Anodic Stripping Voltammetric Determination of Lead (II) and Cadmium (II) by Using a Carbon Nanotubes Paste Electrode Modified with Ion Exchange Synthetic Resin

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determination of sulfur compounds in gasoline using mercury film electrode by square wave voltammetry

A sensitive method based on square wave voltammetry is described for the quantitative determination of elemental sulfur, disulfide and mercaptan in gasoline using a mercury film electrode. These sulfur compounds can be quantified by direct dissolution of gasoline in a supporting electrolyte followed by subsequent voltammetric measurement. The supporting electrolyte is 1.4 mol L-1 sodium acetate and No acetic acid in methanol. Chemical and optimum operational conditions for the formation of the mercury film were analyzed in this study. The values obtained were a 4.3 mu m thickness for the mercury film, a 1000 rpm rotation frequency, -0.9 V applied potential and 600 s depositing time. Voltammetric measurements were obtained using square wave voltammetry with detection limits of the 3.0 x 10(-9), 1.6 x 10(-7) and 4.9 x 10(-7) mol L-1 for elemental sulfur, disulfide and mercaptan, respectively. (C) 2007 Elsevier Ltd. All rights reserved.

The Determination of Methanol Using an Electrolytically Fabricated Nickel Microparticle Modified Boron Doped Diamond Electrode

A nickel modified boron doped diamond (Ni-BDD) electrode and nickel foil electrode were used in the determination of methanol in alkaline solutions. The Ni-BDD electrode was electrodeposited from a 1 mM Ni(NO(3))(2) solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)(2)/NiOOH redox couple to electrocatalyse the oxidation of methanol. Methanol was determined to limits of 0.3 mM with a sensitivity of 110 nA/mM at the Ni-BDD electrode. The foil electrode was less sensitive achieving a limit of 1.6 mM and sensitivity of 27 nA/mM. SEM analysis of the electrodes found the Ni-BDD to be modified by a quasi-random microparticle array.

Cathodic stripping voltammetric determination of ceftazidime in urine at a hanging mercury drop electrode

A method was developed for the differential-pulse cathodic stripping voltammetric determination of ceftazidime with a hanging mercury drop electrode using its reduction peak at -0.43 V in Britton-Robinson buffer pH 4.0. The optimum accumulation potential and time were -0.15 V and up to 60 s, respectively. Linear calibration graphs were obtained from 1 x 10(-8) M and 1.5 x 10(-7) M. The limit of determination was calculated to be 5 x 10(-9) M. The coefficient of variation was 4% (n = 7) at 1 x 10(-7) M ceftazidime. The effect of various components of urine on the voltammetric response was studied, and creatinine, uric acid, urea, and glucose were shown to interfere in the method. Ceftazidime bound to human albumin gives a unique stripping peak at -0.48 V. Recoveries of 87% +/- 2% of the ceftazidime (n = 5) were obtained from urine spiked with 1.27 mu g ml(-1) using C-18 solid phase extraction cartridges. (C) 1997 Academic Press.

Cathodic stripping voltammetric detection and determination at a hanging mercury-drop electrode of dye contaminants in purified biomaterials: study of the human serum albumin and reactive dye 120 system

Procion red HE-3B (RR120) is an example of dye currently used in affinity purification. A method is described for determining trace amounts of RR120 dye contaminant in human serum albumin by cathodic stripping voltammetry. The method is based on a measure of a well-defined peak at -0.58 V, obtained when samples of HSA protein (0.01-2% w/v) containing dye concentrations are submitted to a heating time of 330 min at 80degreesC in NaOH, pH 12.0 and the samples are removed to a solution containing Britton-Robinson buffer, pH 4.0. Using an optimum accumulation potential and tune of 0 V and 240 s, respectively, linear calibration curves were obtained from 1.0 X 10(-9) to 1.0 X 10(-8) mol 1(-1) for RR120 dye. Leakage/hydrolysis of reactive red 120 from an agarose support (e.g. at pH 2 or 12) can also be conveniently determined at very low levels (sub-mug ml(-1)) by means of cathodic stripping voltammetry, which involves adsorptive accumulation of the dye onto the hanging mercury-drop electrode. (C) 2002 Elsevier B.V. B.V. All rights reserved.

