112,003 research outputs found
Multiwavelength observations of N 66 in the SMC: unveiling photodissociation interfaces and star formation
No full textWe present new observations of the major star-forming region N66 in the Small Magellanic Cloud and of its surroundings, which add to those presented in Contursi et al. (2000, Paper I). High-sensitivity CO observations allowed the detection of molecular gas associated with the H II region, for which a high-resolution image in [O III] lambda 5007 is presented. We also present images in the v(1-0) S(1) line of H-2 at 2.12 mu m and in the adjacent continuum. This material reveals an interesting photodissociation region. We show that the molecular gas that has not yet been photodissociated by the UV radiation of the stars is in hot, dense clumps with a very small surface filling factor. We discovered several embedded stars or stellar associations, and suggest that three successive stellar generations have already taken place in less than 3 million years
Cobalt oxide electrodeposition on various electrode substrates from alkaline medium containing Co-gluconate complexes: a comparative voltammetric study
No full textAbstract: A study regarding the electrodeposition of Co oxides from alkaline medium containing 12 mM gluconate ligand and 12 mM Co2+ on glassy carbon, Au, Pt, Ni, Ti and ITO electrode substrate was carried out through cyclic voltammetry technique. Films of cobalt oxides were deposited either anodically by voltage cycling (100 mV s(-1)) between -0.3 and 0.6 V (SCE) or by potentiostatic conditions at potential comprised between 0.2 and 0.6 V for a fixed time of deposition. Analysis of the voltammetric experimental data clearly showed that the rate of cobalt oxide electrodeposition process decreases in the order Au > Pt > GC, Ni > Ti, ITO and the massive cobalt electrodeposition does not proceed to an appreciable extent until potentials of 0.3-0.4 V (SCE) is reached. The effect of the scan rate on the peak potential, peak current, an
HIGHLY DISPERSED RHODIUM PARTICLES ON MULTI-WALLED CARBON NANOTUBES FOR THE ELECTROCHEMICAL REDUCTION OF NITRATE AND NITRITE IN ACID MEDIUM
No full textThe rhodium particles can be electrodeposited on a glassy carbon electrode, previously modified with multi-walled carbon nanotubes (MWCNTs), by voltage cycling between 0.4 V and-0.3 V vs. SCE (30 cycles) in 50 mM H 2SO4 containing 4.0 mM RhCl3. This proposed modified electrode is useful to facilitate the electrocatalytic reduction of nitrate and nitrite ions in acid medium. The mechanism of the electrocatalytic reduction of nitrate and nitrite ions in the hydrogen region of potentials was critically considered using voltammetric and DC/pulsed amperometric detection techniques. The GC/MWCNT-Rh electrode shows interesting sensitivity and temporal reproducibility towards nitrite and nitrate reduction under constant and pulsed applied potentials, respectivel
A New Strategy for As(V) Biosensing Based on the Inhibition of the Phosphatase Activity of the Arsenate Reductase from Thermus thermophilus
No full textArsenic (As) pollution is a widespread problem worldwide. In recent years, biosensors based on enzymatic inhibition have been developed for arsenic detection, making the study of the effect of inhibitors on the selected enzymatic activity crucial for their setup. The arsenate reductase of Thermus thermophilus HB27, TtArsC, reduces As(V) into As(III), but is also endowed with phosphatase activity. This work investigates the inhibitory effects of As(V) and As(III) on phosphatase activity by taking advantage of a simple colorimetric assay; the results show that both of them are non-competitive inhibitors affecting the Vmax but not the KM of the reaction. However, their Ki values are different from each other (15.2 ± 1.6 μM for As(V) and 394.4 ± 40.3 µm with As(III)), indicating a higher inhibitory effect by As(V). Moreover, the inhibition-based biosystem results to be selective for As(V) since several other metal ions and salts do not affect TtArsC phosphatase activity; it exhibits a sensitivity of 0.53 ± 0.03 mU/mg/μM and a limit of detection (LOD) of 0.28 ± 0.02 μM. The good sensitivity and specificity for As(V) point to consider inhibition of TtArsC phosphatase activity for the setup of a novel biosensor for the detection of As(V)
PULSED ELECTRODEPOSITION OF NICKEL/PALLADIUM GLOBULAR PARTICLES FROM AN ALKALINE GLUCONATE BATH. AN ELECTROCHEMICAL, XPS AND SEM INVESTIGATION.
