CN117825646A - Mixed reagent for COD detection, COD detection reagent tube and COD detection method - Google Patents
Mixed reagent for COD detection, COD detection reagent tube and COD detection method Download PDFInfo
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- 239000003153 chemical reaction reagent Substances 0.000 title claims abstract description 146
- 238000001514 detection method Methods 0.000 title claims abstract description 88
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 81
- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 claims abstract description 60
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 55
- 238000006243 chemical reaction Methods 0.000 claims abstract description 37
- DOBUSJIVSSJEDA-UHFFFAOYSA-L 1,3-dioxa-2$l^{6}-thia-4-mercuracyclobutane 2,2-dioxide Chemical compound [Hg+2].[O-]S([O-])(=O)=O DOBUSJIVSSJEDA-UHFFFAOYSA-L 0.000 claims abstract description 30
- 229910000370 mercury sulfate Inorganic materials 0.000 claims abstract description 29
- 229910000367 silver sulfate Inorganic materials 0.000 claims abstract description 28
- YPNVIBVEFVRZPJ-UHFFFAOYSA-L silver sulfate Chemical compound [Ag+].[Ag+].[O-]S([O-])(=O)=O YPNVIBVEFVRZPJ-UHFFFAOYSA-L 0.000 claims abstract description 28
- 238000004364 calculation method Methods 0.000 claims description 53
- 238000002835 absorbance Methods 0.000 claims description 42
- 230000029087 digestion Effects 0.000 claims description 33
- 238000000034 method Methods 0.000 claims description 23
- 238000002798 spectrophotometry method Methods 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 3
- 238000011049 filling Methods 0.000 claims description 2
- 238000004321 preservation Methods 0.000 claims description 2
- 238000004065 wastewater treatment Methods 0.000 abstract description 2
- 239000000126 substance Substances 0.000 description 53
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 50
- 239000001301 oxygen Substances 0.000 description 50
- 229910052760 oxygen Inorganic materials 0.000 description 50
- 230000000052 comparative effect Effects 0.000 description 18
- 239000000243 solution Substances 0.000 description 17
- 238000002156 mixing Methods 0.000 description 12
- 239000002994 raw material Substances 0.000 description 12
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 9
- 238000005070 sampling Methods 0.000 description 9
- 239000007788 liquid Substances 0.000 description 8
- 239000012086 standard solution Substances 0.000 description 7
- 238000005259 measurement Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- YUVLVONHNMXKBW-UHFFFAOYSA-L [Ag+2].OS(O)(=O)=O.[O-]S([O-])(=O)=O Chemical compound [Ag+2].OS(O)(=O)=O.[O-]S([O-])(=O)=O YUVLVONHNMXKBW-UHFFFAOYSA-L 0.000 description 4
- IMBKASBLAKCLEM-UHFFFAOYSA-L ferrous ammonium sulfate (anhydrous) Chemical compound [NH4+].[NH4+].[Fe+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O IMBKASBLAKCLEM-UHFFFAOYSA-L 0.000 description 4
- 238000012795 verification Methods 0.000 description 4
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 239000000460 chlorine Substances 0.000 description 3
- 229910052801 chlorine Inorganic materials 0.000 description 3
- 238000010992 reflux Methods 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 238000004448 titration Methods 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- 239000002351 wastewater Substances 0.000 description 3
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000013043 chemical agent Substances 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000003203 everyday effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 229940074994 mercuric sulfate Drugs 0.000 description 1
- 229910000372 mercury(II) sulfate Inorganic materials 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000005375 photometry Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000001632 sodium acetate Substances 0.000 description 1
- 235000017281 sodium acetate Nutrition 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
Classifications
-
- 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]
-
- 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
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/20—Controlling water pollution; Waste water treatment
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- Food Science & Technology (AREA)
- Analytical Chemistry (AREA)
- Molecular Biology (AREA)
- Biomedical Technology (AREA)
- Biodiversity & Conservation Biology (AREA)
- Medicinal Chemistry (AREA)
- Physics & Mathematics (AREA)
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Abstract
The invention discloses a mixed reagent for COD detection, a COD detection reagent tube and a COD detection method, and belongs to the field of wastewater treatment. A mixed reagent for COD detection comprises sulfuric acid, potassium dichromate, mercury sulfate, silver sulfate and pure water; the mixed reagent comprises the following components in percentage by mass: sulfuric acid (75.0-83.5%), potassium dichromate (0.5-1.0%), silver sulfate (0.6-1.5%), mercury sulfate (1.2-1.4%), and pure water for the rest; or sulfuric acid (84.5-90.0%), potassium dichromate (0.5-1.0%), silver sulfate (0.3-0.5%), mercury sulfate (1.5-2.5%), and pure water for the rest; it can realize the output of mixed reagent with actual conversion coefficient k of 2072 + -5%.
