A method for sulfur determination in diesel fuel employing near infrared spectroscopy, variable selection and multivariate calibration is described. The performances of principal component regression (PCR) and partial least square (PLS) chemometric methods were compared with those shown by multiple linear regression (MLR), performed after variable selection based on the genetic algorithm (GA) or the successive projection algorithm (SPA). Ninety seven diesel samples were divided into three sets (41 for calibration, 30 for internal validation and 26 for external validation), each of them covering the full range of sulfur concentrations (from 0.07 to 0.33% w/w). Transflectance measurements were performed from 850 to 1800 nm. Although principal component analysis identified the presence of three groups, PLS, PCR and MLR provided models whose predicting capabilities were independent of the diesel type. Calibration with PLS and PCR employing all the 454 wavelengths provided root mean square errors of prediction (RMSEP) of 0.036% and 0.043% for the validation set, respectively. The use of GA and SPA for variable selection provided calibration models based on 19 and 9 wavelengths, with a RMSEP of 0.031% (PLS-GA), 0.022% (MLR-SPA) and 0.034% (MLR-GA). As the ASTM 4294 method allows a reproducibility of 0.05%, it can be concluded that a method based on NIR spectroscopy and multivariate calibration can be employed for the determination of sulfur in diesel fuels. Furthermore, the selection of variables can provide more robust calibration models and SPA provided more parsimonious models than GA.

No abstract

No abstract

Os solos de terra preta arqueológica são ricos em matéria orgânica, contêm fragmentos cerâmicos e artefatos líticos e apresentam nutrientes em concentrações mais elevadas do que outros tipos de solos. Com o intuito de contribuir com informações sobre concentrações de micronutrientes disponíveis em solos de terra preta, foram avaliadas através de extrações químicas sequenciais, a distribuição e disponibilidade de Cu, Fe, Mn e Zn em um perfil de terra preta arqueológica no município de Juruti, estado do Pará. As maiores concentrações de Cu, Fe, Mn e Zn no perfil são encontradas na fração residual. Este estudo mostrou que ferro, manganês e zinco são preferencialmente disponíveis a partir das frações, associados aos óxidos de Fe-Mn, variando de 1265,39 a 1818,12 mg kg The archaeological black earth soils are rich in organic matter, contain ceramic fragments and lithics artifacts and feature nutrients in higher concentrations than other types of soils. To contribute information about micronutrient concentrations available in black earth soils, the distribution and availability of Cu, Fe, Mn and Zn in the archaeological black earth profile from the municipal district of Juruti, Pará State, was evaluated through sequential chemical extractions. The largest concentrations of Cu, Fe, Mn and Zn in the profile are found in the residual fraction. This study showed that the iron, manganese and zinc are preferentially available from the fractions associated with Fe-Mn oxides ranging from 1265.39 to 1818.12 mg kg -1 , 0.83 to 48.51 mg kg -1 and 1.92 to 12.05 mg kg -1 respectively, and the copper from organic matter, ranging from 0.13 to 0.45 mg kg -1 .

Groundwater were sampled at 17 sampling locations of five districts of Belém City (Pará State, Brazil) in 2011, with objective of evaluate the quality of groundwater sampled in tubular wells potentially used for human consumption. For all groundwater samples were analyzed seven physicochemical parameters and nine trace elements determined by graphite furnace atomic absorption spectrometry (GF AAS). From these results and to better understand the physical and chemical behavior of these waters, multivariate methods such as principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to conduct a more thorough evaluation of the original data. The physicochemical parameters studied showed that the groundwater sampled in tubular wells from districts of Marco and Sacramenta had the highest total dissolved solids (140.0 to 244.5 mg L-1), electrical conductivity (198.3 to 340.2 µS cm-1) and turbidity (1.75 to 2.75 UNT) values, indicating the influence of anthropogenic activities contamination in the region, mainly related to the discharge of domestic effluents. In groundwater samples were found 10.4 to 460.5 µg L-1 Fe, 2.0 to 35.2 µg L-1 Cu, < LOD (0.08 µg L-1) to 0.68 µg L-1 Cd, < LOD (0.02 µg L-1) to 5.7 µg L-1 Cr, < LOD (0.01 µg L-1) to 2.3 µg L-1 Ni and < LOD (0.10 µg L-1) to 13.5 µg L-1 Pb. Furthermore, PCA explained 85.8% of the total variance, while the HCA confirmed the correlations found in PCA, allowing evaluating the degree of similarity between samples and identifying the districts most prone to groundwater contamination.