2.1 Chemicals
All chemicals, including Ferrous sulfate (FeSO4.7H2O, Carlo Erba), sodium hydroxide (NaOH, Carlo Erba), acetonitrile (Sigma-Aldrich), 2,4-dichlorophenoxyacetic acid (2,4-D, Sigma-Aldrich), hydrogen peroxide (H2O2, Carlo Erba), Sodium fluoride (NaF, Sigma-Aldrich), sodium bicarbonate (NaHCO3,Sigma-Aldrich) and Milli-Q water were used to perform all the experiments. All the reagents were of analytic grade and used without further purification.