EFFICIENCY OF ATMOSPHERIC PRESSURE NITROGEN GAS REMOTE PLASMA STERILIZATION AND THE CLARIFICATION OF STERILIZATION MAJOR FACTORS

Experiments reported here were conducted using atmospheric nitrogen gas remote plasma with a pulsed power source. The sterilization efficiency, major sterilization factors and most appropriate sterilization conditions were determined. By varying several factors such as hotplate temperature, relative humidity, water vapor supply location, etc., the most appropriate sterilization conditions were identified. The temperature of the hotplate was varied from 55 °C to 75 °C and with this 20 °C increase in temperature, sterilization was completed in half the time. In this experiment, it was confirmed that the combined effect of a relative humidity (RH) of 0.5% and nitrogen gas was superior to the use of nitrogen gas alone. Furthermore, it was clarified that the optimal humidity was in the range of 0-5 % RH. When RHs of 0, 0.5 and 5% were tested, 0.5% RH was found to be optimal for sterilization. The location of the water vapor supply was changed relative to the hotplate, and use of the most remote port upstream of the reactor resulted in the most efficient sterilization. In addition, the results correlated with the amount of NO radicals generated. The NO radical is the precursor of OONOã??- (peroxynitrite anion radical). The sterilization factors associated with this experiment were NO radicals, H2O2, OH radicals, O2ã??- (superoxide anion radicals) and OONOã??-. Only OONOã??- production correlated with sterilization efficiency. Therefore, OONOã??- is thought to be the major factor for nitrogen gas plasma sterilization. In addition, as already described, the highest sterilization efficiency was with 0.5% RH and the amount of OONOã??- produced correlated with the RH. These data support the idea that OONOã??- is the major contributing factor for nitrogen gas plasma sterilization. The D values for this experiment were approximately 10 min.