Implementation of an automatic standard addition method in a flow-batch system: application to copper determination in an alcoholic beverage by atomic absorption spectrometry

A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow-batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow-batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaça”, available in Brazil. A SAM has been recommended for these analyses because “Cachaças” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow-batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n=6) and 0.2 mg l⁻¹, respectively, for 1.0-7.0 mg l⁻¹ Cu. By using five standard addition levels, the sample throughput was 70 h⁻¹ and the consumption of sample and standard solution were 1.5 and 0.5 ml per analysis, respectively.     

A study about the stabilization of anatase phase at high temperatures on sol-gel cerium and copper doped titania and titania-silica powders

Copper and cerium oxides doped titania samples, as well as silica-titania samples were prepared through sol-gel process by using titanium butoxyde as precursor. The obtained samples were characterized by X-ray diffractometry and scanning electron microscopy. The main objective of the proposed study is to promote the stabilization of anatase phase at high temperatures. The obtained experimental results show that cerium doped titania samples stabilizes the anatase phase until 800 °C, whereas copper doped samples calcinated at the same temperature are a mixture of anatase and rutile phases. So, CeO₂ is a better stabilizer for anatase phase than CuO. On the other hand, based on previously reported data it can be concluded that both, CeO₂ and CuO are better stabilizers for anatase phase than SnO₂. It is also verified that the total amount of silica in the titania-silica double oxide increases the temperature required for crystallization, and as a consequence, the anatase phase is stabilized at higher temperatures i.e. up to 1200 °C.     

Laser-induced quantum adsorption of neutral atoms in dielectric surfaces

We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is calculated, considering the adatoms’ interaction with the crystal phonons. PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj     

Electrostatic surface shape resonances of a finite number of ridges

The resonance properties of localized electrostatic surface modes associated with a finite number of ridges on an otherwise planar surface are investigated. Numerical solutions of the homogeneous integral equations that describe the electromagnetic fields in the vicinity of the ridges are used to obtain the dispersion relation of surface plasmons. The frequencies of the electrostatic surface shape resonances are calculated for ridges with Gaussian, Lorentzian, sinusoidal, exponential, and triangular profiles. We show the existence of splittings of the plasmon frequencies, which depends on the surface profile function and on the distance between the ridges. Considering the ridge with a sinusoidal profile, we obtain the limit on the number of ridges which generates a frequency splitting of the electrostatic surface shape resonances, whose frequency values converge to those of the dispersion relation of surface plasmons on one-dimensional sinusoidal grating. Received: 24 June 1997 / Received in final form: 5 September 1997 / Accepted: 15 September 1997     

Surface plasmons on a quasiperiodic grating

A method is presented for calculating the frequencies of non-retarded surface plasmons propagating on a semi-infinite medium with a surface profile described by a one-dimension quasiperiodic function. The profiles are generated, in analogy with previous work on quasiperiodic superlattices, by repeating unitary cells constructed according to an inflation rule. Dispersion relations are obtained for a semi-infinite free-electron metal as the active medium, with surface profiles obeying the Fibonacci and Thue-Morse sequences.Received: 24 June 2003, Published online: 19 November 2003PACS: 73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations) - 71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons     

Cladonia verticillaris (lichen) can exhibit defense mechanisms against Rn-222 under controlled conditions

Journal of Radioanalytical and Nuclear Chemistry - This study aimed to evaluate the effects of the Rn-222 progeny on the lichen Cladonia verticillaris under controlled conditions. The results...     

Degenerate Landau levels for tripod-type cold atoms in U(2) Abelian gauge field

New data for positronium beam production efficiency are presented. As a converter of positrons to forward-going positronium, O₂ has been found to be as good as CO₂ from ～250 to 400 eV. Preliminary data is also presented for the production efficiency from Ar at 2.8 eV.     

Production of Enzymes by Paenibacillus chitinolyticus and Paenibacillus ehimensis to Obtain Chitooligosaccharides

Obtaining oligosaccharides from chitosan has been the focus of several studies in the pharmaceutical, chemical, food, and medical areas, due to their functional properties. Here, we evaluated the production potential of biologically functional chitooligosaccharides using enzymes extracts produced by Paenibacillus chitinolyticus and Paenibacillus ehimensis. After 48 h of fermentation, these microorganisms were able to produce chitosanases, which generated oligomers with a degree of polymerization between dimers and hexamers. The maximum conversion of chitosan to oligomers was 99.2 %, achieved after 12 h incubation of chitosan with enzymes produced by P. ehimensis. The chitooligosaccharides generated were capable of scavenging the 2,2-diphenyl-1-picrylhydrazyl radical, reaching a maximum scavenging rate of 61 and 39 % when produced with P. ehimensis and P. chitinolyticus enzymes, respectively. The use of these enzymes in the crude form could facilitate their use in industrial applications.     

Quantum interference effects in the Br2 electronic predissociation: Dependence upon the molecular properties

The occurrence of quantum interference in the Br₂ electronic predissociation has been observed for the first time. It is also shown that the quantum interference effects are strongly dependent upon the representation of the molecular properties, such as the kinetic coupling and the transition dipole moment. The fast Fourier transform method implemented within the wave packet formalism was used to simulate the time evolution of the molecular system under the influence of single monochromatic ultrashort laser pulses. The quantum interference has been inferred from the oscillatory behavior of the autocorrelation functions, which have also been used to calculate the cross-sections, the branching ratios, and the selectivity. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004