Description
Technical Field
The invention belongs to the field of wastewater treatment, and particularly relates to a mixed reagent for COD detection, a COD detection reagent tube and a COD detection method.
Background
Chemical oxygen demand COD (Chemical Oxygen Demand) is the amount of reducing substances to be oxidized in a water sample under certain conditions by chemical methods; the units are generally: mg/L. Chemical Oxygen Demand (COD) is one of the comprehensive indexes for the pollution of organic matters and other reducing substances to the reaction water body, the greater the COD value is, the more serious the pollution degree of the water body is, and the more serious the COD value is, the dissolved oxygen in the water body can be consumed in the degradation process to unbalance the oxygen in the water body, so that the water body is polluted, and therefore, the detection of the chemical oxygen demand becomes very important.
The existing COD detection methods include the following methods as described in the "Water and wastewater monitoring analysis method (fourth edition)": potassium dichromate (a), coulomb (B), rapid closed catalytic digestion (spectrophotometry) (B), energy-saving heating (B), chlorine correction for high chlorine wastewater (high chlorine wastewater) (a). The A-type method is the national or industry standard (or equivalent to the standard method), and the B-type method is proved to be a mature unified method through intensive domestic research and multiple laboratory verification.
Wherein, the environmental protection department standard HJ828-2017 is that the measuring range of dichromate method for water quality chemical oxygen demand is 16-700 mg/L, 10ml is sampled, the digestion time is 120 minutes, the anti-interference is that chloride ion is less than or equal to 1000mg/L, and the calibration of ferrous ammonium sulfate concentration and the quantitative calculation are required to be carried out every day.
The environmental protection department standard HJ/T399-2017 quick digestion spectrophotometry for measuring the water quality chemical oxygen demand, the low range is (15-150) mg/L, the high range is (100-1000) mg/L, 2ml is sampled, the digestion time is 15 minutes, the anti-chloride ion interference is less than or equal to 1000mg/L, and the quantitative calculation formula is required to be recalibrated each time when the reagent is replaced.
Chemical oxygen demand, COD, is measured spectrophotometrically by placing a reagent in a specific apparatus and in a set wavelength environment. The quantitative calculation formula is: COD value = kxa+b, where a is absorbance, k is sensitivity, b is blank intercept; the value of k is different according to the configuration of each reagent, and the ideal sensitivity k value is 1968-2175 reagent, so that the signal value of the sensor of the instrument for measuring COD can be ensured to be in an ideal range, the reagent in the range is lacking in the market at present, and the reagent has very wide application prospect, and a plurality of water quality detection instruments need to use the reagent.
In addition, in the patent of "a reagent for measuring chemical oxygen demand and a method for preparing a digestion solution thereof" of the prior publication No. CN104330405A, a reagent for measuring chemical oxygen demand and a method for preparing a digestion solution thereof are disclosed. The measuring range of the method is (50-800) mg/L, the sampling is 2.5ml, and the anti-chloridion interference is less than or equal to 1000mg/L. The method still needs to prepare the digestion liquid by itself, and meanwhile, the digestion liquid needs to be manually added into the colorimetric tube according to the operation steps, so that the method is complex.