No full textNickel oxide species, palladium metal and complex Ni-Pd particles were deposited on the glassy carbon electrode by pulsed electrochemical conditions from 0.5 M NaOH solution containing 5 mM gluconate ion, 0.5 mM Ni(NO 3)2 and/or 2 mM Pd(NO3)2. The electrodeposition process was performed using the following potentials and pulse durations: E1 = -1.0 V and E2 = +0.8 V vs. SCE, t 1 = 50 ms and t2 = 50 ms for the relevant times of 600 s. The nickel oxide particles were deposited during the anodic pulse of potentials, while the palladium particles were deposited during the cathodic sequence of the potential pulses. The Ni-Pd system shows an acceptable character of electrochemical reversibility and a high affinity for oxygen adsorption. The XPS and SEM techniques were used in order to define the surface chemical composition and the actual morphology of the deposited material. An average surface chemical composition of Pd0.5Ni was established and the composite appears formed of well dispersed single globular particles having an average size comprised between 50 nm and 150 nm of diameter
Electrocatalytic oxidation of some hydrazine compounds at glassy carbon electrode modified with Co-gluconate complex.
No full textCobalt oxyhydroxide modified glassy carbon electrodes (GC/Co) prepared by anodic electrodepostion in alkaline solution containing gluconate ions as ligand species have been characterized and proposed as sensing probes for the detection of hydrazine compounds. Under cyclic voltammetry and chronoamperometric conditions, the electrooxidation processes of hydrazines on the GC/Co are severely attenuated indicating strong and irreversible adsorption of the analyte on the electrode surface with subsequent formation of stable films with fouling effects on the catalytic sites. On the contrary, under flowing conditions the hydrazine compounds show well-defined and reproducible peaks with good analytical performance. Flow injection analysis (FIA) carried out at constant applied potential of 0.3 V vs. Ag/AgCl (4 M?KCl) and using a flowing stream of 0.1 M NaOH solution containing 50 mu M Co2L22- as on-line modifier, shows limits of detection (LODs) comprised between 0.5 mu M for hydrazine and 2 mu M for 1,2-dimethyhydrazine. Regression analysis, shows linear ranges spanning over about three orders of magnitude above the detection limits with coefficients of correlation better than 0.96
CARBOHYDRATE AND ALDITOL ANALYSIS BY HIGH-PERFORMANCE ANION-EXCHANGE CHROMATOGRAPHY COUPLED WITH ELECTROCHEMICAL DETECTION AT A COBALT-MODIFIED ELECTRODE.
No full textA cobalt oxyhydroxide film dispersed on a carbon electrode surface was characterized and proposed as an amperometric sensor for determination of alditols and carbohydrates in flowing streams. Complex mixtures of carbohydrates were separated by anion-exchange chromatography using a moderately alkaline solution as mobile phase. The cobalt modified electrode (GC-Co) was employed under a constant applied potential of 0.5 V (vs Ag/AgCl). Under these experimental conditions the detection limits (S/N=3) for all analyzed electroactive molecules ranged between 0.3 mumol L-1 and 1.5 mumol L-1 and the dynamic linear ranges spanned generally three orders of magnitude above the relevant detection limits. Analytical determinations of carbohydrates and alditols in red and white wines, are reported
ISOCRATIC ION CHROMATOGRAPHIC DETERMINATION OF UNDERIVATIZED AMINO ACIDS BY ELECTROCHEMICAL DETECTION
No full textAn isocratic chromatographic separation with amperometric detection of underivatized amino acids at a copper oxyhydroxide modified glassy carbon electrode is described. A simple and sensitive quantitation procedure of amino acids without the need of tedious and time-consuming derivatization step was achieved by coupling anion-exchange chromatography with electrochemical detection. The effects of hydroxide, nitrate and acetonitrile concentration in the mobile phase on the capacity factors and peak resolution was evaluated. Under the optimized isocratic chromatographic conditions (i.e. 60 mM NaOH) and under constant applied potentials (i.e. 0.55 V versus Ag/AgCl) the detection limit ranged between 4 and 24 pmol injected and the linear dynamic range spanned generally over three or four order of magnitude for all investigated amino acid compounds. Direct determination of several common free amino acids in beer and milk samples were performed
ELECTROCHEMICAL AND SPECTROSCOPIC CHARACTERIZATION OF A TUNGSTEN ELECTRODE AS A SENSITIVE AMPEROMETRIC SENSOR OF SMALL INORGANIC IONS.
