pKa, pH and Efficacy of Weak Acids and Peracetic Acid
It has been noted in the literature and well established that the antimicrobial attributes of acids vary
based on pH, as the ratio of undissociated molecular species to ionized (dissociated) molecular species
changes. A number of references regarding this phenomenon are given in Russell, Hugo & Ayliffe’s
Principles and Practice of Disinfection, Preservation & Sterilization, Chapter 2.3.
Figure 1 shows the expected trend.
HA% = active acidity (undissociated)
A% = dissociated weak acid
Figure 1: Dependence of biocidal efficacy on pH and species present. Taken from Principles and Practice of
Disinfection, Preservation & Sterilization, pg. 24. The chart depicts the general response of organic (weak) acids.
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