Determinação de elementos-traço: relatório de dois exercícios interlaboratoriais

Results of two intercomparison exercises are reported. In the first one, the participants were asked to determine Cd, Cu, Pb and Zn, at the sub mg mL-1 level, in an acidified aqueous solution. In the second one, the participants were asked to determine mercury (total) in two homogeneous biological samples, hair and fish. The exercises were considered satisfactory and few reported results were discharged (3s criteria).

Análise de cabelo: uma revisão dos procedimentos para a determinação de elementos traço e aplicações

Aspects related to the quality of human hair analysis are presented, such as sample collection, sample preparation, determination of trace elements and application examples. Also the hair morphology, the importance of this analysis and its uses and meanings are discussed.

Os 200 anos da pilha elétrica

In celebration of the 200th anniversary of the electric pile, invented by Alessandro Volta, a synopsis of his letter to The Royal Society (London) and of his biography is presented.

Especiação de metais-traço em sedimentos de florestas de manguezais com Avicennia e Rhizophora

Speciation studies of Fe, Cr, Co, Ni and Cu on reactive fraction (adsorved on oxides, hydroxides, carbonates and clay minerals) and pyrite were performed in Avicennia schaueriana and Rhizophora mangle sediments from Amapá shoreline-Brazil. The soil under Avicennia showed a higher heavy metal concentration in reactive fraction than under Rhizophora. The soil under Rhizophora showed low heavy metal bioavailability, having an increasing association with pyrite across sediment section.

Intervalos de referência para elementos menores e traço em cabelo humano para a população da cidade do Rio de Janeiro - Brasil

Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of twenty minor and trace elements in hair samples from an urban population group (N = 1775), aiming at the establishment of reliable hair reference intervals. Statistical evaluation of the data with respect to age, sex and anatomic region was performed by multivariant analysis and according to recommendations of the International Federation of Clinical Chemistry (IFCC). The results show that mainly age and anatomic region (scalp or pubis) influence significantly the concentration of several elements. Comparison of the here calculated reference intervals with those previously published and used by clinical laboratories for this population showed larger discrepancies and the need for an urgent revision of these data.

Medidas de resistividade elétrica DC em sólidos: como efetuálas corretamente

This paper deals with the most common methods for determining the dc electrical resistivity in solid materials. A brief overview of the fundamental concepts related to the electrical resistivity on materials is introduced. Undoubtedly, the most common and useful procedure to determine the electrical resistivity (rho) is the fourpoint probe method. Some crucial mistakes regarding the experimental procedure and the appropriated correction factors are found in the literature. Thus, the correction factor for the most common sample geometries were gathered and revised in order to provide an easy way to use and apply them.

Avaliando a contaminação por elementos traço em atividades de maricultura: resultados parciais de um estudo de caso realizado na ilha de Santa Catarina, Brasil

Adopting the perspective of human health risk assessment, an interdisciplinary research group has been investigating since 1998 the quality of mussels and oysters cultivated in coastal zones of Santa Catarina State. Evaluation of physico-chemical parameters considered relevant in measuring the degree of eutrophication showed values compatible with the dynamics of well balanced environmental systems. Concentrations of metallic and semi-metallic elements in seawater and bivalves were found to be similar to or lower than those found in Chile, Greenland and the USA. Further investigations focusing upon sediments will provide new and useful data for the management of sustainable mariculture strategies in Brazil.

Variabilidade espacial e sazonal da concentração de elementos-traço em sedimentos do sistema estuarino de Santos-Cubatão (SP)

Multi-element analyses of sediment samples from the Santos-Cubatão Estuarine System were carried out to investigate the spatial and seasonal variability of trace-element concentrations. The study area contains a rich mangrove ecosystem that is a habitat for tens of thousands of resident and migratory birds, some of them endangered globally. Enrichments of metals in fine-grained surface sediments are, in decreasing order, Hg, Mn, La, Ca, Sr, Cd, Zn, Pb, Ba, Cu, Cr, Fe, Nb, Y, Ni and Ga, relative to pre-industrial background levels. The maximum enrichment ranged from 49 (Hg) to 3.1 (Ga). Mercury concentrations were greater in the Cubatão river than in other sites, while the other elements showed greater concentrations in the Morrão river. Concentrations of Mn were significantly greater in winter and autumn than in summer and spring. However, other elements (e.g. Cd and Pb) showed the opposite, with greater concentrations in summer and spring. This study suggests that seasonal changes in physical and chemical conditions may affect the degree of sediment enrichment and therefore make the assessment of contamination difficult. Consequently, these processes need to be considered when assessing water quality and the potential contamination of biota.