SUBSTITUTIONAL DONOR RELATED STATES AND AU/GE/NI CONTACTS TO ALXGA1-XAS

Current-voltage measurements performed on bulk AlxGa1-xAs equipped with Au/Ge/Ni contacts reveal surprising deviations from ohmic behaviour when the temperature is lowered to that of liquid nitrogen. Significant differences are observed between samples with x = 0.3 (direct band-gap material) and x = 0.5 (indirect band-gap material). The dominant states of the donor atoms Si (doping) or Ge are found to be responsible for such behaviour. Evidence for the existence of an effective-mass X-valley metastable state is also presented.

Preparation and characterization of LiNi0.8Co0.2O2/PANI microcomposite electrode materials under assisted ultrasonic irradiation

A preparation method for a new electrode material based on the LiNi0.8Co0.2O2/polyaniline (PANI) composite is reported. This material is prepared by in situ polymerization of aniline in the presence of LiNi0.8Co0.2O2 assisted by ultrasonic irradiation. The materials are characterized by XRD, TG-DTA, FTIR, XPS, SEM-EDX, AFM, nitrogen adsorption (BET surface area) and electrical conductivity measurements. PANI in the emeraldine salt form interacts with metal-oxide particles to assure good connectivity. The dc electrical conductivity measurements at room temperature indicate that conductivity values are one order of magnitude higher in the composite than in the oxide alone. This behavior determines better reversibility for Li-insertion in charge-discharge cycles compared to the pristine mixed oxide when used as electrode of lithium batteries. (c) 2005 Elsevier B.V. All rights reserved.

Use of a carbon paste electrode modified with spinel-type manganese oxide as a potentiometric sensor for lithium ions in flow injection analysis

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel-type manganese oxide (lambda-MnO2), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li+ against other alkali and alkaline-earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6 x 10(-5) - 1.0 x 10(-2) mol L-1 with a slope 78.9 +/- 0.3 mV dec(-1) over a wide pH range 7 - 10 (Tris buffer), without interference of other alkali and alkaline-earth metals. For a flow rate of 5.0 mL min(-1) and a injection sample volume of 408.6 muL, the relative standard deviation for repeated injections of a 5.0 x 10(-4) mol L-1 lithium ions was 0.3%.

DEVELOPMENT OF A CHEMICALLY MODIFIED ELECTRODE BASED ON CARBON PASTE AND FUNCTIONALIZED SILICA-GEL FOR PRECONCENTRATION AND VOLTAMMETRIC DETERMINATION OF MERCURY(II)

A mercury-sensitive chemically modified electrode (CME) based on modified silica gel-containing carbon paste was developed. The functional group attached to the silica gel surface was 3-(2-thiobenzimidazolyl)propyl, which is able to complex mercury ions. This electrode was applied to the determination of mercury(II) ions in aqueous solution. The mercury was chemically preconcentrated on the CME prior to voltammetric determination by anodic stripping in the differential-pulse mode. A calibration graph covering the concentration range from 0.08 to 2 mg l-1 was constructed. The precision for six determinations of 0.122 and 0.312 mg l-1 Hg(II) was 3.2 and 2.9% (relative standard deviation), respectively. The detection limit for a 5-min preconcentration period was 0.013 mg l-1. A study for foreign ions was also made.

Cathodic stripping voltammetric determination of ceftazidime with reactive accumulation at a poly-L-lysine modified hanging mercury drop electrode

Ceftazidime is hydrolysed only slowly at pH 10 at room temperature. This is indicated by a small cathodic stripping voltammetric peak obtained at pH 10 at a hanging mercury drop electrode at about -0.6 V which corresponds to the reduction of the hydrolysis product. This peak is enhanced more than tenfold by the addition of poly-L-lysine (PLL) to the electrolyte solution. The optimum accumulation potential is between 0 and -0.1 V: the size of the peak decreases steadily, however, as the accumulation potential is moved to more negative potentials and is about one-sixth the size for accumulation at -0.4 V. Existing knowledge of the organic chemistry of cephalosporins indicates that the accumulation must involve an aminolysis reaction of the unprotonated PLL with the beta-lactam ring of the ceftazidime. The limit of detection (3 sigma) in standard solutions was calculated to be 1 x 10(-10) mol l(-1). The detection limit in buffer solution containing 1% of urine was calculated to be 5 x 10(-9) mol l(-1), i.e. 5 x 10(-6) mol l(-1) in the urine. (C) 1999 Elsevier B.V. B.V. AU rights reserved.

