Solid-phase extraction of trace Au(Ⅲ) with SDG and determination by the catalytic spectrophotometric method

The new catalytic kinetic spectrophotometric method for Au(Ⅲ) determination was developed and validated.It was based on the catalytic effect of gold on the oxidation of sudan red Ⅲ by ammonium peroxodisulfate ((NH4)2S2O8) with nitrilo triaeetic acid as an activator in microemulsion and H2SO4 medium.Under optimum conditions,there was the linearity of the calibration curve in the concentration range from 0 to 20 μg/L Au(Ⅲ) at 520 nm.The relative standard deviation was 3.0% with a correlation coefficient of 0.9986.The detection limit achieved was 9.75×10-5 μg/mL.A new method using a column packed with sulfhydryl dextrose gel (SDG) as a solid-phase extraetant has been developed for the preeoncentration and separation of Au(Ⅲ) ions.The method has been applied to the determination of trace gold with satisfactory results.     

Analysis of trace mercury in water by solid phase extraction using dithizone modified nanometer titanium dioxide and cold vapor atomic absorption spectrometry

A new method for analysis of trace mercury in water samples was developed, based on the combination of preconcentration/separation using dithizone-modified nanometer titanium dioxide (TiO2) as a solid phase extractant and determination by cold vapor atomic adsorption spectrometry (CVAAS). Dithizone was dissolved with alcohol and loaded on the surface of nano-sized TiO2 powders by stirring. The static adsorption behavior of Hg2 on the dithizone-modified nanoparticles was investigated in detail. It was found that excellent adsorption ratio for Hg2 could be obtained in the pH range of 7-8 with an oscillation time of 15 min, and a 5 mL of 3.5 mol·L-1 HCl solution could quantitatively elute Hg2 from nanometer TiO2 powder. Common coexisting ions caused no obvious influence on the determination of mercury. The mechanisms for the adsorption and desorption were discussed. The detection limit (3σ) for Hg2 was calculated to be 5 ng·L-1. The proposed method was applied to the determination of Hg2 in a mineral water sample and a Zhujiang River water sample. By the standard addition method, the average recoveries were found to be 94.4%-108.3% with RSD (n = 5) of 2.9%-3.5%.     

Separation of indium(Ⅲ),gallium (Ⅲ),and zinc(Ⅱ)with Levextrel resin containing di(2-ethylhexyl)phosphoric acid(CL-P204):Part Ⅰ. Selection of separation conditions

A kind of Levextrel resin separation process was developed for separation of indium (Ⅲ), gallium (Ⅲ), and zinc (Ⅱ) from aqueous sulfate solution with Levextrel resin containing di(2-ethylhexyl) phosphoric acid (CL-P204). The aim of the research is to collect preliminary results for a pilot-scale production. Properties of adsorbing indium (Ⅲ), gallium (Ⅲ),and zinc (Ⅱ) from sulfate solution with the Levextrel resin were first studied by batch operation and column operation. The optimum pH, adsorption capacities and concentrations of stripping agents for indium (Ⅲ), gallim (Ⅲ) were tested. The separation order of indium (Ⅲ), gallim (Ⅲ), and zinc (Ⅱ) from sulfate solution with CL-P204 Levextrel resin was found that indium (Ⅲ) could be first separated by adsorbing at the acidity of 1.0 mol/L whereas gallium (Ⅲ) and zinc (Ⅱ) could not, and they were adsorbed together by adsorbing at pH = 2.8, then separated from each other by stripping with 0.1 and 0.5mol/L hydrochloric acid, respectively. The recoveries of three metal ions were all higher than 99%. The cyclic properties of this resin are well.     

