eutech-instruments waterproof c401 colorimeter User Manual

Measurement: Chlorine, Free & Total

 

 

C401/301/201/102/101 

 

 

 

14

 All instruments are factory calibrated and user 

calibration is not recommended. However, if a Chlorine standard can be 
prepared, measured accurately and qualified by a different method 
(titration, for example) or another instrument of higher precision and 
accuracy, then a Chlorine standard in the 4.1-5.0 ppm Cl

2

 range can be 

used. Please refer to Section 3.2 Chlorine, Free & Total, for details.  

Chlorine exists in water as Un-Combined (Free) Chlorine and Combined 
Chlorine. The concentration of Free Chlorine can be determined directly 
and the concentration of Combined Chlorine may be calculated by 
subtracting the concentration of Free Chlorine from that of Total Chlorine. 

In the Free Chlorine test method Un-Combined Chlorine reacts directly 
with DPD (N,N-diethyl-p-phenylenediamine) in a conditioned sample to 
give a pink color.  In the Total Chlorine test method Combined Chlorine 
reacts with potassium iodide to form tri-iodide ions.  The tri-iodide ions and 
the Free Chlorine present react with DPD in a conditioned sample to give 
a pink color. 

The depth of the pink color produced is proportional to the concentration of 
Chlorine.  The amount of 525nm light absorbed by the pink color is 
accurately measured by the meter and then converted into the Chlorine 
concentration.