Specificity and selectivity improvement in doping analysis using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry was used for the identification of forty doping agents. The improvement in the specificity was remarkable, allowing the resolution of analytes that could not be done by one-dimensional chromatographic systems. The sensitivity observed for different classes of prohibited substances was clearly below the value required by the World Anti-Doping Agency. In addition time-of-flight mass spectrometry gives full spectrum for all analytes without any interference from the matrix, resulting in selectivity improvements. These results could support the implementation of an exhaustive monitoring approach for hundreds of doping agents in a single injection.

Determinação de Cu, Fe, Mn, Zn e do teor de proteína total em amostras de trigo e soja após procedimento de extração sequencial

A sequential extraction procedure was applied to wheat and soybean seed samples. The total protein content (determined by two distinct methods: Bradford and bicinchoninic acid-BCA) and distribution of Cu, Fe, Mn and Zn in each fraction was determined. The sequential extraction employed four different solutions: water, 0.5 mol L-1 NaCl, ethanol/water (70:30 v v-1) and 0.5 mol L-1 NaOH. For both samples, the highest concentration of metals was observed in those extracts associated with globulin-type proteins using NaCl solution. Regarding protein content, higher levels were obtained using the BCA method.

Distribuição de Zn, Pb, Ni, Cu, Mn e Fe nas frações do sedimento superficial do Rio Cachoeira na região sul da Bahia, Brasil

The metal distribution in the surface sediment fractions of the Cachoeira River was evaluated based on the fractionation method using a five-step sequential extraction. The determination of metals was made by flame atomic absorption spectrophotometry (F AAS). Zn, Pb and Cu exhibit higher concentrations in the residual fraction of the sediment from sites that receive discharges from urban and industrial zones. High levels of Ni (60 ± 1 to 447 ± 9 µg L-1) were found in the river water, which may be detrimental to the "health" of rural communities that utilize the river water for domestic purposes without treatment.

Avaliação da mineralização de arroz em sistema de refluxo para a determinação de Cu, Fe, Mn e Zn por FAAS

This paper describes the evaluation of a new method of sample preparation using a cold finger system with continuous water flow for rice analysis by flame atomic absorption spectrometry. The limits of detection for Cu, Fe, Mn and Zn for the proposed method were 0.36, 1.84, 2.12 and 0.16 mg kg-1, respectively. The RSDs were lower than 6.0% for all elements and the CRM analyzed showed values with 95% agreement. The proposed method is simple and safe for the proposed objective and does not require the use of mixtures of acid or special equipment for sample preparation.

Preparation and evaluation of magnetic chitosan particles modified with ethylenediamine and Fe(III) for the removal of Cr(VI) from aqueous solutions

The adsorption of Cr(VI) in aqueous solution by magnetic particles of crosslinked chitosan-ethylenediamine-Fe(III) (MPCh-EDA-FeCL) was studied in a batch system. Fe3+ in the MPCh-EDA-FeCL permitted that adsorption of Cr(VI) occurred with maximum efficiency between pH 3 and 11. The maximum adsorption capacity at pH 7.0 was 81.04 mg g-1 at 25 ºC. The adsorption kinetic process was described by the pseudo-second-order model. Thermodynamic parameters indicated spontaneous, exothermic and chemical adsorption nature. The adsorbent was successively regenerated using a 0.1 mol L-1 NaOH solution. Results were satisfactory for treatment of wastewater from the electroplating industry.

ANÁLISE EXPLORATÓRIA DAS CONCENTRAÇÕES DOS METAIS NA, CA, MG, SR E FE EM EXTRATO AQUOSO DE PETRÓLEO, DETERMINADOS POR ICP OES, APÓS OTIMIZAÇÃO EMPREGANDO PLANEJAMENTO DE EXPERIMENTOS

AbstractThe purpose of this study was to evaluate the best operating conditions of ICP OES for the determination of Na, Ca, Mg, Sr and Fe in aqueous extract of crude oil obtained after hot extraction with organic solvents (ASTM D 6470-99 modified). Thus, the full factorial design and central composite design were used to optimize the best conditions for the flow of nebulization gas, the flow of auxiliary gas, and radio frequency power. After optimization of variables, a study to obtain correct classification of the 18 samples of aqueous extract of crude oils (E1 to E18) from three production and refining fields was carried out. Exploratory analysis of these extracts was performed by principal component analysis (PCA), hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA), using the original variables as the concentration of the metals Na, Ca, Mg, Sr and Fe determined by ICP OES.

