Determinação de Mn e Zn em arroz empregando espectrometria de fluorescência de raios x de energia dispersiva

A simple, fast and inexpensive method was developed to determine essential elements in pellets of rice samples using energy dispersive X-ray fluorescence spectrometry (EDXRF). The accuracy and precision were evaluated using Standard Reference Material (rice flour NIST 1568a), and yielding relative standard deviation below 5%. The paired t-test showed good agreement within 95% confidence values. The detection limits (3σ) of Mn and Zn were 5.1 and 2.2 mg kg-1, respectively. The proposed method proved to be effective when used to determine Mn and Zn in commercial samples of rice without go by stage of decomposition

Talanta

Texto completo: acesso restrito. p.2043–2047Determination of Cr(VI) and Cr(III) in water samples by inductively coupled argon plasma-atomic emission spectrometry (ICP-AES) was performed indirectly employing an on-line system. For this purpose a column with copper shavings was used to reduce Cr(VI) to Cr(III) in acidic media, generating Cu(II) ions in the flow path. This process permitted the evaluation of concentrations in the range of 1–50 mg/l. The protocol allowed a throughput of 100 samples per hour with 10% precision in the concentration

Microchimica Acta

Texto completo: acesso restrito . p. 271-278In the present paper, a preconcentration procedure for manganese determination in seawater samples by flame atomic absorption spectrometry (FAAS) is proposed. It is based on the solid phase extraction of manganese(II) ions as a 4-(2-pyridylazo-resorcinol) (PAR) chelate using activated carbon as sorbent. Optimization of the experimental parameters (pH, activated carbon mass, PAR mass and shaking time) was carried out using a two-level full factorial design (24) and two Doehlert matrix designs. The results of the factorial design, considering the analysis of variance (ANOVA), demonstrate that all these factors and their interactions (pH × PAR mass; pH × activated carbon mass and activated carbon mass × shaking time) are statistically significant. Final optimization was carried out using Doehlert matrix designs considering the results of the factorial design. The validation process evaluated the following parameters: effect of other metal ions, calibration curve, precision, accuracy and robustness. The procedure allows manganese determination in seawater samples with limits of detection (3σ/S) and quantification (10σ/S) of 16 ng L−1 and 53 ng L−1 respectively, and a preconcentration factor of 152. The analysis of certified reference materials demonstrated that the proposed procedure can also be used for manganese determination in biological samples. The procedure is not affected by matrix interferences and could be satisfactorily applied in manganese determination in seawater samples. Manganese determination in surface seawater samples collected from the shore of Salvador city, Brazil, was performed, and concentrations ranging from 0.51 to 2.59 µg L−1 were found

Microchemical Journal

p. 77– 83A method for preconcentration and determination of trace amounts of cadmium in high saline samples is described. It is based on the adsorption of the metal in the activated carbon as complex cadmium(II)–4-(2-pyridylazo-resorcinol) (PAR). The final determination was carried by flame atomic absorption spectrometry (FAAS). The optimization of extraction parameters such as the pH effect, PAR mass, activated carbon mass and shaking time was carried out using a two-level full factorial design (24) and two Doehlert matrix designs. The results of the factorial design, considering the analysis of variance (ANOVA), demonstrate that all these factors are statistically significant, as well as the interactions (pH PAR mass), (pH activated carbon mass) and (activated carbon mass shaking time). The final optimization was carried out using Doehlert matrix designs considering the results of the factorial design. The recoveries were quantitative (96.0–106.7%) for seawater samples spiked with Cd at concentrations of 0.125 and 0.625 Ag lÿ1. A preconcentration factor of 149 was obtained. The effect of diverse metallic ions on the proposed procedure was investigated too. The procedure was used for cadmium determination in surface seawater samples collected in Salvador City, Brazil. The cadmium content in the analysed samples varies from 0.035 to 0.17 Ag lÿ1. These results are agreement with other data reported in the literature

Journal of the Brazilian Chemical Society

p. 846-852.Uma análise de variância de três fatores foi usada para testar a significância do tipo de recipiente, tipo de material e número de replicatas na preparação de amostras de sedimento utilizando um banho ultra-sônico. A extração convencional com HCl 1,0 mol L-1, por 0,5, 4 e 12 h, foi modificada, e o banho ultra-sônico foi aplicado para diminuir o tempo de preparo de amostras. Os metais traço foram medidos por ICP OES. Os melhores resultados foram obtidos com frascos de Teflon® com base plana. Com exceção do Ni, constatou-se que é possível trabalhar no banho de ultrasom em triplicatas, sem comprometer a eficiência e/ou precisão da extração. A eficiência de extração melhorou com o aumento no tempo de sonicação de 1 para 50 min. Para a maioria dos elementos, a extração assistida por radiação ultra-sônica pode reduzir o tempo convencional de extração de 12 h para 50 min ou menos (i.e. 6 min para Pb). A precisão obtida foi comparável aos valores obtidos com a extração convencional. O método proposto é rápido, barato e uma boa alternativa para o levantamento da biodisponibilidade e potencial de mobilidade de metais em sedimentos.São Paul

