Determination of Peracetic Acid by Potentiometric Titration

The application that describes the determination of AcOH and PAA in a single titration using aqueous NaOH as titrant. The large difference between the pKa values of AcOH (4.75) and PAA (8.2) enables the determination of both species using a single titration.

Background

Peracetic acid (also peroxyacetic acid, PAA, CH₃COOOH) can be obtained by mixing hydrogen peroxide with acetic acid (AcOH). Because of its strong oxidizing character, PAA is often used as bleach or disinfectant. The main field of application is the sterilization of plastic bottles in the bottled beverage production. Upon mixing hydrogen peroxide and acetic acid, the following equilibrium is slowly settled:

𝐶𝐻₃𝐶𝑂𝑂𝐻+𝐻₂𝑂₂ ←→ 𝐶𝐻₃𝐶𝑂𝑂𝑂𝐻+𝐻₂𝑂

The formation of this equilibrium is very slow but can be accelerated by the presence of strong acids. Solutions with PAA contents between 2.5 and 40 % are commercially available. A dilution of the mixture with water leads to a new equilibrium with a lower PAA content.

The determination of PAA is commonly performed by redox titrations. PAA oxidizes iodide to iodine, which is then titrated with thiosulfate. The hydrogen peroxide, which is always present in the solution needs to be titrated first, e.g. with potassium permanganate, because it interferes with the iodometric titration. Apart from the high complexity, this method has the drawback that it relies on the use of sulfuric acid, which catalyzes a shift of the equilibrium to lower PAA contents during the sample preparation.

Alternatively, the mixture can be titrated with a strong base such as NaOH. The large difference between the pKa values enables the determination of both species using a single titration. If performed quickly, the dilution of the sample barely affects the equilibrium between AcOH and PAA.

This method has been developed using an Excellence Titrator with the InMotion autosampler. However, it can easily be adapted and used for Compact Titrators with the Rondolino autosampler or with the manual titration stand.

The Application Includes:

• Introduction
• Sample Preparation and Procedures
• Chemistry
• Instruments and Accessories
• Measured Values
  
• Method in Detail

And method files ( .lmt and .xml) for direct import and implemention on the instrument.