Ba-DOPED ZnO MATERIALS: A DFT SIMULATION TO INVESTIGATE THE DOPING EFFECT ON FERROELECTRICITY

ZnO is a semiconductor material largely employed in the development of several electronic and optical devices due to its unique electronic, optical, piezo-, ferroelectric and structural properties. This study evaluates the properties of Ba-doped wurtzite-ZnO using quantum mechanical simulations based on the Density Functional Theory (DFT) allied to hybrid functional B3LYP. The Ba-doping caused increase in lattice parameters and slight distortions at the unit cell angle in a wurtzite structure. In addition, the doping process presented decrease in the band-gap (Eg) at low percentages suggesting band-gap engineering. For low doping amounts, the wavelength characteristic was observed in the visible range; whereas, for middle and high doping amounts, the wavelength belongs to the Ultraviolet range. The Ba atoms also influence the ferroelectric property, which is improved linearly with the doping amount, except for doping at 100% or wurtzite-BaO. The ferroelectric results indicate the ZnO:Ba is an strong option to replace perovskite materials in ferroelectric and flash-type memory devices.

Thermal decomposition and stability in a series of heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X=Cl, Br, I)

Heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X= Cl, Br, I), which have metal-metal bonds, have been prepared in order to study their thermal stabilities as a function of the halogen coordinated to mercury atoms. The characterization of the above complexes was carried out by elemental analysis, IR and NMR spectroscopies. Their thermal behaviour has been investigated and the final product was identified by IR spectroscopy and by X-ray powder diffractogram.

Estudo eletroquímico de Fe[Fe(CN)5NO] em eletrodo de pasta de grafite

Nitroprussiato de ferro (FeNP) foi sintetisado e caracterizado por Infravermelho e absorção atômica. FeNP foi incorporado em eletrodo de pasta de grafite empregando-se como técnica de estudo a voltametria cíclica. O comportamento eletroquímico do eletrodo de pasta de grafite contendo FeNP apresenta dois processos eletródicos com potencial médio (Em) de (Em)1 = 0,24 V e (Em)2 = 0,85 V ( KCl =1,0M; v = 20 mV.s-1 vs ECS) atribuídos aos pares redox ( FeII/FeIII ) e FeII(CN)5NO/ FeIII(CN)5NO, respectivamente. A intensidade de corrente dos pares redox aumenta, linearmente com a velocidade de varredura indicando um controle de adsorção. O eletrodo de pasta de grafite modificada com FeNP apresenta estabilidade por vários dias. O estudo eletroquímico do eletrodo de pasta de grafite modificada com FeNP foi examinado em várias soluções de eletrólitos suporte sendo que a natureza do cátion afetam a intensidade de corrente e os potenciais dos pares redox ,deslocando (Em)1 para potenciais mais positivos na sequência: K+ >Na+>Li+ enquanto que a natureza do anion (Cl-, NO3-,SO4=) não afeta os pares redox. Os voltamogramas obtidos em diferentes concentrações de KCl (0,05 - 2,5 M)exibem deslocamentos do (Em)1 para potencial de valores mais positivos. Este deslocamento é linear com a variação da concentração do eletrólito suporte. A inclinação da reta é de 66 mV por década de concentração indicando a ocorrência de um processo quase nernstiano. O potencial médio permanece praticamente constante em pH entre os valores de 3,0 e 8,0. Um outro processo eletródico com (Em)3 = 0,47 V ocorre em pH < 3, sendo este atribuído a formação de novas espécies intermediárias.

Determinação direta e simultânea de Al, As, Fe, Mn e Ni em cachaça por espectrometria de absorção atômica em forno de grafite

Este trabalho propõe um método simples, rápido e confiável para determinação direta e simultânea de Al, As, Fe, Mn e Ni em cachaça por espectrometria de absorção atômica em forno de grafite (GFAAS). A superfície superior da plataforma do tubo de grafite foi revestida com filme à base de tungstênio (WxCyOz).O programa de aquecimento otimizado (temperatura, tempo de rampa, tempo de patamar) foi o seguinte: secagem 1 (100ºC, 5 s, 5 s); secagem 2 (120ºC, 5 s, 5 s); pirólise (1300ºC, 10 s, 30 s); atomização (2200ºC, 1 s, 6 s) e limpeza (2550ºC, 1 s, 3s). Os desvios padrões relativos (n=3) foram < 4,4%, < 0,7%, < 11%, < 6,0%, < 1,2% para os elementos Al, As, Fe, Mn e Ni, respectivamente. A exatidão foi avaliada por meio de testes de adição e recuperação dos analitos em 8 amostras de cachaças comerciais, e as recuperações situaram-se nos seguintes intervalos: 80 - 105% (Al), 81 - 92% (As), 82 - 108% (Fe), 83 - 106% (Mn), 83 - 108% (Ni). Os limites de detecção calculados foram 9,7 µg L-1 Al, 2,3 µg L-1 As, 12 µg L-1 Fe, 14 µg L-1 Mn e 0,8 µg L-1 Ni.

