CN113884451A - Method for measuring chemical oxygen demand in high-chlorine water - Google Patents
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 89
- 239000000460 chlorine Substances 0.000 title claims abstract description 48
- 229910052801 chlorine Inorganic materials 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 title claims abstract description 33
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 25
- 239000001301 oxygen Substances 0.000 title claims abstract description 25
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 25
- 239000000126 substance Substances 0.000 title claims abstract description 25
- 230000029087 digestion Effects 0.000 claims abstract description 48
- 238000002835 absorbance Methods 0.000 claims abstract description 36
- 229910021607 Silver chloride Inorganic materials 0.000 claims abstract description 16
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 claims abstract description 16
- 238000005259 measurement Methods 0.000 claims abstract description 10
- 239000002244 precipitate Substances 0.000 claims abstract description 9
- 230000000694 effects Effects 0.000 claims abstract description 7
- 238000002133 sample digestion Methods 0.000 claims abstract description 7
- 229910000367 silver sulfate Inorganic materials 0.000 claims abstract description 6
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 10
- 230000009977 dual effect Effects 0.000 claims description 9
- 238000001816 cooling Methods 0.000 claims description 7
- 238000010521 absorption reaction Methods 0.000 claims description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 3
- 238000004445 quantitative analysis Methods 0.000 claims description 3
- 238000003379 elimination reaction Methods 0.000 abstract description 11
- 238000002798 spectrophotometry method Methods 0.000 abstract description 9
- 230000008030 elimination Effects 0.000 abstract description 4
- 239000000523 sample Substances 0.000 description 27
- 229910000372 mercury(II) sulfate Inorganic materials 0.000 description 14
- 239000000243 solution Substances 0.000 description 12
- 238000002474 experimental method Methods 0.000 description 8
- 239000007788 liquid Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 5
- 238000010992 reflux Methods 0.000 description 5
- 238000004448 titration Methods 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 230000000873 masking effect Effects 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 231100000167 toxic agent Toxicity 0.000 description 2
- 239000003440 toxic substance Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 238000000149 argon plasma sintering Methods 0.000 description 1
- 238000003556 assay Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000012898 sample dilution Substances 0.000 description 1
- 239000012488 sample solution Substances 0.000 description 1
- 239000013049 sediment Substances 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 238000012360 testing method 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
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
- G01N21/3151—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using two sources of radiation of different wavelengths
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/18—Water
- G01N33/1806—Biological oxygen demand [BOD] or chemical oxygen demand [COD]
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- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Spectroscopy & Molecular Physics (AREA)
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- Engineering & Computer Science (AREA)
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- Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)
Abstract
The invention discloses a method for measuring chemical oxygen demand in high-chlorine water, which utilizes Ag in digestion solution2SO4With Cl‑Combined to form AgCl precipitate mask Cl‑(ii) a Dual-wavelength isoabsorption Cr elimination method with 446nm as measurement wavelength and 545nm as reference wavelength3+And AgCl to K2Cr2O7The effect of absorbance; 3.00mLAg2SO4‑H2SO4(2:100)+1.00mL0.200mol/L(1/6K2Cr2O7) +2.00mL water sample or blank or standard sample digestion system, rapid digestion, spectrophotometry determination, can directly determine 1000 < Cl‑High-chlorine water with the concentration less than or equal to 5000mg/L and COD less than or equal to 600 mg/L; when Cl is present‑When the concentration is less than or equal to 2000mg/L, 1:100 Ag is adopted2SO4‑H2SO4And according to Cl‑Concentration adjustment of Ag2SO4The concentration was measured directly.
Description
Technical Field
The invention relates to the technical field of water quality detection and analysis, in particular to a method for determining chemical oxygen demand in high-chlorine water.
Background
The chemical oxygen demand of water quality is one of the main monitoring indexes of the environmental water quality standard, and reflects the degree of pollution of the water body by reducing substances. Therefore, the determination of the chemical oxygen demand in water quality is of great significance to the analysis and monitoring of water quality.
