A method for Cr(VI) speciation in synthetic saliva after releasing from orthodontic brackets, using silica nanoparticles organofunctionalized with (3-aminopropyl)triethoxysilane (APTES) for Cr(III)/Cr(VI) separation and GF AAS determination is proposed. Under the optimized conditions, Cr(VI) speciation was performed using 150 mg of silica organofunctionalized with 2.0% (v v-1) of APTES at pH 8. It was observed different sensitivity when calibrations of GF AAS were performed using Cr(III) or Cr(VI) as standard solutions. Consequently, calibrations using stoichiometric mixtures (Cr(III) + Cr(VI)) were used for total Cr determination and calibration using Cr(VI) was used only for the determination of this specie. The reliability of the proposed silica-APTES separation procedure and GF AAS determination was checked by addition of both species in synthetic saliva. Recoveries ranging from 97 to 110% were obtained. The repeatability, based on the relative standard deviation (RSD) inter days was less than 6%. A corrosion test was carried out on 20 orthodontic brackets from two different models, after immersion in synthetic saliva (pH=6.0) at 37 °C with agitation (125 rpm) for 24 h. It was observed that about 40% of the total chromium released from the analyzed orthodontic brackets was Cr(VI).

The determination of essential (B, Ca, Co, Cu, Cr, Fe, K, Li, Mg, Mn, P, S, Se, Si, V, and Zn), non-essential (Al, Ba, Sn, Sr, and Ti), and potentially toxic (As, Cd, and Pb) elements in graviola pulp by inductively coupled plasma optical emission spectrometry (ICP OES) and graphite furnace atomic absorption spectrometry (GF AAS) is proposed. Samples were digested in a closed-vessel microwave oven. The accuracy of the proposed method was checked by citrus leaves standard reference analysis. Limits of quantification (LOQ) were in the range of 0.039 mg g-1 (Ti) to 22 mg g-1 (K) for ICP OES and 0.011 mg g-1 (Cd) to 0.62 mg g-1 (Se) for GF AAS. According to the recommended dietary reference intake (DRI), graviola pulp can be considered a good source of B, Cu, K, Mg, and Mn. For all analysed samples the concentrations of As, Cd, and Pb were below the LOQ.

Neste trabalho, as distribuições sazonais de Al, Ca, Cu, Fe, K, Mg, Na, Pb, Zn e de íons majoritários (Cl-, PO4(3-), NO3-, SO4(2-), HCOO-, CH3COO-, oxalato, succinato, Na+, NH4+, K+, Mg2+ e Ca2+) foram estudadas na fração PM10 (material particulado menor que 10 mm) na cidade de São Paulo (abril de 2003 a maio de 2004). Os níveis atmosféricos mais elevados foram encontrados para os íons inorgânicos SO4(2-), NO3-, Cl- e PO4(3-), e dentre os íons orgânicos, oxalato e formiato. Os níveis atmosféricos para elementos foram: Fe > Al > Ca > K > at > Mg > Zn > Cu > Pb. As fontes relevantes foram: (i) queima de combustíveis e/ou queima de biomassa (NO3-, HCOO-, C2O4(2-), K+, Mg2+, Ca2+, Fe, Pb, Zn, Al, Ca, K e Mg), (ii) conversão gás-partícula (SO4(2-) e NH4+) e (iii) spray marinho (Cl-, Na+ e Na).

This study deals with the seasonal distribution of Al, Ca, Cu, Fe, K, Mg, Na, Pb and Zn and water soluble ions (Cl-, PO4(3-), NO3-, SO4(2-), HCOO-, CH3COO-, oxalate, succinate, Na+, NH4+, K+, Mg2+ and Ca2+) found in PM10 samples (particulate matter less than 10 mm in diameter) São Paulo City, Brazil, (April 2003-May 2004). Higher atmospheric levels were found for SO4(2-), NO3-, Cl- and PO4(3-) while the main organic anions were oxalate and formate. Atmospheric levels for elements were: Fe > Al > Ca > K > Na > Mg > Zn > Cu > Pb. Some sources were predominant for some species: (i) fuel burning and/or biomass burning (NO3-, HCOO-, C2O4(2-), K+, Mg2+, Ca2+, Fe, Pb, Zn, Al, Ca, K and Mg), (ii) gas-to-particle conversion (SO4(2-) and NH4+) and (iii) sea salt spray (Cl-, Na+ and Na).

