An analytical method for the determination of Al, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Na and Zn in breast of conventional, country and Christmas chicken and turkey samples using microwave induced plasma optical emission spectrometry (MIP-OES) technique was developed. Samples were decomposed in a digester block with a reflux system under conditions optimized using a central composite design as it follows: 2 g of sample, in 7.5 mL of HNO3 during 180 min at 160 °C. The accuracy was evaluated by the analysis of standard reference material SRM 1546 meat homogenate (94 to 108%) and also by addition and recovery tests (80 to 121%). The highest concentrations, in mg kg-1, of Al (2.77), Ca (88.3), Cu (1.99), Fe (3.65), K (3236), Mg (292.62) and Na (312.03) were found in the breast of conventional chicken sample. Zinc presented high value in the breast of turkey sample (10.6 mg kg-1). However, the found concentrations were lower than the daily consumption limit established by supervisory agencies and reference limits from Brazilian legislation. Cadmium, Cr and Hg presented values below limit of quantification. In this way, it is evident that chicken breast should be consumed in a complementary way in a healthy diet.

This work presents the development of an analytical method for sample preparation aiming at the K determination in silicate rocks (basalt, monzogranite and shale fines) following ultrasound dissolution and analysis by F AES. Sample preparation method was optimized by using fractional factorial designs. The following optimal conditions were obtained for each silicate rock: 0.1 g of sample mass for any of the three samples, and volumes of HNO3, HCl and HF, respectively, of 2.5, 0.8 and 2.5 mL for basalt; 3.5, 0.8 and 2.5 mL for monzogranite, and 2.5, 1.0 and 2.0 mL for shale fines. Sample dissolution was achieved by using the ultrasound bath at room temperature (25 °C) for 1 hour. The accuracy was evaluated through the analysis of two certified reference materials, for which there was no statistical difference between the certified and the found K concentration values (95% confidence level). The K concentrations determined were: 1.45 ± 0.01 for basalt; 4.19 ± 0.03 for monzogranite and 1.60 ± 0.02 for shale fines. The developed method presented accurate and reliable results for K amounts in silicate rocks and is simple and safe, which are important features for the implementation of a methodology as a routine analysis.

The objective of this study was to evaluate the concentration of Cu, Zn, Cr and Pb in different species of fish collected in the estuarine and limnic regions of the São Gonçalo channel, located in the Patos-Mirim lagoon complex in the coastal plain of Rio Grande do Sul State (Southern Brazil) during 2013 (autumn, winter and spring) and 2014 (summer). Fish samples were decomposed in a digester block with a reflux system under conditions optimized using a central composite design as it follows: 250 mg of fish sample, 5 mL HNO3, 2 mL H2O2 during 2 h at 150 °C. The concentrations obtained ranged from 6.7 to 12.0 mg kg -1 for Cu; 1.8 to 23.6 mg kg -1 for Zn; 37 to 487 µg kg -1 for Pb; and 40 to 1268 µg kg -1 for Cr. The highest concentrations of Cu, Zn and Pb, were observed in fishes collected at locations in the estuarine region and Cr showed high levels, especially in the limnic region. The samples of the species Loricariichthys anus (viola) showed the highest concentrations of all analytes investigated.

This paper presents a study involving the development of a new mini polytetrafluoroethylene (PTFE) vessel project for biological sample preparation in micro scale in closed system with microwave radiation for subsequent determination of Cd, K, Mg and Na by atomic spectrometry techniques. All experiments were carried out in micro quantities of samples (up to 20 mg) and reagents (300 µL of HNO3) for 5 min at 350 W. Certified reference materials of biological samples (bovine muscle and liver) were used to evaluate the accuracy of the proposed system and the results obtained were in agreement with the certified value at 95% of confidence (t -test). Relative standard deviations (RSD) were lower than 8.0% for all elements. The proposed method is not only easy and fast, but it is also based on the use of an inexpensive system for sample digestion.

