Chemical Oxygen Demand (COD) is an important water quality parameter used to determine the amount of oxygen consumed by organic matter in water through oxidation. This test is based on a chemical oxidation reaction, usually carried out with potassium dichromate in a strongly acidic environment.

2. Required Chemicals

1. Testonic Potassium Dichromate Solution (0.25N)

2. Testonic Silver Sulfate (Sulfuric Acid) Solution

3. Testonic Ferroin Indicator Solution

4. Testonic FAS - Ferroin Ammonium Sulfate Titration Solution (0.1 N)

5. Testonic Potassium Dichromate Solution 0.0167M - 0.1N (With Mercury Sulfate)

3. Testing Procedure

3.1. Sample Preparation

1. The water sample is homogenized.

2. 10 mL of water sample is taken into a 250 mL reactor tube.

3. 10 mL of Testonic Potassium Dichromate Solution (0.25N) is added.

4. 20 mL of Testonic Silver Sulfate (Sulfuric Acid) Solution is added and mixed carefully.

3.2. Oxidation Process

1. The lid is tightly closed and the mixture is shaken thoroughly.

2. The sample is heated in a reflux system at 150°C for 2 hours.

3. After cooling, the sample is transferred to a 250 mL volumetric flask and completed to 250 mL with pure water.

3.3. Titration

1. Add 3-4 drops of Testonic Ferroin Indicator Solution.

2. Titration is performed with Testonic FAS - Ferroin Ammonium Sulfate Titration Solution (0.1 N).

3. Titration is terminated when the color change from blue-green to red.

3.4. Calculation

The COD value is calculated with the following formula:

Here:

• A: Volume of FAS solution used for blank sample (mL)

• B: Volume of FAS solution used for sample sample (mL)

• N: Normality of FAS solution (0.1 N)

• V: Sample volume (mL)

4. Safety Precautions

• Sulfuric acid and potassium dichromate are toxic and corrosive, appropriate protective equipment (goggles, gloves) should be used.

• A well-ventilated laboratory should be used when heating the sample.

• Waste should be disposed of in accordance with environmental regulations.

This procedure is a reliable method for determining the amount of organic pollutants in water.

With correct chemical dosages and titration techniques, precise Measurements can be obtained.