In the patent of the prior publication No. CN114199798A, a method for rapidly measuring the high-range COD is disclosed. The range of the method is (100-1300) mg/L, 2.0ml is sampled, the digestion time is 120 minutes, and the anti-interference chloride ions are less than or equal to 2000mg/L; the method still needs to prepare the digestion liquid by oneself, and meanwhile, the digestion liquid needs to be manually added into the colorimetric tube according to the operation steps, so that the method is complex; and recalibrating the quantitative calculation formula and adjusting the range according to the actual application condition.
The existing COD measuring method needs to temporarily and manually configure the reagent, the detection time is long, and recalibration is needed for each use.
Disclosure of Invention
The invention aims to solve the technical problem of providing a high-range COD measurement prefabricated reagent which can realize the production of a mixed reagent with the actual conversion coefficient k of which the numerical value is 2072+/-5%.
The invention relates to a mixed reagent for COD detection, which comprises sulfuric acid, potassium dichromate, mercury sulfate, silver sulfate and pure water; the mixed reagent comprises the following components in percentage by mass:
sulfuric acid (75.0-83.5%), potassium dichromate (0.5-1.0%), silver sulfate (0.6-1.5%), mercury sulfate (1.2-1.4%), and pure water for the rest; or (b)
84.5 to 90.0 percent of sulfuric acid, 0.5 to 1.0 percent of potassium dichromate, 0.3 to 0.5 percent of silver sulfate, 1.5 to 2.5 percent of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises, by mass, 80% of sulfuric acid, 1.0% of potassium dichromate, 0.5% of silver sulfate, 1.5% of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises 75 mass percent of sulfuric acid, 1.0 mass percent of potassium dichromate, 1.5 mass percent of silver sulfate, 1.2 mass percent of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises 84.5 mass percent of sulfuric acid, 0.6 mass percent of potassium dichromate, 0.5 mass percent of silver sulfate, 1.6 mass percent of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises 86 mass percent of sulfuric acid, 0.7 mass percent of potassium dichromate, 0.6 mass percent of silver sulfate, 2.5 mass percent of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises 87.5 mass percent of sulfuric acid, 0.53 mass percent of potassium dichromate, 0.88 mass percent of silver sulfate, 1.76 mass percent of mercury sulfate and the balance of pure water.
As a further improvement of the invention, the mixed reagent comprises 89.8 mass percent of sulfuric acid, 0.57 mass percent of potassium dichromate, 0.95 mass percent of silver sulfate, 1.2 mass percent of mercury sulfate and the balance of pure water.
The invention relates to a COD detection reagent tube, which comprises a mixed reagent and a digestion colorimetric tube; the COD detection reagent tube is prepared by pre-filling 2.0-3.5 ml of mixed reagent into a digestion colorimetric tube for airtight preservation to obtain a detection reagent tube with the measuring range of (100-2000) mg/L;
the COD detection reagent tube is measured by spectrophotometry under the wavelength of 620nm within the range of COD content of (100-2000) mg/L, and accords with the quantitative calculation formula of COD value=kxA+b; wherein A is absorbance, k is conversion coefficient, b is blank intercept; the value of the conversion coefficient k is 2072 + -5%.
As a further improvement of the present invention, the amount of the mixed reagent in the COD detection reagent tube was 3.0ml.
The invention discloses a COD detection method, which comprises the following steps:
s1, transferring 2.00mL of pure water into a 1# detection reagent tube, screwing a tube cover and sealing;
s2, heating at 165 ℃ for 20 minutes, and cooling to room temperature;
s3, additionally taking 2.00mL of water sample to be detected in the 2# detection reagent tube, screwing the tube cover to be airtight, and repeating the step S2;
s4, under the condition of 620nm wavelength, taking the 1# detection reagent tube as a reference, and measuring the value of the 2# detection reagent tube to obtain the COD content in the water sample to be measured.
