Electrodeposition of gold nanoclusters on overoxidized polypyrrole film modified glassy carbon electrode and its application for the simultaneous determination of epinephrine and uric acid under coexistence of ascorbic acid.

A novel biosensor was fabricated by electrochemical deposition of gold nanoclusters on ultrathin overoxidized polypyrrole (PPyox) film, formed a nano-Au/PPyox composite on glassy carbon electrode (nano-Au/PPyox/GCE). The properties of the nanocomposite have been characterized by field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and electrochemical investigations. The nano-Au/PPyox/GCE had strongly catalytic activity toward the oxidation of epinephrine (EP), uric acid (UA) and ascorbic acid (AA), and resolved the overlapping voltammetric response of EP, UA and AA into three well-defined peaks with a large anodic peak difference. The catalytic peak currents obtained from differential pulse voltammetry increased linearly with increasing EP and UA concentrations in the range of 3.0x10(-7) to 2.1x10(-5) M and 5.0x10(-8) to 2.8x10(-5) M with a detection limit of 3.0x10(-8) and 1.2x10(-8) M (s/n=3), respectively. The results showed that the modified electrode can selectively determine EP and UA in the coexistence of a large amount of AA. In addition, the sensor exhibited excellent sensitivity, selectivity and stability. The nano-Au/PPyox/GCE has been applied to determination of EP in epinephrine hydrochloride injection and UA in urine samples with satisfactory results.

Study of the adsorption and oxidation of antioxidant rutin by cyclic voltammetry-voltabsorptometry.

The adsorption and oxidation behavior of rutin was studied by in-situ UV spectroelectrochemistry in a long optical-path thin-layer electrochemical cell with a graphite-wax electrode. The dynamic UV spectra of rutin under potentiostatic oxidation were recorded, which indicated the formation of o-quinonic structure. During the repetitive cyclic potential scans, cyclic voltabsorptomogram was recorded at the three characteristic wavelengths 346, 254 and 296 nm, respectively. The profiles obtained showed two types of concentration fluctuation of species in solution, resulting from adsorption/desorption and redox reaction, respectively. Using derivative cyclic voltabsorptometry the contribution of the species in solution to the total current was estimated, and then the current of every step involved in the proposed redox mechanism was obtained for the first time. The result shows that rutin underwent a nearly reversible redox reaction in which the total current is mostly due to the contribution of adsorbed species. The present work developed cyclic voltabsorptometry into a useful tool for investigating redox process involving coupled adsorption/desorption steps.

Development of a new electrochemical hydride generator with tungsten wire cathode for the determination of As and Sb by atomic fluorescence spectrometry.

A novel electrochemical hydride generator has been developed for the determination of As and Sb. This newly devised hydride generator is constructed from a flowing electrolytic cell, in which the tungsten wire is selected as cathode. Compared with some cathode material usually used in electrochemical hydride generator, the tungsten cathode is of better interference tolerance, corrosion-resistant and longer working time. The characteristics of the cathode material, hydride generating efficiency and interferences of concomitant have been studied in detail. The detection limits (3sigma) of As and Sb in sample solution were 0.10mugL(-1) and 0.15mugL(-1), the precisions for 11 replicate measurements of 20mugL(-1) As and Sb were 1.3% and 1.7%. The electrochemical hydride generator coupled with atomic fluorescence spectrometry has been applied to the determination of total As and Sb in tobacco samples.

[In situ UV-visible absorption spectrum monitoring the electrochemical degradation of PAn films].

Kinetic degradation process of PAn films during aniline polymerization was in situ monitored by UV-Visible absorption spectrum. The effects of anodic potential, acidity and monomer concentration on the degradation process were also investigated. The experiment results displayed that the more positive the anodic potential, the higher the acidity of the solution, the higher the concentration of aniline, the faster the PAn films degradation speed. Which was similar to the results obtained when the kinetic degradation process of PAn films was studied in blank solutions by cyclic voltammetry.

Electrochemical determination of serotonin and the competitive adsorption with dopamine at 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide lipid film modified by glassy carbon electrode.

A novel and effective approach to sensitively determine serotonin, known as 5-hydroxytryptamine (5-HT), has been proposed based on a 5,5-ditetradecyl-2-(2-trimethylammonioethyl)-1,3-dioxane bromide (DTDB) self-assembled lipid bilayer membrane modified glassy carbon electrode (DTDB/GCE). A DTDB/GCE shows the strong electrocatalysis for the oxidation of 5-HT, with the peak potential shifted to less positive value of 0.376 V vs. SCE, and effectively eliminates the interference from ascorbic acid (AA), even in the presence of 100-fold concentration of AA. Differential pulse voltammetry (DPV) gave a linear current for 5-HT from 2.0 x 10(-7) to 1.0 x 10(-5) M. At the DTDB/GCE, the oxidation of 5-HT was controlled by the adsorption process; for 5-HT coexisting with DA, the competitive adsorption was observed.

Effect of pH on inhibition and enhancement of luminol-H2O2-Co2+ chemiluminescence by phenolic compounds and amino acids.

