Selective Detection of p-Phenylenediamine in Hair Dyes Based on a Special CE Mechanism Using MnO2 Nanowires

We report a novel approach for selective determination of p-phenylenediamine in hair dyes using beta-MnO2 nanowires modified glassy carbon (GC) electrodes through an electrochemical co-deposition process with chitosan hydrogel. A special CE (chemical reaction and electron transfer) process on the surface of beta-MnO2 nanowires modified GC electrode is proposed and proved by cyclic voltammetry and UV-Vis spectroscopy in the presence of p-phenylenediamine. p-Phenylenediamine can react with MnO2 nanowires to produce diimine and the equilibrium of the two-electron and two-proton redox process of p-phenylenediamine on the electrode is changed, and consequently the reductive current is enhanced significantly. At a constant potential of 0 V vs. SCE, other main components of hair dyes including o-, m-phenylenediamine, catechol, resorcinol, and p-dihydroxybenzene do not interfere in the determination of p-phenylenediamine in the amperometric measurement because of their much lower chemical reaction activities with MnO2 nanowires. It shows a determination range of 0.2-150 mu M and a low detection limit of 50 nM to response p-phenylenediamine. This modified electrode is successfully used to analyze the amount of p-phenylenediamine in hair dyes without preseparation procedures.