The above instruments should meet the requirements of the technical requirement of the quick tester for COD photometry and the detection method (HJ 924-2017).
Compared with the prior art, the invention has the beneficial effects that:
the COD detection reagent tube is ready to use, is convenient and quick, only needs 30 minutes for detecting the sample, and operators do not need to directly contact chemicals.
2. The detection reagent tube can be prefabricated and produced, and the reagent is stored in the digestion colorimetric tube in a sealing way, and the storage life is longer than 3 years.
3. The chlorine ion resistance is strong: fully plays the masking capability of the mercury sulfate, and the chloride ion with improved anti-interference capability is less than or equal to 2000mg/L.
4. The measuring range is wide: the linear range of detection is as large as (100-2000) mg/L.
5. The mixed reagent with the value of the conversion coefficient k of 2072 + -5% can be accurately obtained.
Drawings
FIG. 1 is a quantitative calculation formula of example 1 of the present invention;
FIG. 2 is a quantitative calculation formula of example 2 of the present invention;
FIG. 3 is a quantitative calculation formula of example 3 of the present invention;
FIG. 4 is a quantitative calculation formula of example 4 of the present invention;
FIG. 5 is a quantitative calculation formula of example 5 of the present invention;
FIG. 6 is a quantitative calculation formula of example 6 of the present invention;
FIG. 7 is a quantitative calculation formula of example 7 of the present invention;
FIG. 8 is a quantitative calculation formula of example 8 of the present invention;
FIG. 9 is a quantitative calculation formula of example 9 of the present invention;
FIG. 10 is a quantitative calculation formula of example 10 of the present invention;
FIG. 11 is a quantitative calculation formula of example 11 of the present invention;
FIG. 12 is a quantitative calculation formula of comparative example 1 (HJ/T399 high range) of the present invention;
fig. 13 is a quantitative calculation formula of comparative example 3 (hash high scale) of the present invention.
Detailed Description
Example 1
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 1
The balance in the mixed reagent of this example was pure water. Adding 2.0mL of mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, wherein an X-axis is taken as absorbance A, a Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2144.6. The water quality instrument presets the calculation formula.
TABLE 2 example 1 absorbance A versus Chemical Oxygen Demand (COD) standard value
Example 2
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 3 Table 3
The balance in the mixed reagent of this example was pure water. Adding 2.0mL of mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, wherein an X-axis is taken as absorbance A, a Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2005.1. The water quality instrument presets the calculation formula.
TABLE 4 example 2 absorbance A versus Chemical Oxygen Demand (COD) standard values
Example 3
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 5
The balance in the mixed reagent of this example was pure water. Adding 3.2mL of mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, wherein an X-axis is taken as absorbance A, a Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2168.9. The water quality instrument presets the calculation formula.
TABLE 6 example 3 absorbance A versus Chemical Oxygen Demand (COD) standard value
Example 4
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 7
The balance in the mixed reagent of this example was pure water. 3.1mL of a sampling mixed reagent is added into a digestion colorimetric tube to prepare a detection reagent tube, the X-axis is taken as absorbance A, the Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2139.5. The water quality instrument presets the calculation formula.
TABLE 8 example 4 absorbance A versus Chemical Oxygen Demand (COD) standard values
Example 5
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 9
The balance in the mixed reagent of this example was pure water. 3.1mL of a sampling mixed reagent is added into a digestion colorimetric tube to prepare a detection reagent tube, the X-axis is taken as absorbance A, the Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2063.6. The water quality instrument presets the calculation formula.
TABLE 10 example 5 absorbance A versus Chemical Oxygen Demand (COD) standard value
Example 6
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 11
The balance in the mixed reagent of this example was pure water. Adding 2.9mL of mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, wherein an X-axis is taken as absorbance A, a Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2072. The water quality instrument presets the calculation formula.
