CN112710747B - Method for setting value of chemical oxygen demand standard solution - Google Patents
Method for setting value of chemical oxygen demand standard solution Download PDFInfo
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- CN112710747B CN112710747B CN202011472928.1A CN202011472928A CN112710747B CN 112710747 B CN112710747 B CN 112710747B CN 202011472928 A CN202011472928 A CN 202011472928A CN 112710747 B CN112710747 B CN 112710747B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/26—Conditioning of the fluid carrier; Flow patterns
- G01N30/28—Control of physical parameters of the fluid carrier
- G01N30/30—Control of physical parameters of the fluid carrier of temperature
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/26—Conditioning of the fluid carrier; Flow patterns
- G01N30/28—Control of physical parameters of the fluid carrier
- G01N30/32—Control of physical parameters of the fluid carrier of pressure or speed
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/86—Signal analysis
- G01N30/8675—Evaluation, i.e. decoding of the signal into analytical information
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/26—Conditioning of the fluid carrier; Flow patterns
- G01N30/28—Control of physical parameters of the fluid carrier
- G01N30/32—Control of physical parameters of the fluid carrier of pressure or speed
- G01N2030/324—Control of physical parameters of the fluid carrier of pressure or speed speed, flow rate
Abstract
The invention discloses a method for fixing the value of a chemical oxygen demand standard solution, which comprises the following steps: the method comprises the following steps: dissolving silver nitrate into ultrapure water to form a shielding agent; step two: adding the shielding agent into a chemical oxygen demand standard solution to be measured, shaking and standing; step three: filtering the chemical oxygen demand standard solution after standing and fixing the volume by using ultrapure water; step four: performing ion chromatographic analysis on the chemical oxygen demand standard solution with the constant volume to obtain chromatographic analysis data of potassium ions; step five: comparing the chromatographic analysis data of the potassium ions with a potassium ion concentration chromatographic curve chart to obtain a concentration value rho (K) of the potassium ions in the chemical oxygen demand standard solution after the volume is fixed in the step three; step six: according to the formula rho (COD) Cr )＝7.5M(O 2 ) The concentration rho (COD) of the chemical oxygen demand standard solution to be measured is calculated Cr ) M (O) in the formula 2 ) M (K) is the relative molecular mass of elemental potassium.
Description
Technical Field
The invention relates to the field of standard solution determination, in particular to a method for fixing a value of a chemical oxygen demand standard solution.
Background
The chemical oxygen demand standard substance solution is an important reference solution for monitoring and measuring the water quality pollution degree. The content accuracy of the potassium hydrogen phthalate directly influences the accuracy of water quality monitoring, so that the content is required to be fixed in the proportioning process.
The conventional determination method is still used in the value determination process of the chemical oxygen demand standard substance solution in the current market, namely, potassium dichromate and ferrous sulfate solutions are used as determination reagents through heating digestion, and a mercuric sulfate solution is required to be added to remove chloride ion interference; the potassium dichromate solution and the ferrous sulfate solution are prepared at present, the operation is complex, the recovery rate is not high, and the mercuric sulfate solution has strong toxicity and is not beneficial to the safety of a laboratory. The whole measuring process is manual, and more manpower, material resources and time are consumed.
Therefore, a rapid and highly safe method for fixing the chemical oxygen demand standard solution is required to solve the above problems.
Disclosure of Invention
The invention aims to provide a new technical scheme for fixing the value of a chemical oxygen demand standard solution.
According to a first aspect of the present invention, there is provided a method for valuing a chemical oxygen demand standard solution, comprising the steps of:
the method comprises the following steps: dissolving silver nitrate into ultrapure water to form a shielding agent, wherein the concentration of the silver nitrate in the shielding agent is not lower than 100 g/L;
step two: adding the shielding agent with the same volume into a chemical oxygen demand standard solution to be measured, vibrating and standing;
step three: filtering the chemical oxygen demand standard solution after standing and fixing the volume by using ultrapure water;
step four: performing ion chromatographic analysis on the chemical oxygen demand standard solution with the constant volume to obtain chromatographic analysis data of potassium ions;
step five: comparing the chromatographic analysis data of the potassium ions with a potassium ion concentration chromatographic curve chart to obtain a mass concentration value rho (K) of the potassium ions in the chemical oxygen demand standard solution after the volume is fixed in the step three;
step six: according to the formula rho (COD) Cr )＝7.5M(O 2 ) The chemical oxygen demand standard solution to be measured is calculated outChemical oxygen demand concentration of (1) (COD) Cr ) M (O) in the formula 2 ) M (K) is the relative molecular mass of elemental potassium.
