[Indirect determination of rare earth elements in Chinese herbal medicines by hydride generation-atomic fluorescence spectrometry].

Based on their similarity in chemical properties, rare earth elements were able to form stable coordinated compounds with arsenazo III which were extractable into butanol in the presence of diphenylguanidine. The butanol was removed under reduced pressure distillation; the residue was dissolved with diluted hydrochloric acid. As was released with the assistance of KMnO4 and determined by hydrogen generation-atomic fluorescence spectrometry in terms of rare earth elements. When cesium sulfate worked as standard solution, extraction conditions, KMnO4 amount, distillation temperature, arsenazo III amount, interfering ions, etc were optimized. The accuracy and precision of the method were validated using national standard certified materials, showing a good agreement. Under optimum condition, the linear relationship located in 0.2-25 microg x mL(-1) and detection limit was 0.44 microg x mL(-1). After the herbal samples were digested with nitric acid and hydrogen peroxide, the rare earth elements were determined by this method, showing satisfactory results with relative standard deviation of 1.3%-2.5%, and recoveries of 94.4%-106.0%. The method showed the merits of convenience and rapidness, simple instrumentation and high accuracy. With the rare earths enriched into organic phase, the separation of analytes from matrix was accomplished, which eliminated the interference. With the residue dissolved by diluted hydrochloric acid after the solvent was removed, aqueous sample introduction eliminated the impact of organic phase on the tubing connected to pneumatic pump.

Electrochemical method assisted immobilization and orientation of myoglobin into biomimetic brij 56 film and its direct electrochemistry study.

A simple cyclic voltammetric method was applied to assemble and orient a model protein, namely, myoglobin (Mb), into a biocompatible Brij 56 film. Ultraviolet-visible and circular dichroism spectra indicated that Mb in Brij 56 matrix preserved its secondary structure. Fourier transform infrared spectra confirmed the formation of hydrogen bonds between Mb and Brij 56. These hydrogen bonds acted as the electron tunnel to transfer electrons from Mb's active sites to the underlying glassy carbon electrode. Effective direct electron transfer of Mb was realized with the presence of a couple of quasi-reversible and well-defined redox peaks at -310 mV (vs standard calomel electrode) in the studied potential range. The peaks were attributed to the redox couple of heme Fe(II)/Fe(III) of the well-oriented Mb in Brij 56 matrix. The surface coverage and the electron transfer rate (ks) of Mb immobilized into the Brij 56 film was ∼4.9×10(-11) mol cm(-2) and 72.6±3.0 s(-1), respectively. An excellent electrocatalytic response of the immobilized Mb toward nitrite in the absence of electron transfer mediators was observed. These results emphasized that the biomimetic Brij 56 could be used as an attractive material for immobilizing proteins and constructing biosensors.

Reagentless biosensor for phenolic compounds based on tyrosinase entrapped within gelatine film.

A simple and new reagentless phenolic compound biosensor was constructed with tyrosinase immobilized in the gelatine matrix cross-linked with formaldehyde. The morphologies of gelatine and gelatine/tryosinase were characterized by SEM. The tyrosinase retains its bioactivity when being immobilized by the gelatine film. Phenolic compounds were determined by the direct reduction of biocatalytically liberated quinone at -0.1 V vs SCE. The process parameters for the fabrication of the enzyme electrode were studied. Optimization of the experimental parameters has been performed with regard to pH, operating potential, temperature and storage stability. This biosensor exhibits a fast amperometric response to phenolic compounds. The linear range for catechol, phenol, and p-Cresol determination was from 5 x 10(-8) to 1.4 x 10(-4) M, 5 x 10(-8) to 7.1 x 10(-5)M, and 1 x 10(-7) to 3.6 x 10(-5)M, with a detection limit of 2.1 x 10(-8) M, 1.5 x 10(-8) M, and 7.1 x 10(-8 )M, respectively. The enzyme electrode retained ca.77% of its activity after 7 days of storage at 4 degrees C in a dry state. The proposed sensor presented good repeatability, evaluated in terms of relative standard deviation (R.S.D.=8.6%) for eight different biosensors and was applied for determination in water sample. The recovery for the sample was from 99.0% to 99.8%.