The later approach was followed in the current study utilizing a derivatization procedure developed by Tai et al.12 that was slightly modified for the current application. The probe selected for the fluorescence experiments is the disodium salt of terephthalic acid (NaTA). NaTA react with hydroxyl radicals to form 2-hydroxyterephthalic acid (HTA), that gives a bright stable fluorescence (ìanalyzing ) 425 nm, ìexcitation ) 315 nm).13 Terephthalic acid and its disodium salt are extensively used in radiation and sonochemical studies.13,14