Preferably, the potassium ion concentration chromatogram graph is mainly obtained by the following steps:
selecting at least three potassium reference reagents with different concentrations;
performing chromatographic analysis on the potassium reference reagent and removing a fluctuation value to obtain reference chromatographic data of potassium ions;
and (3) drawing a curve by taking the concentration of the potassium reference reagent as an abscissa and taking the reference chromatographic data of potassium ions as an ordinate, and obtaining a chromatographic curve chart of the potassium ion concentration.
Preferably, the preparation method of the potassium reference reagent comprises the following steps: taking at least three parts of potassium nitrate purity standard substances with different weights, respectively adopting ultrapure water to dissolve and fix the volume to be consistent with the volume fixed by the chemical oxygen demand standard solution in the third step.
Preferably, the reference chromatographic data of potassium ions is obtained by the following method:
adding the shielding agent with the same amount in the second step into a nitric acid solution with the mass fraction of 2%, and fixing the volume to be consistent with the volume of the potassium reference reagent by using ultrapure water to form a blank reference solution, wherein the volume ratio of the nitric acid solution to the shielding agent is 1: 10;
carrying out chromatographic analysis on the blank reference solution to obtain a fluctuation value;
and subtracting the fluctuation value from the initial data obtained after the chromatographic analysis of the potassium reference reagent to obtain the reference chromatographic data of the potassium ions.
Preferably, the method for acquiring the fluctuation value is as follows: and carrying out at least three times of chromatographic analysis on the blank reference solution to obtain a reference initial value, and averaging the obtained reference initial values to obtain the fluctuation value.
According to one embodiment of the disclosure, the chemical oxygen demand standard solution is subjected to valuing by using the method, heating digestion is not needed, so that the method is not limited by heating to a certain temperature, and has high valuing efficiency, high speed and good repeatability;
and because the interference factors are removed by adding the shielding agent, the use of reagents with stronger toxicity such as mercuric sulfate and the like is avoided, and the safety in the experimental process is improved;
compared with a common digestion titration method, the method does not need to be specially equipped with a digestion heating device, simultaneously uses a container made of common materials, does not need to consider high temperature resistance, only adds one treatment reagent silver nitrate in the whole process, and saves reagent purchase cost in a laboratory; meanwhile, manual titration operation is not needed, so that labor is saved.
Other features of the present invention and its advantages will become apparent from the following detailed description of exemplary embodiments of the invention.
Detailed Description
Various exemplary embodiments of the present invention will now be described in detail. It should be noted that: the relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.
The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.
Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.
In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.
Example one
A method for valuing a chemical oxygen demand standard solution comprises the following steps:
the method comprises the following steps: dissolving silver nitrate into ultrapure water to form a shielding agent;
in the step, the concentration of silver nitrate in the shielding agent is 100g/L, so that the excessive silver nitrate exists in the shielding agent to remove chloride ions, and the excessive silver nitrate still exists in the solution in an ion form, so that the solution form and the ion chromatography mobile phase cannot be influenced. The method avoids the situation that the ion chromatography is damaged and the value cannot be quickly determined due to the generation of mercury caused by the disproportionation reaction when the mercurous sulfate is used.
Step two: adding the shielding agent into a chemical oxygen demand standard solution to be measured, shaking and standing;
in the step, the chemical oxygen demand standard solution to be determined is pretreated, namely equal volume of shielding agent is added into the chemical oxygen demand standard solution to be determined, and the equal volume of shielding agent can completely remove chloride ions in the chemical oxygen demand standard solution to be determined.
After ultrasonic oscillation is adopted, standing is carried out for 60 minutes in a constant temperature environment of 20 ℃ so as to ensure the thorough reaction.
Step three: filtering the chemical oxygen demand standard solution after standing and fixing the volume by using ultrapure water;
in this step, the chemical oxygen demand standard solution after standing is filtered through a quantitative filter paper, and is repeatedly washed and filtered with ultrapure water, and the volume is fixed in a volumetric flask.
