Resumo em Inglês:

Solid-phase microextraction (SPME) via on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBHA) and gas chromatographic determination is considered a technique of choice in many analytical fields for formaldehyde (FA) monitoring. Vapor phase adsorption models of experimentally loaded PFBHA on porous divinylbenzene (DVB) SPME were investigated at 60°C, 35 cm s−1 of air velocity, in a 1-64 min range: with the fiber completely exposed, loaded PFBHA was about 276 μg. Among the models tested, i.e. heat transfer, pseudo-second-order (PSO), Elovich, intra-particle diffusion, extra-particle diffusion and Langmuir, PFBHA adsorption was best fit by the PSO model, showing agreement with experimental data (272 μg). The sampling rate of FA in our conditions, obtained with a permeation tube system, was in agreement with literature (17.4 and 18.3 mL min−1, respectively). Thus, an overall standardization of the sampling phase is presented, leaving the sampling time as the most crucial parameter to be set for future applications.

Resumo em Português:

EFFECTS OF MULTIPLE STRUCTURES AND TORSIONAL ANHARMONICITY FOR THE HYDROGEN ABSTRACTION REACTIONS OF THE THMETHYL BUTANOATE BY H RADICAL. Thermal rate constants for the hydrogen abstraction reactions of the methyl butanoate (MB) by H radical were estimated by applying the multistructural canonical variational theory with small-curvature tunneling (CVT/SCT). The conformational search was performed at MPWB1K/6-31+G(d,p) level of theory and 68 distinguishable conformers for MB and transition state located. The multistructural and torsional anharmonicity effects were corrected through the rovibrational partition functions calculated with the multistructural method based on a coupled torsional potential, MS-T(C). The MS-CVT/SCT thermal rate constants are shown in good concordance with previous combustion models. After fitting the rate constants in a four-parameters equation, the activation energy showed a temperature dependence. The product branching ratios indicate a preference for (Rα) until 500 K. Above this temperature, the contribution of other reactions becomes relevant, especially for (Rβ).

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Methanol present in wastewater from the biodiesel industry can become an atmospheric pollutant and an environmental liability of effluents. This article proposes the development and performance evaluation of two spectroscopic methods, ATR-FTIR and UV-Vis, to identify and quantify methanol in aqueous media. The results of both ways exhibited remarkable linear detection, with a coefficient of determination (r2) > 0.99, wide working range, and relative standard deviation (RSD) < 12%. In the ATR-FTIR method, the detection and quantification limits were 0.064 and 0.128% m V-1, respectively. The UV-Vis method presented lower limits (0.005 and 0.008% m V-1, respectively). Finally, the methods were successfully applied to quickly and sensitively quantify the methanol present in wastewater from biodiesel-washing in a wide concentration range of 0.008-0.641% m V-1. Therefore, we evidenced the feasibility of spectroscopic methods in quality control for identifying and quantifying methanol in aqueous solution, with potential for application in biodiesel production industries and research laboratories. Mainly by ATR-FTIR, in the region of 1300-900 cm-1, as it proved to be more environmentally friendly, faster, and cheaper than the GC-FID method.

Resumo em Português:

WASTE MANAGEMENT IN THE LABORATORIES OF THE UNIVERSITY OF ÉVORA (2007-2021). Waste generated in university laboratories is an important component of university waste management, especially regarding their hazardousness and, also, the cost involved in their forwarding. To make a good management of this waste, it is essential to know the amount generated and the composition. However, this type of information remains scarce. In this work, waste from the laboratories of the University of Évora (Portugal) was surveyed from 2007 to 2021, using existing records. In the 15 years under analysis, the laboratories of the University of Évora generated about 61 tonnes of waste, 88% of which were hazardous and 66% were in the liquid state. In addition, only 3% of this waste was subjected to recovery operations. Moreover, the COVID-19 pandemic contributed to a double increase in hospital waste generated and to a substantially decreased of hazardous liquid waste from the laboratory activity, especially in the first year of the pandemic. In 2021, the second year of the pandemic, there was a “return to normality”, reaching the highest value of waste generated in the laboratories, of 8.6 tonnes. Finally, possible solutions for improving laboratory waste management were also discussed.

Resumo em Inglês:

Stripping analysis was proposed for the voltammetric determination of trace cadmium and lead in local rice wine alcoholic beverages. A bismuth-antimony film electrode (Bi-SbFE) was employed for accumulative preconcentration of trace metals by adding 4 mg L−1 of bismuth and 1 mg L−1 of antimony directly to the sample solution and simultaneously depositing bismuth, antimony, and trace cadmium and lead target metals on the glassy carbon electrode by applying a fixed potential of –1.1 V versus the Ag/AgCl reference electrode for 300 s. Pre-treatment parameters for mineralization of the sample were optimized using the wet acid digestion procedure. Under the optimum conditions, linear calibration graphs ranging 20-200 μg L−1 for Cd and Pb were obtained with detection limits of 0.22 and 0.62 μg L−1 and limits of quantitation 0.73 and 2.07 μg L−1, respectively. Reproducibility values for seven replicate analyses of 50 μg L−1 Cd and Pb were 3.6 and 3.3%, respectively. The developed method was successful for Cd and Pb analyses in Thai rice wine samples and results were validated by the flame atomic absorption spectrometric method. Most samples were not contaminated with Cd and Pb. The amount of Cd contaminants in only one of rice wine sample was still lower than the maximum permitted level of Cd in wine.