The effect of pH on inhibition and enhancement of luminol-H2O2-Co2+ chemiluminescence (CL) by 18 phenolic compounds and 20 amino acids was studied. It was found that most of the tested compounds showed an inhibiting effect at lower pH and an enhancing effect at higher pH. At a midrange pH, for some phenolic compounds with two ortho-position -OH, both an inhibiting and an enhancing peak were simultaneously observed. UV-visible spectra of the tested phenolic compounds at different pH values were studied. The mechanism for CL inhibition and enhancement was proposed. It is likely that the competition of the -OH or the -NH2 group and other reducing groups in the molecules with luminol for O2*- led to the CL inhibition. A reaction of -COO(-) and quinone or ketone formed by phenolic compounds at higher pH via deprotonation with O2*- also resulted in the CL enhancement.

Flow injection analysis of gallic acid with inhibited electrochemiluminescence detection.

A flow injection (FI)-electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)(3)(2+)/tri- n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0x10(-9) mol/L and a dynamic concentration range of 2x10(-8)-2x10(-5) mol/L. The relative standard deviation (RSD) was 1.0% for 1.0x10(-6) mol/L gallic acid ( n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine-Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)(3)(2+)/TPrA ECL system was the interaction of electrogenerated Ru(bpy)(3)(2+*) and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.

[In-situ FTIR study of hybrid copper-cobalt hexacyanoferrate film modified electrode].

The study on the in-situ FTIR spectroelectrochemistry of a hybrid copper-cobalt hexacyanoferrate film modified platinum electrode was carried out. The variation of the FTIR spectra was well correlated to the redox process of CuCoHCF. The relative contribution of Cu(II) and Co(II) to the stretching vibration of CN was found to vary with the applied potential.

Cathodic electrochemiluminescence of Ru(bpy)(3)(2+)/Nafion coated on graphite oxide electrode in purely aqueous solution.

Two cathodic electrochemiluminescence (ECL) peaks have been obtained at -0.99 and -1.80 V (vs. SCE), respectively, from Ru(bpy)(3)(2+)/Nafion coated onto a graphite oxide electrode in purely aqueous solution under cyclic voltammetric (CV) conditions, without addition of any reducing or oxidative reagents. These two ECL peaks were found to correlate to initial scan direction, pH, and reversal potential. Nafion played an important role in the generation of these two ECL peaks because no cathodic emission was observed in the system without Nafion. It seems that a part of Ru(bpy)(3) (3+) electrogenerated at positive potential can remain in the Nafion, even at negative potentials. It was con fi rmed that Ru(bpy)(+) was formed at -1.80 V by addition of S(2)O(8) (2-). The ECL peak at -0.99 V is attributed to the reaction of Ru(bpy)(3+) and OH(-). The ECL peak at -1.80 V is probably due to the annihilation reaction of Ru(bpy)(3+) and Ru(bpy)(+).

[Study on S-benzyl-N-(ferrocenyl-1-methyl-metylidene)-dithiocarbazate nickel (II)/cobalt (II) complexes by in-situ FTIR spectroelectrochemistry].

Comparative studies were carried out by using electrochemistry and in-situ FTIR spectroelectrochemistry for nonlinear optical complexes, S-benzyl-N-(ferrocenyl-1-methyl-metylidene)-dithiocarbazate nickel (II)/cobalt (II) complexes (Ni(LSB)2/Co (LSB)2). The results indicated that Ni(LSB)2 involves two consecutive reversible one-electron oxidation steps, while Co(LSB)2 involves only one two-electron oxidation step. Ni(LSB)2 complex that has a square planar configuration exhibits a moderately strong electronic communication between the two-ferrocene moieties, taking place through the skeleton chain of the ligand due to the extensive electron delocalization in the whole molecule and leads to the appearance of a strong nu c-c vibration band at 1,453 cm-1 during the oxidation process, while Co(LSB)2 complex that has a tetrahedral configuration shows low electron delocalization and has two almost identical ferrocene moieties.

Electrochromatography with a 2.7 mm inner diameter monolithic column.

Monolithic columns of 2.7 mm I.D. have been prepared and used in electrochromatography (EC) separation. Although capillary electrochromatography (CEC) has higher separation efficiency, it displays some shortcomings, such as limited sample loadability and restricted concentration detectability etc. In this paper, we investigate the feasibility of EC separation with millimeter diameter monolithic columns. By using a designed preparation method of monolithic column packed with about 150 microm quartz sand, the effect of Joule heating can be reduced, and the processes of frit making and column packing can be avoided. The concentration detectability of the EC is improved comparing with that of CEC. Moreover, the separation efficiency of 52,000 plates/m was achieved with a 70 mm length and 2.7 mm I.D. monolithic column.

Electrochemiluminescence of luminol in alkaline solution at a paraffin-impregnated graphite electrode.

