Multivariate optimization of simple procedure for determination of Fe and Mg in cassava starch employing slurry sampling and FAAS.

A slurry sampling procedure has been developed for Fe and Mg determination in cassava starch using flame atomic absorption spectrometry. The optimization step was performed using a univariate methodology for 200mg samples and a multivariate methodology, using the Box-Behnken design, for other variables, such as solvent (HNO3:HCl), final concentration (1.7molL-1) and time (26min). This procedure allowed determination of iron and magnesium with detection limits of 1.01 and 3.36mgkg-1, respectively. Precision, expressed as relative standard deviation (%RSD), was of 5.8 and 4.1% (n=10) for Fe (17.8mgkg-1) and Mg (64.5mgkg-1), respectively. Accuracy was confirmed by analysis of a standard reference material for wheat flour (NIST 1567a), which had certified concentrations of 14.1±0.5mgkg-1 for Fe and 40±2.0mgkg-1 for Mg, and the concentrations found using proposed method were 13.7±0.3mgkg-1 for Fe and 40.8±1.5mgkg-1 for Mg. Comparison with concentrations obtained using closed vessel microwave digestion was also realized. The concentrations obtained varied between 7.85 and 17.8mgkg-1 for Fe and 23.7-64.5mgkg-1, for Mg. The simplicity, easily, speed and satisfactory analytical characteristics indicate that the proposed analytical procedure is a good alternative for the determination of Fe and Mg in cassava starch samples.

Genotoxicity Effects in Freshwater Fish from a Brazilian Impacted River.

This study evaluated the incidence of nuclear abnormalities (NA) in four fish species from an impacted river in Northeastern Brazil, characterized by accumulation of heavy metals and organic sewage. Two carnivores (Serrasalmus brandtii and Hoplias malabaricus) and two omnivore species (Oreochromis niloticus and Geophagus brasiliensis), used as food sources by local populations, were collected during the dry and the rainy season along Contas River basin. Nuclear abnormalities (bulbs, binuclei, lobes, micronuclei, notches, and vacuoles) were reported in all fish samples, with high occurrence in S. brandtii and H. malabaricus, species commonly found in local fish markets. This result agrees with previous analyses of accumulation of trace metals in both species, suggesting an association of genotoxic effects and biomagnification. Moreover, native specimens collected near urban areas presented higher frequencies of NA while O. niloticus seems to be more tolerant to environmental contamination. Therefore, effective policies are required to reduce the contamination of Contas River, since pollution by xenobiotics are potential threats to both local biodiversity and human population.

Development of a cloud-point extraction method for copper and nickel determination in food samples.

A new, simple and versatile cloud-point extraction (CPE) methodology has been developed for the separation and preconcentration of copper and nickel. The metals in the initial aqueous solution were complexed with 2-(2'-benzothiazolylazo)-5-(N,N-diethyl)aminophenol (BDAP) and Triton X-114 was added as surfactant. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the copper and nickel contents were measured by flame atomic absorption spectrometry. The variables affecting the cloud-point extraction were optimized using a Box-Behnken design. Under the optimum experimental conditions, enrichment factors of 29 and 25 were achieved for copper and nickel, respectively. The accuracy of the method was evaluated and confirmed by analysis of the followings certified reference materials: Apple Leaves, Spinach Leaves and Tomato Leaves. The limits of detection expressed to solid sample analysis were 0.1 microg g(-1) (Cu) and 0.4 microg g(-1) (Ni). The precision for 10 replicate measurements of 75 microg L(-1) Cu or Ni was 6.4 and 1.0, respectively. The method has been successfully applied to the analysis of food samples.

Multivariate technique for optimization of digestion procedure by focussed microwave system for determination of Mn, Zn and Fe in food samples using FAAS.

This article describes the development by response surface methodology (RSM) of a procedure for iron, zinc and manganese determination by flame atomic absorption spectrometry (FAAS) in food samples after digestion employing a focussed microwave system. A Doehlert matrix was used to find optimal conditions for the procedure through response surface study. Three variables (irradiation power and time and composition of oxidant solution-HNO(3)+H(2)O(2)) were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 12min, 260W and 42% (v/v) for irradiation time, irradiation power and percent of H(2)O(2) in solution, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials and by comparison with a well-established closed vessel microwave dissolution methodology.

Factorial design in the optimization of preconcentration procedure for lead determination by FAAS.

The present paper proposes a preconcentration procedure for lead determination using flame atomic absorption spectrometry (FAAS). It is based on lead(II) ions extraction as brilliant cresyl blue (BCB) complex and its sorption onto Diaion HP-2MG, a methacrylic ester copolymer. The optimization step was carried out using factorial design and the variables studied were pH, shaking time and reagent concentration. In the established experimental conditions, lead can be determinate with a limit of detection of 3.7mugL(-1) lead (N = 20) and a relative standard deviation of 7% for a lead concentration of 100mugL(-1). The accuracy was confirmed by analysis of a certified reference material, the stream sediment furnished by National Research Centre for Certified Reference Materials (NRCCRM), China (GBW 07310). Effect of other ions in the procedure proposed was also studied. The method was applied for lead determination in real samples of water, tea, soil and dust. Tests of addition/recovery in the experiments for lead determination in water samples revealed that the proposed procedure could be applied satisfactorily for analysis of these samples.