Detecting Residual Peracetic Acid

After using peracetic acid (PAA) as a terminal disinfectant in the bottling plant or elsewhere, it is important to ensure that no traces of peracetic acid remain on surfaces which will contact food or water.

The easiest way to do this is by using test strips which show different degrees of colour at each concentration level.  However, the lowest measurable level detected by most PAA-specific strips is 5mg/l (ppm).  So, there is no information about residual PAA in the range 0-5ppm.

There is a way around this if you consider the composition of peracetic acid.  It is not a single substance, but a mixture of hydrogen peroxide, peracetic acid and acetic acid in equilibrium.  The equilibrium can shift under the influence of temperature, rate of degradation and water content, plus other factors.

                                                PAA Composition (1)

The peroxide concentration (by volume) is approximately 3.5 times that of acetic acid and approximately 6 times that of the peracetic acid initially formed.  Therefore, a peroxide type residual test strip may be used to safely estimate residual peracetic levels because they will always be lower than that of the peroxide.

Peroxide test strips are available in the range 0.0 - 0.2 - 2.0 - 5.0 ppm.

(1) Vern Taaffe - Reprocessing Products Corp - January 5, 2004