Interaction between air plasma-produced aqueous 1O2 and the spin trap DMPO in electron spin resonance

A series of electron spin resonance (ESR) experiments is done to quantitatively measure the concentrations of aqueous O-1(2) and center dot OH produced by a surface micro-discharge air plasma device. O-1(2) is tested to be existed in the plasma treated solution by using the spin trap of TEMP. However, the unexpected DMPOX spectrum is observed in measuring center dot OH by the spin trap of 5,5-Dimethyl-1- Pyrroline-N-Oxide (DMPO). With more chemical scavenger experiments, it is found that removal of aqueous O-1(2) leads to the disappearance of DMPOX in ESR. Therefore, the generation of DMPOX is directly related to the oxidation of DMPO by plasma-produced aqueous O-1(2). This oxidation process and interactions between DMPO and chemical scavengers used in experiments can all be well explained by a proposed reaction mechanism. The revelation of interactions between aqueous O-1(2) and the spin trap DMPO shows that the observation of spectra of DMPOX in the ESR measurement can be regarded as a marker of high concentrations of plasma-produced O-1(2) in liquid. These results also prove the existence of interactions between spin traps and non-targeted plasma-produced reactive species in ESR experiments. Also, these results have offered a better understanding of the use of spin traps such as DMPO in the plasma-induced highly oxidative aqueous environment. Published by AIP Publishing.