Os efeitos do cozimento doméstico na distribuição de proteínas, compostos orgânicos e Fe em feijão (Phaseolus vulgaris L.) foram investigados. Extração seqüencial com diferentes agentes extratores (mistura de metanol e clorofórmio 1:2 v/v, água, NaCl, etanol e NaOH) foi usada para extrair lipídeos, albuminas, globulinas, prolaminas e glutelinas, respectivamente. A determinação de Fe por espectrometria de absorção atômica com forno de grafite (GF AAS), de proteínas pelo método de Bradford e compostos orgânicos por espectrometria de massas por tempo de vôo acoplada à ionização dessortiva de matriz por laser (MALDI-TOF MS) foram feitas nesse trabalho. Altas concentrações de albuminas, globulinas e glutelínas foram encontradas em feijão cru, enquanto que em grãos cozidos, albuminas e glutelínas foram os principais tipos de proteínas. Os espectros de MALDI-TOF MS do feijão cru e cozido revelaram que o cozimento doméstico alterou os pesos moleculares dos compostos orgânicos, uma vez que nos grãos cozidos foram encontrados compostos entre 2 e 3,5 kDa, os quais não estavam presentes no feijão cru. Além disso, no feijão cozido foi também observada a presença de quatro compostos de alto peso molecular (12-16 kDa), sendo que em grãos crus há somente um (ca.15,2 kDa). Nos grãos crus foi possível observar que Fe está principalmente associado a albuminas, globulinas e glutelínas. Para os grãos cozidos, Fe está presente em alta concentração em albuminas e globulinas.

The effects of domestic cooking on proteins, organic compounds and Fe distribution in beans (Phaseolus vulgaris L.) were investigated. Sequential extraction with different extractant solutions (mixture of methanol and chloroform 1:2 v/v, water, 0.5 mol L-1 NaCl, 70% v/v ethanol and 0.5 mol L-1 NaOH) were used for extracting lipids, albumins, globulins, prolamins and glutelins, respectively. Iron determination by graphite furnace atomic absorption spectrometry (GF AAS), proteins by Bradford method and organic compounds by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were carried out in this work. High concentration of albumins, globulins and glutelins were found in raw beans, while in the cooked beans, albumins and glutelins are main proteins types. The MALDI-TOF MS spectra of raw and cooked beans revealed that the domestic cooking altered the molecular weight of the organic compounds, since that in the cooked beans were found compounds between 2 and 3.5 kDa, which were not presented in the raw beans. Besides this, in cooked beans were also observed the presence of four compounds of high molecular weight (12-16 kDa), being that in the raw grains there is only one (ca. 15.2 kDa). In raw grains is possible to observe that Fe is mainly associated to albumins, globulins and glutelins. For cooked grains, Fe is associated to albumins and globulins.

Um procedimento analítico limpo baseado em extração em ponto nuvem é descrito para a determinação de cobre e ferro em materiais vegetais. Após a digestão da amostra em frascos fechados em forno de microondas, empregando mistura oxidante diluída (HNO3 + H2O2), os íons metálicos foram simultaneamente extraídos como complexos hidrofóbicos formados com 1,2-tiazolilazo-2-naftol (TAN) usando Triton X-114 como agente extrator. Íons cobre e ferro foram determinados por espectrometria de absorção atômica com chama (FAAS) e ferro também por espectrofotometria de absorção molecular UV-Vis. Nas medidas por FAAS, os limites de detecção (99,7% de confiança) foram estimados em 1 e 10 μg L-1 para cobre e ferro, respectivamente. Respostas lineares para ambos os analitos foram observadas no intervalo de 25-200 μg L-1. O fator de enriquecimento foi estimado em 30, com extração quantitativa dos complexos avaliada por medidas na solução sobrenadante remanescente após extração. Para a determinação de ferro por espectrofotometria UV-Vis, o limite de detecção (99,7% de confiança) foi estimado em 1 μg L-1, com resposta linear entre 6 e 60 μg L-1. A exatidão do procedimento foi avaliada pela determinação dos metais em materiais de referência certificados e os resultados foram concordantes com os valores certificados no nível de confiança de 95%. O consumo de reagentes foi de 1 mL HNO3, 1,1 mL H2O2, 50 mg Triton X-114 e 150 μg TAN por determinação.

