Electron Paramagnetic Resonance Spectroscopy (EPR)
Radicals are paramagnetic, therefore, they are detectable by electron paramagnetic resonance spectroscopy (EPR). Due to the low concentration and the short lifetime of these highly reactive species, a direct measurement by EPR is not possible. Using so-called spin traps, radicals can be stabilized. The spin traps form a paramagnetic and characteristic adduct with the radicals. In the ZIK plasmatis group ‘plasma-liquid-effects’ different spin traps are used, for instance, 5-tert-Butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, sodium salt (Carboxy-PTIO), and 2,2,6,6-tetramethyl-4- piperidone hydrochloride (TEMPD-HCl). By the use of these oxygen, hydrogen, nitrogen, sulfur centered radicals as well as non-radicals (e.g. singlet delta oxygen and ozone) can be analyzed after plasma treatment.
The used system is an X-band (equals to microwave frequency of 9.87 GHz) EPR (EMXmicro, Bruker BioSpin GmbH, Rheinstetten, Germany) with the evaluation software (Xenon software with Xenon Spin Counting module, Bruker BioSpin, Rheinstetten, Germany).