Zaofan Zhao

Determination of trace nitrite by catalytic polarography in ferrous iron thiocyanate medium

Abstract This paper concludes that (FeSCNNO)+ is formed in a solution that contains ferrous iron (ammonium ferrous sulfate), thiocyanate (sodium thiocyanate), nitrite (sodium nitrite) and sodium perchlorate (supporting electrolyte). With a Dropping Mercury Electrode (DME), this ternary complex has three reduction waves at −0.5, −0.8 and −1.0 V vs. SCE, respectively. In the presence of oxygen, a catalytic wave related to the first reduction (−0.5 V) is used for the determination of trace nitrite in the concentration range of 3×10−8 to 1 × 10−6M. The detection limit is 1 × 10−8M (0.46 ppb NO2−). The mechanism of the electrode process has been studied by linear sweep polarography (LSP), dc polarography, cyclic voltammetry, and controlled potential coulometry. The reduction process is proposed to be: 4B + O2 + 4H+ → 4A + 2H2O with (FeSCNNO)+ad formed in the following steps: 3NO2− + 2H+ → 2NO + NO−3 + H2O Fe2+ + SCN− + NO → (FESCNNO)+ (FeSCNNO)+ ⇆ (FeSCNNO)+ad

VOLTAMMETRIC AND AMPEROMETRIC DETERMINATION OF ASCORBIC ACID AT A CHEMICALLY MODIFIED CARBON FIBRE MICROELECTRODE

A carbon fibre microelectrode was modified by electrodeposition of a thin copper-heptacyanonitrosylferrate (CuHNF) film on its surface. The film showed the ability to catalyse electrochemical oxidation of ascorbic acid. The catalytic reaction was limited either by diffusion, or by the electrochemical reaction of the catalyst. A linear, cyclic voltammetric response for ascorbic acid was obtained between 5.0 x 10(-5) and 6.0 x 10(-3)M. By amperometric measurements the linear range could be extended to 8.0 x 10(-6)-2.0 x 10(-3)M. The modified electrode showed good stability and reproducibility.

Electrochemical study of copper-heptacyanonitrosylferrate film modified electrodes: Preparation, properties and applications

Abstract Novel inorganic film modified electrodes have been prepared by electrodeposition of a thin copper-heptacyanonitrosylferrate (CuHNF) film on electrode surfaces. These modified electrodes exhibit two pairs of highly reversible voltammetric peaks at 0.12 V/SCE and 0.59 V/SCE in electrolytes containing alkali metal ions which correspond to the Cu(I)/Cu(II) and Fe(II)/Fe(III) transitions, respectively. Fourier transform IR, Mossbauer and X-ray photoelectron spectra show that the thin films deposited on the electrode surface are indeed composed of CuHNF. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry. The modified electrodes show an electrocatalytic effect on the oxidation of ascorbic acid and hydrogen peroxide and the reduction of hydrogen peroxide. The kinetics of the catalytic reactions were investigated using rotating-disk electrodes. The high stability of the modified electrodes makes them attractive in practical applications.

Electrochemical sensor of nitrite based on an inorganic film modified glassy carbon electrode

The electrocatalysis of nitrite in solutions at an inorganic film modified glassy carbon electrode was studied. The modifier was an electrodeposited thin inorganic film of the copper-heptacyanonitrosylferrate (CuHNF). Cyclic voltammetry of the modified electrode in a nitrite solution revealed that both oxidation and reduction of nitrite were catalyzed and the electrocatalytic currents were controlled by the diffusion of nitrite. Voltammetric and amperometric responses were investigated. When applied as an amperometric sensor in a flow injection system, the modified electrode permitted detection at — 0.55 V, over 500 mV lower than at the naked electrode surface. A linear response range extending from 1 × 10−6 to 1 × 10−3M nitrite was obtained, with a detection limit of 3 × 10−7M. The relative standard deviation for 50 repetitive injections with a 5 × 10−5M nitrite solution was less than 4%. The procedure was applied to the determination of nitrite in saliva and nitrate.