A green analytical procedure exploiting cloud point extraction for determination of copper and iron in plant materials is presented. After sample digestion with a diluted oxidant mixture (HNO3 + H2O2) in a closed vessel microwave oven, metal ions were simultaneously extracted as hydrophobic complexes formed with 1,2-tiazolylazo-2-naphthol (TAN) using Triton X-114 as extracting agent. Copper and iron were determined by flame atomic absorption spectrometry (FAAS) and iron also by UV-Vis spectrophotometry. For FAAS, the detection limits (99.7% confidence level) were estimated as 1 and 10 μg L-1 for copper and iron, respectively. Linear responses for both analytes were observed in the 25-200 μg L-1 range. The enrichment factors were estimated as 30 for both analytes and the extraction was quantitative, as evaluated by measurements in the supernatant solution remaining after extraction. For iron determination by UV-Vis spectrophotometry, the detection limit was estimated as 1 μg L-1, with linear response within 6 and 60 μg L-1. The accuracy of the procedure was evaluated by determination of the metals in certified reference materials and the results agreed with the certified values at the 95% confidence level. In the whole procedure, the reagent consumption was 1 mL HNO3, 1.1 mL H2O2, 50 mg Triton X-114 and 150 μg TAN per determination.

Este trabalho descreve a utilização da análise por redissolução potenciométrica (PSA) sobre eletrodos de filme de mercúrio para a determinação de zinco em água de coco. Foi desenvolvida metodologia para o tratamento de tais amostras por ultra-som, otimizada para a determinação de zinco total por PSA. Um mililitro de amostra foi tratado com 2 mL da mistura 1:1 (v/v) de HCl concentrado e H2O2 (30% m/v) dentro de frascos fechados (4 mL) em um banho ultrassônico seguido de uma etapa de aquecimento em banho-maria por 15 min. Esta metodologia foi otimizada para a determinação de zinco total e foi validada através de análise direta das amostras por espectrometria de absorção atômica com forno de grafite (GFAAS). O limite de detecção obtido pelo método proposto por PSA foi de 1.35 µg L-1 (aplicando 45 s de pré-concentração). Tentativas para quantificar cobre nas mesmas amostras mostraram que o conteúdo deste metal é menor que o limite de detecção de ambas as técnicas, GFAAS e PSA (0.030 µg L-1 depois de 600 s de pré-concentração) com eletrodos de ouro.

This work describes the application of potentiometric stripping analysis (PSA) at mercury film electrodes for zinc determination in coconut water. A sample ultrasound-assisted treatment was developed and optimised for the total zinc determination by PSA. One milliliter of sample was treated with 2 mL of 1:1 (v/v) concentrated HCl and H2O2 (30% m/v) mixture in closed (4 mL) vessels under sonication (in ultrasonic bath), followed by a thermal step (in a boiling bath, for 15 min). This methodology was optimised for total zinc determination and was validated by graphite furnace atomic absorption spectrometry (GFAAS) analysis utilizing the sample without any treatment. The limit of detection obtained by the proposed PSA method was 1.35 µg L-1 (applying 45 s of preconcentration). Attempts to evaluate the amount of copper in the same sample show that the content of this metal is lower than the detection limits of both techniques, GFAAS and PSA (0.030 µg L-1 after 600 s of preconcentration) at gold film electrodes.

