Specificity of detection methods of nitrites and ozone in aqueous solutions activated by air plasma

Abstract

Air transient spark (TS) discharge generates cold plasma, which is a rich source of reactive oxygen and nitrogen species (RONS). The gaseous products both in ambient air and air humidified by water electrospray (ES) are nitrogen oxides (NO and NO2). The rotational and vibrational temperatures determined by optical emission spectroscopy (OES) are lower with water ES through the discharge than in ambient air, which reduces the formation of NOx. The investigation of the specificity of Griess colorimetric assay for the detection of long‐lived nitrites in plasma activated solutions confirms its accuracy by comparison with ion chromatography (IC) and excludes possible interferences with hydrogen peroxide by using the enzyme catalase. Examination of the specificity of the Indigo blue assay for ozone detection shows strong interferences with the peroxynitrite chemistry. Phenol as the chemical probe confirms that the TS air discharge produces no aqueous ozone.

Evaluation of Oxidative Species in Gaseous and Liquid Phase Generated by Mini-Gliding Arc Discharge

“…Further details on the air plasma chemistry leading to NOx formation in the transient spark discharge can be found in [1,2,46].…”

“…However, even without the presence of O 3 indigo could have been affected by interference with other RONS present in plasma treated water, for instance via formation of OH radicals, probably formed as a decay product from peroxynitrites. More detailed discussion on the suitability of indigo blue method for O 3 detection in plasma activated water can be found in [46]. Approximately 0.8 mg/L of "apparent" O 3 was recorded for 5 min GA treatment in DI.…”

Chemical Detection of Short-Lived Species Induced in Aqueous Media by Atmospheric Pressure Plasma

“…Kovačević et al measured ozone delivery to the plasma-exposed liquid using iodometry, while the solubilised ozone remaining in the liquid after the CAP treatment was detected with decolourisation of indigo trisulphonate [72]. However, recently, Tarabová et al reported that indigo dyes decay in reactions with other RONS, e.g., secondary •OH radicals produced in liquids after the plasma exposure [73]. The non-selectivity of the iodometric method is due to the other oxidising RONS [72].…”

“…Benedikt and co-workers detected oxygen atoms in aqueous solutions of phenol, with further MS analysis of the formed hydroxylated products [70,71]. However, hydroxylation of phenol can also occur in a reaction with hydroxyl radicals [73,75].…”

“…− and NO 3 − , which are detected colorimetrically [20,48,72,73], the radical nitric oxide itself is monitored using spin trapping and EPR. Many EPR methods of detection of nitric oxide are known in biological milieu.…”