TABLE 12 example 6 absorbance A and Chemical Oxygen Demand (COD) standard values
Example 7
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 13
The balance in the mixed reagent of this example was pure water. 3.2mL of a sampling mixed reagent is added into a digestion colorimetric tube to prepare a detection reagent tube, the X-axis is taken as absorbance A, the Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2128.1. The water quality instrument presets the calculation formula.
TABLE 14 example 7 absorbance A versus Chemical Oxygen Demand (COD) standard value
Example 8
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 15
The balance in the mixed reagent of this example was pure water. 3.5mL of a sampling mixed reagent is added into a digestion colorimetric tube to prepare a detection reagent tube, the X-axis is taken as absorbance A, the Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2075.2. The water quality instrument presets the calculation formula.
TABLE 16 example 8 absorbance A versus chemical oxygen demand (C0D) standard value
Example 9
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 17
The balance in the mixed reagent of this example was pure water. Sampling 2.0mL of mixed reagent, adding the mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, taking an X axis as absorbance A, taking a Y axis as a Chemical Oxygen Demand (COD) standard value unit as mg/L, calibrating a quantitative calculation formula under the wavelength of 620nm of a water quality instrument, wherein the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 4708.2. The water quality instrument presets the calculation formula.
TABLE 18 example 9 absorbance A versus Chemical Oxygen Demand (COD) standard values
Example 10
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
TABLE 19
The balance in the mixed reagent of this example was pure water. Sampling 4.0mL of mixed reagent, adding the mixed reagent into a digestion colorimetric tube to prepare a detection reagent tube, taking an X axis as absorbance A, taking a Y axis as a Chemical Oxygen Demand (COD) standard value unit as mg/L, calibrating a quantitative calculation formula under the wavelength of 620nm of a water quality instrument, wherein the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2676.6. The water quality instrument presets the calculation formula.
TABLE 20 example 10 absorbance A versus Chemical Oxygen Demand (COD) standard values
Example 11
The mixing reagent for COD detection in this embodiment is prepared from the following raw materials:
table 21
The balance in the mixed reagent of this example was pure water. 3.6mL of a sampling mixed reagent is added into a digestion colorimetric tube to prepare a detection reagent tube, the X-axis is taken as absorbance A, the Y-axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the 620nm wavelength of a water quality instrument, the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2445.8. The water quality instrument presets the calculation formula.
TABLE 22 example 11 absorbance A versus Chemical Oxygen Demand (COD) standard values
The configuration ratio is not limited to the above embodiment.
Conclusion: from the formulation and quantitative calculation formula diagrams of examples 1 to 8, it can be seen that the mixed reagent comprises the following components in percentage by mass: sulfuric acid (75.0-83.5%), potassium dichromate (0.5-1.0%), silver sulfate (0.6-1.5%), mercury sulfate (1.2-1.4%), and pure water for the rest; or sulfuric acid (84.5-90.0%), potassium dichromate (0.5-1.0%), silver sulfate (0.3-0.5%), mercury sulfate (1.5-2.5%) and pure water. The values of the conversion coefficients k of the reagents produced in the above compounding ranges were 2072.+ -. 5%, and it can be seen from examples 9 to 11 that the conversion coefficients k deviate seriously from 2072.+ -. 5% beyond the ranges in the above formulations.
Comparative example 1
The preparation of the mixed reagent with high measuring range (100-1000) mg/L is carried out according to the quick digestion spectrophotometry for measuring the water quality chemical oxygen demand of HJ/T399-2007.
1. Standard potassium dichromate solution: c (1/6K) 2 Cr 2 O 7 )＝0.500mol/L；
2. Mercury sulfate solution: ρ (HgSO) 4 ) =0.24 g/mL. Adding 48.0g of mercury sulfate into 200mL of sulfuric acid solution in portions, stirring and dissolving;
3. silver sulfate-sulfuric acid solution: ρ (Ag) 2 SO 4 ) =10g/L. 5.0g of silver sulfate was added to 500mL of sulfuric acid, and the mixture was allowed to stand for 1 to 2 days with stirring to dissolve the silver sulfate.
