Chlorine Detection: Smell But No Color?


In our actual test environment, there are many indicators to be measured, Residual chlorine is one of the indicators that often needs to determine.

Recently, we received feedback from users: When using the DPD method to measure residual chlorine, it clearly smelled a heavier smell, but the test did not show color. What is the situation? (Note: The user's disinfectant margin requirements are relatively high)

Regarding this phenomenon, let’s analyze with you today!

First of all, the most extensive method for detecting residual chlorine is DPD spectrophotometry. According to EPA, the residual chlorine range of the DPD method is generally 0.01-5.00 mg/L.

Secondly, hypochlorous acid, the main component of free residual chlorine in water, has oxidizing and bleaching properties. When measuring the residual chlorine by the DPD method, when the residual chlorine content in the water sample is too high, after the DPD is completely oxidized and colored, the remaining more residual chlorine reflects the bleaching property, and the color is bleached.

In view of this situation, we recommended two solutions as below:

1. When using the DPD method to detect residual chlorine, you can dilute the water sample with pure water to make the residual chlorine within the range of 0.01-5.00 mg/L, and then perform the detection.

2. You can directly select equipment that detects high concentrations of residual chlorine for detection

In fact, in the actual test, you will encounter various problems. When measuring residual chlorine by DPD method, you obviously smell a heavier smell, but there is no color in the test. The above is our sharing. I hope it will be helpful to your test work. If you have other questions or better methods, you can also contact us in time for more communication. I believe you will have a satisfactory answer to the problems you encounter

Thank you!!!

Post time: Jun-17-2021