Step four: performing ion chromatographic analysis on the chemical oxygen demand standard solution with the constant volume to obtain chromatographic analysis data of potassium ions;
step five: comparing the chromatographic analysis data of the potassium ions with a potassium ion concentration chromatographic curve chart to obtain a mass concentration value rho (K) of the potassium ions in the chemical oxygen demand standard solution after the volume is fixed in the step three;
step six: according to the formula rho (COD) Cr )＝7.5M(O 2 ) The concentration rho (COD) of the chemical oxygen demand standard solution to be measured is calculated Cr ) M (O) in the formula 2 ) M (K) is the relative molecular mass of elemental potassium.
In this step, potassium hydrogen phthalate has the molecular formula C 8 H 5 KO 4 The potassium element mass concentration rho (K) is obtained through the steps, and the concentration rho (C) of the potassium hydrogen phthalate is obtained 8 H 5 KO 4 )＝ρ(K)·M(C 8 H 5 KO 4 )/M(K)；
It is obtained from the molecular formula of potassium hydrogen phthalate, which requires 7.5 oxygen molecules, i.e. rho (COD), to completely oxidize one molecule of potassium hydrogen phthalate Cr )＝7.5ρ(C 8 H 5 KO 4 )/M(C 8 H 5 KO 4 )；
Therefore, the two equations are combined and simplified to obtain the formula after being processed
ρ(COD Cr )＝7.5M(O 2 )/M(K)·ρ(K)
Further, a specific value of the measured chemical oxygen demand concentration of the chemical oxygen demand standard solution can be obtained.
In this or other embodiments, the potassium ion concentration chromatogram is derived primarily by:
step 11: selecting at least three potassium reference reagents with different concentrations;
in this step, the potassium reference reagent is prepared by the following method: at least three parts of potassium nitrate purity standard substances with different weights are respectively dissolved by ultrapure water, and after ultrasonic oscillation, the volume is constant to be consistent with that of the chemical oxygen demand standard solution after constant volume, so as to ensure the consistency of the experimental environment in the chromatographic analysis process.
Step 12: performing chromatographic analysis on the potassium reference reagent to obtain reference chromatographic data of potassium ions;
in this step, the prepared potassium reference reagents are separately subjected to chromatography, and at least three different reference chromatographic data are obtained, which are, for example, peak area/peak height values in the chromatography.
Step 13: and (3) drawing a curve by taking the concentration of the potassium reference reagent as an abscissa and taking the reference chromatographic data of potassium ions as an ordinate, and obtaining a chromatographic curve chart of the potassium ion concentration.
In the step, the concentration of at least three configured potassium reference reagents is taken as an abscissa, the abscissa is marked, corresponding reference chromatographic data is taken as an ordinate to obtain at least three coordinate points, and the coordinate points are connected to obtain a potassium ion concentration chromatographic graph.
According to the embodiment, the chemical oxygen demand standard solution is subjected to valuing by using the method, heating digestion is not needed, so that the method is not limited by heating to a certain temperature, and has the advantages of high valuing efficiency, high speed and good repeatability;
and because the interference factors are removed by adding the shielding agent, the use of reagents with stronger toxicity such as mercuric sulfate and the like is avoided, and the safety in the experimental process is improved;
the method is used for valuing the chemical oxygen demand standard solution, does not need heating digestion, is not limited by heating to a certain temperature, and has high valuing efficiency, high speed and good repeatability;
and because the interference factors are removed by adding the shielding agent, the use of reagents with stronger toxicity such as mercuric sulfate and the like is avoided, and the safety in the experimental process is improved;
compared with a common digestion titration method, the method does not need to be specially equipped with a digestion heating device, simultaneously uses a container made of common materials, does not need to consider high temperature resistance, only adds one treatment reagent silver nitrate in the whole process, and saves reagent purchase cost in a laboratory; meanwhile, manual titration operation is not needed, so that labor is saved.
Example two
In the embodiment, a blank reference solution is further included in the process of making the potassium ion concentration chromatographic chart, the shielding agent with the same amount in the step two is added into a nitric acid solution with the mass fraction of 2%, and the volume is fixed to be consistent with that of the potassium reference reagent by using ultrapure water, so that the blank reference solution is formed, wherein the volume ratio of the nitric acid solution to the shielding agent is 1: 10.
And carrying out chromatographic analysis on the blank reference solution to obtain a fluctuation value, and subtracting the fluctuation value from initial data obtained after the chromatographic analysis of the potassium reference reagent to obtain the reference chromatographic data of potassium ions.
