Introduction: Peracetic acid (PAA) is a highly effective disinfectant against a wide range of viruses and bacteria. Its versatility, cost-effectiveness, and ability to quickly decontaminate large areas make it an ideal choice. PAA is also environmentally friendly and safe, as it does not produce any harmful by-products. However, to ensure its efficacy, it is crucial to maintain the optimal concentration of PAA in the solution. Objective: The objective of the study is to investigate the use of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy as a method for quantifying the concentration of peracetic acid (PAA), which comes in quaternary equilibrium mixture in commercial formulation. The study also aims to determine the rate constants and equilibrium constant for the production of PAA in various conditions, including the presence of catalyst and stabilizer. Methods: The spectra of all chemicals in PAA solution obtained in FT-IR Spectrometer were compared to identify the characteristic peaks of PAA, which were then computed using normal mode analysis at B3LYP/6-31G(d) level by Gaussian 09. The ATR-FTIR was used to measure time-dependent PAA signals until they reached equilibrium in three different conditions: (1) Acetic acid (10 to 17.4 M) and hydrogen peroxide (5 M), (2) with sulfuric acid as catalyst, and (3) with phosphoric acid as stabilizer. The collected data was analyzed through regression analysis, in which curves and rate law formulas were fitted to obtain the rate constants for peracetic acid synthesis and hydrolysis. Results: This study shows that ATR-FTIR spectroscopy can detect and quantify peracetic acid with a characteristic peak at 1753 cm−1. The proposed method is applicable to all peracetic acid solutions, including those with stabilizers and catalysts. The ATR-FTIR method offers advantages such as short detection time, simple operation, small sampling volume, and accurate measurement. Moreover, the accuracy of this quantitative method is confirmed by the fact that the reaction rate constants deduced from the fitted curves are more consistent with the actual reaction rate constants than those of the reference data based on KI titration method.
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