Kelly G. Fernandes

Evaluation and application of bismuth as an internal standard for the determination of lead in wines by simultaneous electrothermal atomic absorption spectrometry

A method for the direct determination of Pb in wines by simultaneous multi-element atomic absorption spectrometry (SIMAAS) using a transversely heated graphite atomizer, Zeeman-effect background corrector and internal standardization is proposed. Bismuth was used as an internal standard and Pd(NO3)2 plus Mg(NO3)2 as chemical modifier to stabilize both the analyte and the internal standard. The implementation of two pyrolysis steps avoided any build-up of carbonaceous residues on the graphite platform. All diluted samples (1 + 1 v/v) in 0.2% v/v HNO3 and reference solutions (5.0-50 microg l(-1) Pb in 0.2% v/v HNO3) were spiked with 25 microg l(-1) Bi. For a 20 microl aliquot dispensed into the graphite tube, a good correlation (r = 0.9997) was obtained between the ratio of the analyte signal to the internal standard signal and the analyte concentration of the reference solutions. The electrothermal behaviour of Pb and Bi in red, white and rosé wines were compared. In addition, absorbance variations due to changes in experimental conditions, such as atomizer temperature, integration time, injected sample volume, radiation beam intensity, graphite tube surface, dilution and sample composition, were minimized by using Bi as internal standard. Relative standard deviations of measurements based on integrated absorbance varied from 0.1 to 3.4% and from 0.5 to 7.3% (n = 12) with and without internal standard correction, respectively. Good recoveries (91-104%) for Pb spikes were obtained. The characteristic mass was 45 pg Pb and the limit of detection based on integrated absorbance was 0.9 microg l(-1) Pb. Internal standardization increased the lifetime of the tube by 25%. Direct determinations of Pb in wines with and without internal standardization approaches were in agreement at the 95% confidence level. The repeatability and the tube lifetime were improved when using Bi as internal standard. The improvement in accuracy using an internal standard was only observed when the analytical results were affected by errors.

Determination of vanadium in human hair slurries by electrothermal atomic absorption spectrometry

This work describes an analytical procedure for vanadium determination in human hair slurries by electrothermal AAS using longitudinal heating (LHGA) and transversal heating (THGA) graphite furnace atomizers. The samples were powdered using cryogenic grinding and the hair slurries containing 0.2% (m/v) were prepared in three different media for determination of vanadium: 0.14molL(-1) HNO(3), 0.1% (v/v) Triton X-100 and 0.1% (v/v) water soluble tertiary amines (CFA-C, pH 8). The limits of detection (LOD), limits of quantification (LOQ), and characteristic masses obtained were 0.28, 0.95mugL(-1) and 35pg (LHGA) and 0.34, 1.13mugL(-1) and 78pg (THGA), respectively. The accuracy of the analytical results obtained by the proposed procedure in both equipments was confirmed by a paired t-test at the 95% confidence level and compared with a conventional procedure based on acid digestion.

Determination and fractionation of barium in Brazil nuts

Diversas estrategias para preparo de amostra, determinacao e fracionamento, tais como espectrometria de absorcao atomica com atomizacao eletrotermica em forno de grafite (GF AAS) e espectrometria de emissao optica com plasma acoplado indutivamente com configuracao axial (ICP OES), foram empregadas para o fracionamento de bario em Castanha-do-Para. Esse alimento e amplamente apreciado tanto pelo valor nutricional, quanto pelo sabor agradavel. A analise quimica de Castanha-do-Para nao e trivial devido a matriz complexa. O fracionamento de bario em Castanha-do-Para foi estudado devido a toxicidade desse elemento e a correlacao entre a forma quimica e a absorcao. Os teores totais de bario nas amostras de Castanha-do-Para variaram entre 860 e 2084 mg kg-1. Extracoes sequenciais foram feitas com base na solubilidade em diferentes meios e composicao quimica envolvendo lipidios, proteinas e compostos de baixa massa molecular (LMW). Teores mais elevados de bario foram determinados nas fracoes LMW e insoluvel em agua que variaram entre 778-1606 e 551-1520 mg kg-1, respectivamente. Esses resultados indicaram a indisponibilidade de bario presente nesse alimento ao organismo humano. Baseando-se nos teores de bario e enxofre nas diferentes fracoes e em calculos estequiometricos para as possiveis reacoes envolvidas pode-se inferir que bario se encontra principalmente na forma de BaSO4. Experimentos termogravimetricos tambem confirmaram essa suposicao.

