Nan Lu

Application of the sol-gel technique to polyoxometalates: towards a new chemically modified electrode

Abstract A novel chemically-modified electrode containing 12-molybdophosphoric acid was achieved on the surface of platinum electrode by sol-gel technique. The electrochemical behavior of the modified electrode was characterized by cyclic voltammetry in detail. The film electrode obtained was very stable and exhibited electrocatalytic response for reduction of bromate, chlorate and hydrogen peroxide. Hydrogen peroxide was determined amperometrically at the modified electrode in the concentration range of 3×10 −2 to 2×10 −5 M and a detection limit of 7×10 −6 M (signal-to-noise ratio 3).

Electrochemical determination of iodide on a vanadium oxide-polypropylene carbonate coated glassy carbon electrode.

A vanadium oxide-modified glassy carbon electrode was simply and conveniently fabricated by casting vanadium tri(isoproxide) oxide (VO(OC(3)H(7))(3)) and poly(propylene carbonate) (PPC) onto the glassy carbon electrode surface. The electrochemical properties of iodide at the VO(OC(3)H(7))(3)-PPC film-modified glassy carbon electrode were investigated by cyclic voltammetry, and an anodic peak was observed at approximately +0.71V (vs. SCE). Based on this, a sensitive and convenient electrochemical method was proposed for the determination of iodide. Flow injection amperometry (FIA) exhibited a good linear relationship with the concentration of iodide in the range of 5x10(-7)molL(-1) and 1x10(-3)molL(-1), and the detection limit was 1x10(-7)molL(-1). Quantitative recovery of iodide in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodide in dry edible seaweed. The concentrations of iodide measured by this method are in good agreement with those obtained by spectrophotometric method.

Voltammetric determination of 5-hydroxydole-3-acetic acid in human gastric juice

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.

Enhancing reproducibility of SALDI MS detection by concentrating analytes within laser spot

Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI TOF MS) has become one of the most important analytical methods due to its less interference at low molecular weight range. However, it is still a challenge to obtain a good reproducibility of SALDI TOF MS because of the inhomogeneous distribution of analyte molecules induced by coffee ring effect. We propose a universal and reliable method to eliminate the coffee ring effect by concentrating all the analyte molecules within the laser spot. This method exhibits an excellent reproducibility of spot-to-spot and substrate-to-substrate, and the relative standard deviations (RSDs) for different concentrations are lower than 12.6%. It also performs good linear dependency (R2 > 0.98) in the log-log plot with the concentration range of 1nM to 1μM, and the limit of detection for R6G is down to 1fmol.