Rafael de Queiroz Ferreira

Green chemistry provides a framework for redesigning laboratory practices to reduce environmental and safety impacts. In elemental analysis, replacing highly concentrated acids during sample preparation represents an important step toward more-sustainable practices. This study evaluates three didactic case studies based on the use of diluted nitric acid for sediment preparation in analytical and environmental chemistry courses. The participants included secondary technical students in biotechnology (n = 5) and undergraduate chemistry students (n = 43) from the analytical and environmental chemistry course, who were encouraged to critically evaluate conventional procedures that employ concentrated acids. Before classroom implementation, the alternative protocol based on diluted nitric acid was examined to ensure its analytical feasibility. Data were collected through questionnaires, responses completed by students in a structured monitoring form during the activities. The students proposed new alternatives and different approaches to solving problems related to chemical activities. The results demonstrated that this approach enabled students to integrate new knowledge in a critical, creative, and collaborative manner. Furthermore, the didactic strategy provided favorable conditions and essential experiences for training future chemical professionals who are aware of and reflective of their actions.

Objectives: To evaluate the effect of quaternary ammonium compound (QAC) disinfection on the radiographic image quality and chemical integrity of photostimulable phosphor (PSP) plates. Methods: Radiographic image quality was assessed using 2 radiographs of an acrylic-block and 2 radiographs of an aluminum step-wedge acquired before disinfection and after 10 groups with 10 disinfections each. These radiographs were acquired with 2 PSP plates. Brightness, noise, uniformity, contrast, and presence of artifacts were analyzed. Analysis of variance compared gray values between disinfections (α = 0.05). Chemical integrity was assessed using mid-infrared Fourier-transform infrared (FTIR) spectroscopy on the PSP plates tube side, comparing disinfected plates with a non-disinfected control. Metal disk corrosion of the plates was visually inspected. Results: Brightness decreased after 100 disinfections compared with radiographs obtained after 20 disinfections (P = .026). Uniformity increased for all disinfection groups compared with baseline radiographs (P < .001). Radiographs obtained after 100 disinfections showed higher contrast than those acquired after 20 disinfections (P = .005). Noise did not differ (P > .05). Artifacts were observed after 40 disinfections. Fourier-transform infrared analysis showed hydration followed by degradation of the PSP plates after 100 disinfections. Metal disk corrosion occurred after 10 disinfections. Conclusions: Quaternary ammonium compound disinfection affected brightness, uniformity, contrast, produced artifacts, chemical changes, and metal disk corrosion of the PSP plates. Advances in knowledge: This study is the first to assess the impact of disinfecting PSP plates with QAC. Results showed that QAC is not a viable option since its use produced changes in image quality and integrity degradation.

A experimentação contextualizada e problematizada pode fomentar a participação de estudantes do ensino superior em química, além de aprimorar suas habilidades para diversos temas científicos. Este trabalho teve como objetivo desenvolver e aplicar uma atividade experimental problematizada (AEP) baseada na determinação da composição inorgânica majoritária de amostras de mel de abelhas sem ferrão (ASF). Para isso, os estudantes realizaram dois experimentos: teste de chamas e espectrometria de fluorescência de raios X (XRF). A estratégia didática permitiu mobilizar conhecimentos de química inorgânica no contexto dos méis de ASF de forma colaborativa e experimental. Por meio dos indicadores de desenvolvimento de capacidades (IDC), verificou-se que os estudantes mobilizaram habilidades analíticas (RM: 5,8–6,1), práticas (RM: 5,2–6,0) e criativas (RM: 5,1–6,1), evidenciando progresso positivo durante a AEP. Os resultados indicam que a AEP contextualizada contribui para a formação inicial de licenciandos em química, promovendo aprendizagem significativa, desenvolvimento de competências experimentais e integração entre teoria e prática.

Sensitive and selective ochratoxin A (OTA) detection in challenging food matrices (wheat, coffee) is achieved using a cost-effective electrochemical method. The approach utilizes commercial carbon black-graphite screen-printed electrodes (SPE CB-G) enhanced via in situ modification with cetyltrimethylammonium bromide (CTAB). Adsorptive stripping differential pulse voltammetry (AdSDPV) parameters are rigorously optimized using central composite design (CCD), resulting in an optimal deposition time of 205 s and a CTAB concentration of 80 μmol L–1. The method achieves a limit of detection (LOD) of 1.39 ng mL–1 and a limit of quantification (LOQ) of 4.20 ng mL–1 in 0.2 mol L–1 phosphate buffer (pH 7.0) solution. In roasted and ground Arabica coffee (Coffea arabica), the method demonstrates a LOD of 2.70 ng mL–1 and a LOQ of 8.20 ng mL–1, with recovery rates ranging from 94.64 to 109.86%, compliant with key regulatory standards. The presence of CTAB minimizes the matrix effects and ensures reliable and reproducible results. This optimized SPE-based sensor offers a practical and efficient alternative to conventional methods for routine food safety monitoring.

Chemical compounds found in stingless bee honey (SBH) may impact their biological properties; therefore, the establishment of quality control and standardization protocol is essential. This study investigated the chemical composition and antioxidant capacity of SBH produced by Melipona species from the Espírito Santo state (Brazil). A comprehensive characterization of SBH was conducted using Fourier transform mid-infrared (FT-MIR) and nuclear magnetic resonance (NMR) spectroscopy combined with chemometrics tools. A principal component analysis (PCA) model based on FT-MIR signals showed the separation betweenMelipona capixaba and Melipona quadrifasciata. Volatile organic compounds (VOCs) were detected by gas chromatography–mass spectrometry (GC–MS), and the more abundant classes of the classes were carboxylic acids, ketones, aldehydes, and alcohols. Moreover, the PCA model based on partial GC–MS chromatograms allows the grouping into M. capixaba and M. quadrifasciata. Simple phenols such as p-cresol and allyl guaiacol were also identified in SBH. In addition, total phenolic contents (TPC) and total flavonoid contents (TFC) had selective correlations with total antioxidant capacity (TAC). A high Pearson correlation was observed between TPC and ceric reducing antioxidant capacity (CRAC), although there were low correlations among TAC values. Chemometrics combined with phenolics and antioxidant capacity are comprehensive approaches to determine the identity and quality of SBH.