Fábio Alan Carqueija Amorim

In this work, a miniaturized and sustainable method was developed, based on the fluorimetric reaction with 2,3-diaminonaphthalene (DAN) in an acid medium, for the determination of trace amounts of nitrite in different water samples using a hydrophobic cellulose substrate platform. The innovation consists of the use of a nonwettable cellulose substrate that suspends stable microdroplets, enabling direct measurement of fluorescence on the front surface and mitigating the signal attenuation inherent in traditional hydrophilic paper devices. The cellulose substrate acted both as a solid support for the reaction and as a holder for microdroplet suspension during fluorescence signal acquisition. The method was designed to reduce reagent consumption and waste generation by operating at the microliter scale, using a total reaction volume of 15 μL. The procedure showed great tolerance to the presence of 11 potentially interfering ions, evaluated at concentrations relevant to water samples. The values obtained for the limit of detection were 0.35 μg L–1, the limit of quantification was 1.17 μg L–1. The precision, based on the relative standard deviation (RSD%), was 3.5% (N = 7). The method was successfully applied to various natural waters, with recoveries ranging from 83 to 115%. With an AGREEprep score of 0.77, the procedure significantly reduces reagent consumption and waste, offering an environmentally friendly and low-cost alternative to conventional laboratory assays and providing a simple and sensitive alternative for laboratory-based environmental monitoring of nitrite.

Uma maneira eficaz de se aproveitar os resíduos agrícolas é convertê-los na forma de carvão ativado, o qual possui diversas utilidades, incluindo a purificação de água. Com este objetivo o carvão ativado derivado do caroço de manga (Mangifera indica L.) foi utilizado como adsorvente para a remoção de íons chumbo presentes em soluções aquosas preparadas. A manga foi lavada, seca e teve seu caroço removido para ser preparado como carvão, através da pirolise s 400°C, seguido da ativação com H₂SO₄ 1:1 (v/v) por 12 horas e lavagem do material para liberar os poros do material. O processo de adsorção foi realizado em batelada, introduzindo 30 mL de solução de Pb(II) 50 mg L^-1 e uma determinada massa do carvão em tubos cônicos com tampa, submetidos a agitação orbital. Após o tempo estabelecido o adsorvente foi separado por filtração e o teor de Pb(II) restante no filtrado foi feita a determinação no FAAS. Os estudos mostraram uma remoção de 90% na concentração de Pb(II)^. O adsorvente proposto mostrou-se eficiente para remoção de Pb(II) em soluções aquosas, sendo viável sua aplicação no tratamento de efluentes químicos aquosos.

A method based on ultrasound-assisted emulsification liquid–liquid microextraction (USAEME) for cadmium determination by flame atomic absorption spectrometry (FAAS) was developed in this work. USAEME is based on the use of the mixture of 1,2-dichloroethane and trichloroethylene as an acceptor phase, 2-(2-bromo-5-pyridylazo)-5(diethylamino)phenol (Br-PADAP) as a chelating reagent, and ethanol as a dispersive solvent. The composition of the extraction and dispersive solvents, the volume of the extraction solvent, pH, and the sonication time were optimized using the multivariate strategy. The limits of detection and quantification calculated under optimum conditions were, respectively, 0.39 and 1.33 μg L^−1, and the obtained enrichment factor was 21. The accuracy was tested by the analysis of certified reference materials. The method was applied to cadmium determination in bivalve mollusks, water, and urban wastewater from Pontal Bay, Bahia, Brazil. The proposed method is simple, fast, and efficient, and uses small amounts of organic solvents for the determination of cadmium.

Fish are important sources of protein, making them very significant in the human diet. Although the consumption of this food is beneficial for health, it is essential that the product does not contain inorganic components above the limits recommended by the current legislation. Therefore, a method for determination of elements in fish (Mugil cephalus) samples was optimized. A simplex centroid mixture design with restriction was applied for optimization of the acid digestion of samples in an open system under reflux in order to evaluate the best ratio between the reagents HNO₃, H₂O₂ and H₂O. The results indicated that more intense analyte signals were obtained when a mixture containing 3.6 mL of HNO₃ (65% v/v), 0.4 mL of H₂O₂ (30% v/v) and 6.0 mL of H₂O was used. The accuracy of the method was assessed with a CRM of oyster tissue (NIST 1566b). The method presented relative standard deviations (RSDs) of 3.54%; 3.82%; 4.81% and 3.50% for Zn, Fe, Cu and S, respectively. The detection limits were 0.002 mg kg⁻¹ for Cu and Zn and 0.02 mg kg⁻¹ for Fe and S. The proposed method was applied for the determination of Zn, Fe, Cu and S in fish samples. A Kohonen Self-Organizing Map (KSOM) with K-means implementation was applied to better delimit the boundary between groups and the spatial and temporal influence on how concentrations of the chemical elements were perceived. To verify the separation, the Davies–Bouldin and Silhouette indices were used, obtaining 0.5374 and 0.8541, respectively, indicating satisfactory separation.