Distribuição, fracionamento e mobilidade de elementos traço em sedimentos superficiais

The gold and iron mining activities in the Velhas River yield considerable amounts of suspended solids as well as metals to the hydrological system of the region. The risks were assessed by sequential extraction procedures. They were carried out in sediment samples, aiming to evaluate the presence of Co, Cr, Cu, Ni, Zn and As. Although being at high levels in some parts of the river (e.g. As 527 mg g-1 and Cr 475 mg g-1) they are associated with the residual fraction. Mobility factors were also calculated and show that these species are enriched along the river, e.g. for As 0.02 at the spring and 0.33 at the high course of the river.

Efeitos da poluição atmosférica (litorânea e industrial) em isoladores da rede elétrica da região metropolitana de Salvador

The performances of eight kinds of insulators from electrical distribution lines in Salvador-BA, Brazil, were evaluated considering the chemical and physical local environmental pollution. The parameters that were chosen as characteristic for the insulators' properties were leakage current and partial electrical discharge. A data storage processing system and a communication link to the lab were built for data acquisition. The results show that the main contribution to the poor performance of the insulators is settleable magnetite particulate matter on the insulator in addition to the long term wetness time, t4.

Elementos-traço e sódio em suco de uva: aspectos nutricionais e toxicológicos

Eight trace elements were determined in 20 Brazilian brands of grape juice, distributed over the country. Highest measured concentrations (As: 0.016; Cd: 0.010; Cr: 0.060; Cu: 1.28; Ni: 0.032; Pb: 0.016; Sb: 0.0040 and Zn: 1.44 mg L-1) comply with Brazilian maximal tolerance levels for inorganic contaminants (As: 0.5; Cd: 0.5; Cr: 0.1; Cu: 30; Ni: 3; Pb: 0.4; Sb: 1 and Zn: 25 mg L-1). Determination of arsenic species has shown inorganic As(V) as predominant in most samples. Sodium concentrations, nowadays a major public health concern, were also measured, showing an average of 149 mg L-1. Analytical results for this element were much higher than label concentrations, showing the need for better quality control.

Montagem e caracterização elétrica de pilhas a combustível de óxido sólido (PaCOS)

This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm², according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

Determinação de metais traço no material particulado em suspensão em Ouro Preto, Minas Gerais

The determination of the airborne particulate matter (PTS) mass and trace metals concentrations were performed in three sites in Ouro Preto, MG, Brazil. It was evaluated 288 samples. The legal limit of annual geometric average (60 µg m-3) to PTS concentrations didn't exceed, but the legal limit for 24 h (240 µg m-3) did in three measurements. Seven metals (Al, Cr, Cu, Fe, Mn, Ni, Pb) analysed by ICP-AES were quantified in 18 samples. Aluminum and iron showed the highest concentrations, indicating the contribution of the soil and of one aluminum plant. The high nickel concentration is probably due to vehicular emissions and industrial combustion processes.

Desenvolvimento e avaliação de um porta-amostra de baixo custo para caracterização elétrica de materiais cerâmicos

Conventional sample holder cells used to the electric characterization of ceramics at high temperature consists of an alumina tube and platinum wires and plates using a complex design. The high cost materials used in the conventional sampler holder cell were replaced by stainless steel and conventional ceramics. The sample holder was validated by characterizing yttria-stabilized-zirconia in a temperature range of 25 to 700 ºC. The results do not present variations, discontinuity or unusual noise in the electric signals. Several samples were characterized without maintenance, which demonstrates that the sample holder is electric and mechanic adequate to be used to electrical characterization of ceramics up to 700 ºC.

Determinação do ponto de névoa em surfactantes não iônicos por espectroscopia de impedância elétrica

In this paper, we analyze the use of electrical impedance spectroscopy applied to determination of cloud point. The slope of admittance measured at 100 kHz is reduced to temperature above the critical value which characterizes the phase transition, in a strong indication that this process is activated during the clouding. Additionally to this study we explored the influence of parameters such as additives and temperature on the performance of phase separation of residues (silver nanoparticles) by cloud point extraction. The interaction with salt maximizes the separation of chemical residues in a progressively reduced temperature.