Electrocatalytic reduction of nitrite at a glassy carbon electrode surface modified with palladium(II)-substituted Keggin type heteropolytungstate Original Research Article

A potassium salt of palladium(II)-substituted Keggin type heteropolytungstate, K6[(H2O)PdSiW11O39] (abbreviated as PdSiW11 in the following), was used to fabricate a new kind of chemically modified electrode (CME) by potential scanning on the surface of glassy carbon electrode. Characterization of this modified electrode was conducted by Fourier transform infrared reflection absorption spectroscopy (FTIRRAS), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). FTIRRAS and XPS showed that the species on the electrode surface sustained the same Keggin type structure as that of the heteropolytungstate in buffer solution. A couple of waves was observed on the PdSiW11 CME, which was assigned to the redox process of the palladium center in the heteropolytungstate. This CME had high electrocatalytic activity towards nitrite reduction and exhibited good reproducibility and stability. The catalytic peak current was found to be linear with the nitrite concentration in the range 1–20 mmol/l with a correlation coefficient of 0.998. The PdSiW11 CME is successfully applied as an electrochemical detector to monitor nitrite in flow injection analysis (FIA). The linear range is over three orders of magnitude and the detection limit is 24.0 pmol for nitrite determination. The relative standard deviation (RSD) for ten successive measurements of 1.0 mmol/l nitrite in FIA is found to be 3.3%.