Praktikum Kualitas Air DTPKL: Analisis COD (Chemical Oxygen Demand) di Lab. TPKL Universitas Jember

Introduction

This tutorial provides a step-by-step guide for conducting a Chemical Oxygen Demand (COD) analysis in a laboratory setting, as demonstrated in the DTPKL Praktikum at Universitas Jember. COD measurement is crucial for assessing the organic material in water samples, which is essential for water quality management and environmental protection.

Step 1: Prepare the Equipment and Materials

Before starting the analysis, gather all necessary equipment and materials:

• Glassware: COD vials, beakers, and pipettes
• Chemicals: Potassium dichromate, sulfuric acid, and other reagents specified in your lab protocol
• Heating device: Hot plate or furnace for digestion process
• Cooling system: Ice bath or cooling water for post-digestion cooling

Practical Tip: Ensure all glassware is clean to avoid contamination.

Step 2: Collect and Prepare Water Samples

Collect water samples that you intend to analyze. Follow these guidelines:

• Use clean, sterilized containers to avoid introducing contaminants.
• Label each sample clearly with date, location, and any other relevant information.
• If samples cannot be analyzed immediately, store them in a cool, dark place to prevent degradation.

Common Pitfall: Avoid using samples that have been sitting out for an extended period, as they may not represent the original water quality.

Step 3: Add Reagents to Samples

For the COD analysis, follow these sub-steps:

1. Measure a specific volume of the water sample (usually 50 mL).
2. Add a predetermined amount of potassium dichromate solution.
3. Carefully add concentrated sulfuric acid to the mixture. Always add acid to water, not the other way around, to prevent exothermic reactions.

Practical Tip: Conduct this step in a fume hood or well-ventilated area to avoid inhaling harmful vapors.

Step 4: Digest the Samples

Digest the prepared samples to facilitate the reaction between potassium dichromate and organic matter:

• Place the vials in a heating device set to 150°C for 2 hours.
• Ensure the samples are securely closed to prevent evaporation and contamination.

Practical Tip: Monitor the temperature closely to maintain consistent conditions throughout the digestion process.

Step 5: Cool and Dilute Samples

After digestion, let the samples cool down to room temperature:

• Use an ice bath if necessary to speed up cooling.
• Once cooled, dilute the samples with distilled water to bring them to a workable volume (usually 100 mL).

Common Pitfall: Inadequate cooling can lead to inaccurate readings in subsequent steps.

Step 6: Measure the COD

Using a spectrophotometer, measure the COD in each sample:

1. Prepare a calibration curve using standard solutions of known COD values.
2. Measure the absorbance of each sample at the specified wavelength (typically around 600 nm).
3. Compare the sample absorbance to the calibration curve to determine the COD.

Practical Tip: Ensure the spectrophotometer is properly calibrated before taking measurements.

Conclusion

Conducting a COD analysis involves careful preparation, precise handling of chemicals, and systematic measurement techniques. By following these steps, you can accurately assess the organic pollution levels in water samples. For further exploration, consider studying other water quality parameters or using different analysis methods to broaden your understanding of environmental monitoring.