COD (Chemical Oxygen Demand) is a widely used analytical test that measures the amount of oxygen required to oxidize organic and inorganic matter in water. It is an important parameter for assessing water quality and the efficiency of wastewater treatment processes.

For an in-depth understanding of how COD vials operate in water testing, please refer to this article: "The Working Principle of COD Vial."

COD Test Tubes

High-quality COD test tubes are generally made of 5.0 borosilicate glass, which has excellent resistance to thermal shock and chemical erosion. A good COD test tube should be easy to use, easy to inject and drain the solution, and not prone to leaking.

COD test tubes are specially designed glass tubes used in the COD analysis process. These tubes contain a known amount of potassium dichromate (an oxidizing agent) and sulfuric acid, along with a catalyst. The key features of

COD test tubes include:

Capacity: 10 mL, with a maximum capacity of 12 mL

Height: 10 ± 0.02 cm

Diameter: 1.58 ± 0.02 cm

Neck Inner Diameter: 0.95 ± 0.02 cm

Neck Outer Diameter: 1.50 ± 0.02 cm

The high optical glass quality ensures accurate colorimetric analysis of the COD results.

COD Test Procedure

The 16mm COD test procedure involves the following steps:

1. A water or wastewater sample (typically 2 mL) is added to the COD test tube containing the digestion reagent and a catalyst.

2. The tube is capped with a polypropylene, PTFE-lined cap and heated in a block digester at 150°C for 2 hours.

3. During the heating process, the organic matter in the sample is oxidized by the potassium dichromate, reducing it to a greenish trivalent chromium compound.

4. The COD concentration is determined by measuring the absorbance of the digested sample using a spectrophotometer at a specific wavelength, depending on the COD range:

Low Range (5-150 ppm): measured at 420 nm

High Range (20-1500 ppm): measured at 620 nm

Want to know more about COD Test Tube, please check this article: COD Test Tube with PP Screw Cap for Water Analysis

Sample preparation and handling

Wastewater and sewage samples may contain undissolved or particulate matter. Such samples can be homogenized with a blender before testing to improve accuracy and repeatability. The amount of water required to dilute the sample depends on the COD range of the test tube.

COD Ranges and Applications

COD test tubes are available in different ranges to accommodate various sample concentrations:

Low Range: 5-150 ppm

High Range: 20-1500 ppm

These ranges are suitable for analyzing a wide variety of water samples, including:

a. Raw water for treatment

b. Wastewater from industrial and municipal sources

c. Effluents from wastewater treatment plants

d. Surface waters and groundwater

By using the appropriate COD test tube range based on the expected COD concentration, accurate results can be obtained for effective water quality monitoring and treatment process control.

For more information on COD test tubes and their applications in water analysis, refer to this article: "How the COD Test Tube is Used in Water Analysis."

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