sample, the sample is heated in a boiling water bath for 30min, certain organic matters and inorganic reducing substances in the sample are oxidized by the potassium permanganate, after the reaction, excessive sodium oxalate is added to reduce the residual potassium permanganate, and then excessive sodium oxalate is added back to the standard solution of potassium permanganate, and the permanganate index in the sample is obtained through calculation.
Currently, the measurement methods adopted by permanganate index automatic analyzers include spectrophotometry and titration. Titration methods are also classified into absorbance titration and potentiometric titration. The potentiometric titration method carries out end point judgment through the oxidation-reduction potential of the solution, can well avoid the defect that spectrophotometry and absorbance titration method are easily influenced by turbidity and chromaticity of water body, and is widely applied. However, regardless of the measurement method, the permanganate index automatic analyzer has the defect of low quality control qualification rate in practical application, and in practical application, quality control requires standard substance verification and does not allow modification of key parameters, recalibration of the instrument and the like.
As the permanganate index is a relative index, any factors such as digestion reaction temperature, digestion time, components of a standard sample (mostly sodium oxalate) and the like are changed, the oxidation rate of potassium permanganate can be influenced, and the accuracy of a detection result is further influenced. At present, the technical designs of the permanganate index automatic analyzer on the market, such as digestion reaction temperature, digestion time and the like, and the adopted standard sample components are not completely consistent with GB 11892-1989, and the heating mode, titration end point judgment and the like are also different, so that the oxidation rate of potassium permanganate is unstable, and when the potassium permanganate is checked by glucose standard substances, the relative error exceeds +/-10%, and the check is disqualified.
Disclosure of Invention
In view of the foregoing drawbacks and deficiencies of the prior art, it is an object of the present invention to at least address one or more of the above-identified problems of the prior art, in other words, to provide a method and system for end point analysis of titration based on an automatic permanganate index analyzer that meets one or more of the aforementioned needs.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
a method for endpoint analysis of titration based on an automatic permanganate index analyzer, comprising:
s1, starting titration, and performing potassium permanganate titration of a first titration stage on a digestion solution in a digestion tank; the digestion solution contains a water sample to be detected and a reducing agent, and is continuously stirred in the titration process;
s2, in a first titration stage, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process, and judging whether the potential is larger than a potential threshold; if yes, go to step S3;
s3, reducing the amount of each drop of potassium permanganate in the titration process, and entering the potassium permanganate titration in the second titration stage;
s4, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process in the second titration stage, and establishing a dynamic titration curve corresponding to the potential of the digestion liquid, the response time of an electrode, the titration reaction temperature, the stirring speed of the digestion liquid, the volume of a reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started;
s5, judging the point with the largest slope based on the dynamic titration curve as a titration end point.
Preferably, the dynamic titration curve is:
wherein P is the potential of the digestion solution, V 0 To add volume of potassium permanganate before titration starts, V 1 V is the volume of the reducing agent 2 For the dropwise adding volume of potassium permanganate after the start of titration, T is the response time of an electrode, v is the stirring speed of digestion liquid, T is the titration reaction temperature, T 0 To counteract the reaction temperature, k 0 、k 1 、k 2 、k 3 、k 4 And c are constants.
Preferably, the titration frequency of the second titration phase is lower than the titration frequency of the first titration phase.
Preferably, in the step S1, the sample preparation process of the digestion solution in the digestion tank includes the following steps:
s01, metering and quantifying a water sample to be measured, sulfuric acid and part of potassium permanganate solution, feeding the water sample to a digestion tank for heating, and timing after the temperature reaches the digestion reaction temperature;
s02, collecting the potential of the mixed solution in the digestion tank at intervals of a preset period to judge whether the mixed solution is in an oxidation state currently or not; if so, when the constant temperature time reaches the preset time, the temperature is reduced to the titration reaction temperature, and then the rest potassium permanganate solution is added at one time;
s03, adding a reducing agent to obtain a digestion solution.
