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Chemical oxygen demand determination method for water bodies

A technology of chemical oxygen demand and determination method, applied in the field of low concentration chemical oxygen demand determination, can solve the problems of difficulty in judging the end point of titration, insufficient sample digestion, increase of uncertain factors, etc. Chlorine ability, avoid high test results, wide range of effects

Active Publication Date: 2012-07-18
CHINA PETROLEUM & CHEM CORP +1
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The national standard method can improve the determination accuracy of low-concentration samples to a certain extent by reducing the concentration of working reagents, and has a high oxidation rate and good chlorine resistance. increase in certainty
In addition, this method is time-consuming, complex equipment, and large amount of reagents, which is not suitable for the rapid determination of samples in batches.
COD Cr The rapid measurement instrument achieves rapid determination through the combination of rapid digestion and spectrophotometry, but its sample oxidation rate is lower than that of the national standard method, and the lower detection limit is higher, so the precision and accuracy of the determination of low-concentration samples are not ideal.
Using microwave digestion-spectrophotometry to detect non-volatile and low-concentration COD Cr Determination of samples can greatly reduce the digestion time and improve the degree of sample digestion, but the microwave power and digestion time must be accurately selected according to different water quality before digestion, otherwise it will lead to insufficient or excessive digestion of the sample, which will significantly affect the accuracy. influences

Method used

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  • Chemical oxygen demand determination method for water bodies
  • Chemical oxygen demand determination method for water bodies
  • Chemical oxygen demand determination method for water bodies

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0041] This example is used to illustrate the accuracy of the method of the present invention.

[0042] Determination of COD of a sample by low concentration chromium method in national standard GB11914-89 Cr , prepare 3 parallel samples to be tested and 1 blank sample, and measure the COD of 3 samples to be tested after reflux digestion for 2 hours Cr And take its arithmetic mean value as the comparison true value.

[0043] Adopt the method of the present invention to measure sample COD Cr Values, one blank sample and one sample to be tested were prepared. Use a sealed glass digestion tube (φ16mm×120mm) to prepare the sample to be digested, the sample volume is 2ml, the total volume of potassium dichromate solution and mercury sulfate solution is 1ml (the volume ratio of the two is 2:1), the volume of silver sulfate-sulfuric acid solution is 4ml ;After the sample is sealed, it is digested at 165°C for 15 minutes, and then treated with microwave for 15 seconds, the microwav...

Embodiment 2

[0050] This example is used to illustrate the repeatability of the method of the present invention.

[0051] Measure the COD of a certain sample according to the method of the present invention Cr value. The ratio of the sample to be digested and the digestion control parameters are the same as those in Example 1. One blank sample and one sample to be tested were prepared. Adjust the pH after the digestion is completed and cool to room temperature (the pH of the sample to be tested is 7.9, corresponding to a dilution rate of 1.57; the pH of the blank sample is 8.1, and the corresponding dilution rate is 1.76); shake the sample well, and use a 0.25 μm nylon membrane to Samples are filtered. The mass concentration of hexavalent chromium ions in the sample to be tested and the blank sample after digestion and cooling were determined by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and the sample to be tested was continuously...

Embodiment 3

[0056] This example is used to illustrate the parallelism of the measurement results of the method of the present invention.

[0057] Determination of COD of a low-concentration chlorine-containing sample by the method of the present invention Cr value. Prepare 1 blank sample and 5 samples to be tested in parallel. Use a sealed glass digestion tube (φ16mm×120mm) to prepare the sample to be digested, the sample volume is 2ml, the total volume of potassium dichromate solution and mercury sulfate solution is 1ml (the volume ratio of the two is 2:1), the volume of silver sulfate-sulfuric acid solution is 4ml ; After the sample is sealed, it is digested at 165°C for 15 minutes, and then treated with microwave for 10 seconds, the microwave frequency is 2800MHz, and the power is 3700w; See Table 3 for the corresponding dilution ratio; shake the sample well and filter it with a 0.25 μm nylon membrane. Measure the mass concentration of hexavalent chromium ions in each parallel sampl...

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Abstract

The invention relates to a chemical oxygen demand determination method for water bodies. The method includes the following steps of: (1) carrying out sample preparation and digestion according to the industry standard HJ / T399-2007; (2) using microwaves to process the sample obtained in step 1; (3) regulating the pH value of the sample obtained in step 2, and filtering the sample; (4) using an elemental speciation analysis method to determine the hexavalent chromium ion content in the sample obtained in step 3; (5) calculating the chemical oxygen demand. The method is applicable to the determination of various low-concentration CODCr samples, such as production water, domestic water, municipal water and wastewater, and in particular, the method is applicable to the high-precision and rapid determination of samples with predicted CODCr value less than 20mg / L.

Description

technical field [0001] The invention relates to a method for measuring the chemical oxygen demand of water body, in particular to a method for measuring the chemical oxygen demand of low concentration. Background technique [0002] Chemical Oxygen Demand (Chemical Oxygen Demand, hereinafter referred to as COD) is the amount of oxidant consumed when a sample is treated with a strong oxidant under certain conditions, and the result is converted into the corresponding oxygen amount, in mg / L. COD is a water quality index that reflects the content of reducing substances in water bodies. Since the main reducing substances in polluted water bodies are mostly organic matter, it is often used as a comprehensive index to characterize the content of organic matter in water bodies. According to the oxidant used, the COD determination method can be divided into manganese method (national standard GB / T15456-2008) and chromium method (national standard GB11914-1989). Mn and COD Cr expres...

Claims

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Application Information

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IPC IPC(8): G01N33/18G01N1/28G01N1/44G01N30/02G01N30/72G01N27/447G01N27/64
Inventor 杨青张莉高峰马欣
Owner CHINA PETROLEUM & CHEM CORP
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