Identifying the chloroperoxyl radical in acidified sodium chlorite solution

Abstract

The present study identified the active radical species in acidic sodium chlorite and investigated the feasibility of quantifying these species with the diethylphenylenediamine (DPD) method. Electron spin resonance (ESR) spectroscopy was used to identify the active species generated in solutions containing sodium chlorite (NaClO2). The ESR signal was directly observed in an acidified sodium chlorite (ASC) aqueous solution at room temperature. This ESR signal was very long-lived, indicating that the radical was thermodynamically stable. The ESR parameters of this signal did not coincide with previously reported values of the chlorine radical (Cl●) or chlorine dioxide radical (O = Cl●-O and O = Cl-O●). We refer to this signal as being from the chloroperoxyl radical (Cl-O-O●). Quantum chemical calculations revealed that the optimal structure of the chloroperoxyl radical is much more thermodynamically stable than that of the chlorine dioxide radical. The UV-visible spectrum of the chloroperoxyl radical showed maximum absorbance at 354 nm. This absorbance had a linear relationship with the chloroperoxyl radical ESR signal intensity. Quantifying the free chlorine concentration by the DPD method also revealed a linear relationship with the maximum absorbance at 354 nm, which in turn showed a linear relationship with the chloroperoxyl radical ESR signal intensity. These linear relationships suggest that the DPD method can quantify chloroperoxyl radicals, which this study considers to be the active species in ASC aqueous solution.

Elucidation of composition of chlorine compounds in acidic sodium chlorite solution using ion chromatography

“…Based on ESR experiments, Kawada et al proposed that the species that exhibits maximum absorption at 365 nm is the chlorine peroxide radical [14], which is consistent with the results of our experiment. Sodium chlorite solution cannot be measured by the DPD method, but sodium chlorite acidified with sulfuric acid can be measured (Fig 4).…”

“…The intensity of the peaks at 256 and 292 nm gradually decreased upon sulfuric acid treatment, but that of the peak at 365 nm increased with increasing sulfuric acid concentration. It is unknown what the 210 nm peak corresponds to, but the 256 nm peak is due to sodium chlorite [ 14 ]. However, there was no isosbestic point between sodium chlorite solution (256 nm) and sodium hypochlorite solution (292 nm) in the measured absorption spectra.…”

“…To identify the compounds, many measurement methods have been developed and used to date. Absorption photometry, iodometric titration (KI), the N , N -diethyl- p -phenylenediamine sulfate (DPD) method, and electron spin resonance (ESR) are usually used to identify and quantify chlorine compounds contained in chlorous acid solution [ 14 , 15 ]. The results obtained are also used as indicators of bactericidal activity [ 11 ].…”

Inactivation of human norovirus by chlorous acid water, a novel chlorine-based disinfectant

“…Thus, it is plausible that CA damages HuNoV by attacking specific amino acids in the viral capsid protein. Recently, we identified a novel reactive oxygen species, the chloroperoxyl radical (ClOO・), in acidified sodium chlorite (ASC), and this radical is long-lived and a main source of oxidizing power of ASC [20]. Since CA is a stabilized form of ASC and a long-lived disinfectant, it is plausible that ClOO・ is a main active component of CA.…”