Yoichi Nakashima

Physicochemical properties of bactericidal plasma-treated water

Plasma-treated water (PTW), i.e. distilled water (DW) exposed to low-temperature atmospheric pressure helium plasma, exhibited strong bactericidal activity against Escherichia coli in suspension even within a few minutes of preparation. This effect was enhanced under acidic conditions. The bactericidal activity of PTW was attenuated according to first-order kinetics and the half-life was highly temperature dependent. The electron spin resonance (ESR) signal of an adduct of the superoxide anion radical () was detected in an aqueous solution using a spin-trapping reagent mixed with PTW, and adding superoxide dismutase to the PTW resulted in a loss of the bactericidal activity and weakening of the ESR adduct signal of in the spin-trapping. These results suggest that plays an important role in imparting bactericidal activity to PTW. Moreover, molecular nitrogen was required both in the ambient gas and in the DW used to prepare the PTW. We, therefore, suggest that the reactive molecule in PTW with bactericidal effects is not a free reactive oxygen species but nitrogen atom(s)-containing molecules that release , such as peroxynitrous acid (ONOOH) or peroxynitric acid (O2NOOH). Considering the activation energy for degradation of these species, we conclude that peroxynitric acid stored in PTW induces the bactericidal effect.

Ion-exchange chromatographic analysis of peroxynitric acid

Ion-exchange chromatographic analysis of peroxynitric acid (O2NOOH) was performed by combining an acidic eluate with an UV-vis detector and immersing the separation column in an ice-water bath. The decomposition behavior of peroxynitric acid in the solution was also studied using this system. The fraction for the peroxynitric acid peak was collected. Ion-exchange chromatographic analysis of this fraction, after standing at room temperature for 24h, showed that the decomposition products were mainly nitrate ions with a very small amount of nitrous acid. The peroxynitric acid peak area correlated perfectly with the total amount of decomposition products. The ion-exchange chromatographic isolation allowed us to evaluate the molar extinction coefficient of peroxynitric acid precisely in a wider wavelength range than previous reports. The value decreases monotonically from 1729±26M(-1)cm(-1) at 200nm to 12.0±0.5M(-1)cm(-1) at 290nm.