Pka, Ph And Efficacy Of Weak Acids And Peracetic Acid Page 2

By rearranging the weak acid dissociation equilibrium equation into a formula known as the

Henderson-Hasselbach equation, it is possible to calculate the percent of each species present in

solution at each pH, given only the known pKa of the weak acid. By superimposing our efficacy data of

peracetic acid (from Perasan MP-2) obtained at different pHs, we arrive at a plot that matches Figure 1

quite nicely, when shifted to the right to allow for the difference in the pKa constant. This information is

presented in Figure 2.

Figure 2: Dependence of the measured biocidal efficacy on pH and species present in a Peracetic Acid solution. A

HOCl (chlorine) curve is also included for reference.

The above “Biocidal Efficacy” line graph is derived from the average data below at time 1, 5 and 10

minutes. Low concentrations of Perasan MP-2 were chosen because higher ppm levels resulted in

microbiological plates that were unreadable (zero CFU/ml).

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