The influence of the structural and microstructural characteristics of graphitic precursors on the production of graphite oxide (GO) is investigated in the present work. Six different graphitic precursors were used to produce GO following a modified Hummers method, namely: natural graphite, commercial lubricant graphite, milled graphite, graphite flakes, high-purity graphite and graphite recycled from Li-ion batteries. The products were characterized by X-ray diffraction (XRD), thermogravimetry, solid-state 13C nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). 13C NMR spectra revealed the presence of epoxy, hydroxyl, carbonyl and lactol groups in the synthesized GOs. However, the oxidation degree of each product was found to be dependent on the average crystallite size (Lc) and particle size of the graphitic precursors, with the best GO samples being produced from the milled graphite and the graphite recycled from ion-Li batteries. These results were rationalized in terms of the structural and microstructural differences among the graphitic precursors, as revealed by the XRD patterns and SEM images, evidencing the importance of the correct choice of the precursor aiming the achievement of a well-developed structure for the GO product.

In this work, the photochemical vapor generation (PVG) coupled with atomic absorption spectrometry and a pre-concentration step with an Au column was used for the determination of Hg in biological samples and ethanol fuel. PVG with pre-concentration showed an up to 250-fold higher sensitivity compared to the approach without pre-concentration. The accuracy of analysis of biological samples was evaluated using certified reference materials (fish tissues), while for ethanol fuel samples, recovery tests were employed (91%). Analytical curves were linear (R > 0.99) in the studied range of 2.5 to 10 µg L-1 for conventional PVG and 0.2 to 0.5 µg L-1 for PVG with the pre-concentration step. For the last, the limits of detection reached for biological samples and ethanol fuel were 0.02 and 0.01 µg L-1, respectively. The systems presented are simple, sensitive and safe for the control of low Hg concentrations in different samples. However, only the system using pre-concentration with an Au column was capable of obtaining the reproduced signals of Hg in low concentrations of the order of 0.2 µg L-1.

In the first part of this paper, two acid decomposition procedures for the determination of Al, Ca, Fe, Mg, Mn and Zn contents in yerba mate samples by inductively coupled plasma optical emission spectrometry (ICP OES) were compared. Using a reflux system, the samples were treated with a mixture of HNO3 and H2O2 for 3 hours at 220 °C in the digester block. The results from five commercial yerba mate samples were compared with the results obtained from microwave digestion. Good agreement between the procedures at a 95% confidence level was obtained with relative standard deviation (RSD) values lower than 10.0%. The accuracy was evaluated using addition and recovery experiments (80.5 to 112.8%). In the second part, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Pb and Zn concentrations were evaluated in the yerba mate infusion. The results showed that elements such as Na, K, Mg and Zn are easily transferred to the hot water used for the infusion. For Pb and Cd, the concentrations found in the analyzed samples were lower than the values established by Brazilian legislation.

This paper describes the evaluation of a method for determination of Cd and Pb in xanthan gum samples by Graphite Furnace Atomic Absorption Spectrometry (GF AAS) using NH4H2PO4 as the chemical modifier. The sample preparation was performed using a reflux system adapted in the digestion tubes. With this system it was possible to increase the temperature of the digester block above the boiling point of the reaction medium, preventing loss of analyte and excessive evaporation of acids during heating. Samples were digested with HNO3 for 3 h in a digester block at 220 ºC. The limits of detection for Cd and Pb were 2.2 and 33.8 ng g-1, respectively. The RSDs for both analytes were, on average, lower than 5.0% and accuracy was verified by recovery tests, yielding values in the 83-100% range.

A esterificação direta de naftoquinonas mostrou-se uma tarefa difícil. Metodologias mais comuns envolvem a aplicação de cloretos de acila em piridina ou anidridos, entretanto, quando ácidos de cadeia longa são utilizados tais metodologias se mostram ineficientes devido aos baixos rendimentos obtidos. Apresentamos uma nova síntese de ésteres de cadeia longa de juglona baseado na esterificação de Steglich utilizando um ácido de Lewis barato como cocatalisador. Rendimentos obtidos são consideravelmente maiores do que os reportados previamente. Química computacional foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram testados como inibidores de deposição de parafinas em petróleo. Éster palmítico da juglona foi capaz de reduzir 4 ºC na temperatura de início de aparecimento de cristais (WAT) do óleo estudado, representando uma redução de 1,5% m/m de parafinas normais precipitadas.

Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained are considerably better than those found previously. Computational chemistry was used to evaluate the effects of CeCl3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors in crude oil. Palmitic ester of juglone was able to lower 4 ºC on the wax appearance temperature (WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.

This paper describes the evaluation of simple and fast solubilization methods for the determination of Ca, Mg, and K in glycerin samples from biodiesel production by atomic spectrometry. The solubilization in water was compared with two other methods: solubilization in formic acid and solubilization in ethanol. Using solubilization in water, determination of the three analytes was possible; the values of limits of detection for Ca, K, Mg were 0.31, 0.06, and 0.16 mg kg−1, respectively. Because no adequate reference material was available, the accuracy was evaluated by assessing the recoveries tests with both solubilization methods; the evaluation ranged from 90% to 115%, with values of relative standard deviation >8%, indicating good accuracy of the measure. Four crude glycerin samples obtained from biodiesel plants of Rio Grande do Sul were analyzed after treatment with the different methods of solubilization, and the obtained results of Ca, Mg, and K concentration were in agreement with the values obtained from both solubilization methods. Therefore, solubilization in water is concluded to be a simpler, faster, and viable method for sample preparation of glycerin.

Apresenta-se um procedimento alternativo para o preparo das amostras de biodiesel para a determinação elementar por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES), baseado na formação de emulsão da amostra (10% m/v) com ácido fórmico (15% v/v) e Triton X-100 (0,1% m/v). Estas concentrações foram otimizadas e os padrões e amostras emulsionados mostraram-se estáveis por pelo menos 3 h. As condições experimentais (1500 W de potência da radiofrequência e 0,5 L min-1 de vazão do Ar nebulizador) foram otimizadas a partir das recomendadas pelo fabricante do equipamento, com uma solução contendo 10 mg L-1 de todos os analitos, preparada com óleo base nas mesmas condições da emulsão. Os efeitos de matriz foram investigados, observando as inclinações das curvas de adição de analito para diferentes amostras de biodiesel. Os resultados mostraram que a calibração externa com soluções contendo padrões inorgânicos emulsionados pode ser utilizada. Os limites de detecção encontrados (em mg kg-1) foram 0,121; 0,008; 0,006; 0,001; 0,006; 0,071; 0,241 e 0,024 para Ca, Cu, Fe, Mn, Mg, Na, K e Si, respectivamente. A exatidão do procedimento para o Ca, Mg, K e Na foi avaliada por meio da análise de um padrão multielementar de biodiesel B100 (Conostan) e as recuperações variaram entre 91 a 107%. O procedimento proposto usa reagentes com baixa toxicidade e mostrou ser uma alternativa simples e direta de preparação de amostras para determinação de metais em biodiesel por ICP OES com limites de detecção adequados para essas análises.

It is presented an alternative procedure for preparation of biodiesel samples for elemental determination by inductively coupled plasma optical emission spectrometry (ICP OES), based on the sample (10% m/v) emulsion formation with formic acid (15% v/v) and Triton X-100 (0.1% m/v). These concentrations were optimized and the stability of emulsified aqueous standards and samples was found to be of at least 3 h. Experimental conditions (1500 W of RF power and 0.5 L min-1 of Ar nebulizer flow rate) were optimized from those recommended by the equipment manufacturer, with a solution containing 10 mg L-1 of each analyte prepared with mineral oil in the same conditions of the emulsion. Matrix effects were investigated by observing the slopes of analyte addition curves for different biodiesel samples. Results showed that external calibration with inorganic aqueous standard solutions in the emulsion medium should be used. Limits of detection obtained (in mg kg-1) were 0.121, 0.008, 0.006, 0.001, 0.006, 0.071, 0.241 and 0.024 for Ca, Cu, Fe, Mn, Mg, Na, K and Si, respectively. The accuracy of the procedure for Ca, Mg, K and Na was assessed by the analysis of a multi-element standards B100 biodiesel (Conostan) and the recoveries ranged from 91 to 107%. The proposed procedure used low toxicity reagents and showed to be a simple and straightforward alternative of sample preparation for metal determination in biodiesel by ICP OES with limits of detection adequate for those analyses.

