Liquisys M CCM223/253 Commissioning
Endress+Hauser 45
Free chlorine is understood as the sum of elementary chlorine (Cl
2
), hypochlorous acid
(HOCl) and hypochlorite ions (OCl
–
). These forms of chlorine are able to kill bacteria,
inactivate viruses and oxidize organic substances within a short period of time.
Combined chlorine
Combined chlorine refers to the forms of chlorine in water and consists of chemical
compounds made up of chlorine and ammonia (NH
3
) or ammonium (NH
4
+
) entstehen.
Combined chlorine still has a disinfectant property, but far less than that of free chlorine.
Total chlorine
Total chlorine is the sum of free chlorine and combined chlorine.
Measuring free chlorine with the CCS140 and CCS141 sensors
Molecular chlorine (Cl
2
) is present at pH values < 4. Consequently, hypochlorous acid
(HOCl) and hypochlorite (OCl– remain as components of free chlorine within the range of
pH 4 to 11.
As hypochlorous acid splits up (dissociates) with an increasing pH value to form
hypochlorite ions (OCl
–
) and hydrogen ions (H
+
), the amounts of the individual
components of free effective chlorine change with the pH value. For example, if the
amount of hypochlorous acid is 97% at pH 6, it drops to approx. 3% at pH 9.
A0002017
31 Basic representation of pH compensation
A Measured value with pH compensation
B Measured value without pH compensation
C pH compensation
The CCS140 or CCS141 chlorine sensors selectively measure the amount of hypochlorous
acid in amperometric measurement.. This works as a powerful disinfectant in a watery
solution. In contrast to this, hypochlorite is an extremely weak disinfectant. Therefore,
when used as a disinfectant at higher pH values, the effectiveness of chlorine is limited. As
hypochlorite ions cannot permeate the sensor membrane, the sensors do not record this
value.
Measuring total chlorine with the CCS120 sensor
If, in addition to free available chlorine, ammonium is also present in the medium -
preferably water - chloramines (Cl
n
NH
m
) form quickly. This compound is formed in various
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