Development of a spectrophotometric method for on-site analysis of peroxygens during in-situ chemical oxidation applications

Activated peroxygens are frequently used as active agents in in-situ chemical oxidation (ISCO) contaminated site remediation applications, and fast and simple quantitative analysis of these species on site is necessary. In this work, the use of a spectrophotometric method based on classic iodometric titration is studied for quantitative analysis of S₂O₈²⁻ and H₂O₂. Instead of a back-titration step, the absorbance of the yellow iodide colour was measured at 352 nm in the presence of a bicarbonate buffer. A linear calibration curve was obtained from 0 to 0.1 mM for both S₂O₈²⁻ and H₂O₂. By dilution, the method can be used for all concentrations typically applied in the field. Concerning pH dependence, neutral pH levels caused no significant error whereas pH levels above 8 caused a 9% and 6% deviation from the theoretical peroxygen concentrations. Furthermore, the method showed little dependence on other matrix components, and absorbance was stable (<2% change) for more than a week. Overall, the method proved to be fast and simple, which are important features for a field method.