Orthotolidine (OT) test and Orthotolidine – Arsenite (OTA) test
Free chlorine combines with ammonia and nitrogen of organic matter to form ‘Chloramines’
Chloramines are not efficient residual disinfectants
Yet these get included in the Total chlorine content of the water to be tested
We intend to measure only the ‘free residual chlorine ’ as this only will provide protection from subsequent contamination
We can measure ‘free chlorine ’ using OT test 10 seconds reading
We can measure ‘total chlorine ’ using OT test 5 minutes reading
‘Combined chlorine ’ = total chlorine - free chlorine