Electrochemical Behavior of Er(Ⅲ）In N,N-dimethylformamide

The cyclic voltammetry, current-time curve at potential step and potential-time curve of galvanostatic method were used to investigate the electrochemical behavior of Er(Ⅲ) in ErCl3-LiClO4-DMF(N, N-dimethylformamide) system on Pt and Cu electrodes. Results indicate that the electroreducation of Er(Ⅲ) to Er(0) is irreversible on Pt and Cu electrodes, the diffusion coefficient and electron transfer coefficient of Er(Ⅲ) in 0.01mol/L ErCl3-0.1mol/L LiClO4-DMF system at 303K are 1.96×10-6 cm2*s-1 and 0.081 respectively. The Er metal film was prepared by galvanostatic electrolysis on Cu electrode in ErCl3-LiClO4-DMF system at 40A*m-2(current density). The deposites composed of Er over 95%(mass fraction) were obtained.     

Voltammetry and fluorescence studies on the interaction between Eu(phen)_3~(+3)and DNA

The binding mode of Eu(phen) 3+3 with DNA is studied by fluorescence and voltammetric methods. From the Scatchard graph and the fluorescence quenching phenomenon, it is concluded that the mode of interaction between Eu(phen)3+3 and DNA is intercalation bind by inserting the phen ?-? conjugate surface between the base pairs of the DNA duplex. Voltammetry was used to confirm the results obtained from the fluorescence method, the result from both methods agrees with each other. The binding constant (K) and the binding site size (ns) were calculated from voltammetric data such as the shifts in potential and limiting currents in the process of adding DNA, according to the positive shifts of peak potential. It was considered that the complex of the +2 ion interacted more favorably with the nucleotide bases than that of the +3 ion by hydrophobic interaction.     

Separation of indium (Ⅲ), gallium (Ⅲ), and zinc (Ⅱ) with Levextrel resin containing di(2-ethylhexyl) phosphoric acid (CL-P204): Part I. Selection of separation conditions

A kind of Levextrel resin separation process was developed for separation of indium (Ⅲ), gallium (Ⅲ), and zinc (Ⅱ) from aqueous sulfate solution with Levextrel resin containing di(2-ethylhexyl) phosphoric acid (CL-P204). The aim of the research is to collect preliminary results for a pilot-scale production. Properties of adsorbing indium (Ⅲ), gallium (Ⅲ), and zinc (Ⅱ) from sulfate solution with the Levextrel resin were first studied by batch operation and column operation. The optimum pH, adsorption capacities and concentrations of stripping agents for indium (Ⅲ), gallium (Ⅲ) were tested. The separation order of indium (Ⅲ), gallium (Ⅲ), and zinc (Ⅱ) from sulfate solution with CL-P204 Levextrel resin was found that indium (Ⅲ) could be first separated by adsorbing at the acidity of 1.0 mol/L whereas gallium (Ⅲ) and zinc (Ⅱ) could not, and they were adsorbed together by adsorbing at pH = 2.8, then separated from each other by stripping with 0.1 and 0.5 mol/L hydrochloric acid, respectively. T     

Synthesis,characterization,and thermostability of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(Ⅱ)

Owing to the adaptability to large scale processing,excellent composition control and film uniformity,the metal-organic chemical vapor deposition(MOCVD)technique is a promising process for high-temperature superconductor YBa2Cu3O7-δ(YBCO)preparation.In this technique,the evaporation characteristics and thermostability of adopted precursors in whole process will decide the quality and reproducible results of YBCO film.In the present report,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(Ⅱ)(Cu(TMHD)2)was synthesized by the interaction of copper acetate hydrate with TMHD in methanol solution,and its structure was identified by FTIR,1H NMR,and EI-MS spectroscopy.Subsequently,thermal property and the kinetics of decomposition were systematically investigated by nonisothermal thermogravimetric analysis methods(TGA)at different heating rates in streams of N2,and the average apparent activation energy of evaporation process was evaluated by the Ozawa,Kissinger,and Friedman methods.The possible conversion function was estimated through the Coats-Redfern method to characterize the evaporation patterns and followed a phase boundary reaction mechanism by the contracting area equation with average activation energy of 85.1 kJ·mol-1.     

