A linguagem escrita nos cursos de graduação em química

There is no question that students majoring in chemistry graduate with underdeveloped writing skills. Many educators have expressed concern about the obvious deficiencies in student writing. This article is designed to aid professors interested in teaching writing skills in their classrooms and laboratories.

Qualidade de medições em química analítica. Estudo de caso: determinação de cádmio por espectrofotometria de absorção atômica com chama

Calculation of uncertainty of results represents the new paradigm in the area of the quality of measurements in laboratories. The guidance on the Expression of Uncertainty in Measurement of the ISO / International Organization for Standardization assumes that the analyst is being asked to give a parameter that characterizes the range of the values that could reasonably be associated with the result of the measurement. In practice, the uncertainty of the analytical result may arise from many possible sources: sampling, sample preparation, matrix effects, equipments, standards and reference materials, among others. This paper suggests a procedure for calculation of uncertainties components of an analytical result due to sample preparation (uncertainty of weights and volumetric equipment) and instrument analytical signal (calibration uncertainty). A numerical example is carefully explained based on measurements obtained for cadmium determination by flame atomic absorption spectrophotometry. Results obtained for components of total uncertainty showed that the main contribution to the analytical result was the calibration procedure.

Relato de uma experiência: recuperação e cadastramento de resíduos dos laboratórios de graduação do Instituto de Química da Universidade Federal do Rio Grande do Sul

An experience aiming to promote a residue interchange and recovery between the teaching laboratories of the Chemistry Institute of this University is described. At the present, several residues interchange have already appeared as advantageous. To make the work easier, a software has been developed in order to keep a record of all the residues generated by the teaching laboratories. Standard labels have been developed for the residues in order to organize them. The software and the label design are described.

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.

O conceito de incerteza aplicado aos processos de medição associados à preparação de uma solução de referência para calibração

The implementation of a quality assurance program in chemical analytical laboratories, that can aid in demonstrate the quality of their results, is an issue of great concern. As a consequence, it is mandatory to give an estimate of the confidence that can be placed on the obtained results. An useful measure of this confidence is the measurement uncertainty and, nowadays, a result without the corresponding uncertainty statement cannot be considered reliable. This paper presents a summary of the most important mechanisms for the evaluation and reporting of the measurement uncertainty. In implementing these principles, it is described the measurement uncertainty estimation associated with the preparation of a uranium elemental reference solution at 2.4 mg.kg-1 from the corresponding certified reference material (in this example at 1003 mg.kg-1).

Utilização de índices r e R obtidos de programas interlaboratoriais para o controle de precisão de método analítico: Determinação de água por Karl Fischer

Values of repeatability (r) and reproducibility (R) are parameters of an analytical method. They are related to the maximum difference between two results of analysis (permissible range) and can be obtained by interlaboratorial comparisons. They represent great importance for the quality control of the results and decisions about the fitness-for-purpose of the method. Water determination in fuel oil samples were performed by 16 laboratories, using the Karl Fischer reaction, during the period from June 1997 to December 1999. Values of r and R were presented. Discussion is made in terms of the main factors that would be contribution to analytical method variabilities and uncertainties of final results.

Construção e aplicação de eletrodo de aço inoxidável UNS S31254 como eletrodo indicador em titulações condutimétricas

UNS S31254 SS electrodes have been built to substitute platinum in conductimetric titrations. The electrodes were tested in both acid-basic titration (chloridric acid and sodium hydroxide) and precipitation titration (sodium chloride and argentum nitrate as titrant). The practical application was exemplified from conductimetric tritations of HF ¾ HNO3 mixtures used in metalurgical industry to passivate stainless steels. The results were compared with those obtained using commercial platinum electrodes. The equivalent volumes obtained were comparable within 3% experimental error. Its application depends on the nature of electrolyte. These results have shown that stainless steel, less expensive than platinum (about three order of magnitude), can substitute platinum electrodes in routine analyses and didactic laboratories.

Um banho termostático de baixo custo (temperatura ambiente até 0ºC)

Thermal baths to decrease ambient temperature are an indispensable tool for most research and teaching laboratories, especially those in tropical or equatorial regions. A simple and inexpensive thermal bath has been developed based on a scratched compressor. It has three possible setups for cooling: sample immersed into the bath, sample flowing through the bath, and cooling liquid flowing in a jacket around the sample. It has been tested for 40 months. The temperature ranges from room temperature to 0 °C, when using water. The repeatability is better than 3% and the precision varies from 0.5% to 2%.

A extração de cafeína em bebidas estimulantes: uma nova abordagem para um experimento clássico em química orgânica

Caffeine extraction procedures from water soluble and water insoluble materials for preparing stimulating beverages are described. Water soluble materials used were instant tea and coffee and water insoluble materials were, among others, guaraná powder and maté leaves. The extraction of caffeine from water soluble materials, especially instant tea, is more suitable for an organic chemistry teaching laboratory than the classic experiment using tea leaves, due to the economy of time and a larger amount of extracted caffeine. The procedure is time-saving and requires only a four-hour period. The experiments illustrate the extraction process as used in undergraduate organic chemistry laboratories.

