Use of electrochemical techniques to characterize methamidophos and humic acid specifically adsorbed onto Pt and PtO films

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to study methamidophos (MAP) and humic acid (HM) specifically adsorbed onto Pt and PtO films in pH-7.0 universal buffer. The approach was found to be sufficiently selective for use in studies involving adsorption of species in environmental systems (e.g., soil minerals), typically evaluated by batch experiments and high performance liquid chromatography (HPLC) or gas chromatography (GC). The proposed method allowed quantification of active hydrogen adsorption sites blocked by HM, both when this compound is adsorbed alone or co-adsorbed with MAP. At higher amounts of MAP in the adsorption solution, the compound was co-adsorbed more effectively than HM (kept at constant concentration). In the case of sequential specific adsorption, the first compound adsorbed typically predominates over the second. EIS was more effective for determining the number of blocked active sites on Pt than CV, which was superior for PtO films.