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.

This paper describes the optimization of a sample preparation method using response surface methodology for Al, Cd, Cu, Fe, Mg, Mn, Mo, Na, Ni and Ti determinations in samples of rice husk and rice husk ash by MIP OES. Sample preparation was performed using a reflux system adapted to the digestion tubes. This system allowed the decomposition of the samples without the necessity of replacement of the acids during this step without any loss of volatile elements. The decompositions were performed with 3.6 mL of HNO3 and 1.4 mL of H2SO4 for 205 min in a digester block at 225 ºC. The detection limit for determination of respective analytes in both samples were satisfactory. The RSDs for the analytes were less than 10%. Moreover, the accuracy of the method can be verified by recovery tests, whose values ranged from 82 to 115% for husk samples and 82 to 120% for ashes. The proposed method was presented as a simple, safe and low cost procedure being suitable for sample preparation and subsequent determination of metals by MIP OES.

In this work, two sample preparation procedures for subsequent determination of Na, K, Ca and Mg by techniques of atomic spectrometry in samples of Brazilian cream cheese were evaluated. The determinations were performed on two equipments, F AAS and MIP OES, which presented similar results, being evident the advantages of MIP OES since it is a multielementar technique with low operational cost and high efficiency. The first procedure was carried out by acidic decomposition (HNO3/H2SO4) in a reflux system, and the second used the alkaline solubilization with tetramethylammonium hydroxide. The accuracy was verified by recovery tests and the results were between 80 and 104% for both procedures. A comparison with a reference procedure was also performed and no significant differences have been observed at the 95% confidence level. The evaluated elements were not in accordance with the values indicated on the labels of all products, showing the importance for monitoring these products. The methods of sample preparation proposed showed to be simple, inexpensive, providing accurate and precise results, and are a promising alternative to be used for the quality control of these routine test samples.

This paper describes the method optimization using response surface methodology for Cu, Fe, Zn and Na determinations in coal and ash samples by spectrometry techniques. The sample preparation was performed using a recirculation system adapted in the digestion tubes. This system allowed increase of temperature in the digester block above the boiling point of the reaction medium, avoiding acid evaporation during the heating. The digestions were realized with HNO3 and H2O2 for 1 h in a digester block at 145 °C. The limits of detection for determination of Cu, Fe, Zn and Na in both samples were satisfactory. The RSD for the analytes were lower than 6.0%. Statistical tests showed that results for all analytes do not vary significantly with official method (ASTM), considering a confidence limit of 95%. Besides, the accuracy was verified by recovery tests, whose values ranged from 92.7 to 104.7% in coal, and 98.7 to 115.3% in ash.

The aim of this study was to evaluate the performance of a reflux system adapted in the digestion tubes in sample preparation of xanthan gum for subsequent determination of Ca, Cu, K, Mg, Na and Zn by using spectrometric techniques. Through the proposed method, the samples were digested with HNO3 for 3 h in a digester block at 220 °C. The accuracy of the method was evaluated by comparing the results with another sample preparation method and by using recovery tests, which results vary between 83 and 103%. The efficiency of digestion was assessed and significant results were verified through residual carbon values, which were five times lower compared to conventional acid digestion in open system, with use of HNO3 and HClO4. The proposed methodology is a simple and accurate analytical strategy, which does not require the use of special equipment, neither a mixture of strong oxidizing acid in the sample preparation.

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.

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.

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.