4. Standard potassium dichromate solution in step 1 and mercury sulfate solution in step 2 are mixed according to the following formula 2: mixing in proportion of 1.
5. Taking 1.0ml of the mixed solution in the step 4 and 4.0ml of the silver sulfate-sulfuric acid solution in the step 3, and adding the mixed solution into a digestion colorimetric tube.
6. 2.0ml of water sample is taken and added into the digestion colorimetric tube in the step 5, and the mixture is heated for 20min at the temperature of 165 ℃.
The raw materials are as follows:
table 23
According to the sampling method in the above method, 5mL of the reagent was obtained. The X axis is taken as absorbance A, the Y axis is taken as a Chemical Oxygen Demand (COD) standard value unit as mg/L, a quantitative calculation formula is calibrated under the wavelength of 620nm, and the COD value=kxA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 3466.2.
TABLE 24 comparative example 1 absorbance A and Chemical Oxygen Demand (COD) standard values
Comparative example 2
Preparation of high-range (16-700) mg/L reagent according to HJ828-2017 water quality chemical oxygen demand measurement dichromate method
1. Potassium dichromate standard solution c (1/6K) 2 Cr 2 O 7 ) =0.250 mol/L. 12.258g of potassium dichromate is accurately weighed and dissolved in water, and the volume is fixed to 1000ml.
2. Mercury sulfate solution, p=100 g/L. 10g of mercuric sulfate is weighed, dissolved in 100ml of sulfuric acid solution and uniformly mixed.
3. Silver sulfate-sulfuric acid solution: ρ (Ag) 2 SO 4 ) =10g/L. 5.0g of silver sulfate was added to 500mL of sulfuric acid, and the mixture was allowed to stand for 1 to 2 days with stirring to dissolve the silver sulfate.
4. Ferrous ammonium sulfate standard solution, c [ (NH) 4 ) 2 Fe(SO 4 ) 2 ·6H 2 O)]And about 0.05mol/L. 19.5g of ferrous ammonium sulphate was weighed out and dissolved in water, 10ml of sulphuric acid was added and after cooling the solution, it was diluted to 1000ml.
5. 10.0ml of water sample, 5.0ml of potassium dichromate standard solution, 15ml of silver sulfate-sulfuric acid solution and 2H of reflux on an electric furnace are taken.
6. After the completion of the reflux, the COD value was calculated by titration with a standard solution of ferrous ammonium sulfate.
Comparative example 3
The COD detection reagent with the commodity number of 2125925-CN produced by Hach company in the United states, wherein the measuring range is 20-1500 mg/L, 2.0ml of water sample is taken and heated at 150 ℃ for 120min, the X-axis is taken as absorbance A, the Y-axis is taken as Chemical Oxygen Demand (COD) standard value unit as mg/L, and under the wavelength of 620nm, a quantitative calculation formula is calibrated, wherein the COD value=kXA+b, wherein A is absorbance, k is a conversion coefficient, and b is a blank intercept; the value of the conversion coefficient k is 2243.6.
TABLE 25 comparative example 3 absorbance A and Chemical Oxygen Demand (COD) standard values
Verification conclusion:
1. examples 1 to 8 and comparative example 1 span range verification:
1.1. under the same environment, each example and comparative example 1 are subjected to experimental comparison, and the values in the measuring range are measured by using Chemical Oxygen Demand (COD) standard solutions with different concentrations, and the results are as follows:
table 26
As can be seen from Table 26, the analysis deviation of the detection results of the digestion liquid samples prepared by the reagent of the invention is within 5% of the range specified by the national recommended standard, and the detection data is true and reliable. Examples 9-11 can be seen to deviate by more than 5%.
1.2. Sodium acetate is used as a standard substance to prepare a COD standard solution with the concentration of 2000mg/L, the oxidability is tested, the reliability of the measuring range is determined, and the result is as follows.