Padronização interna em espectrometria de absorção atômica

This paper describes a review on internal standardization in atomic absorption spectrometry with emphasis to the systematic and random errors in atomic absorption spectrometry and applications of internal standardization in flame atomic absorption spectrometry and electrothermal atomic absorption spectrometry. The rules for selecting an element as internal standard, limitations of the method, and some comments about the application of internal standardization in atomic absorption spectrometry and the future of this compensation strategy are critically discussed.

Spectrophotometric determination of phosphite in fertilizers in a flow injection system with online sample preparation

A flow injection system with online sample preparation is proposed for the determination of phosphite in liquid fertilizers by spectrophotometry. After loop-based injection, phosphite is oxidized by an acidic permanganate solution (1.0 10−2 mol L−1 KMnO4 + 1.0 mol L−1 H2SO4) in a heated reactor (50 °C). The phosphate generated is then determined by the molybdenum blue method. Influence of flow rates, temperature, and concentration and order of addition of reagents, sample volume, and reactor configuration for the blue complex formation on recorded signals were investigated. The flow system was applied to phosphite determination in commercial samples of liquid fertilizers. The proposed system handles about 80 samples per hour [0.05–0.40% (w/v) H3PO3; R = 0,9998), consuming about 80 μL sample, 1 mg KMnO4, 25 mg (NH4)6Mo7O24, and 10 mg ascorbic acid per determination. Results are precise [relative standard deviation ≤ 3.5% for 0.1% (w/v) H3PO3, n = 12] and in agreement with those obtained by gravimetry at 95% confidence level.

Evaluation of the mixtures ammonium phosphate/magnesium nitrate and palladium nitrate/magnesium nitrate as modifiers for simultaneous determination of Cd, Cr, Ni and Pb in mineral water by GFAAS

A method is described for the simultaneous determination of Cd, Cr, Ni and Pb in mineral water samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer (THGA) and a longitudinal Zeeman-effect background correction system. The electrothermal behavior of analytes during pyrolysis and atomization steps was studied without modifier, in presence of 5 mg Pd and 3 mg Mg(NO3)2 and in presence of 50 mg NH4H2PO4 and 3 mg Mg(NO3)2. A volume of 20 mL of a 0.028 mol L-1 HNO3 solution containing 50 mg L-1 Ni and Pb, 10 mg L-1 Cr and 5 mg L-1 Cd was dispensed into the graphite tube at 20 °C. The mixture palladium/magnesium was selected as the optimum modifier. The pyrolysis and atomization temperatures were fixed at 1000 °C and 2300 °C, respectively. The characteristic masses were calculated as 2.2 pg Cd, 10 pg Cr, 42 pg Ni and 66 pg Pb and the lifetime of the graphite tube was around 600 firings. Limits of detection based on integrated absorbance were 0.02 mg L-1 Cd, 0.94 mg L-1 Cr, 0.45 mg L-1 Ni and 0.75 mg L-1 Pb, which exceeded the requirements of Brazilian Food Regulation that establish the maximum permissible level for Cd, Cr, Ni and Pb at 3 mg L-1, 50 mg L-1, 20 mg L-1 and 10 mg L-1, respectively. The recoveries of Cd, Cr, Ni and Pb added to mineral water samples varied within the 93-108%, 96-104%, 87-101% and 98-108% ranges, respectively. Results of analysis of standard reference materials (National Institute of Standards and Technology: 1640-Trace Elements in Natural Water; 1643d-Trace Elements in Water) were in agreement with certified values at the 95% confidence level.