No full textCyclic voltammetry was used to investigate the electrochemical behaviour of the tungsten oxide films toward the electroreduction of BrO3- ClO2- and NO2- ions in acidic medium. The effects of the temperature, scan rate, pH, chemical composition of the electrolytic solutions, were investigated and the reduction mechanism was critically discussed.
The reduction currents, evaluated in cyclic voltammetry and measured at -0.250 V versus SCE, increased linearly on increasing analyte concentration up to 20, 55 and 45 mM for nitrite, chlorite and bromate ions, respectively. The detection limits, evaluated in cyclic voltammetry, were 0.1, 0.4 and 0.7 mM for BrO3-, ClO2- and NO2-, respectively.
The tungsten oxide film was successfully characterized as an amperometric sensor for the analytical determination of BrO3- ClO2- and NO2- ions in flowing stream. Operating under constant applied potential of -0.3 V versus Ag/AgCl the good reproducibility of the peak height and background current level during consecutive injections, indicates the absence of fouling effects and the potential applicability of the amperometric sensor for the routine analytical determination of the investigated inorganic ions. Considering the low values of the background currents (ca. 1.1 +/- 0.1 mu A) obtained in acidic and not deoxygenated carrier electrolyte, the tungsten sensing electrode seems to compete favourably with other common sensors for the amperometric determination of electroactive molecules under cathodic conditions.
The X-ray photoelectron spectroscopy technique (XPS) was used in order to evaluate the chemical composition of the tungsten film upon electrochemical treatment in 0.1 M H2SO4 Solution. Independently of the electrochemical treatment in acid solution, the tungsten surface electrode is generally composed by 50-60% of W-0, 35-40% of W6+ and traces of W2+ oxide species
CHARACTERIZATION OF BISMUTH ADATOM-MODIFIED PALLADIUM ELECTRODES. tHE ELECTROCATALYTIC OXIDATION OF ALIPHATIC ALDEHYDES IN ALKALINE SOLUTIONS.
No full textPalladium-bismuth films supported on glassy carbon substrates were prepared by cathodic electrodeposition of palladium ad subsequent adsorption of bismuth species on the electrode surface. A mechanism regarding the irreversible adorption process of bismuth species on the palladium surface, was described. The resulting active film was characterized, and in particular, the electrooxidation of some aliphatic aldehydes was investigated in moderately alkaline solutions. The bismuth adlayer increases the overall rate of the oxidative processes through a combination of a third body mechanism and a true catalyst. The oxidation currents of propionaldehyde, evaluated in cyclic voltammetry increased linearly on increasing analyte concentration up to 8 mM. Under chronoamperometric conditions at the constant applied potential of -0.2 V versus SCE, the resulting calibration plot for propionalclehyde analysis was linear over the range of 1.5-8 mM with a correlation coefficient better than 0.97. Throughout the XPS investigation Pd 3d and Bi 4f detailed regions an average chemical composition of the surface composite film of Pd96 +/- 2Bi4 +/- 2 was evaluated
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