How can manganese interferences in a chlorine test be eliminated?

Document ID

Document ID TE1570

Version

Version 3.0

Status

Status Published

Published Date

Published Date 25/01/2018
Question
How can manganese interferences in a chlorine test be eliminated?
Summary
Eliminating manganese interferences in chlorine analysis
Answer
Manganese interference can be eliminated using potassium iodide and sodium arsenite.

The sample is tested twice: once with pretreatment and once without. Testing the sample without pretreatment will give a result due to chlorine and oxidized manganese (and oxidized chromium).Testing the sample with pretreatment will give a result due to the oxidized manganese (and oxidized chromium) without chlorine. Subtraction then gives the true chlorine value.

Potassium iodide and sodium arsenite work together to remove chlorine from the sample. At a neutral pH, chlorine is the only species which will oxidize iodide to iodine. The reaction between chlorine and iodide removes chlorine from the sample. The iodine is then removed from solution with arsenite. At this point, there should be no chlorine in the sample.

Manganese interference can also be eliminated by switching to the indophenol method for chlorine. This is discussed in the  Hach Disinfection Series - Step 7 page on the Hach website.