Preferably, in the step S02, the potassium permanganate solution is added in portions before the potential of the mixed solution is in the oxidized state.
Preferably, the digestion reaction temperature is 90-100 ℃.
Preferably, the titration reaction temperature is 70-80 ℃.
Preferably, the predetermined time period is 10-20 min.
The invention also provides a titration endpoint analysis system based on the permanganate index automatic analyzer, which applies the titration endpoint analysis method according to the scheme, and comprises the following steps:
the potential acquisition module is used for acquiring the potential of the digestion liquid;
the potential judging module is used for judging whether the potential of the digestion solution is larger than a potential threshold value;
the titration control module is used for controlling the amount of each drop of potassium permanganate in the titration process;
the dynamic titration curve module is used for dynamically titrating the titration curve corresponding to the potential of the digestion solution, the response time of the electrode, the titration reaction temperature, the stirring speed of the digestion solution, the volume of the reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started;
and the titration end point judging module is used for judging the point with the maximum slope based on the dynamic titration curve, namely the titration end point.
Preferably, the dynamic titration curve is:
wherein P is the potential of the digestion solution, V 0 To add volume of potassium permanganate before titration starts, V 1 V is the volume of the reducing agent 2 For the dropwise adding volume of potassium permanganate after the start of titration, T is the response time of an electrode, v is the stirring speed of digestion liquid, T is the titration reaction temperature, T 0 To counteract the reaction temperature, k 0 、k 1 、k 2 、k 3 、k 4 And c are constants.
Compared with the prior art, the invention has the beneficial effects that:
according to the titration end point analysis method and system, the titration end point is pre-warned in real time through the potential of the electrode, and when the titration is close to the end point, the titration speed is controlled in advance, so that the titration is fully reacted, the purpose of accurate titration is achieved, and the purpose of rapid measurement is also achieved. Particularly, the dynamic titration curve established by the invention further improves the judgment precision of the titration end point by cooperatively considering the influence of titration environmental factors (including temperature, response time of an electrode, stirring speed and the like).
Drawings
FIG. 1 is a flow chart of a titration endpoint analysis method based on a permanganate index automatic analyzer in accordance with example 1 of the present invention;
FIG. 2 is a graph showing the potential versus titration volume for the titration process of example 1 of the present invention;
FIG. 3 is a block diagram of a titration endpoint analysis system based on an automatic permanganate index analyzer in accordance with example 1 of the present invention.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention, specific embodiments of the present invention will be described below with reference to the accompanying drawings. It is evident that the drawings in the following description are only examples of the invention, from which other drawings and other embodiments can be obtained by a person skilled in the art without inventive effort.
Example 1:
as shown in fig. 1, the titration endpoint analysis method based on the permanganate index automatic analyzer of the present embodiment specifically includes the following steps:
s1, starting titration, and performing potassium permanganate titration of a first titration stage on a digestion solution in a digestion tank; the digestion solution contains a water sample to be detected and a reducing agent, and is continuously stirred in the titration process;
in the step S1, the sample preparation process of the digestion solution in the digestion tank includes the following steps:
s01, metering and quantifying a water sample to be measured, sulfuric acid and part of potassium permanganate solution, feeding the water sample to a digestion tank for heating, and timing after the temperature reaches the digestion reaction temperature; the digestion reaction temperature is 90-100 ℃, and can be determined according to actual application requirements.
S02, collecting the potential of the mixed solution in the digestion tank at intervals of a preset period to judge whether the mixed solution is in an oxidation state currently or not; if so, when the constant temperature time reaches the preset time, the temperature is reduced to the titration reaction temperature, and then the rest potassium permanganate solution is added at one time; the titration reaction temperature can be determined between 70 ℃ and 80 ℃ according to actual application requirements; the predetermined time length can be determined between 10 and 20 minutes according to actual application requirements.