Electrochemical behavior of Cu(Ⅱ) reduced in CH3OH and DMSO

The cyclic voltammetry and the potential-time curve after galvanostatic electrolysis were used to study the electrode processes of Cu(Ⅱ) in CH3OH solution and DMSO solution. The electroreduction of Cu(Ⅱ) to Cu on a Pt electrode proceeds in two steps: Cu(Ⅱ) + e = Cu(Ⅰ); Cu(Ⅰ) + e = Cu. The reduction potential of Cu(Ⅱ) in DMSO solution is more negative than that in CH3OH solution, and the diffusion coefficient of Cu(Ⅱ) ion in DMSO solution is larger than that in CH3OH solution because the polarity of DMSO is larger than that of CH3OH observably and has a stronger solvating power.     

Formation of black nickel in leaching solution containing ammonia and chloride

The black nickel formation process in leaching solution containing ammonia and chloride was investigated in terms of cyclic voltammetric and galvanostatic reduction techniques. The structure of black nickel was examined by means of X-ray diffraction technique. The results show that in the scanning region, two oxidization current peaks are observed during the positive sweep, one of which is attributed to a valence state transformation of Ni(OH)2 to high valence nickel compound(black nickel), and the other is caused by nitrogen evolution. During the formation process of black nickel, γ-NiOOH probably tends to self-discharge with water to form a-Ni(OH)2. As a result, it is observed that Ipa/Ipc (Ipc-anodic peak current; Ipc-cathodic peak current) maintains at a constant with the scanning rate increasing. Two reduction current peaks in cyclic vohammogram and two potential plateaus in galvanostatic reduction curve for black nickel are ascribed to the reduction of various oxidization states of nickel oxide. The potential plateaus at about 0.75 V reach the maximum in galvanostatic reduction curves. Black nickel presents amorphous structure.     

Comparative study on biosorption of Pb(Ⅱ) and Cr(Ⅵ) by Synechococcus sp.

The comparative study on adsorptions of Pb(Ⅱ) and Cr(Ⅵ) ions by free cells and immobilized cells of Synechococcus sp.was performed,in which different aspects including Zeta potential of the cells,the influence of pH,temperature and initial concentration of metal ions,as well as adsorption kinetics and mechanism were referred.The lyophilized free cells have a surface isoelectric point at pH 3,and the correlative experiment indicates that there is an electrostatic adsorption feature of Cr(Ⅵ) and Pb(Ⅱ).The immobilization of the free cells by Ca-alginate does not significantly modify the adsorption features of the biosorbent.The absorption processes of Cr(Ⅵ) and Pb(Ⅱ) on both free and immobilized cells are apparently affected by pH and the initial concentration of metal ions in the bulk solution,but are much weakly affected by temperature in the test range of 10-50 ℃.The slow course of biosorption follows the first order kinetic model,the adsorption of Pb(Ⅱ) obeys both Langmuir and Freundlich isotherm models,while the adsorption of Cr(Ⅵ) obeys only Freundlich model.FT-IR results indicate that carboxylic,alcoholic,amide and amino groups are responsible for the binding of the metal ions,and reduction of Cr(Ⅵ) to Cr(Ⅲ) takes place after Cr(Ⅵ) adsorbs electrostatically onto the surface of the biosorbents.     

Removal of Co(Ⅱ) from aqueous solutions by NKC-9 strong acid resin

A strong acidic ion exchange resin(NKC-9)was used as a new adsorbent material for the removal of Co(Ⅱ)from aqueous solutions.The adsorption isotherm follows the Langmuir model.The maximum adsorption capacity of the resin for Co(Ⅱ)is evaluated to be 361.0 mg/g by the Langmuir model.It is found that 0.5 mol/L HCl solution provides effectiveness of the desorption of Co(Ⅱ)from the resin.The adsorption rate constants determined at 288,298 and 308 K are 7.12×10-5,8.51×10-5and 9.85×10-5s-1, respectively.The apparent activation energy(Ea)is 12.0 kJ/mol and the adsorption parameters of thermodynamic are-H Θ=16.1 kJ/mol,-SΘ=163.4 J/(mol·K),-G Θ 298 K=-32.6 kJ/mol,respectively.The adsorption of Co(Ⅱ)on the resin is found to be endothermic in nature.Column experiments show that it is possible to remove Co(Ⅱ)ions from aqueous medium dynamically by NKC-9 resin.     

