Simultaneous quantification of aqueous peroxide, nitrate, and nitrite during the plasma-liquid interactions by derivative absorption spectrophotometry

A derivative absorption spectroscopic method is used in situ to simultaneously trace and quantify the aqueous peroxide (H2O2), nitrate (NO-3) and nitrite (NO-2) generated during plasma-liquid interactions. The results indicate that the time evolutions of H2O2, and generated from the plasma-liquid interactions strongly depend on the solution's pH value, which varies with the plasma treatment. The concentrations of aqueous H2O2, and increase independently from each other during the plasma treatment when the solution's pH value is higher than 3.0. However, when the solution's pH value is less than 3.0, most of the aqueous (∼71.5%) will exist in the form of molecular nitrous acid since the pK a of nitrous acid is 3.4, the aqueous is mainly formed from the reaction between H2O2 and as well as the decomposition of molecular HNO2, which leads to a continuous increase of concentration and an appearance of the maximum concentrations of H2O2 and as the pH value of the solution reaches 3.0.