In addition, before the potential of the mixed solution is in an oxidation state, the potassium permanganate solution is added in batches, so that the self-adaptive adjustment of the volume of the added potassium permanganate is realized, a large amount of surplus potassium permanganate is ensured not to influence the residual volume after sodium oxalate is added due to self-heating decomposition, the volume consumed by titration of the potassium permanganate standard solution is further influenced, and finally the accuracy of the measured value is influenced.
S03, adding a reducing agent to obtain a digestion solution.
S2, in a first titration stage, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process, and judging whether the potential is larger than a potential threshold; if yes, go to step S3;
s3, reducing the amount (for example, half-drop amount) of each drop of potassium permanganate in the titration process, and performing potassium permanganate titration in a second titration stage; in addition, the titration frequency of the second titration phase is less than the titration frequency of the first titration phase.
S4, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process in the second titration stage, and establishing a dynamic titration curve corresponding to the potential of the digestion liquid, the response time of an electrode, the titration reaction temperature, the stirring speed of the digestion liquid, the volume of a reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started;
wherein, the dynamic titration curve is:
wherein P is the potential of the digestion solution, V 0 To add volume of potassium permanganate before titration starts, V 1 V is the volume of the reducing agent 2 For the dropwise adding volume of potassium permanganate after the start of titration, T is the response time of an electrode, v is the stirring speed of digestion liquid, T is the titration reaction temperature, T 0 To counteract the reaction temperature, k 0 、k 1 、k 2 、k 3 、k 4 And c are constants. In addition, as the potential value of the titration end point is related to the initial potential value of the titration time, the initial potential value needs to be deducted, so that the judgment precision of the titration end point is further improved; wherein, the initial potential value is related to the total volume of potassium permanganate added in the solution before titration and digestion reaction temperature.
S5, judging the point with the largest slope based on the dynamic titration curve as a titration end point.
Specifically, the process of determining the titration endpoint in this embodiment is specifically as follows:
1. the potential value P of the digestion liquid in the titration process is measured in real time through the electrode, and the volume V of the dripped potassium permanganate is controlled 2 And the speed of titration;
2. as shown in fig. 2, the change in potential is divided into three phases: stage A-quick titration, the residual reducing agent in the solution is excessive, so that the dripping amount of potassium permanganate is small, and the titration speed and unit dripping volume of potassium permanganate can be accelerated; the potential value is basically unchanged at the low level in the stage, because the potential value of the reducing agent is displayed; b stage-slow titration, along with increasing dropping volume of potassium permanganate, the amount of the rest reducing agent is smaller and smaller, the titration speed and unit dropping volume of potassium permanganate are slowed down before the potassium permanganate approaches to the end point, and because potential value mutation points are needed to be found, the slower the titration speed is, the better the dropping volume is, and the smaller the dropping volume is, the better the dropping volume is; the potential value will gradually increase in this stage; and C, in an excessive titration stage, after the rest reducing agent is reacted completely, the dripped potassium permanganate is excessive, and the potential value is stabilized at a high position again, so that the titration reaction is completed and the titration is stopped.
3. According to the three stages of the titration process, the dynamic titration curve is drawn as shown in fig. 2, and in the B stage, the potential is related to the response time of an electrode, the reaction temperature of a solution, the stirring speed of the solution, the volume of a reducing agent and the dripping volume of potassium permanganate, and the dynamic titration curve is fitted according to experimental data and experience values.
4. And (3) deriving according to a dynamic titration curve relation of the B-stage potential and the dropwise adding volume of the potassium permanganate, and finding out the point with the maximum slope to obtain a titration end point.
The permanganate index automatic analyzer of the embodiment uses a variable-speed volumetric titration method, which is superior to the commercial titration method for controlling the titration speed by titration volume; and the titration end point is pre-warned in real time through the potential of the electrode, and when the titration is close to the end point, the titration speed is controlled in advance, so that the titration is fully reacted, the purpose of accurate titration is achieved, and the purpose of rapid measurement is also achieved.