Neste trabalho foram determinados Cu, Fe, Mn and Zn em extratos de castanha-do-Pará (Bertholletia excelsa), semente de cupuaçu (Theobroma grandiflorum) e polpa de coco (Cocos nucifera) usando extração sólido-líquido e espectrometria de absorção atômica com atomização eletrotérmica. Foram empregadas diferentes soluções extratoras (mistura de metanol e clorofórmio 1:2 v/v, água, 0,5 mol L-1 NaCl, 70% v/v etanol e 0,5 mol L-1 NaOH) para extração de lipídios, albuminas, globulinas, prolaminas e glutelinas, respectivamente. As concentrações de proteínas encontradas na castanha-do-pará foram maiores do que aquelas encontradas na semente de cupuaçu e polpa de coco. Nas frações lipídicas foram encontradas maiores concentrações de Fe em castanha-do-pará e semente de cupuaçu e Zn em polpa de coco. As determinações dos elementos nos extratos proteicos de castanha-do-pará indicaram que eles estão ligados, preferencialmente, às albuminas, globulinas e glutelinas. O mesmo comportamento não foi observado para semente de cupuaçu e polpa de coco. As concetrações dos elementos variaram para os diferentes extratos proteícos. Em geral, as maiores concentrações de proteínas foram determinadas nos extratos em NaOH. Por outro lado, as menores concentrações de Cu, Fe, Mn e Zn foram encontradas nessa fração.

In this work Cu, Fe, Mn and Zn were determined in extracts of Brazil-nut (Bertholletia excelsa), cupuassu (Theobroma grandiflorum) seeds and coconut (Cocos nucifera) pulp, using solid-liquid extraction and electrothermal atomic absorption spectrometry. Different extractant solutions (mixture of methanol and chloroform 1:2 v/v, water, 0.5 mol L-1 NaCl, 70% v/v ethanol, and 0.5 mol L-1 NaOH) were used for extracting lipids, albumins, globulins, prolamins and glutelins, respectively. The protein concentrations determined in Brazil-nut are higher than those observed for cupuassu and coconut pulp. The analysis of lipid fractions reveals high concentations of Fe in Brazil-nut and cupuassu seed and Zn in coconut pulp. For Brazil-nut, these elements are mainly associated to albumin, globulin and glutelin fractions. The same behaviour was not observed for cupuassu seed and coconut pulp. The element concentrations changed in each protein fraction. In general, high concentrations of proteins were determined in NaOH extractants. On the other hand, low concentration of Cu, Fe, Mn and Zn were found in this fraction.

Neste trabalho são propostos métodos analíticos rápidos para a determinação direta de Al, Cu e Fe em água de coco não processada por espectrometria de absorção atômica com atomização eletrotérmica. Para a determinação de Fe, 100 µL das amostras foram diluídos com 1400 µL de solução 0,1% v/v HNO3. Alíquotas de 10 µL desta solução foram injetadas no tubo de grafite sem a adição de modificador químico. Para as determinações de Al e Cu, as amostras foram minimamente diluídas (1250 µL amostra + 250 µL de solução 0,6% v/v HNO3 + 0,6% m/v Triton X-100) nos frascos do amostrador automático. Nesse caso, alíquotas de 10 µL de uma mistura oxidante (15% v/v H2O2 + 1% v/v HNO3) foram co-injetadas com 15 µL das amostras ou soluções analíticas de referências no tubo de grafite. A mistura oxidante minimizou a formação de resíduos carbonáceos sobre a superfície grafítica e aumentou o tempo de vida do tubo de grafite em 75%, proporcionando mais de 200 ciclos de aquecimento. Os limites de detecção e massas características foram 1,0 mg L-1 e 30 pg para Al, 0,7 µg L-1 e 20 pg para Cu, e 2,0 µg L-1 e 10 pg para Fe, respectivamente. Testes de adição e recuperação foram realizados para estimar a exatidão do método proposto (104 ± 1% para Al, 98 ± 3% para Cu, e 97 ± 1% para Fe).

