Avaliação das condições de precipitação do azul da Prússia sobre pó de grafite visando o desenvolvimento de eletrodos de pasta de carbono para a quantificação de nitrito

An amperometric FIA method for nitrite quantification based on nitrite electroreduction and employing a carbon paste electrode (CPE) chemically modified with iron hexacyanoferrate (HCF) as an amperometric detector was developed. The influence of experimental conditions on the preparation of the electrode materials was evaluated and the materials obtained in each study were used for the development of modified electrodes. The electrochemical sensors were prepared by a fast, simple, and inexpensive procedure, and the long-term performance of the electrodes were quite satisfactory as the stability was maintained over one year. HCF was an effective redox mediator for nitrite electroreduction in acidic media, allowing nitrite detection at +0.2 V vs. Ag/AgClsat, which is a potential free of possible interfering species that are normally present in food and water samples. The electrochemical cell used in the FIA system was similar to a batch injection analysis cell, enabling recirculation of the carrier solution. This is an attractive feature because it allows the use of a high flow rate (6 mL min-1) leading to high sensitivity and analysis speed, while keeping reagent consumption low. The proposed method had a detection limit of 9 μmol L-1 and was successfully employed for nitrite quantification in spiked water and sausage samples. The obtained results were in good agreement with those provided by the spectrophotometric official method. At a 95 % confidence level it was not observed statistical differences neither in nitrite content nor in the precision provided by both methods. The experimental conditions for the synthesis of HCF were optimized and the best electrode material was prepared by mixing FeCl3, K4[Fe(CN)6] and carbon powder subjected to an acid and thermal treatment (400 ºC), followed by ultrasonic agitation at 4 °C. This material was used to construct an electrode with improved analytical performance to reduce nitrite, which presented greater stability compared to HCF film electrodeposited on the EPC, showing that the preparation procedure of the electrode material is an effective strategy for the development of HCF modified electrodes.

Concepções dos professores da educação básica sobre as feiras de ciência

Currently the Science fairs in Brazil have gained great incentive, examples are the regulations that the government has been implementing in education and the financing of public calls for events throughout the national territory. However, even with this incentive, some researchers point out that the scientific fairs and shows are still interpreted as an extemporaneous work by teachers. In order to know the views of basic education teachers about the fairs of Science, proposed to carry out this research. Given this situation, based mediation theory and sociocultural interaction Vygotsky (2001), the theory of instrumentalism Dewey (2002) and the proposed education through research Galiazzi e Moraes (2002), we sought to understand the importance of fair and their benefits as well as the presence in the talks of respondents. In order to analyze the answers of respondents, used to discourse analysis proposed by Eni Orlandi (2009), in which it is observed and is an interpretation of the speech of teachers, considering their interpretation and how to shape their thinking on the research object. In analyzing the results of the survey, it was noted that the teachers interviewed know the importance and objectives of science fairs, however experience difficulties that often does not allow these events to be carried out. In seeking to assist them to minimize these difficulties, it was realized the need for a product to make available guidance on how to develop research projects and assemblies of science fairs, that would provide an education for the research. Thus, resulting from research, was set up a blog and a booklet with texts, articles and report templates.