Orthotolidine test for residual chlorine determination

Introduction:
The orthotolidine test is a commonly used method for the determination of residual chlorine in water. It is a colorimetric test that detects the presence of free and combined chlorine in water.

Principle:
The orthotolidine test is based on the reaction between chlorine and orthotolidine in the presence of an acid. The reaction produces a yellow-brown color that is proportional to the amount of residual chlorine in the water.

Procedure:
The procedure for the orthotolidine test involves the following steps:

1. Collect a water sample in a clean container.
2. Add a few drops of orthotolidine reagent to the water sample.
3. Add a few drops of hydrochloric acid to the water sample.
4. Mix the contents of the container thoroughly.
5. Wait for the color to develop, which should take no more than 1 minute.
6. Compare the color of the water sample to a standard color chart to determine the concentration of residual chlorine in the water.

Advantages:
The orthotolidine test is a simple, inexpensive, and reliable method for the determination of residual chlorine in water. It can be used in the field and does not require specialized equipment.

Limitations:
The orthotolidine test is only capable of detecting free and combined chlorine, and cannot differentiate between the two. It can also be affected by the presence of other oxidizing agents in the water, such as bromine or ozone.

Conclusion:
The orthotolidine test is a useful tool for the determination of residual chlorine in water. It is widely used in the water treatment industry and can help ensure that water is safe for consumption.