Fast and reliable methods for the direct determination of Al, Cu and Fe in unprocessed coconut water by electrothermal atomic absorption spectrometry are proposed. For Fe determination, 100 µL of sample were diluted with 1400 µL of 0.1% v/v HNO3. Aliquots of 10 µL of this solution were injected into the graphite tube without any chemical modifier. For Al and Cu determinations, samples were slightly diluted (1250 µL of sample + 250 µL of 0.6% v/v HNO3 + 0.6% m/v Triton X-100) directly into the auto sampler cups. In this case, aliquots of 10 µL of an oxidant mixture (15% v/v H2O2 + 1.0% v/v HNO3) were co-injected with 15 µL of samples or analytical solutions into the graphite tube. The oxidant mixture minimized the carbonaceous residues formation and increased graphite tube lifetime in 75%, allowing up to 200 heating cycles. The detection limits and characteristic masses were 1.0 mg L-1 and 30 pg for Al, 0.7 µg L-1 and 20 pg for Cu, and 2.0 µg L-1 and 10 pg for Fe, respectively. The reliability of the proposed methods was evaluated by addition and recovery tests (104 ± 1% for Al, 98 ± 3% for Cu, and 97 ± 1% for Fe).

The use of an internal standard (IS) in ET AAS can be considered a new trend after the commercial introduction of a simultaneous spectrometer. The evaluation of experimental data to choose the most appropriate IS can be done by comparing correlation graphs. They were used to verify the resemblance among the simultaneous measurements obtained for the analyte(s) and the IS by inductively coupled plasma optical emission spectrometry (ICPOES). The judicious selection of IS by using correlation graphs for determinations by ET AAS can be exploited to improve the precision and accuracy of the analytical results. Therefore, a new approach for studying the use of IS in ET AAS is presented.

Um estudo sistemático para verificar as interferências provocadas por Na+, K+, Ca2+, Mg2+, Cl-, NO3-, SO4(2-) e PO4(3-) nos processos de atomização simultânea de As, Cd, Pb e Se foi realizado utilizando um espectrômetro de absorção atômica com atomização eletrotérmica. A mistura de 250 mg W + 250 mg Rh foi termicamente depositada sobre a plataforma do tubo de grafite e utilizada como modificador químico permanente. O ajuste compromissado dos parâmetros do programa de aquecimento (Tp = 650 ºC e Ta = 2200 ºC) diminuiu a eficiência de decomposição e volatilização térmica de alguns interferentes durante a etapa de pirólise, tornando a atomização simultânea de As, Cd, Pb e Se mais suscetível à interferências. Os ânions Cl- e SO4(2-) causaram as interferências mais severas, enquanto NO3- somente afetou a atomização dos elementos estudados quando presente em elevadas quantidades (> 27 mg). O ânion PO4(3-) provocou uma forte interferência negativa sobre o Se. As interferências causadas pelos cátions Na+, K+, Mg2+, Ca2+ afetaram principalmente o Cd, sendo que os cloretos dessas espécies provocaram interferências mais intensas do que os nitratos.

A systematic study of Na+, K+, Ca2+, Mg2+, Cl-, NO3-, SO4(2-) and PO4(3-) interference on the simultaneous atomization of As, Cd, Pb and Se was carried out using an electrothermal atomic absorption spectrometer. The mixture 250 mg W + 250 mg Rh was thermally deposited on the graphite tube platform and used as permanent chemical modifier. The compromised heating program adjustments (Tp = 650ºC and Ta = 2200ºC) diminished the thermal decomposition and volatilization efficiency of the interfering species during the pyrolysis step. The Cl- and SO4(2-) anions caused the most severe interference, while NO3- only affected the analytes' atomization when high amounts (> 27 mg) were used. The anion PO4(3-) produced a strong negative interference on the Se absorbance signals. The presence of Na+, K+, Ca2+ and Mg2+ prejudiced mainly Cd, and the interference effects of Cl- salts were more pronounced than NO3- salts.