The behavior of luminol electrochemiluminescence (ECL) at a paraffin-impregnated graphite electrode (PIGE) at different applied potentials was studied. Five ECL peaks were observed at 0.31, 0.59, 1.09, 1.54, and -0.58 V versus SCE, respectively, being related to potential scan direction and ranges, N2, O2, pH of the solution, and KCl concentration. The emission spectra of various ECL peaks at different potentials showed that all ECL peaks were initiated by luminol reactions. X-ray diffraction demonstrated that a simple mixture was formed between graphite and paraffin. The fluorescence spectra on the surface of the PIGE suggested that certain groups on the graphite were oxidized when the positive potential was applied to the electrode. In the presence of O2, three main ECL peaks were obtained in 0.1 mol/L KCl at pH 12.2. The ECL peak at 0.59 V with a shoulder is likely due to the reaction of luminol radicals with O2 and further electrooxidation of luminol radicals. The ECL peak at 1.54 V was suggested to be due to the electrooxidation of OH- to HO2- at higher potential and then to O2-, which reacted with luminol to produce light emission. Moreover, the oxygen-containing functional groups formed by the oxidation of the surface of the graphite electrode might enhance the ECL. At -0.58 V, the dissolved oxygen in solution was reduced to HO2-, resulting in light emission. At a potential higher than 1.64 V, ClO- was formed, leading to a broad emission wave and enhancement of the ECL peak at -0.58 V upon the reversal scan. Under nitrogen atmosphere, an ECL peak appeared at 1.09 V. At this potential, OH- was oxidized to O2, followed by the reaction with luminol to generate light emission. At pH 13.2 or 0.5 mol/L KCl, the shoulder of the ECL peak at 0.59 V became an ECL peak at 0.31 V. The conversion of luminol radicals into excited 3-aminophthalate may undergo two routes. Under these conditions, two routes might proceed at a different rate to form another ECL peak. It is concluded that luminol ECL could be readily excited by various oxygen-containing species electrogenerated at different applied potentials. Three strong ECL peaks obtained at different potentials on the PIGE might be of a potential to improve analytical selectivity and sensitivity for the detection of some analytes.

Determination of noradrenaline and dopamine in pharmaceutical injection samples by inhibition flow injection electrochemiluminescence of ruthenium complexes.

Two maximal potential-resolved flow injection-electrochemiluminescent (FI-ECL) peaks were observed for Ru(bpy)(3)(2+)/TPrA system at 0.90 and 1.05 V, and for Ru(phen)(3)(2+)/TPrA at 1.01 and 1.25 V (vs. Ag/AgCl) in pH 8.0 phosphate buffer solutions. Sensitive ECL inhibition effects were observed in the presence of noradrenaline and dopamine for both of these systems. Therefore, an FI-ECL inhibition method for determination of noradrenaline and dopamine has been developed. Under optimal conditions, linear responses between logarithm of ECL intensity changes and logarithm of sample concentration were found for noradrenaline in the linear range (LR) of 4x10(-8)-1x10(-5) moll(-1) with theoretical detection limit (DL) of 2.5x10(-8) moll(-1) for Ru(bpy)(3)(2+)/TPrA system, and in LR of 2x10(-8)-2x10(-5) moll(-1) with DL of 7.1x10(-9) moll(-1) for Ru(phen)(3)(2+)/TPrA system; and for dopamine in LR of 8x10(-8)-2x10(-5) moll(-1) with DL of 5.2x10(-8) moll(-1) for Ru(bpy)(3)(2+)/TPrA system, in LR of 4x10(-8)-2x10(-5) moll(-1) with DL of 1.5x10(-8) moll(-1) for Ru(phen)(3)(2+)/TPrA system. It was applied for determination of commercial pharmaceutical injection samples with satisfied results. The mechanism of the inhibition effects was proposed in the preliminary way.

Potential-resolved electrochemiluminescence of ru(bpy)3(2+)/C2O4(2-) system on gold electrode.

The electrogenerated chemiluminescence of Ru(bpy)3(2+)/C2O4(2-) system on a pre-polarized Au electrode was studied using a potential-resolved electrochemiluminescence (PRECL) method. Two anodic ECL peaks were observed at 1.22 V (vs. SCE) (EP1), 1.41 V (vs. SCE) (EP2), respectively. The effects of the concentration of oxalate and Ru(bpy)3(2+), adsorbed sulphur, CO2, O2, pH of the solution and pretreatment of the Au electrode on the two PRECL peaks were examined. The surface state of the pre-oxidized gold electrode was also studied using the X-ray photoelectron spectroscopy (XPS) technique. Moreover, comparative studies on i-E and I-E curves were carried out and a possible mechanism involving both the catalytic and the direct electro-oxidation pathways was proposed for the ECL of Ru(bpy)3(2+)/C2O4(2-) system. EPI is attributed to the Ru(bpy)3(2/3+) reaction catalysed by C2O4(2-) to generate Ru(bpy)3(2+)*. EP2 is likely because C2O4(2-) was oxidized at the electrode to form CO2(-)*, followed by reaction with Ru(bpy)3(3+) to generate Ru(bpy)3(2+)*.