Validation of in situ diagnostics for the detection of OH and H₂O₂ in liquids treated by a humid atmospheric pressure plasma jet

A humid atmospheric pressure plasma jet was used to treat an aqueous liquid. The transport of hydrogen peroxide and hydroxyl from the plasma to the liquid was analyzed. Two in situ liquid diagnostics for each species were compared and validated. In the case of H2O2, a spectrophotometric approach using ammonium metavanadate and electrochemical sensing based on Prussian blue carbon paste electrodes was applied. Both methods show very good agreement in trends and absolute values. The detection of OH was performed by terephthalic acid (TA) dosimetry and its distribution was visualized by the chemiluminescence of luminol. There, the measurement using TA resembles the luminol measurements and vice versa, and a very good agreement between both methods was found.