Search

A novel kind of electrode for determination of ammonium nitrophenylhydroxyamine (Cupferron) was developed via an easy and effective immobilization method using an acid-catalyzed sol-gel technique. The electrode comprised uranyl nitrate (UO2(NO3)2) immobilized by the thin silica sol-gel film on a glassy carbon electrode (GCE). The UO2(NO3)2 retained its good preconcentration characteristic when being doped by the sol-gel film. Cupferron was determined by the direct reduction at the silica sol-gel immobilized UO2(NO3)2 electrode. Moreover its electrochemical behavior was also investigated. The determination conditions for Cupferron were optimized. The UO22+ film electrode still retained high stability after three months. The experimental results show that this method for Cupferron determination possessed good reproducibility and applicability.

A new method is developed for the catalytic oxidation of ascorbic acid (AA) at a graphite-zeolite-modified electrode doped with iron(III) (Fe3+Y/ZCME), in which iron(III) exchanged in zeolite Y can act as catalyst to oxidize AA. First, the electrochemical behavior of iron(III) incorporated in the zeolite Y-modified electrode was studied. The results illustrate that diffusion controls the ferric/ferrous redox process at the Fe3+Y/ZCME. The anodic current of this process increases with the supporting electrolyte concentration of non-size-excluded cation and was suppressed when using size-excluded cation. Second, the catalytic oxidation of AA was explored at Fe3+Y/ZCME. With constant potential amperometric measurements optimal conditions for AA determination were obtained. The working potential was 0.55 V (vs. SCE); the supporting electrolyte was 0.1 M KNO3Or 0.05 M Na2HPO4-KH2PO4buffer solution (pH 6.8). The response current exhibits a linear relationship with the concentration of AA over the range of 1.58×10–6–2.15×10–2 M. When samples of urine, and fruit were analyzed with Fe3+Y/ZCME, we obtained AA recovery of 98–102%, and a relative standard deviation lower than 3%. Meanwhile, interferences from other ions and organic substances were examined.

A method for the determination of the major serotonin metabolite--5-hydroxyindole-3-acetic acid (5-HIAA) in human gastric juice by cyclic voltammetry was described. The measurement conditions were investigated. The potential window was chosen from +0.1 to +0.9 V, the supporting electrolyte was 0.025 M PBS solution (pH 2.0). The method allowed determination in the concentration range from 2.0 x 10(-7) to 2.0 x 10(-5) M and a detection limit of 80 nM. When samples of gastric juice were analyzed with the method, we obtained the mean content of 5-HIAA in the gastric juice. Meanwhile, interference from other ions and substances were examined. The experimental results indicate that the method for the determination of gastric juice samples is successful.