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Sigrist M.,National University of Santa | Albertengo A.,National University of Santa | Beldomenico H.,National University of Santa | Tudino M.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy
Journal of Hazardous Materials

A simple and robust on-line sequential injection system based on solid phase extraction (SPE) coupled to a flow injection hydride generation atomic absorption spectrometer (FI-HGAAS) with a heated quartz tube atomizer (QTA) was developed and optimized for the determination of As(III) in groundwater without any kind of sample pretreatment. The method was based on the selective retention of inorganic As(V) that was carried out by passing the filtered original sample through a cartridge containing a chloride-form strong anion exchanger. Thus the most toxic form, inorganic As(III), was determined fast and directly by AsH3 generation using 3.5molL-1 HCl as carrier solution and 0.35% (m/v) NaBH4 in 0.025% NaOH as the reductant. Since the uptake of As(V) should be interfered by several anions of natural occurrence in waters, the effect of Cl-, SO4 2-, NO3 -, HPO4 2-, HCO3 - on retention was evaluated and discussed. The total soluble inorganic arsenic concentration was determined on aliquots of filtered samples acidified with concentrated HCl and pre-reduced with 5% KI-5% C6H8O6 solution. The concentration of As(V) was calculated by difference between the total soluble inorganic arsenic and As(III) concentrations. Detection limits (LODs) of 0.5μgL-1 and 0.6μgL-1 for As(III) and inorganic total As, respectively, were obtained for a 500μL sample volume. The obtained limits of detection allowed testing the water quality according to the national and international regulations. The analytical recovery for water samples spiked with As(III) ranged between 98% and 106%. The sampling throughput for As(III) determination was 60samplesh-1. The device for groundwater sampling was especially designed for the authors. Metallic components were avoided and the contact between the sample and the atmospheric oxygen was carried to a minimum. On-field arsenic species separation was performed through the employ of a serial connection of membrane filters and anion-exchange cartridges. Advantages derived from this approach were evaluated. HPLC-ICPMS was employed to study the consistency of the analytical results. © 2011 Elsevier B.V. Source

Ricci A.M.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Calvo E.J.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Martin S.,University of Liverpool | Nichols R.J.,University of Liverpool
Journal of the American Chemical Society

(Figure Presented) A comparison of the electrochemical gating of molecular conduction by a redox [Os(bipyridine)(pyridine)Cl] complex tethered to Au(111) with two different metal-molecule junctions in a scanning tunneling microscope nanogap is presented. The same redox molecular structure was tethered by mercaptobenzoic acid or reduction of the aryldiazonium salt of p-aminobenzoic acid, resulting in a Au-S or Au-C bond, respectively. A two-step electron-transfer mechanism with vibrational relaxation of the redox molecule is apparent in each case. Copyright © 2009 American Chemical Society. Source

Iriel A.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Lagorio M.G.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy

Flower fluorescence has been previously proposed as a potential visual signal to attract pollinators. In this work, this point was addressed by quantitatively measuring the fluorescence quantum yield (Φf) for flowers of Bellis perennis (white, yellow, pink, and purple), Ornithogalum thyrsoides (petals and ovaries), Limonium sinuatum (white and yellow), Lampranthus productus (yellow), Petunia nyctaginiflora (white), Bougainvillea spectabilis (white and yellow), Antirrhinum majus (white and yellow), Eustoma grandiflorum (white and blue), Citrus aurantium (petals and stigma), and Portulaca grandiflora (yellow). The highest values were obtained for the ovaries of O. thyrsoides (Φf=0.030) and for Citrus aurantium petals (Φf=0.014) and stigma (Φf=0.013). Emitted photons as fluorescence were compared with reflected photons. It was concluded that the fluorescence emission is negligible compared to the reflected light, even for the most fluorescent samples, and it may not be considered as an optical signal in biocommunication. The work was complemented with the calculation of quantum catches for each studied flower species to describe the visual sensitization of eye photoreceptors. © 2010 Springer-Verlag. Source

Factorovich M.H.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Molinero V.,University of Utah | Scherlis D.A.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy
Journal of the American Chemical Society

Classical thermodynamics is assumed to be valid up to a certain length-scale, below which the discontinuous nature of matter becomes manifest. In particular, this must be the case for the description of the vapor pressure based on the Kelvin equation. However, the legitimacy of this equation in the nanoscopic regime can not be simply established, because the determination of the vapor pressure of very small droplets poses a challenge both for experiments and simulations. In this article we make use of a grand canonical screening approach recently proposed to compute the vapor pressures of finite systems from molecular dynamics simulations. This scheme is applied to water droplets, to show that the applicability of the Kelvin equation extends to unexpectedly small lengths, of only 1 nm, where the inhomogeneities in the density of matter occur within spatial lengths of the same order of magnitude as the size of the object. While in principle this appears to violate the main assumptions underlying thermodynamics, the density profiles reveal, however, that structures of this size are still homogeneous in the nanosecond time-scale. Only when the inhomogeneity in the density persists through the temporal average, as it is the case for clusters of 40 particles or less, do the macroscopic thermodynamics and the molecular descriptions depart from each other. © 2014 American Chemical Society. Source

Minaberry Y.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Jobbagy M.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Jobbagy M.,University of Buenos Aires
Chemistry of Materials

Free-standing macroporous bioglass scaffolds were prepared by a sol-gel route. The ice-segregation-induced self-assembly method was employed to structure a bioglass aqueous sol in the form of green monoliths with a well-defined macroporosity. The achieved texture was essentially preserved after a mild annealing at 873 K. The texture can be properly tuned by typical variables such as the freezing rate or sol concentration. In addition to these physical preparative variables, the acidity level plays a key role in preventing the silica condensation, keeping the primary building units in the early stages of the sol-gel transition and allowing the obtainment of large macropores. The chemical homogeneity of the resulting bioglass was enough to ensure a proper in vitro biomineralization response, resulting in a well-distributed hydroxyaopatite-like nanoparticulated layer. © 2011 American Chemical Society. Source

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