Nutrients in Amazonian Black Earth from Caxiuanã Region

Dispersion of nutrients in Amazonian black earth (ABE) can provide information on human activities of the inhabitants of the Amazon region. Studies on the pH, available phosphorus (P), organic matter (OM) and the exchangeable cations Ca2 + and Mg2 + were performed on soil samples from horizons A1 and A2 over an area with TPA (north-south and east-west) at a site called Ilha de Terra, located in the Conservation Unit Caxiuana National Forest, Melgaco County, Brazil. The results indicated that the OM and Ca2+ are the ones with greater dispersion. Higher correlations were found between OM-Ca-Mg to near the central area. This leads to the inference that the dispersion geochemistry of MO, Ca, Mg and P in archaeological sites with TPA is related to past human activities.

Distribution and availability of copper, iron, manganese and zinc in the archaeological black earth profile from the Amazon region

Os solos de terra preta arqueologica sao ricos em materia orgânica, contem fragmentos cerâmicos e artefatos liticos e apresentam nutrientes em concentracoes mais elevadas do que outros tipos de solos. Com o intuito de contribuir com informacoes sobre concentracoes de micronutrientes disponiveis em solos de terra preta, foram avaliadas atraves de extracoes quimicas sequenciais, a distribuicao e disponibilidade de Cu, Fe, Mn e Zn em um perfil de terra preta arqueologica no municipio de Juruti, estado do Para. As maiores concentracoes de Cu, Fe, Mn e Zn no perfil sao encontradas na fracao residual. Este estudo mostrou que ferro, manganes e zinco sao preferencialmente disponiveis a partir das fracoes, associados aos oxidos de Fe-Mn, variando de 1265,39 a 1818,12 mg kg-1, 0,83 a 48,51 mg kg-1 e 1,92 a 12,05 mg kg-1, respectivamente, e o cobre a partir da materia orgânica, variando de 0,13 a 0,45 mg kg-1.

Avaliação do uso da casca do fruto e das folhas de Caesalpinia ferrea Martius como suplemento nutricional de Fe, Mn e Zn

As plantas medicinais podem ser usadas como fontes alternativas de nutrientes minerais na dieta alimentar. Elementos como ferro, manganes e zinco apresentam biodisponibilidade variavel em funcao de suas formas quimicas (especies) presentes em um alimento. Este trabalho tem como objetivo avaliar o teor e a biodisponibilidade de ferro, manganes e zinco em extratos da casca do fruto e das folhas de Caesalpinia ferrea Martius por Espectrometria de Absorcao Atomica com Chama (FAAS). Os agentes extratores testados foram as solucoes de NaOH 0,05 mol. L-1, tampao Tris-HCl 0,05 mol.L-1 (pH= 8), tampao Tris-HCl 0,05 mol.L-1 (pH = 8) em dodecil sulfato de sodio (SDS) 1% (m/v), HCl 0,05 mol.L-1 e agua quente (60 oC). A casca do fruto e as folhas de Caesalpinia ferrea Martius apresentaram niveis altos de ferro e manganes quando comparados aos de outras plantas medicinais. Os elementos estudados mostraram predominante associacao com compostos de alta e baixa massa molecular, especies soluveis e insoluveis em agua. Dentre os elementos analisados, o ferro apresentou melhor biodisponibilidade na casca do fruto e nas folhas. Manganes e zinco se mostraram mais biodisponivel nas folhas. A casca do fruto e as folhas de Caesalpinia ferrea Martius podem ser uma fonte alternativa de ferro, manganes e zinco na dieta alimentar.

Classificação multivariada de ervas medicinais da Região Amazônica e suas infusões de acordo com sua composição mineral

In this study, the mineral composition of leaves and teas of medicinal plants was evaluated. Ca, Cu, Fe, Mg, Mn e Zn were determined in the samples using flame atomic absorption spectrometry. Principal component analysis was applied to discriminate the samples studied. The samples were divided within the 2 groups according to their mineral composition. Copper and iron were the variables that contributed most to the separation of the samples followed by Ca, Mg, Mn and Zn. The information in the principal component analysis was confirmed by the dendrogram obtained by hierarchical cluster analysis.