By the method, numerical interference generated by other substances except the potassium ions is deducted to obtain more accurate reference chromatographic data of the potassium ions.
In this embodiment or other embodiments, the method for acquiring the fluctuation value includes: and carrying out at least three times of chromatographic analysis on the blank reference solution to obtain a reference initial value, and averaging the obtained reference initial values to obtain the fluctuation value.
Since the response value of the instrument to the blank reference solution may be affected by various factors such as current and the like, at least three times of chromatographic analysis is adopted, and the reference initial value is averaged to obtain a more accurate fluctuation value.
EXAMPLE III
In a specific example of this embodiment, the specific steps are as follows:
step 31: weighing 10.0g of silver nitrate, accurately transferring the silver nitrate to a 100mL beaker, adding 50mL of ultrapure water, oscillating and dissolving for 15 minutes by using 50Hz ultrasonic waves, transferring the solution in the beaker to a volume of 100mL, washing the wall of the beaker by using 20mL of ultrapure water, oscillating and treating for 5 minutes by using 50Hz ultrasonic waves, transferring the ultrapure water in the beaker after ultrasonic oscillation to the same volumetric flask, keeping the volume constant at 100mL, shaking uniformly, and keeping the temperature at 20 ℃;
step 32: accurately transferring 10mL of solution to be detected into a 100mL beaker by using a pipette, adding 10mL of shielding agent, ultrasonically vibrating for 5 minutes by using 50Hz, keeping the temperature to 20 ℃, and standing for 60 minutes;
step 33: and filtering the pretreated solution to be measured by quantitative filter paper, flushing the beaker by using 20mL of ultrapure water after the filtration is finished, continuously filtering the flushing liquid, repeatedly flushing and filtering for 3 times. Transferring all the filtered solution to a 100mL volumetric flask, using ultrapure water to perform constant volume, shaking up, and keeping the constant temperature to 20 ℃;
step 34: a Dionex ICS2000 series ion chromatograph is used and is provided with an automatic generator of non-chemical reagent leacheate, a temperature-controlled conductivity detection cell, a column heater and a vacuum degassing device. The instrument parameters are as follows: column temperature: 40 ℃; the temperature of the pool: 40 ℃; flow rate: 2.0 mL/min; sample introduction amount: 50 mu L of the solution; mode (2): automatic sample introduction; operating time: 15 min; concentration of methylamine sulfonic acid eluent: 25 mmol/L;
injecting the filtered chemical oxygen demand standard substance solution to be determined into an ion chromatograph to obtain the peak area (namely chromatographic analysis data) of the chemical oxygen demand standard solution to be determined;
step 35: and comparing the peak area with the peak area numerical value in a potassium ion concentration chromatographic chart to obtain the mass concentration of the potassium element.
Step 36: chemical oxygen demand (cod) concentration of the chemical oxygen demand (cr method) standard solution to be tested: rho (COD) Cr ) In mg/L according to the formula rho (COD) Cr )＝7.5M(O 2 ) Calculated as/M (K) · ρ (K).
In the above steps, the method for preparing the blank reference solution and three potassium reference reagents with different concentrations is as follows:
blank reference solution: accurately transferring 1mL of concentrated nitric acid into a 100mL volumetric flask by using a pipette, adding 10mL of shielding agent (the maximum concentration of the chemical oxygen demand standard substance is 1000mg/L, and adding 10mL according to the calculation to ensure excess), ultrasonically oscillating for 5 minutes by using 50Hz, fixing the volume by using ultrapure water, and shaking up.
Potassium standard reagent 1: accurately weighing 1.91g of potassium nitrate purity standard substance by using an electronic balance, putting the potassium nitrate purity standard substance into a 100mL volumetric flask, dissolving the potassium nitrate purity standard substance by using ultrapure water, ultrasonically shaking the solution for 5 minutes by using 50Hz, keeping the temperature to 20 ℃, then fixing the volume to 100mL, and shaking the solution uniformly.
Potassium reference reagent 2: accurately weighing 5.73g of potassium nitrate purity standard substance into a 100mL volumetric flask by using an electronic balance, dissolving by using ultrapure water, ultrasonically shaking for 5 minutes by using 50Hz, keeping the temperature to 20 ℃, fixing the volume, and shaking uniformly.