At present, the determination of Chemical Oxygen Demand (COD) of water quality generally adopts a potassium dichromate method, and standard analysis methods comprise a conventional reflux digestion titration method and a rapid digestion spectrophotometry method. HJ 828 + 2017 reflux digestion-titration method: is suitable for the water containing chlorine with COD less than or equal to 700mg/L and chloride concentration more than 1000mg/L (after dilution), HgSO4According to the mass ratio m [ HgSO4]:m[Cl-]The ratio of ≧ 20: 1. In addition, the HJ/T399-4According to the mass ratio m [ HgSO4]:m[Cl-]The ratio of ≧ 40: 1. DB 37/T3737-2019 high-chlorine water quality-determination of chemical oxygen demand-dichromate (reflux digestion-titration method), HgSO4According to the mass ratio m [ HgSO4]:m[Cl-]Addition of ≧ 7.5:1, method suitable for Cl-And the concentration of the water sample is less than 30000 mg/L. Further, HJ/T70-2001 perchloric water quality-determination of chemical oxygen demand-chlorine gas calibration method (reflux digestion-titration method), HgSO4According to the mass ratio m [ HgSO4]:m[Cl-]Addition of ≧ 10:1, method suitable for Cl-Water sample with concentration less than 20000 mg/L.
However, the existing assay standard uses HgSO4Belongs to a highly toxic substance, and the using amount of the water sample is dozens of times or even higher than the COD of the water sample, and is also Cl-Several times to dozens of times, which makes the complex treatment of the waste liquid components difficult and easily causes secondary pollution.
Disclosure of Invention
In view of the above-mentioned disadvantages, the object of the present invention is to provide a method for determining chemical oxygen demand in high-chlorine waterFor 1000mg/L < Cl-High-chlorine water quality of less than or equal to 5000mg/L and COD of less than or equal to 600mg/L is directly measured, and meanwhile, the digestion solution is prepared without adding HgSO4By eliminating Cl-The influence on COD measurement is effectively avoided by HgSO4The use of the utility model and the easy secondary pollution.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for measuring chemical oxygen demand in high-chlorine water, which utilizes Ag in digestion solution2SO4With Cl-Combined to form AgCl precipitate mask Cl-Elimination or substantial reduction of Cl-Quilt K2Cr2O7Oxidizing; dual-wavelength isoabsorption Cr elimination method taking 446nm +/-5 nm as measurement wavelength and 545nm +/-10 nm as reference wavelength3+And AgCl to K2Cr2O7The effect of absorbance; 3.00mLAg2SO4-H2SO4(2:100)+1.00mL0.200mol/L(1/6K2Cr2O7) +2.00mL water sample or blank or standard sample digestion system, rapid digestion, spectrophotometry determination of Cl 1000mg/L & lt-Chemical oxygen demand in high chlorine water with less than or equal to 5000mg/L and COD less than or equal to 600 mg/L.
Further, Cl in the high-chlorine water is obtained by the method for measuring the chemical oxygen demand in the high-chlorine water-When the mass volume ratio is less than or equal to 2000mg/L, Ag with the mass volume ratio of 1:100 is adopted2SO4-H2SO4。
Further, the method for measuring the chemical oxygen demand in the high-chlorine water comprises the following steps:
step (1): mixing 3.00mLAg with a mass-to-volume ratio of 2:1002SO4-H2SO4Adding into a digestion tube, and adding 0.200 mol/L1.00 mL1/6K2Cr2O7Oscillating and mixing the solution evenly;
step (2): slowly adding 2.00mL of water sample or blank or standard sample into the digestion tube obtained in the step (1), oscillating and uniformly mixing, placing the digestion tube into a digestion instrument, digesting for 12-16 min at the temperature of 160-170 ℃, taking out the digestion tube, and placing the digestion tube into water for cooling;
and (3): adding 5.00mL of water into the digestion tube obtained in the step (2), oscillating, uniformly mixing and cooling, and then respectively measuring the absorbance at 446nm and 545nm by using a 10mm absorption cell and taking water as a reference;
and (4): and (3) calculating: a ═ A446－A545；ΔA＝A0－A；
Wherein A is0-blank absorbance, a-water sample or standard absorbance;
and (5): and (4) establishing a delta A and COD concentration standard curve for water sample quantitative analysis according to the calculated value in the step (4).
Further, the digestion instrument parameters in the step (2) are as follows: the temperature is 165 ℃ and the time is 15 min.
Furthermore, the single-wavelength double-beam spectrophotometer in the step (3) uses water as a reference, and the double-wavelength spectrophotometer does not need to be used as a reference.
Further, Ag2SO4-H2SO4Middle Ag2SO4The content of (b) can be adjusted according to the content of chloride in the sample.