Journal of the Brazilian Chemical Society

p. 357-363.Os materiais de controle de qualidade (QCM) têm sido usados rotineiramente no trabalho de laboratório, para preencher a lacuna entre a necessidade e disponibilidade de materiais de referência certificados (CRM). Os QCMs possuem custos relativamente baixos, quando comparados aos materiais de referência certificados (CRMs), sendo uma alternativa viável para a implementação de um sistema de controle de qualidade em laboratórios de várias áreas. Este trabalho descreve a produção de um QCM para determinação de metais em sedimentos estuarinos e os resultados de um exercício interlaboratorial. Estudos de homogeneidade e estabilidade foram realizados, e análises de variância foram aplicadas aos dados. As concentrações de Co, Cu, Cr, Ni, Mn, Pb e Zn, dentro e entre recipientes não foram significativamente diferentes. As condições de armazenagem e temperatura não promoveram variação nos resultados. O QCM produzido foi considerado estável e homogêneo, e pode ser utilizado em cartas de controle de qualidade, avaliação da reprodutibilidade e exercícios interlaboratoriais.São Paul

Spectrochimica Acta Part B: Atomic Spectroscopy

Texto completo: acesso restrito. p.592–595This paper proposes an alternative analytical method using electrothermal atomic absorption spectrometry to determine Mo and V in multiphase gasoline emulsions. Samples were prepared by mixing gasoline with a nitric acid solution (0.1% v/v) and two cationic surfactants. The mixture was sonicated, resulting in an emulsive system. Calibration was done by using the aforementioned solutions with added analyte. The detection limits (3σ) of Mo and V were 0.9 μg l− 1 and 4.7 μg l− 1, respectively. The accuracy and precision of the proposed method were evaluated by the analysis of samples spiked with metallo-organic standard and the relative standard deviation obtained ranged from 1.2% to 4.4% in samples spiked with 2 μg l− 1 of each metal. The recovery rates varied from 91.2% to 101.6%. The proposed method was applied to determine Mo and V in samples of gasoline from different gas stations

Analytica Chimica Acta

Texto completo: acesso restrito. p. 79–84The present paper proposes a procedure for separation, preconcentration and determination of trace amounts of molybdenum in geological samples by using atomic emission spectrometry with inductively coupled plasma (ICP-AES). It is based on the complexation of molybdenum(VI) ions by calmagite reagent and its sorption onto activated carbon. Parameters, such as calmagite amount, pH effect on the complexation and sorption, shaking time, mass of activated carbon, desorption of molybdenum from activated carbon, sample volume, effect of other ions and analytical features like precision, accuracy and others were studied. Results demonstrated that the molybdenum(VI) ions, within the pH range from 1.0 to 3.0, as calmagite complex, had been quantitatively sorbed (>90%) onto activated carbon. The shaking time required for sorption of the complex was 15 min by using 50 mg of activated carbon. A successfully desorption of molybdenum for its determination by ICP-AES was achieved by heating the loaded activated carbon with concentrated nitric acid at 120°C and treating the residue with 20% (v/v) nitric acid solution. The effect of some ions in the separation procedure was assessed and iron(III) should be reduced to iron(II) before the complexation, if present in fairly high amounts. This procedure was also efficient for elimination of spectral interference of aluminium in molybdenum determination by ICP-AES. The precision of the preconcentration method, calculated as the relative standard deviation by using 50.0 μg l−1 molybdenum solutions, was 2.21 and 2.89%, regarding repeatability and reproducibility, respectively. The limit of quantification and detection were 2.50 and 0.75 μg l−1, respectively, for a sample volume of 1000 ml. The achieved enrichment factor was 100. Achieved analytical results for (JR-1) Rhyolite, (RGM-1) Rhyolite, (SGR-1) Green river shale and (IPT-73) iron pure standard reference materials were in good agreement, between 92 and 103% of the certified values. The preconcentration procedure proposed was applied also to determine this element in seawater collected from Salvador City, Bahia, Brazil