The preparation process of COD (Chemical Oxygen Demand) reagents is a crucial part of environmental monitoring and water quality analysis, and it is of great significance for accurately determining the organic content in water samples. The following is a detailed description of the COD reagent configuration process:
1、 Preparation work
1. Safety protection: Before configuring COD reagents, it is necessary to wear personal protective equipment, including lab coats, gloves, goggles, etc., to prevent the reagents from causing harm to the skin and eyes.
2. Material preparation: Prepare the required reagent raw materials, such as potassium dichromate, silver sulfate, concentrated sulfuric acid, etc., and ensure that their purity meets the analytical purity standard. At the same time, prepare the necessary glassware for the experiment, including beakers, measuring cylinders, volumetric flasks, pipettes, etc., and ensure that they are clean and free of contamination.
2、 Reagent configuration steps
1. Potassium dichromate standard solution:
-Weigh 12.258g of standard or superior grade pure potassium dichromate that has been pre dried at 120 ℃ for 2 hours and dissolve it in water. Transfer it into a 250ml volumetric flask, dilute to the standard mark, and shake well.
-The concentration of the solution is 0.250mol/L, which is used for subsequent dilution and calibration.
2. Sulfuric acid silver sulfate catalyst:
-Add 33.3g of silver sulfate to 2500ml of concentrated sulfuric acid, dissolve and mix well, and let it stand for 1-2 days.
-This catalyst is used to promote the oxidation of organic compounds in the sample by potassium dichromate.
3. Mercury sulfate masking agent:
-Weigh the reference material that has been dried at 120 ℃ for 2 hours and dissolve it in 100ml of distilled water or deionized water; Or take 10.2g of analytical pure mercury sulfate and dissolve it in 100ml of distilled water or deionized water.
-This masking agent is used to remove the interference of chloride ions in water samples.
4. Ammonium ferrous sulfate standard titration solution:
-Weigh 39.5g of ferrous ammonium sulfate and dissolve it in water. Add 20ml of concentrated sulfuric acid and dilute to 1000ml after cooling.
-Before use, calibrate its concentration with potassium dichromate working solution and adjust it to 0.1mol/L ± 0.001mol/L.
5. Potassium hydrogen phthalate standard solution:
-Weigh 0.4251g of potassium hydrogen phthalate, which has been pre dried to constant weight at 105-120 ℃, and dissolve it in water. Dilute it to 500ml and mix well.
-The COD value of the solution is 1.176mol/L (O2), which is used for calibrating the instrument.
3、 Precautions
1. Accurate weighing: When weighing reagents, accuracy should be ensured to avoid inaccurate reagent concentration caused by weighing errors.
2. Dissolution and dilution: During the dissolution and dilution process, deionized water or distilled water should be used to avoid introducing impurities.
3. Storage and use: The prepared reagents should be stored in brown glass bottles and kept in a dark place or refrigerated room to avoid the influence of light and temperature on the reagents. When using, it should be taken in moderation as needed to avoid waste.
The configuration process of COD reagents involves multiple steps and multiple reagents, and it is necessary to strictly follow the operating procedures to ensure the accuracy and reliability of the reagents. At the same time, attention should be paid to safety protection and the storage and use requirements of reagents to avoid accidents and ensure the quality of reagents.