Amperometric detection of gold by differential pulse voltammetry using a DNA biosensor

A DNA biosensor with [Ru(DA-bpy)3]Cl2(DA-bpy:4,4'-diamino-2,2'-bipyridine) (RuL) as the electrochemical probe was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between RuL complex and DNA template. Cyclic voltammetry of RuL-DNA film showed a pair of stable and reversible peaks corresponding to the Ru(III)/Ru(II) redox potential of -0.165 V versus Ag|AgCl in pH 7.4 0.1 mol·L-1 Tris-HCl. The electron transfer was expected across the double-strand DNA by an "electron tunneling" mechanism. When the DNA biosensor was immerged in gold (III) buffer solution, the current peak signal (I) of the RuL-DNA supramolecular depressed and △I was linear in the concentration range of Au ion from 1 × 10-7 to 2 × 10-5 mol·L-1 with a regression coefficient of 0.9879. The detection limit was 5 × 10-8 mol·L-1. The developed procedures were applied to the analysis of synthetic samples of real materials with good sensitivity and selectivity.     

Solid-phase extraction of trace Au（Ⅲ） with SDG and determination by the catalytic spectrophotometric method

The new catalytic kinetic spectrophotometric method for Au(III) determination was developed and validated. It was based on the catalytic effect of gold on the oxidation of sudan red III by ammonium peroxodisulfate ((NH4)2S2O8) with nitrilo triacetic acid as an activator in mi- croemulsion and H2SO4 medium. Under optimum conditions, there was the linearity of the calibration curve in the concentration range from 0 to 20 μg/L Au(III) at 520 nm. The relative standard deviation was 3.0% with a correlation coefficient of 0.9986. The detection limit achieved was 9.75 × 10-5 μg/mL. A new method using a column packed with sulfhydryl dextrose gel (SDG) as a solid-phase extractant has been developed for the preconcentration and separation of Au(III) ions. The method has been applied to the determination of trace gold with satisfactory results.     

Determination of Oxide in FLINAK Melt by Electrochemical Titration Technique

The use of K_2NbF_7 as a probe solute for the cyclic voltammetric determination of oxide in FLINAKmelts was studied and demonstrated.This method is based on a complex reaction and the peak current densityof NbF_7~(2-)reduction.The reaction constant was determined to be very large at 973 K.A cyclic voltammetricstandard addition experiment is also employed to determine the amount of oxide in FLINAK melt.The oxidecontent of FLINAK melts is equal to the amount of Nb(V)added minus the amount of NbF_7~(2-)which is ob-tained from the voltammogram.     

Studies on Determination of Ge in Au Alloys by Potassium Iodate Potentiometric Titration Method

The paper presents a new method of determining Ge in gold alloys by potassium iodate potentiometric titration rather than by traditional distillation separation. The influences of conditions such as the reduction acidity, dosage of sodium hypophosphite and reduction time on the determination of Ge were studied. Comparison was made between the influences of end-point indication for potential method and starch method on accruracy and precision of the analysed results, stability and sensitivity of end-point, selectivity of method and so on. The possibility of reaction in an electrochemical way was discussed. Ge in the alloys such as AuGe 12 , AuGeNi 12 2 , AuAgGe 18.8 12.5 and AuAgGeNi 43.8 6 0.2 was measured, respectively, with the relative standard deviation of 0.10%~0.31% and the recoveries of added standard Ge in sample of 99.40%～100.40% when the reduction acidity was 0.40~0.80 mol/L HCl and 3.3 mol/L H 3 PO 4, 15 g sodium hypophosphite and reduction time 40 min. The new method presented is high accuracy and precision in results, good stability and sensibility in end point, easy operation and strong selectivity of determination. When it is applied to analyse actual samples, satisfactory results are achieved.     

