Selective Photometric Determination of Peroxycarboxylic Acids in the Presence of Hydrogen Peroxide

Abstract

A method for the determination of peroxyacetic acid (PAA) and related peroxycarboxylic acids is presented. 2,2′-Azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), one of the most popular substrates for the enzyme peroxidase, is oxidized selectively by PAA to an intensely green radical cation (ABTS ^·+ ) in the presence of hydrogen peroxide. Photometric detection of the product can be performed in four characteristic regions of the visible and near infrared spectrum in the range 405–815 nm. The reaction is accelerated considerably by the addition of iodide without any loss of selectivity. A quantitative reaction, a limit of detection of 1 × 10 ^{- 6} mol l ^{- 1} (76 µg l ^{- 1} ) for PAA and linear calibration graphs over three orders of magnitude are obtained under these conditions. No interferences by several ions at their typical concentrations in tap water could be observed under pH control. Comparative HPLC measurements were used to demonstrate the reliability of the proposed method. The recovery and standard deviation for PAA in real samples (n = 53) using the proposed method was 98 ± 4% of the respective HPLC measurements. Microplates were used as an alternative to cuvettes to analyse a large number of samples per timescale. The method may become a valuable tool for the determination of PAA in disinfection solutions, because reliable analysis results are obtained using standard laboratory equipment. Direct calibration for rapid on-site analysis is performed by using the molar absorptivity of the reaction product.