Factorial design for Fe, Cu, Zn, Se and Pb preconcentration optimization with APDC and analysis with a portable X-ray fluorescence system.

Preconcentration of heavy metals in water with ammonium pyrrolydine dithiocarbamate (APDC) is a common practice in analytical chemistry. A literature review on this topic showed that several authors use this precipitation agent, but in different preconcentration conditions, conducting to divergent results. The objective of this work is to use factorial design to optimize the factors involved in the preconcentration process of heavy metals using APDC. Five factors were studied: sample volume, solution pH, APDC concentration, APDC volume and stirring time. The assays were performed by energy dispersive X-ray fluorescence (EDXRF). The values for detection limits within 95% confidence level, in microg L(-1), were: Fe (6.0+/-0.1), Cu (4.0+/-0.1), Zn (2.0+/-0.1), Se (4.0+/-0.1) and Pb (5.0+/-0.1). The value for quantification limit for the five elements was 20 microg L(-1), with 3% deviation. Multi-element standard solutions were prepared. Precipitation procedure was applied in the spiked solutions and the samples were filtered in cellulose ester membrane for quantification measurements. The optimum values obtained were 300 mL of sample solution, pH 4, 1 mL of 2% APDC and 10 min of stirring time. The concentration results obtained for the validation measurements were satisfactory for in situ survey employing a portable instrument.

Isotopic composition as a tool for assessment of origin and dynamic of organic matter in tropical freshwater.

The isotopic composition (13C and 15N) and C:N ratio of sediment and particulate were investigated to assess the origin and dynamic of the organic matter in two river basins located in the Parana State, Brazil. The main sources of organic matter, plants, litter and soil, were analyzed in the study. This study was carried out during the dry and wet seasons. Although organic matter contribution for the particulate material has been mixed, the main contribution in the two seasons for both rivers was autochthonous characterized by delta13C and C:N ratio values ranging from -31.0 to -21.8 per thousand and from 5.1 to 11.4, respectively. The soil with delta13C values ranging from -25.9 to -20.6 per thousand, and C:N ratio from 10.2 to 15.8, was the main carbon source for the river sediment for the two tributaries in the wet and dry seasons. The sediment delta15N values for both the rivers in the wet season showed an 15N enrichment trend in most of studied sites when compared to the dry season values, suggesting major input of nutrients as dissolved organic nitrogen and sewage nitrate. In the dry season, 14N enriched compounds, could have been used by phytoplankton, causing 15N enrichment. The isotope and C:N ratio data clearly showed that the agricultural activity has been influencing the origin and dynamic of organic matter in the two rivers, with potential biochemical consequences for the lower basin of the major Tibagi river.