The embodiment also provides a titration endpoint analysis system based on the permanganate index automatic analyzer, and the titration endpoint analysis method of the embodiment is applied. Specifically, as shown in fig. 3, the titration endpoint analysis system includes: the device comprises a potential acquisition module, a potential judgment module, a titration control module, a dynamic titration curve module and a titration end point judgment module.
The potential acquisition module of the embodiment is used for acquiring the potential of the digestion liquid; the method is particularly used for collecting the mixed solution in the digestion tank in each stage and the potential of the digestion solution.
The potential judgment module of the embodiment is used for judging whether the potential of the digestion solution is greater than a potential threshold value.
The titration control module of this embodiment is used for controlling the volume and the titration frequency of every drop potassium permanganate in the titration process.
The dynamic titration curve module of the embodiment is used for dynamically titrating the curve corresponding to the potential of the digestion solution, the response time of the electrode, the titration reaction temperature, the stirring speed of the digestion solution, the volume of the reducing agent and the dripping volume of the potassium permanganate after the titration is started;
wherein, the dynamic titration curve is:
wherein P is the potential of the digestion solution, V 0 To add volume of potassium permanganate before titration starts, V 1 V is the volume of the reducing agent 2 For the dropwise adding volume of potassium permanganate after the start of titration, T is the response time of an electrode, v is the stirring speed of digestion liquid, T is the titration reaction temperature, T 0 To counteract the reaction temperature, k 0 、k 1 、k 2 、k 3 、k 4 And c are constants.
The titration end point judging module of the embodiment is used for judging the point with the largest slope based on the dynamic titration curve, namely the titration end point.
More specifically, the application of the titration endpoint analysis method based on the permanganate index automatic analyzer of the present embodiment is as follows:
(1) The permanganate index automatic analyzer measures and quantifies a water sample, sulfuric acid and a part of potassium permanganate solution, heats the water sample, and counts the time after the temperature reaches a specified temperature of 95 ℃; the above quantitative volumes refer to: 25mL of water sample, 1.25mL of 25% sulfuric acid solution and 0.25mL of potassium permanganate solution, and carrying out digestion at a constant temperature of 95 ℃ and continuously stirring in a magnetic stirring mode.
(2) And judging once every 30 seconds of the ORP electrode, and if the ORP electrode is in the oxidation state currently, adding the rest potassium permanganate solution once after the constant temperature time reaches 15 minutes and the temperature is reduced to 80 ℃.
If the ORP judges that the current state is the reduction state, continuously dripping 0.25mL of oxidant, continuously detecting after 30 seconds, and repeating the action until the current state is finished or the oxidation state is reached, wherein the total volume of the oxidant is kept to be 5 mL.
(3) After cooling to 80 degrees celsius, the addition of a reducing agent (e.g., sodium oxalate) was started and the potential of the current electrode was measured.
(4) Recording the current electrode potential, starting titration, namely determining the current electrode potential in real time, wherein the current electrode potential is the A stage.
(5) When the electrode potential is suddenly changed, the titration speed is changed, namely the B stage, and the current electrode potential P is:
(6) Continuously dripping an oxidant potassium permanganate solution, wherein the electrode potential value of the instrument is in a stable state, namely in the C stage, and the current liquid to be measured is in an oxidizing state, so that the titration endpoint is reached before.
(7) According to the B-stage potential P and titration volume V 2 The relation of (2) is derived, and the point with the largest slope is found out to be the titration end point.
(8) Calibrating with a sodium oxalate standard sample, and obtaining permanganate index concentration according to a least square method;
(9) And checking that the results are qualified by using glucose standard substances with different concentrations.
The foregoing is only illustrative of the preferred embodiments and principles of the present invention, and changes in specific embodiments will occur to those skilled in the art upon consideration of the teachings provided herein, and such changes are intended to be included within the scope of the invention as defined by the claims.