Resumo em Português:

THE BEST SUSTAINABLE PRACTICES FOR CHEMICAL WASTE MANAGEMENT IN PUBLIC HIGHER EDUCATION INSTITUTIONS. This work proposes the minimum items for the composition of the best sustainable practices for chemical waste management in higher education institutions (HEI). It was made a bibliographical and documentary review of the Brazilian legislation applicable to the management of chemical waste, with the aim of supporting the elaboration of the best sustainable practices for chemical waste management and propose to assist the technical managers of HEI in the implementation of sustainable and safe management of chemical waste.

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ELECTRONIC TRANSITIONS IN α-FE2O3: THEORETICAL MODELS AND LIMITATIONS. Addressing electronic transitions of hematite (α-Fe2O3) is still considered a topic in active debate, even though it is one of the most widely used compounds from ancient times to the present and also one of the most extensively investigated iron oxides. In this review, a general analysis of the approaches and theoretical models which had been used to explain the electronic absorption spectrum of α-Fe2O3, from the frst proposal presented by Tandon and Gupta (1970) to the more recent results obtained by quantum mechanical calculations, is presented. The analysis of the already published studies is made pointing out the main factors that must be considered to allow a more reliable understanding of the UV-Vis-NIR spectra of α-Fe2O3. Furthermore, controversies in the calculated results are discussed, analysing the suitability of each of the approaches used. Reasons for differences observed in the experimental data reported in the literature are also discussed.

Resumo em Inglês:

Ruminant milk is the lead source of conjugated linoleic acid (CLA) in the human diet, with cis-9, trans-11 CLA being the major among all. Small amounts of trans-10, cis-12 CLA are also found in synthetic supplements. Since both isomers are biologically active with potential health benefits, there is great interest in quantifying them for quality control routines. An alternative method for the analysis of the aforementioned CLAs by fast gas chromatography (GC) is discussed in the present study. The fatty acid methyl ester mixture obtained by alkaline catalysis was injected into a GC equipped with a fame ionization detector (FID) and fitted with an ionic liquid SLB-IL111 chromatographic column (15 m × 0.10 mm × 0.08 µm). Separation was achieved in less than 5 min using a 168 °C isotherm run. Both CLA isomers were quantified by using of single point standard addition statistical approach. Results were contested to those obtained using the recommended 100 m long CP-Sil88 capillary column and none evidence of significant differences was found within 95% confidence interval. Therefore, the proposed method could be valuable to focused regulatory routines of large numbers of samples with greater analytical frequency.

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PRINCIPAL COMPONENT ANALYSIS (PCA) FOR CHEMICAL DATA EVALUATION AND HEAT MAPS PREPARATION: A TUTORIAL. This tutorial shows a step-by-step guide on handling big datasets using principal component analysis (PCA). A dataset of chemical elements’ concentration, emission spectrum, and energy-dispersive X-ray fluorescence (EDXRF) of e-waste were used as examples. Five routines were proposed to apply data processing and PCA calculation focusing data from laser-induced breakdown spectroscopy (LIBS), EDXRF, and heat maps preparation. These routines can be used in various softwares such as MatLab, Octave, R, and Python. PCA was applied in three examples; the first was for concentrations, and the other two were for spectra. An example of heat maps assembling a hyperspectral image of a printed circuit was also described. In addition, a playlist was created on YouTube using the available examples. Therefore, with this tutorial, it may be possible to learn how to deal with a large volume of data by applying PCA. The authors hope to contribute to those researching in the area.

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A COMMENTED TRANSLATION OF ACIDS AND BASES BY GILBERT NEWTON LEWIS. Gilbert Newton Lewis was a distinguished scientist in 20th century History of Chemistry. His work remains relevant for physical chemistry, organic chemistry and coordination chemistry nowadays. Lewis is well known by his propose for chemical bond, based on electron sharing. In 1923 he published two theoretical explanations for acids and bases: the former collaborating with Bronsted and Lowry and the later in his book Valence and the Structure of Atoms and Molecules (1923). In this book, the role of electron pairs in acid base reactions was highlighted decentering explanations from detachment/transfer of hydrogen ion. As a result, more substances could be classified as acids and bases. Also, in the context of organic and coordination chemistry new interpretations for reaction mechanisms showed up. The paper translated here, Acids and Bases (1938), makes a strong empirical description of acids and bases behavior. Lewis designed phenomenological criteria as speed of neutralization reactions, strength of the species acid-base titrations, and its applications as catalysts. In this manuscript, we carried out a commented translation of Lewis Acids and Bases published in 1938, considering it an inspiring source for research and educational applications for Portuguese speaking countries.