The principle of the method of the invention is as follows:
chemical Oxygen Demand (COD) refers to the amount of oxidant consumed to oxidize a reducing substance in a 1 liter sample of water under certain conditions, expressed as mg/L of oxygen mass concentration, the reducing substance excluding Cl-High chlorine water refers to Cl-Water with a content of more than 1000 mg/L. The COD determination is divided into two steps, wherein the first step is water sample digestion, reflux digestion and rapid digestion are carried out, and a certain method is adopted to eliminate Cl in high-chlorine water-Interference of (2); a second step of measurement, which comprises a titration method, a spectrophotometry method and the like, and measurement of the remaining K2Cr2O7Or to form Cr3+Amount of (2) to determine the actual consumption K in the reaction2Cr2O7The amount of (c).
The invention adopts rapid digestion to digest Ag in the solution2SO4With Cl-Combined to form AgCl-masked Cl-Elimination or reduction of Cl-Quilt K2Cr2O7Oxidizing; with K2Cr2O7The maximum absorption wavelength in the visible region is 446nm +/-5 nm, and Cr is used as the measuring wavelength3+The double-wavelength isoabsorption eliminating Cr with the isoabsorption wavelength of 545nm +/-10 nm as a reference wavelength3+And AgCl to K2Cr2O7Influence of Absorbance (Cr)3+Absorbance at 446nm and 545nm are equal; AgCl precipitation or turbidity scatters light almost equally if the wavelength is not too large), absorbance a ═ a446－A545The decrease in absorbance Δ a ═ a was measured0－A(A0Blank absorbance, A-water sample or standard solution absorbance), and establishing a standard curve of delta A and COD concentration for water sample quantitative analysis.
In summary, the invention has the following advantages:
1. the invention provides a method for measuring chemical oxygen demand in high-chlorine water, which utilizes Ag in digestion liquid2SO4With Cl-Combined to form AgCl precipitate mask Cl-Elimination or substantial reduction of Cl-Quilt K2Cr2O7Oxidizing; dual-wavelength isoabsorption Cr elimination method with 446nm as measurement wavelength and 545nm as reference wavelength3+And AgCl to K2Cr2O7Influence of the absorbance. 3.00mLAg2SO4-H2SO4(2:100)+1.00mL0.200mol/L(1/6K2Cr2O7) +2.00mL of water sample or blank or standard sample digestion system, rapid digestion and spectrophotometric determination are adopted, and Cl can be directly determined at 1000 mg/L-Cl-High-chlorine water with the concentration less than or equal to 5000mg/L and COD less than or equal to 600 mg/L.
2. The invention improves the HgSO used for COD determination of the existing standard chlorine-containing water quality4In the present situation, no use of the highly toxic substance HgSO is made4The experiment cost is reduced, new pollution to the environment is reduced, and experiment operators are protected. High-chlorine water COD determination without using HgSO4Elimination of Cl-Interference of (1) by Ag2SO4-H2SO4Providing a sufficient excess of Ag2SO4Make Cl-Elimination or reduction of AgCl precipitate formed by K2Cr2O7Interference of oxidation, using dual wavelengths to eliminate Cr3+And AgClStarch pair K2Cr2O7Influence of the absorbance.
3. In the determination method provided by the invention, the linear range of COD is 25-600 mg/L, and Cl is-The concentration is less than or equal to 5000 mg/L. Simulating the preparation of Cl with the same COD-The precision RSD of the absorbance measured by an experimental method is 3.3 percent for 0, 1000, 2000, 3000, 4000 and 5000mg/L series of water samples respectively; the detection limit of the method is 12 mg/L; containing 2000mg/LCl-The precision RSD of the absorbance of the simulated water sample is 2.9 percent.
4. Compared with the prior national standard method, the invention does not use HgSO4As masking agents to eliminate or reduce Cl-Quilt K2Cr2O7Oxidation and influence on absorbance. Using digestion liquid to remove Ag2SO4As masking agents to eliminate or reduce Cl-Quilt K2Cr2O7Oxidizing, and removing Cr by dual-wavelength isoabsorption spectrophotometry3+And AgCl to K2Cr2O7The effect of absorbance; COD<600mg/L、Cl-The water sample of less than or equal to 5000mg/L can be directly measured without dilution; when a water sample is measured, a large amount of precipitate is generated after the water sample is added according to an experimental method, the water sample can be diluted by 1 time and measured simultaneously, and if COD (chemical oxygen demand) of the measured water sample is basically consistent, Cl is shown-The upper limit is not exceeded, the interference is basically avoided, and the subsequent water sample is directly analyzed.
