Hypochlorous Acid Preparation and Quantification

Reagent-grade NaOCl was purchased from J. T. Baker. Hypochlorous acid was prepared in 154 mM NaCl by acidifying reagent-grade NaOCl to the pH range of 3.5 to 4.0 with dilute HCl. A Beckman pH meter was used to accurately measure the final pH values. The concentration of active total chlorine species in solution expressed as [HOCl]_T (where [HOCl]_T = [HOCl] + [Cl₂] + [Cl₃⁻] + [OCl⁻]) in 0.9% saline was determined by converting all the active chlorine species to OCl⁻ with 0.1 M NaOH and measuring the concentration of OCl⁻. The concentration of OCl⁻ was determined spectrophotometrically at 292 nm (ε = 362 M^{− 1} cm^{− 1})15 (link) with an Agilent 8453 UV-visible spectrophotometer.