Anodic stripping voltammetric determination of aurothiomalate in urine using a screen-printed carbon electrode

This work describes an electroanalytical method for determining gold(I) thiomalate, aurothiomalate, widely used for treatment of reumatoid arthiritis, using a screen-printed carbon electrode (SPCE). Aurothiomalate (AuTM) was determined indirectly at the same electrode by accumulating it first at -1.5 V vs. printed carbon. At this potential in the adsorbed state, the AuTM is reduced to Au(0), which is then oxidized at two steps at -0.22 V and +0.54 V on SPCE. Using optimized conditions of 60 s deposition time, -1.5 V (vs. printed carbon) accumulation potential, 100 mV s(-1) scan rate, linear calibration graphs can be obtained by monitoring the peak at +0.54 V for AuTM in HCl 0.1 mol L-1 from 1.43 x 10(-6) to 1.55 x 10(-4) mol L-1. A limit of detection obtained was 6.50 x 10(-7) mol L-1, and the relative standard deviation from five measurements of 3.0 x 10(-5) mol L-1 AuTM is 4.5%. The method was successfully applied for AuTM determination in human urine sample.

Electrocatalysis of hydrogen evolution reaction on Pt electrode surface-modified by S-2 chemisorption

Kinetic studies of hydrogen evolution reaction (HER) at the surface of Pt in alkaline conditions, reported in this paper, show that electrocatalytic activity is enhanced after adsorption of S-2 ions. EIS and steady-state polarization curve data pointed to an undoubted improvement in performance with the Pt-S cathode that was attributed to higher adsorbed hydrogen coverage. Experimental findings suggested an increase in the electronic density of the modified surface sites that may strengthen the interaction between H2O and the adsorption site and, consequently, accelerates the Volmer step. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10(3)-10(6) V/cm exhibits exp beta U-1/2 behavior with beta = beta(Schottky) below the glass transition temperature (T-g congruent to 90 degrees C), and beta = beta(Poole-Frenkel) above T-g. Coordinated temperature measurements of de currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T-g is consistent with the so-called ''anomalous'' Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. (C) 1996 John Wiley & Sons, Inc.

Simultaneous determination of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry using a glassy carbon-mercury-film electrode

A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% (v/v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-mum thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10(-9)-10(-8) mol L-1 for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples.

Electrochemical reduction and determination of Cibacron Blue F3GA at poly-L-lysine modified glassy carbon electrode

The oxidation of a reactive dye, Cibacron Blue F3GA, CB, (C.I. 61211), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode occurs in two steps at 2.0 < pH < 10 involving one electron transfer each to the amine group leading to the imide derivative. Stable films of poly-L-lysine (PLL) in the presence of glutaraldehyde (GA) 97.5%:2.5% on glassy carbon electrode can be used to detect low levels of dye using its oxidation peak at +0.75V by voltammetry. Linear calibration graphs were obtained for the CB reactive dye, from 1.0 X 10(-6) to 1.0 X 10(-5) mol L-1 in B-R buffer, pH 2.0, using a pre-concentration off-line during 10 min. The detection limit (3 sigma/slope) was calculated to be 4.5 X 10(-8) mol L-1. Films of PLL can readily be applied for the determination of CB dye bearing aminoanthraquinone as chromophore and chlorotriazinyl as reactive group at concentrations at least 100 times lesser than using a glassy carbon electrode without modification. The method described was applied for the determination of CB dye in tap water and raw water collected from the municipal treatment plant with a recovery of 89.2% +/- 5.4 and 88.0% +/- 6.5, respectively. (c) 2005 Elsevier Ltd. All rights reserved.