Selective peracetic acid determination in the presence of hydrogen peroxide using a label free enzymatic method based on catalase

Peracetic acid (PAA) is selectively determined in the presence of hydrogen peroxide (H₂O₂) by using the self-indicating UV–Vis molecular absorption properties of catalase. The PAA reacts with the protein giving an intermediate (Cat-I) which is reduced back by the aminoacid core surrounding the hemegroup. Since the original form of the enzyme and the Cat-I have different UV–Vis absorption properties, the absorbance changes can be used for PAA determination. The H₂O₂/catalase reaction is extremely fast so that neither Cat-I compound nor kinetic interferences are observed. The method permits PAA determination in the 5 × 10⁻⁷ to 1.5 × 10⁻⁵ M range, the reproducibility being between 1% and 10%. Using this method, PAA has been successfully determined in water samples treated with commercial PAA/H₂O₂ biocides. A theoretical study has also been carried out for obtaining a mathematical model able to analytically describe the process.