A dual‐mode optical assay for iron(II) and gallic acid based on Fenton reaction

Abstract The hydroxyl radicals ( · OH) produced by the Fenton reaction of iron(II) and hydrogen peroxide (H 2 O 2 ) can oxidize the colorless 3,3′,5,5′‐tetramethylbenzidine (TMB) to blue oxidized TMB (Ox‐TMB), resulting in a decrease in the fluorescence intensity of the reaction system and an increase in ultraviolet absorption. Ox‐TMB had a visible absorption peak at 625 nm and a fluorescence peak around 420 nm. When gallic acid (GA) was added to the system, Ox‐TMB was reduced to TMB, which made the color of the system disappear and the fluorescence recover. The linear ranges for determination of iron(II) were 0.5–10 μM (fluorometric) and 0.5–20 μM (colorimetric), and the detection limits were 0.25 μM (fluorometric) and 0.28 μM (colorimetric). The linear ranges for determination of GA were 0–80 μM (fluorometric) and 0–60 μM (colorimetric), and the detection limits were 0.31 μM (fluorometric) and 0.8 μM (colorimetric). The results of anti‐interference experiments shew that this dual‐mode assay had very good selectivity for the determination of iron(II) and GA.