Table 27
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Conclusion: examples 1-8, examples 9-11 and comparative example 1 in the range of 100-2000 mg/L have low oxidation efficiency, and the upper range limit is less than 2000mg/L.
2. Examples 1 to 8 and comparative example 1 were validated for their ability to interfere with chloride ions:
2.1. under the same environment, each example and comparative example 1 are subjected to experimental comparison, and the values are measured by Chemical Oxygen Demand (COD) standard solutions with different concentrations at the chloride ion content of 2000mg/L, and the results are as follows:
table 28
Conclusion: examples 1-8, data were essentially viable with 2000mg/L chloride concentration interference, with comparative example 1 reaching less than 2000mg/L.
3. And (5) verifying the accuracy of a Chemical Oxygen Demand (COD) detection reagent.
3.1. The Chemical Oxygen Demand (COD) detection reagent prepared by the invention and the method of comparative example 2 (HJ 828) adopt different types of actual water sample comparison experiments, and the results are as follows.
Table 29
Conclusion: as can be seen from Table 29, the data of the Chemical Oxygen Demand (COD) detection reagent and the conventional titration method of HJ828 satisfy the prescribed error range of 10%. The data is reliable.
3.2. Standard samples with concentration value of (235+/-10) mg/L of GSB 07-316-2014 of water quality chemical oxygen demand of the ecological environment department are purchased, and the reagents of the examples 1 to 8 are tested for accuracy and precision, and the data are as follows:
table 30 accuracy and precision data
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Conclusion: as can be seen from Table 30, the chemical oxygen demand values were all within the range of (235.+ -. 10) mg/L requirements, and the RSD% also meets the requirement of 5% or less.
4. And (3) verifying the applicability of different Chemical Oxygen Demand (COD) detection reagents:
4.1. comparative example 1 and comparative example 3 were read on the quantitative calculation formula of example 6, and the relative errors were calculated, and the results are shown in tables 31 and 32. The test reagent tube of example 6 was read on the quantitative calculation formula (COD test reagent under the number 2125925-CN) of the Hash DR3900 instrument 435, and the data are shown in Table 33.
Table 31 comparative example 1 measurement values and relative errors
Table 32 comparative example 3 measurement values and relative errors
Table 33 example 6 measurement values and relative errors on the Hash 435 quantitative calculation equation
Conclusion: as can be seen from tables 31, 32 and 33, the relative error was more than 5%, the data accuracy was lowered, and the reagents were not mutually applicable.
5. Reagent batch-to-batch consistency verification
5.1. According to the same working curve with the linear correlation coefficient R more than or equal to 0.999, 5 batches of COD detection reagent tubes packaged in different time periods are tested by using a Chemical Oxygen Demand (COD) standard value of 750mg/L, and the data are shown in tables 34 and 35.
TABLE 34 reagent lot to lot consistency
Quantitative calculation formula for different time periods of table 35
Conclusion: looking up the t boundary value table t 0.05/25= 2.060, wherein t 0.05/25=1.75 in the table 34 is smaller than the value in the t boundary value table, which indicates that the average value and the true value have no significant error, and the conversion coefficient K value relative error of the quantitative calculation formula in the table 35 is less than 1%, so that the stability among batches of the COD detection reagent tube can be seen, and the quantitative calculation formula is not required to be calibrated.
In summary, the Chemical Oxygen Demand (COD) detection reagent tube has the advantages of high detection speed, wide range, strong capability of resisting chloride ion interference, and no need of frequent calibration of a quantitative calculation formula.