Electrochemical and physical characterization of Ni-Cu-Fe alloy for chlor-alkali hydrogen cathodes

This work describes the development of an alternative acetate bath for the electrochemical codeposition of Ni-Cu-Fe electrodes at low pH that is stable for several weeks and produces electrodes with good performance for chlor-alkali electrolysis. Physical characterization of the electrode surface was made using X ray absorption spectroscopy (XAS), scanning electron microscopy (SEM) and energy dispersive analysis (EDX). The evaluation of the material as electrocatalyst for the hydrogen evolution reaction (her) was carried out in brine solution (160 g L-1 NaCl + 150 g L-1 NaOH) at different temperatures through steady-state polarization curves. The Ni-Cu-Fe electrodes obtained with this bath have shown low overpotentials for the her, around 0.150 V at 353 K, and good stability under continuous long-term operation for 260 hours. One positive aspect of this cathode is that the polarization behavior of the material shows only one Tafel slope over the temperature range of 298 - 353 K.

Reatividade do [Fe(CO)2(eta2-CS2)(PPh 3)2] frente a compostos de Cu(I): síntese de espécies binucleares heterometálicas contendo CS2 em ponte entre Fe(0) e Cu(I)

Este trabalho contempla a síntese e caracterização espectroscópica de dois compostos carbonílicos heterometálicos do tipo [Fe(CO)3(m-CS2)(PPh3 )(CuX)], X = Cl, ClO4. Os dados provenientes da espectroscopia no infravermelho e de RMN de 31P{¹H} foram conclusivos quanto à proposição da geometria octaédrica distorcida ao redor do átomo de ferro (0), como também sobre a natureza bimetálica de ambos compostos. Estes dados esclareceram o modo de coordenação dos grupos carbonilos, da trifenilfosfina (PPh3), bem como a disposição do ligante dissulfeto de carbono em ponte entre os átomos de Fe (0) e Cu (I).

Spectroscopic analysis of C80 doping with group III and group V elements using semiempirical PM3 molecular modelling technique

Semiempirical calculations at the level of PM3 of theory were carried out to study the structural and electronic properties of C80 and some of its doped derivatives with the elements of group III and V at the level of PM3 of theory. We have selected these elements to be substituted in the fullerene-C80 cage in order to show the effect of such structural change on the electronic properties of the molecules studied. The theoretical IR spectra, some of physical and chemical properties of the molecules studied are obtained and discussed.

Magnetic and transport properties of LaMnO3+δ, La1-xCaxMnO3, La1-xCaxMn1-yFeyO3 and La1-xSrxMn1-yFeyO3

Interest to hole-doped mixed-valence manganite perovskites is connected to the ‘colossal’ magnetoresistance. This effect or huge drop of the resistivity, ρ, in external magnetic field, B, attains usually the maximum value near the ferromagnetic Curie temperature, TC. In this thesis are investigated conductivity mechanisms and magnetic properties of the manganite perovskite compounds LaMnO3+, La1-xCaxMnO3, La1-xCaxMn1-yFeyO3 and La1- xSrxMn1-yFeyO3. When the present work was started the key role of the phase separation and its influence on the properties of the colossal magnetoresistive materials were not clear. Our main results are based on temperature dependencies of the magnetoresistance and magnetothermopower, investigated in the temperature interval of 4.2 - 300 K in magnetic fields up to 10 T. The magnetization was studied in the same temperature range in weak (up to 0.1 T) magnetic fields. LaMnO3+δ is the parent compound for preparation of the hole-doped CMR materials. The dependences of such parameters as the Curie temperature, TC, the Coulomb gap, Δ, the rigid gap, γ, and the localization radius, a, on pressure, p, are observed in LaMnO3+δ. It has been established that the dependences above can be interpreted by increase of the electron bandwidth and decrease of the polaron potential well when p is increased. Generally, pressure stimulates delocalization of the electrons in LaMnO3+δ. Doping of LaMnO3 with Ca, leading to La1-xCaxMnO3, changes the Mn3+/Mn4+ ratio significantly and brings an additional disorder to the crystal lattice. Phase separation in a form of mixture of the ferromagnetic and the spin glass phases was observed and investigated in La1- xCaxMnO3 at x between 0 and 0.4. Influence of the replacement of Mn by Fe is studied in La0.7Ca0.3Mn1−yFeyO3 and La0.7Sr0.3Mn1−yFeyO3. Asymmetry of the soft Coulomb gap and of the rigid gap in the density of localized states, small shift of the centre of the gaps with respect to the Fermi level and cubic asymmetry of the density of states are obtained in La0.7Ca0.3Mn1−yFeyO3. Damping of TC with y is connected to breaking of the double-exchange interaction by doping with Fe, whereas the irreversibility and the critical behavior of the magnetic susceptibility are determined by the phase separation and the frustrated magnetic state of La0.7Sr0.3Mn1−yFeyO3.