References:  DDPD method-Developed by CHEMetrics, Inc.

Because it is a strong disinfectant, peracetic acid is an excellent sanitization agent for the food and beverage industry.  Peracetic acid is used to disinfect equipment, pasteurizers, tanks, pipelines, evaporators, fillers, and contact surfaces in food processing plants.  It is especially effective in eliminating the osmotolerant microbes (e.g. the yeast Zygosaccharomyces bailii) in beverage plants producing high-sugar products. The pulp and paper industry uses peracetic acid as a delignification and bleaching agent.

The DDPD method is a derivative of the DPD method.  In the Peracetic Acid DDPD test method, the sample is treated with an excess of potassium iodide. Peracetic acid oxidizes the iodide to iodine.  The iodine then oxidizes DDPD, a methyl-substituted form of DPD (N, N-diethyl-p-phenylenediamine) to form a purple colored species that is directly proportional to the peracetic acid concentration in the sample.  Results are expressed as ppm (mg/L) peracetic acid.

Various oxidizing agents such as halogens, ozone, ferric ions, and cupric ions will produce high test results.  Hydrogen peroxide does not interfere if present at levels comparable to to the peracetic acid levels.