Jianrong Chen

Determination of lead in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

Cloud point extraction (CPE) has been used for the pre-concentration of lead, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation phase were optimized. Separation of the two phases was accomplished by centrifugation for 15min at 4000rpm. Under the optimum conditions i.e., pH 8.0, cloud point temperature 40 degrees C, [5-Br-PADAP]=2.5x10(-5)moll(-1), [Triton X-114]=0.05%, added methanol volume=0.15ml, pre-concentration of only 10ml sample permitted an enhancement factor of 50-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 0.08mugl(-1). The precision for 10 replicate determinations at 5mugl(-1) Pb was 2.8% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for lead was linear with a correlation coefficient of 0.9984 at levels near the detection limits up to at least 30mugl(-1). The method was successfully applied to the determination of lead in water samples.

Determination of cadmium in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

The formation of a complex with 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP) and cloud point extraction have been applied to the preconcentration of cadmium followed by its determination by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation were optimized. At pH 7.0, preconcentration of only 10 mL of sample in the presence of 0.05% TritonX-114 and 2.5 × 10−6 M 5-Br-PADAP enabled the detection of 0.04 μg/L cadmium. The enrichment factor was 21 for cadmium. The regression equation was A = 0.0439C(μg/L) + 7.2 × 10−3. The correlation coefficient was 0.9995. The precision for 10 replicate determinations at 10 μg/L Cd was 2.7% relative standard deviation (RSD). The proposed method has been applied to the determination of cadmium in water samples.

Immobilization of Prussian blue nanoparticles onto thiol SAM modified Au electrodes for analysis of DL-homocysteine

Prussian blue (PB) nanoparticles were immobilized onto gold electrodes using L-cysteine, 1,3-propanedithiol, and 1,8-octanedithiol as a bridge between the gold surface and the PB nanoparticles by the self-assembly method. The obtained PB/thiol/Au electrodes exhibit direct and indirect electrocatalytic activity toward DL-homocysteine (HCys) oxidation. It is possible for these PB nanoparticles modified electrodes to be used for the determination of HCys.

Preparation of Au/ polypyrrole composite nanoparticles and study of their electrocatalytical reduction to oxygen with (without) lacasse

The colloids of Au/polypyrrole (AuPPy) composite nanoparticles were prepared by oxidizing pyrrole monomer with HAuCl4 in a cetyltrimethylammonium bromide (CTAB) solution. Scanning electron microscopy (SEM) suggests the AuPPy nanoparticles in the form of regular spheres, approximately 200 nm in diameter. The resulting colloid of AuPPy composite nanoparticles strongly adheres to the surface of Au electrodes and exhibits better electrocatalytical reduction of oxygen than bare Au electrodes. It means that the complex procedures of centrifuge and wash are avoided. Also, no linker molecules are needed and the immobilization of nanoparticles is achieved easily in a single-step procedure. The experimental parameters were optimized with regard to the concentration of pyrrole and HAuCl4. The direct electron transfer of laccase is observed after it is immobilized on AuPPy modified electrodes by glutaraldehyde. With the help of mediator 2,2′-azino-bis-(3-ethylbenzothiazoline-sulfonic acid) (ABTS), laccase electrode gives an electrocatalytical reduction wave of oxygen at least at 0.8 V. This material is an excellent choice for the design of metal nanoparticle modified electrodes or biosensors

Electrochemical characterization of Prussian Blue nanoparticles

Mixing of FeCl3 solution with the excess of K4Fe(CN)6 solution results in well-dispersed Prussian Blue (PB) nanoparticles that are stable over at least one month. Polyaniline was deposited onto the PB-nanoparticle-modified electrode to provide its stability. Promising results of the enhanced detection of H2O2 with these PB nanoparticles are described.

ELECTROCHEMICAL BEHAVIORS OF MATRINE AT L-CYSTEINE-MODIFIED ELECTRODES

Matrine is an important natural occurring component in sophora roots. It has a wide range of pharmacological actions. In this work, electrochemical investigation of matrine and its interaction with L-cysteine (L-Cys) is reported. Via the electrochemical approach, we have proved that the distribution coefficients of protonated and deprotonated matrine affect its electrochemical response on Au or L-Cys modified Au electrodes. The study by ultraviolet spectroscopy also finds that the molecular interaction between matrine and L-Cys changes with the distribution coefficients of protonated and deprotonated matrine at different pH value. Compared with the response of matrine on the bare gold electrode, the L-Cys/Au self-assembled monolayers modified electrodes exhibit obviously higher current response toward matrine oxidation. The oxidation current of matrine at L-Cys assembled electrode has a good linear relation in the range of 0.2–5 mM, with the correlation coefficient of 0.989 by cyclic voltammagrams. Electrochemical combined with spectroscopic techniques would provide relatively easy way to better understand the underlying mechanism of matrine/L-Cys interaction and will be helpful for the development of electroanalytical techniques for the determination of matrine.

Controlled synthesis of prussian blue nanoparticles based on polymyxin B/sodium bis(2-ethylhexyl)sulfosuccinate/water/isooctane reverse microemulsion for glucose biosensors

Abstract Prussian blue nanoparticles were synthesized by employing polymyxin B/sodium bis(2-efhylexyl) sulfosuccinate/water/isooctane reverse microemulsion. Fourier transform infrared spectroscopy, scanning electron microscopy and electrochemical methods were used to characterize the resultant nanoparticles, that were subsequently used to fabricate prussian blue-based glucose biosensors. Prussian blue nanoparticles were assembled onto a cysteine-modified Au electrode surface and then glutaraldehyde was used to cross-link glucose oxidase on the Prussian blue modified electrode. Both the electrochemical properties of Prussian blue and biocatalytical performance of glucose oxidase were investigated using cyclic voltammetry. After the biosensors were optimized, the glucose biosensors had a linear range from 6.7 μM to 2.0 mM and a relative standard deviation of 4.38%.

THE ELECTROCHEMICAL STUDY OF SELF-ASSEMBLED 1,3-PROPANEDITHIOL ON GOLD

The electrochemical behaviors of bare/dithiol-modified gold electrode were studied in the PBS solution with/without dithiols. A pair of current peaks between -1.4 and -0.5 V is related to dithiol adsorption or re-adsorption. An oxidative peak at 0.37 V accompanied by a slight peak at 0.03 V is observed between -0.5 and 0.7 V for the bare gold electrode in the thiol solution, which is due to the formation of bilayer. When the potential is scanned to a very positive value at 1.2 V, a new oxidative peak at 1.07 V appears for the bare gold electrode in the dithiol solution or the PBS solution. The assembled dithiols are desorbed, and gold surface is exposed. The study indicates that the 1,3-propanedithiol modified electrodes should be used during the potential range of -0.8 to 0.8 V to keep the assembled layer stable.