Mass spectrometric detection of short-living radicals produced by a plasma needle

A plasma needle is a radio-frequency (rf) micro-discharge operated in a mixt. of helium and air at atm. pressure. This source is designed for medical treatment of living tissues. Therapeutic effects of plasma treatment depend on generation of short-living active radicals: reactive oxygen and nitrogen species (ROS/RNS). In this work we det. the concn. of several ROS and RNS (at. oxygen, nitrogen and hydroxyl radical) by means of threshold ionization mass spectrometry. It is shown that mol. oxygen and nitrogen are substantially dissocd. in the plasma. At. nitrogen and oxygen are the most abundant radicals: the densities are on av. few times 10-4. Hydroxyl radicals are less abundant (10-5 fraction of the total gas d.). As expected, the densities of active species increase with increasing plasma power. Spatial (axial) distributions have been detd.; the radical d. reaches a max. at 2.5 mm away from the rf powered electrode, and it decreases at distances larger than 3.5 mm. The amt. of active radical species is reasonably high, which explains the effectiveness of plasma in bacterial inactivation and tissue treatment. [on SciFinder (R)]