Design and physicochemical stability studies of paediatric oral formulations of sildenafil

Personalized medicine is a challenging research area in paediatric treatments. Elaborating new paediatric formulations when no commercial forms are available is a common practice in pharmacy laboratories; among these, oral liquid formulations are the most common. But due to the lack of specialized equipment, frequently studies to assure the efficiency and safety of the final medicine cannot be carried out. Thus the purpose of this work was the development, characterization and stability evaluation of two oral formulations of sildenafil for the treatment of neonatal persistent pulmonary hypertension. After the establishment of a standard operating procedure (SOP) and elaboration, the physicochemical stability parameters appearance, pH, particle size, rheological behaviour and drug content of formulations were evaluated at three different temperatures for 90 days. Equally, prediction of long term stability, as well as, microbiological stability was performed. Formulations resulted in a suspension and a solution slightly coloured exhibiting fruity odour. Formulation I (suspension) exhibited the best physicochemical properties including Newtonian behaviour and uniformity of API content above 90% to assure an exact dosification process.

Relato de uma experiência pedagógica no ensino de química: formação profissional com responsabilidade ambiental

The toxic heavy metals can not be transformed in other less toxic substances as organic wastes through chemical process. Various chemistry courses at Faculty of Philosophy, Sciences and Humanities (FFCLRP/USP) use heavy metals in their experimental classes. In this context, a course were created: "Heavy Metal Wastes generated in the teaching and research laboratories: disposal or recovery" and has a specific goal to capacitate the students to define the adequate strategy for disposal or recovery of the chemical wastes, in particular heavy metals, through an interdisciplinary approaching. This course was given to 25 students during the second semester of 2000 and 2001. The environmental responsibility desired for the professional and citizen can be promoted.

Avaliação da susceptibilidade magnética usando uma balança analítica

A simple system to measure the magnetic susceptibility of different materials is presented. The system uses an analytical scale with sensitivity on the order of micrograms and a permanent NdBFe magnet, based in the Rankine method. In this apparatus, the sample is placed near to the magnet that is fixed on the scale. Depending on the magnetic properties of the sample, an attractive or repulsive force will appear between the magnet and the magnetizing sample. Measuring this force, registered by the scale as a mass, the magnetic parameters such as: permeability and susceptibility of the sample can be determined. Despite it is simplicity the method is quantitative, precise and easily reproducible in many laboratories, what makes it attractive for teaching experiments.

Hidrogenação de compostos orgânicos utilizando método eletroquímico para geração de hidrogênio in situ: hidrogenação eletrocatalítica

Electrocatalytic hydrogenation (HEC) may be compared to catalytic hydrogenation (HC). The difference between these methods is the hydrogen source: HC needs a hydrogen gas supply; HEC needs a source of protons (solvent) to be reduced at a cathode surface. HEC has presented interesting advances in the last decades due to investigation of the influence of the supporting electrolyte, co-solvent, surfactant, presence of inert gas and the composition of the electrode on the reaction. Several classes of organic compounds have been hydrogenated through HEC: olefins, ketones, aldehydes, aromatics, polyaromatics and nitro-compounds. This paper shows some details about the HEC which may be regarded as a promising technique for the hydrogenation of organic compounds both in industrial processes and in laboratories.

Validação do método de determinação simultânea dos íons brometo e bromato por cromatografia iônica em águas de consumo humano

European Directive (98/83/CE), compulsory after 2008, states that bromate in drinking water must be controlled at levels below 10 mg L-1. Supporting implementation of the Directive, the European Comission has established project SMT4-CT96 2134, in collaboration with various european institutions, aiming at the identification of the interferents to the current analytical method (Ionic Chromatography with Conductimetric Detection - IC/CD), their removal and the automation of pre-treatment and injection steps, as well as the development of alternative methods. EPAL, responsible for the water supply to a great deal of Portuguese regions, has taken steps to meet these requirements. Although not part of such project, this work (the result of a project conducted under a protocol of collaboration between EPAL SA and FCUL - Faculty of Sciences, University of Lisbon), reports on studies of usefulness to laboratories planning to monitor bromate in ozone treated waters, in conditions different from those described in EPA 300.1. Simultaneous determination of bromide is justified by its role as bromate precursor.

Programa de gerenciamento de resíduos dos laboratórios de graduação da Universidade Regional Integrada do Alto Uruguai e das Missões - Campus Erechim

This work presents a proposal for the management of residues from teaching laboratories. The main goals of the proposal are: scale reduction of experiments, reuse of residues as raw materials for new experiments and appropriate treatment and storage of residues. The methodology includes standardized labels for residue classification and registration of experimental classes and their residues in files. The management seemed to be efficient, resulting in a reduction of the amount of reagents utilized and residues generated, and an increase of reutilization of residues. A considerable decrease of needed storage space and suitable methods for correct residue disposal were achieved. We expect that all laboratories, including those exclusively for research activities, become involved, in a near future, in the Residue Management Project of URI - Campus Erechim.