Foram avaliados dois métodos diferentes de preparo de amostras de carnes baseados na solubilização em meios alcalino ou ácido. O objetivo deste estudo foi determinar os teores de Na e K após solubilização com hidróxido de tetrametilamônio (TMAH) temperatura ambiente, e com ácido fórmico e aquecimento em bloco de digestão a 50 ºC por cerca de 2 h. A solubilização alcalina se apresentou como uma metodologia simples e robusta e a melhor alternativa frente aos procedimentos de mineralização convencional, permitindo a solubilização completa das amostras usando pequenas quantidades de TMAH. O método foi validado empregando-se materiais de referência certificada assim como pela comparação com método de digestão convencional com ácido nítrico. Os limites de detecção obtidos foram de 0,8 e 2,0 mg g-1 para Na e K, respectivamente, e se mostraram adequados para o objetivo das análises.

Two different sample preparation methods were evaluated for meat samples employing the solubilization in alkaline or acidic media. The aim of this study was to determine Na and K levels after sample solubilization with tetramethylammonium hydroxide (TMAH) at room temperature, and with formic acid and heating in a digester block at 50 ºC for ca. 2 h. The alkaline solubilization showed to be a simple and robust method and the better alternative in relation to the mineralization conventional procedures, allowing the complete solubilization of the samples even when small quantities of TMAH were used. The method was validated by using certified reference material as well as by comparing with samples digested with nitric acid. The limits of detection obtained were 0.8 and 2.0 μg g-1 for Na and K, respectively, and showed to be adequate for the analysis purposes.

Recentemente, a Associação Brasileira de Normas Técnicas (ABNT) lançou uma série de normas, relacionadas com a determinação de Na, K, Mg e Ca em biodiesel, recomendando procedimentos similares àqueles das normas europeias e americanas, mas também introduzindo uma norma alternativa (ABNT NBR 15556), que possibilita a determinação dos 4 elementos usando a técnica de espectrometria de absorção atômica com chama (F AAS). Neste trabalho, apresentam-se os estudos de otimização e validação que dão suporte a essa norma, bem como a comparação do desempenho de um equipamento com fonte de linhas com outro de fonte contínua. Entre os fatores otimizados, os baixos valores de taxa de aspiração e o uso de uma solução de óleo mineral em xileno para o ajuste da viscosidade entre soluções das amostras e de calibração devem ser destacados. Testes de precisão (repetitividade e precisão intermediária) mostraram valores adequados, comprovando a robustez do método, e os limites de detecção estiveram confortavelmente abaixo daqueles propugnados pelas legislações brasileira e internacional. A exatidão foi confirmada por testes de recuperação e pela participação em exercícios interlaboratoriais de proficiência promovidos pela Agência Nacional de Petróleo, Gás Natural e Biocombustíveis (ANP). A determinação dos 4 elementos por F AAS traz evidentes vantagens econômicas ao produtor, uma vez que se trata de um equipamento mais barato na sua aquisição e manutenção.

Recently, ABNT (Brazilian Association of Technical Standards) has presented a set of norms related to the determination of Na, K, Mg and Ca in biodiesel, recommending procedures similar to those of the European and American norms. However, it has also introduced an alternative norm (ABNT NBR 15556) wherein these 4 elements can be determined by flame atomic absorption spectrometry (F AAS). This work presents the studies that have supported this proposal and compares the performance of linear source equipment with a continuous source one in the application of the norm. Among the optimized factors, the low aspiration rate and the use of mineral oil solution in xylene to adjust the viscosity between samples and calibration solutions are highlighted. Precision tests (repeatability and intermediary precision) have shown adequate values, confirming the robustness of the method. Limits of detection were suitably below the legislation limits. The accuracy was confirmed by recovery tests as well as by the participation in interlaboratory proficiency tests promoted by the National Agency on Oil, Natural Gas and Biofuels (ANP, Brazil). The determination of these 4 elements by F AAS brings evident economic advantages to the producer, once F AAS is less expensive to purchase and maintenance.