Meanwhile, the COD determination of the existing water sample is not divided into high and low ranges due to different COD contents and uses different concentrations of K2Cr2O7And drawing different standard curves by using different detection wavelengths, and the like. The method adopts the same digestion solution (except for Cl)-Adjusting Ag too much2SO4Proportional or water sample dilution), same detection wavelength, same standard curve and no HgSO4. The method provided by the invention is simple and feasible, and the treatment and recovery of the waste liquid are simplified.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
Thus, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
Examples
The experimental procedure for this example is as follows:
the 3.00mLAg samples were taken with a pipette2SO4-H2SO4(2:100) in the digestion tube, 1.00ml of 0.200mol/L (1/6K) is added by a pipette2Cr2O7) Oscillating and mixing the solution evenly; then slowly adding 2.00mL of water sample or blank or standard sample, screwing the digestion tube cap, and uniformly mixing by oscillation. When the temperature of the rapid digestion instrument rises to 165 ℃ and a buzzer sounds, the digestion tube is placed into the digestion instrument, the temperature rises to 165 ℃ again, timing is started, the buzzer sounds after digestion for 15min, the digestion tube is taken out and placed on a metal test tube rack, the digestion tube rack is placed in a water tank for cooling after cooling in the air for about 2min, 5.00mL of water is added into the digestion tube after cooling, and the digestion tube, the water and the buzzer are uniformly mixed and cooled; absorbance at 446nm and 545nm was measured using a 10mm absorption cell with water as a reference (single wavelength dual beam spectrophotometer uses water as a reference, dual wavelength spectrophotometer does not require a reference). Calculating A ═ A446－A545And Δ a ═ a0－A。
Following the experimental procedures described above, the following simulated water samples had the same COD and Cl-Fast digestion-spectrophotometry for investigating HgSO at different concentrations4Whether or not to eliminate Cl-The measured value of COD is influenced, the experimental results are shown in table 1, and Ag in digestion solution is utilized2SO4Whether or not to eliminate Cl-The results of the experiments on the effect of the measured COD values are shown in Table 2.
TABLE 1 chlorine-containing water samples in Ag2SO4-H2SO4Presence or absence of HgSO under the conditions4Experimental values of (2)
Table 1 illustrates: cl-Adding HgSO into water sample of not more than 1000mg/L4Digestion, lower absorbance at 545nm and 600nm indicates less turbidity of the solution, but the absorbance change rate is large due to the lower absorbance at 600nm, voltage fluctuation, instrument reading error and a small amount of turbidity. Containing Cl-HgSO added with 2000mg/L water sample digestion solution4According to the standard HJ/T399-: the high range adopts 600nm +/-20 nm for measurement, the absorbance is large, and the measurement result is seriously high due to the generation of a large amount of AgCl precipitate; in the low range, the absorbance of the water sample is measured to be larger by adopting 440nm +/-20 nm, and the absorbance difference with the blank is smaller or even negative. The high-chlorine water quality HJ/T399-. Expressing A by the difference of absorbance at 446nm and 545nm of dual wavelength, adding HgSO into the digestion solution4The difference of absorbance at double wavelengths is obviously reduced, but HgSO is not added in the digestion solution4The difference value of the absorbance of the double wavelengths is basically unchanged; description of Ag2SO4-H2SO4In the case of sufficient amount, a dual wavelength spectrophotometry Ag is used2SO4Can mask Cl-Elimination of Cl-Effect on COD determination, and HgSO4The addition of (A) inhibits Ag2SO4Masking Cl-。
TABLE 2 digestion of Ag in liquids2SO4Masking effect on different water quality containing chlorine
Table 2 shows that the use of dual wavelengths eliminates most of the light scattering effects well, but not 100% because the high-chlorine water contains a large amount of AgCl precipitates. The data was acquired with time differences at the dual wavelengths, while the suspended sediment was dynamic in the absorption cell. The absorbance at a single wavelength varies greatly, but the difference in absorbance at two wavelengths is relatively stable, and the RSD% is controlled to within 5%, which is desirable in the case of a large amount of precipitation.
