Correlation of plasma generated long-lived reactive species in aqueous and gas phases with different feeding gases

Abstract

Reactive species are believed to play an important role in the treatment effects in both direct and indirect plasma applications. To better understand plasma chemistry and reveal the reactive species generated in the aqueous and gas phases, this study investigated the reactive species (i.e. H2O2, NO 2 − and NO 3 − ) that were generated using two types of plasma jets with different feeding gases (i.e. air, CO2, and N2) and treatment time (i.e. 0, 5, 10 and 20 min) in both aqueous and gas phases. Under the same treatment conditions, the determinations of reactive species in ambient air (X-variable) were carried out using optical absorption spectroscopy (OAS), and the detection of reactive species in plasma-activated water (PAW, Y-variable) was using wet chemical-based colourimetric methods. For both measurements, OAS spectral features and the contents of reactive species in PAW varied from different feeding gases and treatment times. The correlations of X and Y were developed using partial least squares (PLS) regression modelling. High collinearity (R2CVs ∼ 0.955-1) was shown between the independent X and Y. Based on the PLS regression results, the selectivity ratio (SR) algorithm was used to select the most important spectral wavelengths that are highly related to the functional groups of these reactive species.