Um método simples para o tratamento de amostras de carne fresca e processada com hidróxido de tetrametilamônio (TMAH) é proposto para a determinação de Ca, Fe e Mg por espectrometria de absorção atômica com chama (FAAS) e Cu por espectrometria de absorção atômica com forno de grafite (GFAAS). A exatidão foi avaliada por comparação dos resultados usando outros dois procedimentos de preparo de amostra e por análise de materiais de referência certificados. Não houve diferença significativa entre os resultados obtidos, em um nível de confiança de 95%. Os limites de detecção para Ca, Cu, Fe e Mg foram 45,0, 0,2, 16,0 e 0,3 µg g-1, respectivamente. A espectrometria de absorção atômica de alta resolução com fonte contínua em forno de grafite (HR-CS GFAAS) foi empregada para avaliar as interferências espectrais na determinação de Cu. Entretanto, nenhuma interferência foi encontrada. O método proposto é simples, rápido e confiável para análise de produtos cárneos e não requer o uso de equipamentos especiais nem de ácidos fortes no preparo das amostras.

A simple method for treating fresh and processed meat with tetramethylammonium hydroxide (TMAH) is proposed for the determination of Ca, Fe and Mg by flame atomic absorption spectrometry (FAAS) and Cu by graphite furnace atomic absorption spectrometry (GFAAS). The accuracy was evaluated by comparison of the results by using two other sample preparation procedures and by the analysis of certified reference materials. No significant differences between the results were found at the 95% confidence level. Limits of detection for Ca, Cu, Fe and Mg were 45.0, 0.2, 16.0 and 0.3 µg g-1, respectively. High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) was employed to evaluate the spectral interference in the determination of Cu. However, no interference was found. The proposed method is simple, fast and reliable for meat products analysis and does not require especial equipment, neither strong acid for sample preparation.

Um método simples e robusto para a determinação de arsênio em sedimentos por espectrometria de absorção atômica com geração de hidreto (HG-AAS) usando a amostragem em suspensão é proposto. Água régia (5% v/v) e ácido fluorídrico (1% v/v) foram misturados a uma alíquota do sedimento com tamanho de partícula 50 µm e colocados no banho ultra-sônico por 30 min. A suspensão foi deixada em repouso por 48 h para uma extração eficaz do analito para a fase aquosa. O volume final da suspensão foi ajustado com HCl 1 mol L-1. Uma solução de NaBH4 estabilizada com NaOH foi usada como agente redutor. A arsina foi transportada ao tubo T de quartzo aquecido a 900 °C para detecção. Cinco materiais de referência certificados de sedimento foram analisados e as concentrações obtidas foram concordantes com os valores certificados, de acordo com o teste-t para um nível da confiança de 95%, com RSD (desvio padrão relativo) menor que 13%. O limite de detecção (LOD) na amostra foi de 0,6 µg g-1. O procedimento proposto para a determinação de arsênio em sedimentos é preciso, exato e adequado para a análise de rotina de amostras ambientais.

A simple and robust method for the determination of arsenic in sediments by hydride generation atomic absorption spectrometry (HG-AAS) using slurry sampling is proposed. Aqua regia (5% v/v) and hydrofluoric acid (1% v/v) were mixed with an aliquot of the sediment with particle size of 50 µm in an ultrasonic bath for 30 min. The slurry was allowed to stand for 48 h for an effective extraction of the analyte to the aqueous phase. The final volume of the slurry was made up with HCl 1 mol L-1. A NaBH4 solution stabilized with NaOH was used as reducing agent. The arsine was transported to the quartz T-tube heated at 900 °C for detection. Five certified reference materials of sediment were analyzed and the obtained concentrations were in good agreement with the certified values, according to the t-test for a 95% confidence level with RSD (relative standard deviation) lower than 13%. The limit of detection (LOD) in the sample was 0.6 µg g-1. The proposed procedure for arsenic determination in sediment is precise, accurate and adequate for the environmental samples routine analyses.