Metex 8760CLP Total Free Chlorine & pH Analyzer - Manual (Page 22)

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22
Disinfectant Properties of Chlorine
Chlorine is known to be a good disinfectant; it is able to kill living matter in water such as bacteria,
cysts, and spores. Exactly how chlorine works to kill is not known. Studies do agree, however, that
certain forms of chlorine are more effective disinfectants than others. Whatever the chemical reaction, it
is also generally agreed that the relative efficiency of various disinfecting compounds is a function of
the rate of diffusion of the active agent through the cell wall. Factors which affect the efficiency of
destruction are:
• Nature of disinfectant (type of chlorine residual fraction)
• Concentration of disinfectant
• Length of contact time with disinfectant
• Temperature
• Type and concentration of organisms
• pH
HOCl is the most effective disinfectant of all the chlorine forms and is similar in structure to water. The
germicidal efficiency of HOCl is due to the relative ease with which it can penetrate cell walls. This
penetration is comparable to that of water, and can be attributed to both it's modest size and to it's
electrical neutrality.
The concentration of hypochlorous acid is dependent on the pH, which establishes the amount of
dissociation of HOCl to H
+ and OCl - ions. Lowering the temperature of the reacting solution suppresses
the dissociation; conversely raising the temperature increases the amount of dissociation.
The rate of dissociation of HOCl is so rapid that equilibrium between HOCl and the OCl
- ion is
maintained, even though the HOCl is being continuously used up.
The hypochlorite ion (OCl
- ) form of chlorine is a relatively poor disinfectant because of it's inability to
diffuse through the cell wall of microorganisms. The obstacle is the negative electrical charge.