Method for determining COD through rapid digestion

A determination method and rapid technology, applied in the field of analytical chemistry, can solve the problems of heavy metal residual hazards, unsuitable for routine detection, and high price of microwave ovens, so as to facilitate post-processing and environmental protection, reduce labor intensity, and reduce operational risks. Effect

Inactive Publication Date: 2016-11-09
贵州开磷质量检测中心有限责任公司
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  • Abstract
  • Description
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  • Application Information

AI Technical Summary

Problems solved by technology

The price of microwave ovens is also high, and it is difficult to formulate a unified standard method; rapid digestion spectrophotometry uses a sealed tube as the digestion tube, and the spectrophotometric method measures the COD value. This method has the advantages of small space occupation, low energy consumption, and small reagent consumption. The waste liquid is minimized, the energy consumption is small, the operation is simple, safe and stable, accurate and reliable, suitable for large-scale determination, etc., which makes up for the shortcomings of the classic standard method, but it needs to use a spectroscopic instrument, which is not suitable for general routine detection, and The spectrophotometer also uses silver sulfate and mercury sulfate, and the heavy metal residues in the water samples after detection are very harmful

Method used

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  • Method for determining COD through rapid digestion
  • Method for determining COD through rapid digestion
  • Method for determining COD through rapid digestion

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0023] 1) Water sample digestion

[0024] Take 5.00ml of a standard substance sample of known concentration, add 15.00ml of distilled water; add 10ml of 0.050mol / L potassium dichromate, 20ml of concentrated phosphoric acid, a few glass beads to prevent boiling, connect the heating reflux device, add 0.2g MgSO 4 -MnSO 4 The mixture (weight ratio is 2:1) is heated and digested, and when the sample starts to boil, it is timed to digest for 20 minutes.

[0025] 2) Titration

[0026] After reflux, cool to room temperature, add 75.00ml of distilled water, add 3 drops of ferrous iron indicator, titrate to the end point with 0.020mol / L sodium thiosulfate solution, and record the consumption;

[0027] 3) Blank control test

[0028] Use 20ml of distilled water instead of the sample to conduct a blank control test, repeat steps [1) to 2)], record the consumption of sodium thiosulfate solution during blank titration; calculate the COD value according to the formula.

[0029] ...

Embodiment 2

[0032] 1) Water sample digestion

[0033] Take 5.00ml of a standard substance sample of known concentration, add 15.00ml of distilled water; add 13ml of 0.040mol / L potassium dichromate, 25ml of concentrated phosphoric acid, a few glass beads to prevent boiling, connect the heating reflux device, add 0.4g MgSO 4 -MnSO 4 The mixture (weight ratio is 3:1) is heated and digested, and when the sample starts to boil, it is timed to digest for 15 minutes.

[0034] 2) Titration

[0035] After reflux, cool to room temperature, add 100.00ml of distilled water, add 3 drops of ferrous iron indicator, titrate to the end point with 0.015mol / L sodium thiosulfate solution, and record the consumption;

[0036] 3) Blank control test

[0037] Use 20ml of distilled water instead of the sample to enter the blank control test, repeat the operation of steps [1) ~ 2)], record the consumption of sodium thiosulfate solution during blank titration; calculate the COD value according to the formula.

...

Embodiment 3

[0041] 1) Water sample digestion

[0042] Take 5.00ml of a standard substance sample of known concentration, add 15.00ml of distilled water; add 15ml of 0.025mol / L potassium dichromate, 28ml of concentrated phosphoric acid, a few glass beads to prevent boiling, connect the heating and reflux device, and add 0.90g of MgSO 4 -MnSO 4 The mixture (4:1 by weight) was heated and digested, and when the sample began to boil, it was digested for 18 minutes.

[0043] 2) Titration

[0044] After reflux, cool to room temperature, add 90.00ml of distilled water, add 3 drops of ferrous iron indicator, titrate to the end point with 0.025mol / L sodium thiosulfate solution, and record the consumption.

[0045] 3) Blank control test

[0046] Use 20ml of distilled water instead of the sample to enter the blank control test, repeat the operation of steps [1) to 2)], and record the consumption of sodium thiosulfate solution during the blank titration. According to the formula to calculate the COD...

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Abstract

The invention relates to a method for determining COD through rapid digestion. The method comprises the steps of carrying out rapid digestion on a water sample in a phosphoric acid medium under the condition of refluxing in a manner of taking a potassium dichromate solution as an oxidant and taking a MgSO4-MnSO4 mixture as a catalyst, cooling the water sample to room temperature, then, carrying out titration by using a sodium thiosulfate solution till an end by using ferroin as an indicator, and figuring out a COD value according to an equation. According to the method, sulfuric acid-silver sulfate is not used as a cocatalyst, and mercuric sulfate is not used as a chloride ion masking agent, so that the residual of heavy metals in the digested sample is greatly lowered, and aftertreatment on detected water samples and environmental protection are facilitated; meanwhile, the digestion time is short, the accuracy of detection is high, the operation is facilitated, and the labor intensity is lowered, so that the method can serve as a routine method for detecting the COD.

Description

technical field [0001] The invention relates to a method for measuring chemical oxygen demand, which belongs to the field of analytical chemistry. Background technique [0002] Chemical Oxygen Demand (COD) refers to the amount of oxidant consumed to oxidize reducing substances in 1 liter of water sample under certain conditions, which is converted into the oxygen required for each liter of water sample after it is completely oxidized. The number of milligrams expressed in mg / L. It reflects the degree of water pollution by reducing substances. This indicator is also used as one of the comprehensive indicators of the relative content of organic matter. COD reflects the degree of water pollution by reducing substances. Reducing substances in water include organic matter, nitrite, ferrous salt, sulfide, etc. [0003] Common methods for determining chemical oxygen demand: dichromate method, potassium permanganate method, spectrophotometric method, rapid digestion method, rapi...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01N1/44G01N31/16
CPCG01N1/44G01N31/16
Inventor 刘群卢敏王长丽刘娇杨杰
Owner 贵州开磷质量检测中心有限责任公司
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