Determination of lead(II) in aqueous solution using carbon nanotubes paste electrodes modified with Amberlite IR-120

A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of multiwalled carbon nanotubes and Amberlite IR-120. The anodic stripping voltammograms depend, to a large extent, on the composition of the modified electrode and the preconcentration conditions. Under optimum conditions, the anodic peak current at around ?0.57 V is linearly related to the concentration of Pb(II) in the range from 9.6?×?10^?8 to 1.7?×?10^?6 mol L^?1 (R?=?0.998). The detection limit is 2.1?×?10^?8 mol L^?1, and the relative standard deviation (RSD) at 0.24?×?10^?6 mol L^?1 is 1.7% (n?=?6). The modified electrode was applied to the determination of Pb(II) using the standard addition method; the results showed average relative recoveries of 95% for the samples analysed.

Rhodamine B Photodegradation in Aqueous Solutions Containing Nitrogen Doped TiO2 and Carbon Nanotubes Composites

In this work, new results concerning the potential of mixtures based on nitrogen doped titanium dioxide (TiO₂:N) and carbon nanotubes (CNTs) as possible catalyst candidates for the rhodamine B (RhB) UV photodegradation are reported. The RhB photodegradation was evaluated by UV–VIS absorption spectroscopy using samples of TiO₂:N and CNTs of the type of single-walled carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), and single-walled carbon nanotubes functionalized with carboxyl groups (SWNT-COOH) having various concentrations of CNTs. The best photocatalytic performance was obtained for sample containing TiO₂:N and 2.5 wt.% SWNTs-COOH, when approx. 85% of dye removal was achieved after 300 min. of UV irradiation. The reaction kinetics of RhB aqueous solutions containing TiO₂:N/CNT mixtures followed a complex first-order kinetic model. The TiO₂:N/CNTs catalyst induced higher photodegradation efficiency of RhB than TiO₂:N due to the presence of CNTs, which act as adsorbent and dispersing agent and capture the photogenerated electrons of TiO₂:N hindering the electron–hole recombination.     

Preliminary spectroscopic investigation of some PVA membranes gamma irradiated

The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated were investigated by XRD, UV-VIS and Raman spectroscopies. The increase of UV absorbance is observed after irradiation. This behavior is correlated with the scission effect and local ordering of the polymeric chain induced by irradiation. These effects were probed by XRD and Raman spectroscopy.     

Influence of barium source on the characteristics of sol-precipitated BaTiO<Subscript>3</Subscript> powders and related ceramics

In order to obtain pure and fine BaTiO₃ powders with controlled morphology, sol-precipitation methods involving the use of titanium iso-propoxide and of two different barium sources, i.e. barium nitrate and barium acetate, were proposed in this work. The thermal behaviour of the synthesized gels and the X-ray diffraction data obtained for the oxide powders pointed out that, by using Ba(NO₃)₂ as barium source, the decomposition process was completed at lower temperature (750°C) and was accompanied by a more pronounced tendency to obtain a single phase BaTiO₃ composition, by comparison with the synthesis where barium acetate was used as raw material (1100°C). Scanning electron microscopy investigations emphasized the effect of the nature of barium source and synthesis conditions on the morphology of the oxide powders, as well as on the microstructure of the related ceramics.     

Critical evolution of the local order parameters related to the nanopolar domains in Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramics

In the present paper, Pb(Mg_1/3Nb_2/3)O₃ (PMN) ceramics prepared by the columbite method were investigated. The dielectric study indicates typical relaxor properties, with a frequency dispersion in the range of 200–350 K. The relaxor-to-paraelectric phase transition was evidenced by the continuous decrease of the local order parameter derived from the permittivity-temperature data. As a result of the critical behavior, the main Raman modes show anomalies at: (i) ∼150 K; (ii) ∼220 K (i.e. close to the critical temperature reported for the field-induced ferroelectric state in PMN single crystal); (iii) ∼260 K (i.e. the temperature of the permittivity maximum); (iv) ∼350 K (the temperature for initiation of the cluster freezing process T ^*); (v) ∼620 K (Burns temperature). The frequency split of the doublet at ∼605 and ∼500 cm⁻¹ presents a critical behavior related to the local symmetry lowering and to the structure ordering due to a phase transformation which takes place below T ^*. The tunability in the paraelectric state was interpreted in terms of reorientation of the non-interacting nanopolar clusters in a double-well potential. The temperature dependence of the nanopolar domain size also shows anomalies in the range of T ^*. The size and dynamics of the polar nanodomains is essential in determining the functional properties of the Pb(Mg_1/3Nb_2/3)O₃ relaxor.     

Note on Joseph's inequalities in stability theory

Résumé Pour la stabilité linéaire d'un écoulement parallèle, le premier théorème de Joseph [1] a donné le domaine de la stabilité à l'aide de deux courbesM ₁ etM ₂. Nous avons amélioré ce théorème en employant l'enveloppe d'une famille de courbes à laquelle appartiennentM ₁ etM ₂. Nos résultats ci-dessus et ceux de Joseph ont été améliorés encore à l'aide de l'inégalitéI ₂ ² 4I ₁ ² au lieu de .Les simples inégalités nous permettent de faire une limitation plus forte pour la vitesse de l'amplification de la perturbation que celles connues jusqu'à présent en stabilité hydrodynamique.     

Validated ion pair liquid chromatography/fluorescence detection method for assessing the variability of the loratadine metabolism occurring in bioequivalence studies

Inter- and intra-individual variability of the loratadine (LOR) metabolism in Caucasian subjects was assessed during a bioequivalence study for two pharmaceutical formulations (solid oral dosage forms) containing 10 mg of the active substance. The analytical data were obtained by applying a reliable, low-cost and sensitive ion pair liquid chromatography/fluorescence (IPLC/FLD) method for determination of both loratadine and descarboethoxyloratadine (DCL) in human plasma samples. The sample preparation procedure is based on liquid-liquid extraction of the target analytes from alkalinized plasma using diethyl-ether. The separation of the analytes and 8-chloroazatadine as internal standard (IS) was achieved through an isocratic ion pair (IP) elution on a Purospher((R)) STAR RP-18 column. The mobile phase containing sodium dodecyl sulfate (SDS) as ion pairing agent was pumped at a flow rate of 1 mL/min. Fluorescence detection (FLD) was achieved at 280 nm (excitation) and 440 nm (emission) wavelengths. The increased sensitivity of the method is also based on a large sample injected volume (250 microL). Linear response was found over the 0.5-20 ng/mL concentration interval for both target compounds. Low limits of quantification (LLOQ) around 0.3 ng/mL were found for LOR and DCL. Method validation is presented.     

An FT-IR study of sarcoplasmic reticulum solubilization by triton X-100

Low concentrations of the non-ionic detergent Triton X-100 increase the activity of sarcoplasmic reticulum Ca⁺⁺-ATPase without major changes in protein conformation, according to FT-IR spectroscopy in H₂O and D₂O. At higher surfactant concentrations the enzyme activity is inhibited, while changes in protein conformation are seen: The proportion of unordered structure increases at the expenses of-turns and parallel-sheet.     

Desktop near-field thermal-lens microscope for thermo-optical detection in microfluidics

A new compact near-field desktop-sized diode laser thermal-lens microscope for analysis in microfluidics was proposed. A novel beam-alignment and detection systems provided high signal stability and, along with reduced number of optical elements rendered the instrument portable. The detection of nonfluorescent model species (Fe(II)-bathophenanthroline chelate) in water showed good linearity in the range of 5 × 10(-9) to 1 × 10(-4) M, and the limit of detection was 3.5 × 10(-9) M, which corresponded to 3.5 × 10(-7) absorbance units and provided a 20-fold enhancement in sensitivity compared with existing schematic.