Potassium standard reagent 3: accurately weighing 9.55g of potassium nitrate purity standard substance into a 100mL volumetric flask by using an electronic balance, dissolving by using ultrapure water, ultrasonically shaking for 5 minutes by using 50Hz, keeping the temperature to 20 ℃, fixing the volume, and shaking uniformly.
Wherein, the concentration of potassium ions in 3 potassium reference reagents respectively corresponds to the concentration of potassium ions in the reagents when the oxygen demand concentration is 200mg/L, 600mg/L and 1000mg/L, and covers the concentration of potassium ions in the current chemical oxygen demand solution, so that a potassium ion concentration chromatographic chart can be completely drawn as a reference point.
When a potassium ion concentration chromatographic graph is drawn, a Dionex ICS2000 series ion chromatograph is used, 3 pins of blank reference solution, 1 pin of potassium reference reagent 1, 1 pin of potassium reference reagent 2 and 1 pin of potassium reference reagent 3 are respectively recorded, the peak area and/or the peak height of each pin are respectively recorded, and the average value of three data of blank reference solution is obtained to obtain a reference fluctuation value; and subtracting the data obtained by each potassium reference reagent from the reference fluctuation value to obtain the reference chromatographic data of the potassium ions, and drawing a potassium ion concentration chromatographic curve according to the data.
Although some specific embodiments of the present invention have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustrative purposes only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.
Claims (5)
1. A method for fixing the value of a chemical oxygen demand standard solution is characterized by comprising the following steps:
the method comprises the following steps: dissolving silver nitrate into ultrapure water to form a shielding agent, wherein the concentration of the silver nitrate in the shielding agent is not lower than 100 g/L;
step two: adding the shielding agent with the same volume into a chemical oxygen demand standard solution to be measured, vibrating and standing;
step three: filtering the chemical oxygen demand standard solution after standing and fixing the volume by using ultrapure water;
step four: performing ion chromatographic analysis on the chemical oxygen demand standard solution with the constant volume to obtain chromatographic analysis data of potassium ions;
step five: comparing the chromatographic analysis data of the potassium ions with a potassium ion concentration chromatographic curve chart to obtain a mass concentration value rho (K) of the potassium ions in the chemical oxygen demand standard solution after the volume is fixed in the step three;
step six: according to the formula rho (COD) Cr )＝7.5M(O 2 ) The concentration rho (COD) of the chemical oxygen demand standard solution to be measured is calculated Cr ) M (O) in the formula 2 ) M (K) is the relative molecular mass of oxygen and M (K) is the relative fraction of potassiumSub-mass.
2. The method of claim 1, wherein the chromatogram of the potassium ion concentration is obtained by the steps of:
selecting at least three potassium reference reagents with different concentrations;
performing chromatographic analysis on the potassium reference reagent and removing a fluctuation value to obtain reference chromatographic data of potassium ions;
and (3) drawing a curve by taking the concentration of the potassium reference reagent as an abscissa and taking the reference chromatographic data of potassium ions as an ordinate, and obtaining a chromatographic curve chart of the potassium ion concentration.
3. The method for valuing chemical oxygen demand standard solution according to claim 2, wherein the potassium reference reagent is prepared by the following method: taking at least three parts of potassium nitrate purity standard substances with different weights, respectively adopting ultrapure water to dissolve and fix the volume to be consistent with the volume fixed by the chemical oxygen demand standard solution in the third step.
4. The method of claim 3, wherein the reference chromatogram data of potassium ion is obtained by:
adding the shielding agent with the same amount in the second step into a nitric acid solution with the mass fraction of 2%, and fixing the volume to be consistent with the volume of the potassium reference reagent by using ultrapure water to form a blank reference solution, wherein the volume ratio of the nitric acid solution to the shielding agent is 1: 10;
carrying out chromatographic analysis on the blank reference solution to obtain a fluctuation value;
and subtracting the fluctuation value from the initial data obtained after the chromatographic analysis of the potassium reference reagent to obtain the reference chromatographic data of the potassium ions.
5. The method for fixing the chemical oxygen demand standard solution according to claim 4, wherein the fluctuation value is obtained by: and carrying out at least three times of chromatographic analysis on the blank reference solution to obtain a reference initial value, and averaging the obtained reference initial values to obtain the fluctuation value.
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