Claims (8)
1. A method for endpoint analysis of titration based on an automatic permanganate index analyzer, comprising:
s1, starting titration, and performing potassium permanganate titration of a first titration stage on a digestion solution in a digestion tank; the digestion solution contains a water sample to be detected and a reducing agent, and is continuously stirred in the titration process;
s2, in a first titration stage, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process, and judging whether the potential is larger than a potential threshold; if yes, go to step S3;
s3, reducing the amount of each drop of potassium permanganate in the titration process, and entering the potassium permanganate titration in the second titration stage;
s4, collecting the potential of the digestion liquid after each drop of potassium permanganate in the titration process in the second titration stage, and establishing a dynamic titration curve corresponding to the potential of the digestion liquid, the response time of an electrode, the titration reaction temperature, the stirring speed of the digestion liquid, the volume of a reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started;
s5, judging the point with the largest slope based on the dynamic titration curve as a titration end point;
the dynamic titration curve is:
wherein,,Pfor the potential of the digestion solution,V 0 to add volume of potassium permanganate before the start of titration,V 1 in order to achieve a volume of the reducing agent,V 2 to the volume of potassium permanganate added after the start of titration,tfor the response time of the electrode,vin order to achieve the stirring speed of the digestion solution,Tin order to titrate the reaction temperature,T 0 in order to counteract the reaction temperature,k 0 、k 1 、k 2 、k 3 、k 4 、care all constant.
2. The titration endpoint analysis method of claim 1, wherein the second titration phase has a titration frequency that is less than the titration frequency of the first titration phase.
3. The method according to any one of claims 1 to 2, wherein in step S1, the sample preparation process of the digestion solution in the digestion tank comprises the steps of:
s01, metering and quantifying a water sample to be measured, sulfuric acid and part of potassium permanganate solution, feeding the water sample to a digestion tank for heating, and timing after the temperature reaches the digestion reaction temperature;
s02, collecting the potential of the mixed solution in the digestion tank at intervals of a preset period to judge whether the mixed solution is in an oxidation state currently or not; if so, when the constant temperature time reaches the preset time, the temperature is reduced to the titration reaction temperature, and then the rest potassium permanganate solution is added at one time;
s03, adding a reducing agent to obtain a digestion solution.
4. The method according to claim 3, wherein in the step S02, the potassium permanganate solution is added in portions before the potential of the mixed solution is in the oxidized state.
5. The method according to claim 3, wherein the digestion reaction temperature is 90 to 100 ℃.
6. The method according to claim 3, wherein the titration reaction temperature is 70 to 80 ℃.
7. The method of claim 4, wherein the predetermined period of time is 10 to 20 minutes.
8. A titration endpoint analysis system based on an automatic permanganate index analyzer, employing the titration endpoint analysis method as recited in claim 1, wherein the titration endpoint analysis system comprises:
the potential acquisition module is used for acquiring the potential of the digestion liquid;
the potential judging module is used for judging whether the potential of the digestion solution is larger than a potential threshold value;
the titration control module is used for controlling the amount of each drop of potassium permanganate in the titration process;
the dynamic titration curve module is used for establishing a dynamic titration curve corresponding to the potential of the digestion solution, the response time of the electrode, the titration reaction temperature, the stirring speed of the digestion solution, the volume of the reducing agent and the dropwise adding volume of the potassium permanganate after the titration is started;
the titration end point judging module is used for judging the point with the maximum slope based on the dynamic titration curve, namely the titration end point;
wherein the dynamic titration curve is:
wherein,,Pfor the potential of the digestion solution,V 0 to add volume of potassium permanganate before the start of titration,V 1 in order to achieve a volume of the reducing agent,V 2 to the volume of potassium permanganate added after the start of titration,tfor the response time of the electrode,vin order to achieve the stirring speed of the digestion solution,Tin order to titrate the reaction temperature,T 0 in order to counteract the reaction temperature,k 0 、k 1 、k 2 、k 3 、k 4 、care all constant.
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