A tubular electrochemical flow-cell for iridium deposition on the inner surface of pyrolytic graphite tube for permanent chemical modification is proposed. A transversal heated graphite tube was used as working electrode, a cylindrical piece of graphite inserted into the graphite tube as auxiliary electrode, and a micro Ag/AgCl(sat) as reference electrode. Iridium solution in 1.0 mol L-1 HCl, flowing at 0.55 mL min-1 for 60 min was used to perform the electrochemical modification. The applied potential to the flow-cell was - 0.700 V vs Ag/AgCl. Scanning electron microscopy images were taken for thermal and electrochemical modified graphite surface in order to evaluate the iridium distribution. Selenium hydride trapping was used to verify the performance of the proposed permanent chemical modifier.

Um sistema de fluxo acoplado a um forno de microondas focalizadas foi utilizado para digestão em linha de amostras de suco de laranja para a determinação de Ca, Cu, Fe, K, Mg, Mn, Na, P e Zn por espectrometria de emissão ótica com plasma indutivamente acoplado. Uma bobina de reação de PTFE (4,0 m de comprimento e 1,6 mm de diâmetro interno) foi posicionada no interior da cavidade de vidro do forno de microondas focalizadas. Alíquotas de 500 miL de amostra e de 1000 miL de reagente (80% v/v HNO3) foram misturadas em uma confluência e conduzidas para a bobina de reação utilizando ar como carregador. O desvio padrão relativo para cinco determinações da mesma amostra usando o método proposto foi inferior a 5,0%. Boas recuperações variando de 91 a 111% foram obtidas para adições de quantidades conhecidas dos elementos de interesse. Os resultados obtidos, utilizando o sistema de digestão proposto, foram concordantes a um nível de confiança de 95% com aqueles obtidos por digestão total. Com este método de digestão foi possível processar 12 amostras h-1, minimizando contaminações, consumo de amostra e reagentes e gerando pequena quantidade de resíduos.

A flow injection system coupled to focused microwave-assisted oven was used for on-line orange juice sample digestion for determination of Ca, Cu, Fe, K, Mg, Mn, Na, P, and Zn by inductively coupled plasma optical emission spectrometry. The reactor coil was a PTFE tube (4.0 m long and 1.6 mm i.d.) positioned into the commercial glass tube of the focused microwave oven. Aliquots of 500 muL of sample and 1000 muL of reagent (80% v/v HNO3) were mixed in a confluence and carried out to the reactor coil by air carrier. The relative standard deviation for five replicates of sample was lower than 5.0%. Good recoveries varying from 91 to 111% were obtained for added concentrations of the interest elements. The results obtained using the proposed digestion system are in agreement with those obtained for total digestion at the 95% confidence level. With this on-line digestion system was possible to carry out 12 samples h-1, minimizing contamination, saving consumption of samples and reagent and low residue generation.

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.

A flow cell assembled on the original geometry of a graphite tube to achieve permanent chemical modifier is proposed. The graphite tube operates as the working electrode. A stainless steel tube, positioned downstream from the working electrode, was used as the auxiliary electrode. The potential value applied on the graphite electrode was measured against a micro reference electrode (Ag/AgCl) inserted into the auxiliary electrode. Palladium solutions in acetate buffer (100 mmol L-1, pH = 4.8), flowing at 0.5 mL min-1 for 60 min was used to perform the electrochemical modification. A mercury solution (1 ng) was used to evaluate the performance of the permanent palladium modifier.

A tungsten coil atomizer was used to investigate the effect of heating programs with constant or variable drying temperatures on the atomization of Al, Cd, Cr and Pb. The variation of the surface temperature in the tungsten coil furnace can occur during each heating step due to the design of the power supply, that may apply constant voltages during a programmed time. For volatile elements (Cd), losses in sensitivity were observed when the program with a variable temperature was used. On the other hand, these effects are negligible for less volatile elements (Al and Cr) and any tested program, in different acidic media, could be used without appreciable changes in sensitivities. The results allow the establishment of proper heating programs for elements with different thermochemical behavior in the tungsten coil atomizer.