“…Aromatic compounds, such as salicylic acid and phenylalanine, are widely used to this aim, since their reactions with OH radicals, termed aromatic hydroxylations, display very high kinetic constants [17]. The quantitative determination is performed following either the degradation of the probe or the formation of characteristic products that can be easily detected with a lot of analytical techniques like EPR [18,19], high performance liquid chromatography with electrochemical detection (HPLC-ED) [20,21], capillary electrophoresis (EC) [22], gas chromatography/mass spectrometry (GC-MS) [23], chemiluminescence [24], and micellar electrokinetic capillary chromatography (MECC) [25]. The concentration of a characteristic product is expressed by the following equation:…”