Analytical Sciences

Spectroscopic Characterization and the pH Dependence of Bactericidal Activity of the Aqueous Chlorine Solution

Shunji NAKAGAWARA*, Takeshi GOTO*, Masayuki NARA*, Youichi OZAWA*, Kunimoto HOTTA** and Yoji ARATA* *

*Water Research Institute, Sengen 2-1-6, Tsukuba 305-0047, Japan
**Department of Bioactive Molecules, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku, Tokyo 162-0052, Japan

Raman spectroscopic analysis has been used to identify the chemical species that exist in aqueous chlorine solution. The pH dependence of the Raman spectra obtained indicates that there is an equilibrium among hypochlorite ion, hypochlo-rous acid and chlorine. Bactericidal activities of the acidic electrolyzed water, which is generated by electrolysis of an aqueous NaCl solution, were evaluated in the pH range 2 - 9 against Escherichia coli K12 and Bacillus subtilis PCI219 by a semi-quantitative bioassay. The maximum activity was observed between pH 4 and 5 in both bacteria. The Raman and the ultraviolet spectroscopic data, along with chemical analysis data, were used to conclude that the bactericidal activity is quantitatively correlated to the concentration of hypochlorous acid in solution. (Keywords: Acidic electrolyzed water, bactericidal activity, hypochlorous acid, Raman spectra, UV spectra)

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