The use of the modified simplex as an optimization strategy in analytical chemistry.

The multivariate optimization designs most used in analytical chemistry are presented, with a particular focus on the Modified Simplex Method. The sequential movements for this procedure are described in detail by means of an hypotetical example and its application is discussed by using a 3-variable chemical system, where the analytical response, taken as the difference in absorbance, Delta A, due to the absorbance readings of the Mo(VI) catalysed and non catalysed (blank) oxidation of iodide ions with hydrogen peroxide in acid medium, are related to the concentrations of the reagents involved, Other examples from the literature are also cited.191242

CATALYTIC DETERMINATION OF MOLYBDENUM(VI) IN PLANTS USING MONOSEGMENTED CONTINUOUS-FLOW ANALYSIS AND SPECTROPHOTOMETRIC DETECTION

A mono-segmented continuous-flow analysis (MCFA) procedure has been developed for the determination of molybdenum in plants, based on the catalytic oxidation of I- by H2O2 in acid medium as the indicator reaction, with spectrophotometric detection at 350 nm. High sensitivity was achieved using multivariate and univariate screening experiments, optimized reagent concentrations, a reaction time of 130 s and a sampling-loop volume of 300 mul or higher. The reagents were pumped at 1.2 ml min-1 and the sample at 4.7 ml min-1, yielding a sampling rate up to 120 h-1, with negligible carryover. The effects of Fe(III), Ti(IV), W(VI), Cr(VI), V(V), PO43- and ionic strength on the analytical signal were evaluated under these conditions. Only Ti(IV) does not interfere significantly. Hence, a prior separation step is necessary, consisting of an extraction of Mo(VI) into HCl-saturated chloroform as an alpha-benzoin oxime complex. For a reaction time of 130 s and an ambient temperature of 22 +/- 2-degrees-C the calibration graph, obtained by submitting Mo(VI) standards to the extraction procedure, follows the equation DELTAA = -0.0018 + 0.0172 c(Mo) (r2 = 0.998), where DELTAA is the net analytical response, taken as the difference between the catalysed and non-catalysed signals, and c(Mo) is the molybdenum concentration, in ng ml-1. Under these conditions, the linear range extends to 50 ng ml-1, the calculated detection limit is about 1.0 ng ml-1 and the relative standard deviation is close to 1.0% over the entire linear range. The sensitivity and linear ranges of the MCFA procedure can be easily modified by simply changing the sampling volume and the reaction time. The accuracy of the method was evaluated by means of plant samples supplied by the 'International Plant-analytical Exchange' (IPE), from the Wageningen Agricultural University, The Netherlands. The results obtained for the determination of Mo(VI) in these samples were acceptable under the recommended IPE criteria.118221321

Spectrophotometric determination of Mo(VI) in steel using a homogeneous ternary solvent system after single-phase extraction

An alternative procedure for the determination of Mo(VI) with thiocyanate is proposed. According to this procedure, Mo(VI) is extracted with alpha-benzoinoxime by single-phase extraction in a water/ethanol/chloroform homogeneous ternary solvent system at a nominal pH of 2 and then is spectrophotometrically determined, after separation from the matrix in a similar solvent mixture. The determination is performed by forming a homogeneous phase using the solvent containing the extracted metal as one of the components of the reactional solvent system, eliminating the time-consuming metal complex destruction step. Under these experimental conditions, the calibration graph is linear up to 8.00 mu g ml(-1), according to the equation A = 0.005 + 0.143 C-Mo(VI) (r(2) = 0.9999). Using the experimental conditions described, the absorbance readings are stable for periods up to 18 h. The interference of the most common interfering species for this method can be prevented by adding Fe2+ and H2PO4- to the solvent system prior to the extraction step. The accuracy of the proposed method was evaluated by comparing with standard samples determined by atomic absorption measurements with background correction. (C) 1998 Elsevier Science B.V. All rights reserved.47371972

Structurally tuned multiferroic state in BiFeO3-based compounds

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Structurally tuned multiferroic state is demonstrated for BiFeO3-based compounds. The electric and magnetic orders are strongly affected by the coexistence of R3c and Cm phases, i.e., by structural softness through monoclinicity, which leads the multiferroism to be driven by the same cation. The Cm phase enhances the ferroelectric and magnetic responses through Bi/Ba-O and Fe/Ti-O bonds by influencing structural distortions and ion valence. We also show the strong correlations between ferroic orders, structural arrangements, and tuning of the ion valence in the perovskite B site.1112563567Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 24202, 22870]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CNPq [proc. 305129/2010-4]FAPESP [proc. 2008/04025-0]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 24202, 22870]CAPES [082/2007

Ferroic investigations in LuFe2O4 multiferroic ceramics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)In this paper, the ferroic properties of polycrystalline LuFe2O4 samples were carefully investigated, and a dissimilar charge ordered state was identified. Strong dielectric dispersion, between 350 K and 225 K; the formation of cluster glass magnetic phases in the same temperature range; and the existence of a ferrimagnetic transition at 230 K indicate the coupling between the ferroelectric and the magnetic orders. Mossbauer spectroscopic investigations, at room temperature, revealed unbalanced contributions of the ferric and ferrous iron ions to the charge ordered state. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622147]1103Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico do Parana Brazilian agency [10779, 15727]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CNPq [476964/2009-1, 552900/2009-5]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico do Parana Brazilian agency [10779, 15727]FAPESP [2008/04025-0]CAPES [PROCAD 082/2007

Ferroic states and phase coexistence in BiFeO3-BaTiO3 solid solutions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)In this paper structural, electric, magnetic, and Mossbauer spectroscopy studies were conducted in (x) BiFeO3-(1-x) BaTiO3, 0.9 >= x >= 0.3, solid solutions. X-ray diffraction and Rietveld refinement studies indicated the formation of single-phased materials crystallized in a distorted perovskite structure with the coexistence of rhombohedral and monoclinic symmetries. Room temperature ferroelectric hysteresis loops showed that the electric polarization increases with the increase of the BaTiO3 content due to the singular structural evolution of the studied solid solutions. All samples presented weak ferromagnetic ordering, which indicates that the BaTiO3 substitution in the BiFeO3 matrix released the latent magnetization. Mossbauer studies revealed a magnetic spectral signature corresponding to ordered Fe3+ ions, and a decrease of the magnetic hyperfine magnetic fields with the increase of the BaTiO3 content. The composition 0.3BiFeO(3)-0.7BaTiO(3) presented a spectral signature corresponding to a paramagnetic behavior, which strongly suggests that the observed magnetization in this sample is due to the Ti3+ ions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4766450]11210Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [Prots. 22825, 22870]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [proc. 305129/2010-4]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [Prots. 22825, 22870]FAPESP [proc. 2008/04025-0

Magnetic states and valence fluctuations in charge frustrated polycrystalline lutetium ferrite samples

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)LuFe2O4 polycrystalline materials were processed by an innovative protocol using high-energy ball milling and thermal treatments in an argon flux. The results of room-temperature Mossbauer spectroscopy showed different concentrations of Fe2+ and Fe3+ in samples treated for different time periods. Magnetic studies revealed multiple magnetic transitions and showed that valence fluctuations resulted in samples with distinguishable magnetic behaviors. In fact, an additional anomaly in the M x T curve was observed for the LuFe2O4 sample thermally treated for 1 h at 1473 K. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.699670673Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 22870]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPq [proc. 305129/2010-4]Fundacao Araucaria de Apoio ao Desenvolvimento Cientifico e Tecnologico do Parana [22825, 22870]CAPES [Procad 082/2007]FAPESP [proc. 2008/04025-0