HJ828-2017 needs to reflux 2H, 4 reagents are needed to be prepared, and the production amount of waste liquid is about 80ml through titration analysis and calculation by a professional; meanwhile, the spectrophotometry of the colorimetric tube in the HJ/T399-2007 needs to prepare a potassium dichromate solution, a silver sulfate solution, a mercury sulfate solution, and the amount of waste liquid is 7mL, so that the method has more steps. The COD detection reagent with the product number of 2125925-CN produced by Hach company in the United states has a high-range (20-1500) mg/L and a long digestion time of 120 minutes. The Chemical Oxygen Demand (COD) detection reagent waste liquid amount is 5.5mL, the digestion time is 20min, and the method can be used immediately after being started, is convenient and quick, has strong capability of resisting the interference of chloride ions, has a wide range, does not need to calibrate a quantitative calculation formula frequently and does not need to be in direct contact with chemical agents.
Claims (10)
1. A mixed reagent for COD detection, characterized in that: comprises sulfuric acid, potassium dichromate, mercury sulfate, silver sulfate and pure water; the mixed reagent comprises the following components in percentage by mass:
sulfuric acid (75.0-83.5%), potassium dichromate (0.5-1.0%), silver sulfate (0.6-1.5%), mercury sulfate (1.2-1.4%), and pure water for the rest; or (b)
84.5 to 90.0 percent of sulfuric acid, 0.5 to 1.0 percent of potassium dichromate, 0.3 to 0.5 percent of silver sulfate, 1.5 to 2.5 percent of mercury sulfate and the balance of pure water.
2. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises, by mass, 80% of sulfuric acid, 1.0% of potassium dichromate, 0.5% of silver sulfate, 1.5% of mercury sulfate and the balance of pure water.
3. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises 75 mass percent of sulfuric acid, 1.0 mass percent of potassium dichromate, 1.5 mass percent of silver sulfate, 1.2 mass percent of mercury sulfate and the balance of pure water.
4. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises 84.5 mass percent of sulfuric acid, 0.6 mass percent of potassium dichromate, 0.5 mass percent of silver sulfate, 1.6 mass percent of mercury sulfate and the balance of pure water.
5. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises 86 mass percent of sulfuric acid, 0.7 mass percent of potassium dichromate, 0.6 mass percent of silver sulfate, 2.5 mass percent of mercury sulfate and the balance of pure water.
6. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises 87.5 mass percent of sulfuric acid, 0.53 mass percent of potassium dichromate, 0.88 mass percent of silver sulfate, 1.76 mass percent of mercury sulfate and the balance of pure water.
7. The mixed reagent for COD detection according to claim 1, wherein: the mixed reagent comprises 89.8% of sulfuric acid, 0.57% of potassium dichromate, 0.95% of silver sulfate, 1.2% of mercury sulfate and the balance of pure water according to mass percentage.
8. A COD detection reagent tube, characterized in that: comprising the mixed reagent according to any one of claims 1-7 and a digestion cuvette; the COD detection reagent tube is prepared by pre-filling 2.0-3.5 ml of mixed reagent into a digestion colorimetric tube for airtight preservation to obtain a detection reagent tube with the measuring range of (100-2000) mg/L;
the COD detection reagent tube is measured by spectrophotometry under the wavelength of 620nm within the range of COD content of (100-2000) mg/L, and accords with the quantitative calculation formula of COD value=kxA+b; wherein A is absorbance, k is conversion coefficient, b is blank intercept; the value of the conversion coefficient k is 2072 + -5%.
9. The COD detection reagent tube of claim 8, wherein: the amount of the mixed reagent in the COD detection reagent tube was 3.0ml.
10. A COD detection method is characterized in that: the method comprises the following steps:
s1, transferring 2.00mL of pure water into a 1# detection reagent tube, screwing a tube cover and sealing;
s2, heating at 165 ℃ for 20 minutes, and cooling to room temperature;
s3, additionally taking 2.00mL of water sample to be detected in the 2# detection reagent tube, screwing the tube cover to be airtight, and repeating the step S2;
s4, under the condition of 620nm wavelength, taking the 1# detection reagent tube as a reference, and determining the value of the 2# detection reagent tube to obtain the COD content in the water sample to be detected;
the # 1 detection reagent tube and the # 2 detection reagent tube are each a COD detection reagent tube according to any one of claims 8 to 9.
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