Quantitative Estimation of OH Radicals Reacting in Liquid Using a Chemical Probe for Plasma in Contact With Liquid

An accurate quantification method for hydroxyl (OH) radicals is proposed. A pulsed plasma was generated in argon over a solution of disodium terephthalate (NaTA) or 2-hydroxyterephthalic acid (HTA). Since it was confirmed that HTA could be decomposed by the plasma, rate equations for NaTA and HTA were calculated using three parameters: the selectivity of HTA formed by the reaction of NaTA with OH radical, the reaction rate constant of HTA with OH radical, and the OH radical concentration. These parameters were identified by fitting the simulated HTA concentrations to the experimental data from the treatment of NaTA solutions. A selectivity of approximately 0.91% and a rate constant of $3.89 \times 10^{9}$ L/( $\text {mol} \cdot \text {s}$ ) were obtained. Moreover, the amount of OH radicals reacting in the solution was quantified more accurately than by previously reported methods.