2.1. Chemicals and solvents
Hydrogen peroxide (30%, w/v) and ZVI powder were purchased from Kelong chem. (ShangHai, China). HPLC grade acetonitrile and acetic acid were obtained from Merck Co. (Darmstadt, Germany). Orange G and other reagents with analytic reagent grade were purchased from Huipu chemical&apparatus Co. (Hangzhou, China). Solutions were prepared using Millipore water supplied by a Milli-Q water purification system (Molsheim, France).