“…1 Chemical structures of the selected phenolic antioxidants: 1 o-coumaric acid, R 1 =OH; 2 p-coumaric acid, R 3 =OH; 3 ferulic acid, R 2 =OCH 3 , R 3 =OH; 4 caffeic acid, R 2 =R 3 =OH; 5 catechol, R 4 =OH; 6 pyrogallol, R 4 =R 5 =OH; 7 phloroglucinal, R 5 =R 7 =OH; 8 resorcinol, R 5 =OH; 9 hydroquinone, R 6 =OH; 10 p-aminophenol, R 6 =NH 2 ; 11 protocatechuic acid, R 9 =R 10 =OH; 12 gallic acid, R 9 =R 10 =R 11 =OH; 13 salicylic acid, R 8 =OH; 14 m-hydroxybenzoic acid, R 9 =OH; 15 p-hydroxybenzoic acid, R 10 =OH; other substituents are hydrogen atoms unless noted would make it impossible to produce adequate CL signal for evaluating hydroxyl-radical-quenching effects. It is known that the Fenton reaction was completed transiently [28,29], and hydroxyl radicals are short-lived (less that 10 -4 s) under aqueous conditions. Therefore, the generated hydroxyl radicals had already vanished if H 2 O2 was premixed with Fe 2+ -EDTA before luminol was added to start the CL reaction, and only very weak light emission was recorded.…”