Polarographic behavior of 1,4,7-triazacycloanane-N,N'''',N"-tris (meth-ylphonic acid) (NOTP)-Bi(Ⅲ) complex

The polargraphic behavior of Bi(III)-NOTP complex has been investigated in aqueous solution. It was found thatunder the conditions of pH 3.0 and of 0.02 mol/L NH4Cl, the Bi(III)-NOTP system gives a sensitive second order derivativewave at -0.340 V(vs SCE), which is proved to be an adsorptive complex wave. The composition of the complex isBi(III):NOTP. Furthermore, the peak current is linear to the concentration of Bi(III) in the range from 3.0×10-8 to 5.0×10-6mol/L. Artificial and practical samples have been detected with high sensitivity and receptivity.     

Adsorption behavior of Pd(Ⅱ) from aqueous solutions by D201 resin

The adsorption and desorption behaviors of Pd(Ⅱ) on D201 resin were investigated. The effects of parameters including HCl concentrations, initial metal ion concentrations, contact time, and temperature on the adsorption of Pd(Ⅱ) were studied by batch method. The HCl concentration for studying the effects was set from 0.01 to 2 mol·L-1 and the optimal adsorption condition is in 0.01 mol·L-1 HCl solution. The adsorption isotherm of Pd(Ⅱ) on D201 resin was determined and the equilibrium data fitted the Langmui...     

Electrochemical behavior of Cu(II) reduced in CH3OH and DMSO

The cyclic voltammetry and the potential-time curve after galvanostatic electrolysis were used to study the electrode processes of Cu(n) in CH3OH solution and DMSO solution. The electroreduction of Cu(Ⅱ) to Cu on a Pt electrode proceeds in two steps: Cu(Ⅱ) + e = Cu(Ⅰ); Cu(I) + e = Cu. The reduction potential of Cu(n) in DMSO solution is more negative than that in CH3OH solution, and the diffusion coefficient of Cu(Ⅱ) ion in DMSO solution is larger than that in CH3OH solution because the polarity of DMSO is larger than that of CH3OH observably and has a stronger solvating power.     

Modified AlAs/GaAs Double Barrier Quantum Resonant Tunneling Diodes Grown by AP-MOCVD

The MOCVD growth of modified AlAs/GaAs double barrier resonant tunneling diodes(DBRTD)withan A1GaAs chair was reported.The resonances to the first excited states were obtained.The peak-to-valley cur-rent ratio(PVCR)is 1.3 at 77K,room temperature peak current density is 8 kA/cm~2.The resonance voltagesare in agreement with the theoretical approach by transfer-matrix method.Influence of interrupted growthtime at the hetero-interface and incorporation of the AlGaAs chair to the device performances were studiedand the mechanism was discussed.The attempt to add an AlGaAs chair to the DBRTD by MOCVD resultedin improvement in the PVCR and peak current density.     

ELECTROANALYTICAL APPLICATIONS OF CARBOXYL-MODIFIED CARBON NANOTUBE FILM ELECTRODES

The electrochemical behavior of a carboxyl-modified carbon nanotube films was investigated to explore its possibility in electroanalytical applicaton. Cyclic voltammetry of quinone was conducted in 1mol/L Na2SO4, which showed a stable, quasi-reversible voltammetric response for quinone / hydroquinone, and the anodic and the cathodic peak potentials were 0.657V and -0.029V (vs. SCE) at a scan rate of 0.1V.s-1, respectively. Both anodic and cathodic peak currents depended linearly on the square root of the scan rate over the range of 0.01-0.5V.s-1, which suggested that the process of the electrode reactions was diffusion-controlled. Carboxyl-modified carbon nanotube electrodes made it possible to determine low level of dopamine selectively in the presence of a large excess of ascorbic acid in acidic media using derivative voltammetry. The results obtained were discussed in details. This work demonstrates the potential of carboxyl-modified carbon nanotube electrodes for electroanalytical applications.