Desenvolvimento e aplica����o de sistema passivo de coleta de poluentes atmosf��ricos para monitoramento de Cd, Cr, Pb, Cu, Fe, Mn, Zn e particulados totais

The objective of this study was to assess a new monitoring technique of particulate and trace metals in the atmosphere via the use of a passive sampler of air pollutants in the city of Goi��nia. The average particulate weight and average concentrations of metals Fe, Cr, Zn, Pb, Cu, Mn, and Cd were 0.1104 g and 257.5; 23.4; 17.8; 6.7; 1.9; 0.8; 0.2 μg/m��/day, respectively. Higher Pb and Cr concentrations were obtained in areas with intense traffic. This study revealed that it is possible to monitor trace metals with passive sampling, developed at a low cost and operational facility.

Aplica����o de m��todos quimiom��tricos na otimiza����o da extra����o de Ca, Mg, K, Fe, Zn, Cu e Mn em folhas de braqui��ria

This work applied a 2�� factorial design to the optimization of the extraction of seven elements (calcium, magnesium, potassium, iron, zinc, copper and manganese) in brachiaria leaves, determined by flame atomic absorption spectrometry. The factors sample mass and digestion type were evaluated at two levels: 200/500 mg, and dry/wet, respectively. Principal component analysis allowed simultaneous discrimination of all the significant effects in one biplot. Wet digestion and mass of 200 mg were considered the best conditions. The decrease of 60% in sample mass allowed to save costs and reagents. The method was validated through the estimation of figures of merit.

Ternary surface complex: coadsorption of Cu(II), Zn(II), Cd(II) and nitrilotris(methylenephosphonic) acid onto boehmite

This work studies the effect of NTMP (nitrilotris(methylenephosphonic acid)) on the adsorption of Cu(II), Zn(II), and Cd(II) onto boehmite in the pH range 5-9.5. The data were analyzed using the 2-pK constant capacitance model (CCM) assuming ternary surface complex formation. Under stoichiometric conditions, NTMP is more effective for removing Cu(II) than Zn(II) from solution and the contribution of ternary surface complexes are important to model the adsorption of both metals. Under nonstoichiometric conditions and high surface loading with a Me(II)/NTMP ratio of 1:5, Cu(II) and Zn(II) adsorption is significantly suppressed. In the case of Cd(II) the free metal adsorption is the most dominant species.

Simultaneous preconcentration of Cu(II), Cd(II) and Mn(II) on silica-polyethylene glycol and determination by flame atomic absorption spectrometry

A simultaneous solid phase extraction procedure for enrichment of Cu(II), Cd(II) and Mn(II) has been developed. The method is based on adsorption of Cu(II), Cd(II) and Mn(II) ions on polyethylene glycol-silica gel pre-conditioned with acetate buffer (pH 5.5). The adsorbed metal ions are eluted with nitric acid (1 mol L -1) and determined by flame atomic absorption spectrometry. The calibration graph was linear in the range of 2-140 ng mL-1 for Cu(II), 1-40 ng mL-1 for Cd(II) and 4-100 ng mL-1 for Mn(II). The limits of detection were 0.66, 0.33 and 1.20 ng mL-1 for Cu(II), Cd(II) and Mn(II), respectively.

Distribui����o de Zn, Pb, Ni, Cu, Mn e Fe nas fra����es do sedimento superficial do Rio Cachoeira na regi��o 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 ��g 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.

Avalia����o da mineraliza����o de arroz em sistema de refluxo para a determina����o 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.

USO DO PLANEJAMENTO EXPERIMENTAL PARA OTIMIZA����O DE UM PROCEDIMENTO VOLTAM��TRICO PARA DETERMINA����O SIMULT��NEA DAS CONCENTRA����ES DOS METAIS Zn, Cd, Pb E Cu LIVRES EM ��GUA DE COCO

Optimization of the main parameters of SWASV using boron-doped diamond electrode was described for the simultaneous determination of Zn, Cd, Pb and Cu free in coconut water. The values of electroanalytical parameters studied were optimized with the factorial design and center composite design. The optimized parameters for the preconcentration of metals were -1.50 V for potential, and 240 s for deposition time. For SWV, the optimized value was 11.56 mV for step potential. In addition, frequency and pulse height were defined at 100 Hz and 55 mV, respectively. Furthermore, the concentration of the supporting electrolyte (acetate buffer, pH 4.7) was optimized in 0.206 mol L-1. The optimized procedure was applied in two samples of coconut water: natural and processed. The limits of detection (LOD) obtained for Zn, Cd, Pb and Cu were 7.2; 4.4; 3.3 and 1.5 ��g L-1, respectively. The concentrations of Cd and Pb were not detected. On the other hand, the values found for the concentrations of Zn and Cu were: < LOD (29 ��g L-1) and (6.8 �� 0.9) ��g L-1 for the natural sample; and (85.8 �� 4.2) ��g L-1 and (7.7 �� 0.6) ��g L-1 for the processed sample, respectively.

