Artificial neural network employment for element determination in Mugil cephalus by ICP OES in Pontal Bay, Brazil.

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.

Rhodnius spp. are differentiated based on the peptide/protein profile by matrix-assisted laser desorption/ionization mass spectrometry and chemometric tools.

Triatominae are hematophagous insects involved in the transmission of Chagas disease. Among the 19 genera of the subfamily, those with the highest epidemiological importance regarding the dissemination of Trypanosoma cruzi are Panstrongylus, Rhodnius, and Triatoma. Of these three genera, Rhodnius presents the greatest difficulties for specific identification. Thus, there is a need to overcome the difficulties in identifying phenotypes of similar species of this genus. In the present study, the MALDI-TOF MS methodology was used to identify 12 Rhodnius species, among the 21 admitted. The MALDI-TOF MS methodology allowed specific characterization through the identification of peptides and proteins, starting from four different methods of extraction: (A) acetonitrile/formic acid (ACN/AF), (B) acetonitrile/trifluoroacetic acid (ACN/TFA), (C) isopropyl/formic acid (IPA/AF), and (D) methanol/formic acid (MeOH/AF), and four types of MALDI-TOF matrices: α-cyano-4-hydroxycinnamic acid (CHCA), sinapic acid (SA), 6-aza-2-thiothymine (ATT), and 2,6-dihydroxyacetophenone (DHAP). The experiments were performed by combining the four solvents and four matrices to select the best MALDI extraction/matrix. The application of the MALDI-TOF MS technique, through the digital mass spectrometry approach combined with chemometric tools, such as partial least squares-discriminant analysis (PLS-DA), was able to discriminate 12 species of Rhodnius genus, which are difficult to identify using morphological characteristics. Thus, in view of the results obtained, the methodology described in the present article can be applied with speed and efficiency for the discrimination of Triatominae species. Graphical Abstract.