In conclusion, the invention provides a method for measuring the chemical oxygen demand in high-chlorine water, which utilizes Ag in digestion liquid2SO4With Cl-Combined to form AgCl precipitate mask Cl-Elimination or substantial reduction of Cl-Quilt K2Cr2O7Oxidizing; dual-wavelength isoabsorption Cr elimination method taking 446nm +/-5 nm as measurement wavelength and 545nm +/-10 nm as reference wavelength3+And AgCl to K2Cr2O7Influence of the absorbance. 3.00mLAg2SO4-H2SO4(2:100)+1.00mL0.200mol/L(1/6K2Cr2O7) +2.00mL of water sample or blank or standard sample digestion system, rapid digestion and spectrophotometric determination are adopted, and Cl can be directly determined at 1000 mg/L-Cl-High-chlorine water with the concentration less than or equal to 5000mg/L and COD less than or equal to 600 mg/L. In the determination method, the linear range of COD is 25-600 mg/L, and Cl is-The concentration is less than or equal to 5000 mg/L. Simulating the preparation of Cl with the same COD-The precision RSD of the absorbance measured by an experimental method is 3.3 percent for 0, 1000, 2000, 3000, 4000 and 5000mg/L series of water samples respectively; the detection limit of the method is 12 mg/L; containing 2000mg/LCl-The precision RSD of the absorbance of the simulated water sample is 2.9 percent.
The foregoing is illustrative and explanatory only and is not intended to be exhaustive or to supplement or replace the specific embodiments described by those skilled in the art without inventive faculty.
Claims (6)
1. The method for measuring the chemical oxygen demand in the high-chlorine water is characterized in that the method utilizes Ag in digestion solution2SO4With Cl-Combined to form AgCl precipitate mask Cl-(ii) a Double-wavelength isosorption with 446nm +/-5 nm as measuring wavelength and 545nm +/-10 nm as reference wavelengthRemoving Cr3+And AgCl to K2Cr2O7The effect of absorbance; 3.00mLAg with a mass to volume ratio of 2:1002SO4-H2SO41.00mL0.200mol/L of 1/6K2Cr2O7And 2.00mL of water sample or blank or standard sample digestion system, and determining Cl of more than 1000mg/L by adopting rapid digestion and spectrophotometry-Chemical oxygen demand in high chlorine water with less than or equal to 5000mg/L and COD less than or equal to 600 mg/L.
2. The method of determining chemical oxygen demand in a high chlorine water as claimed in claim 1, wherein Cl in the high chlorine water is-When the mass volume ratio is less than or equal to 2000mg/L, Ag with the mass volume ratio of 1:100 is adopted2SO4-H2SO4And (4) carrying out measurement.
3. The method for determining chemical oxygen demand in high chlorine water as claimed in claim 1, comprising the steps of:
step (1): mixing 3.00mLAg with a mass-to-volume ratio of 2:1002SO4-H2SO4Adding into a digestion tube, and adding 0.200 mol/L1.00 mL1/6K2Cr2O7Oscillating and mixing the solution evenly;
step (2): slowly adding 2.00mL of water sample or blank or standard sample into the digestion tube obtained in the step (1), oscillating and uniformly mixing, placing the digestion tube into a digestion instrument, digesting for 12-16 min at the temperature of 160-170 ℃, taking out the digestion tube, and placing the digestion tube into water for cooling;
and (3): adding 5.00mL of water into the digestion tube obtained in the step (2), oscillating, uniformly mixing and cooling, and then respectively measuring the absorbance at 446nm and 545nm by using a 10mm absorption cell and taking water as a reference;
and (4): and (3) calculating: a ═ A446－A545；ΔA＝A0－A；
Wherein A is0-blank absorbance, a-water sample or standard absorbance;
and (5): and (4) establishing a delta A and COD concentration standard curve for water sample quantitative analysis according to the calculated value in the step (4).
4. The method for determining the chemical oxygen demand in the high-chlorine water quality as claimed in claim 3, wherein the digestion instrument parameters in the step (2) are as follows: the temperature is 165 ℃ and the time is 15 min.
5. The method for determining chemical oxygen demand in high chlorine water as claimed in claim 3, wherein the single wavelength dual beam spectrophotometer in step (3) uses water as reference, and the dual wavelength spectrophotometer does not need reference.
6. The method of claim 3, wherein the Ag is added to the high chlorine water2SO4-H2SO4Middle Ag2SO4The content of (b) can be adjusted according to the content of chloride in the sample.
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| CN116990443A (en) * | 2023-09-28 | 2023-11-03 | 山东天信医药科技有限公司 | Accurate detection method for COD in high-chlorine low-COD water sample |
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