Influ��ncia de adi����es de prata na cin��tica de precipita����o da liga Cu-5%Al

A influ��ncia de adi����es de 2%, 4%, 6%, 8% e 10% de prata, em massa, na cin��tica de forma����o e precipita����o de precipitados ricos em prata, na liga Cu-5% Al foi estudada atrav��s de medidas de varia����o da microdureza com a temperatura e o tempo. Os resultados obtidos indicaram que a presen��a da prata aumenta consideravelmente a dureza da liga e tamb��m interfere na cin��tica de precipita����o, com uma mudan��a mecan��stica no processo que est�� relacionada com o teor de prata das ligas.

Estudo da influ��ncia de adi����es de prata na resistividade el��trica da liga Cu-5%Al

Estudou-se a influ��ncia de adi����es de 2, 6 e 8% Ag, em peso, na resistividade el��trica da liga Cu-5%Al, utilizando-se o m��todo dos quatro pontos e um sistema de registro cont��nuo de varia����o da resistividade el��trica com a temperatura. Os resultados obtidos indicaram que a resistividade el��trica da liga aumenta com o aumento da concentra����o de prata e que as inflex��es observadas nas curvas de varia����o da resistividade com a temperatura de aquecimento podem ser atribu��das �� solubiliza����o da prata na matriz de Cu-Al. Observou-se tamb��m que a velocidade de aquecimento da amostra �� um fator importante na intensidade e forma dos eventos observados.

Influ��ncia de adi����es de prata na cin��tica de recristaliza����o da liga CU-5%Al

A influ��ncia de adi����es de 2, 4, 6 e 8% de prata, em peso, na cin��tica de recristaliza����o da liga Cu-5%Al com taxas de deforma����o de 40, 70 e 90%, foi estudada utilizando-se metalografia por microscopia ��ptica e medidas de varia����o do tamanho de gr��o com o tempo e a temperatura de envelhecimento. Os resultados obtidos indicaram uma diminui����o na velocidade de crescimento dos gr��os e na energia de ativa����o correspondente, com o aumento da concentra����o de prata.

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.

Lability of Cd, Cr, Cu, Mn and Pb complexed by aquatic humic substances

The lability of Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) complexed by humic substances (HSs) was investigated by means of ion exchange on cellulose modified with p-aminobenzoic groups (Cell-PAB), using a batch procedure. The HSs were extracted from water samples using adsorption in a column packed with XAD 8 resin. The metal-HS complexes were prepared by adding solutions containing all the aforementioned metal ions ( Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) ). The results indicated that the distribution coefficients (Kd) of Cell-PAB decreased with the presence of HSs, and that the lability of metal fractions complexed by HSs decreases in pH values > 4.0, complexation time > 10 h and HS concentration > 500 mg L-1. The metal exchange between HSs and Cell-PAB exhibited the following order of metal ion lability: Cd < Pb < Mn <FONT FACE=Symbol>@</FONT> Cr < Cu.

Synthesis, characterization and thermal behaviour of solid-state compounds of 2-methoxybenzoate with some bivalent transition metal ions

Solid-state M-2-MeO-Bz compounds, where M stands for bivalent Mn, Co, Ni, Cu and Zn and 2-MeO-Bz is 2-methoxybenzoate, have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), thermogravimetry, derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to have information about the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds.

Complexes of 3,4-dimethoxybenzoic acid anion with Cu(II), Co(II), La(III), and Nd(III)

Physico-chemical properties of 3,4-dimethoxybenzoates of Co(II), Cu(II), La(III) and Nd(III) were studied. The complexes were obtained as hydrated or anhydrous polycrystalline solids with a metal ion-ligand mole ratio of 1 : 2 for divalent ions and of 1 : 3 in the case of trivalent cations. Their colours depend on the kind of central ion: pink for Co(II) complex, blue for Cu(II), white for La(III) and violet for Nd(III) complexes. The carboxylate groups in these compounds are monodentate, bidentate bridging or chelating and tridentate ligands. Their thermal decomposition was studied in the range of 293-1173 K. Hydrated complexes lose crystallization water molecules in one step and form anhydrous compounds, that next decompose to the oxides of respective metals. 3,4 - Dimethoxybenzoates of Co(II) is directly decomposed to the appropriate oxide and that of Nd(III) is also ultimately decomposed to its oxide but with the intemediate formation of Nd2O2CO3.. The magnetic moment values of 3,4-dimethoxybenzoates determined in the range of 76-303 K change from 4.22 ��B to 4.61 ��B for Co(II) complex , from 0.49 ��B to 1.17 ��B for Cu(II) complex , and from 2.69 ��B to 3.15 ��B for Nd(III) complex.

Biheterocyclic ligands: synthesis, characterization and coordinating properties of bis(4-amino-5-mercapto-1,2,4-triazol-3-yl) alkanes with transition metal ions and their thermokinetic and biological studies

The Co(II), Ni(II) and Cu(II) metal ions complexes of Bis(4-amino-5-mercapto-1,2,4-triazol-3-yl) alkanes (BATs) have been prepared and characterized by elemental analysis, conductivity measurements infrared, magnetic susceptibility, the electronic spectral data and thermal studies. Based on spectral and magnetic results, the ligands are tetradentate coordinating through the N and S-atoms of BATs; six-coordinated octahedral or distorted octahedral and some times four-coordinated square planar were proposed for these complexes. Activation energies computed for the thermal decomposition steps were compared. The ligands and their metal complexes were tested in vitro for their biological effects. Their activities against two gram-positive, two gram-negative bacteria and two fungal species were found to vary from moderate to very strong.