Adriane Medeiros Nunes

Determination of mercury in ethanol biofuel by photochemical vapor generation

A new procedure based on exposure of ethanol biofuel samples to UV radiation in the presence of low molecular weight organic acids was developed for the determination of total Hg (inorganic and organometallic species: Hg2+, CH3Hg+ and CH3CH2Hg+) by photochemical vapor generation coupled with atomic absorption spectrometry (photo-CV-AAS). For each species, the optimum conditions for photochemical generation were investigated, including the effects of medium composition, exposure time to the UV radiation and transfer gas flow rate. The accuracy was evaluated by assessing the recoveries of species-specific spikes (91–107%) as well as by assessing recovery from a mixture of all species of the mercury added to the ethanol biofuel samples based on calibration standards prepared in high purity bidistilled ethanol. The limits of detection ranged from 0.05 to 0.09 μg L−1 for all addition and recovery tests, enabling the determination of total Hg. The proposed method is sensitive, simple (no sample pretreatment) and provides a direct approach to the generation of mercury vapor from ethanol biofuel samples while promoting “green” chemistry.

Sample preparation methods for determination of Cd, Pb and Sn in meat samples by GFAAS: use of acid digestion associated with a cold finger apparatus versus solubilization methods

The aim of this study was to present three sample preparation methods for the determination of Cd, Pb and Sn in meat by Graphite Furnace Atomic Absorption Spectrometry (GFAAS): acid digestion, solubilization with tetramethylammonium hydroxide and formic acid. For the digestion with HNO3, a conventional open system with a cold finger was used. This system helped to avoid losses of analytes and reagents by volatilization, permitting to operate at high temperatures applied at a digester block and reducing the digestion time (∼1 h). Solubilizations were performed at room temperature. The slurry was left standing overnight and remained closed until achieving complete solubilization. The temperature program of the graphite furnace was optimized for each element in the different means of preparation samples using a mixture of Pd–Mg. The figures of merit were similar for all sample preparation methods evaluated. The limits of detection obtained for the acid digestion procedure were 0.0006, 0.0164 and 0.0520 μg g−1 for Cd, Pb and Sn, respectively. In order to evaluate the accuracy of the results obtained by the three sample preparation methods, recovery tests for four real meat samples were performed and the recoveries ranged from 93.7 to 109%, supporting the accuracy of the method. Also, different certified reference materials of meat were analyzed and the results obtained were in agreement with the certified value at 95% of confidence (t-test). The best results were obtained by the acid digestion procedure with the cold finger system. This procedure is faster, the system is semi-closed with no significant contamination or loss of analytes by volatilization and it provides a better signal/noise ratio.

Avaliação da mineralização de arroz em sistema de refluxo para a determinação de Cu, Fe, Mn e Zn por FAAS

This paper describes the evaluation of a new method of sample preparation using a cold finger system with continuous water flow for rice analysis by flame atomic absorption spectrometry. The limits of detection for Cu, Fe, Mn and Zn for the proposed method were 0.36, 1.84, 2.12 and 0.16 mg kg-1, respectively. The RSDs were lower than 6.0% for all elements and the CRM analyzed showed values with 95% agreement. The proposed method is simple and safe for the proposed objective and does not require the use of mixtures of acid or special equipment for sample preparation.

Evaluation of sample preparation methods based on alkaline and acid solubilization for the determination of Na and K in meat samples by atomic spectrometric techniques

Foram avaliados dois metodos diferentes de preparo de amostras de carnes baseados na solubilizacao em meios alcalino ou acido. O objetivo deste estudo foi determinar os teores de Na e K apos solubilizacao com hidroxido de tetrametilamonio (TMAH) temperatura ambiente, e com acido formico e aquecimento em bloco de digestao a 50 oC por cerca de 2 h. A solubilizacao alcalina se apresentou como uma metodologia simples e robusta e a melhor alternativa frente aos procedimentos de mineralizacao convencional, permitindo a solubilizacao completa das amostras usando pequenas quantidades de TMAH. O metodo foi validado empregando-se materiais de referencia certificada assim como pela comparacao com metodo de digestao convencional com acido nitrico. Os limites de deteccao obtidos foram de 0,8 e 2,0 mg g-1 para Na e K, respectivamente, e se mostraram adequados para o objetivo das analises.

Determination of Ca, Cu, Fe and Mg in fresh and processed meat treated with tetramethylammonium hydroxide by atomic absorption spectrometry

Um metodo simples para o tratamento de amostras de carne fresca e processada com hidroxido de tetrametilamonio (TMAH) e proposto para a determinacao de Ca, Fe e Mg por espectrometria de absorcao atomica com chama (FAAS) e Cu por espectrometria de absorcao atomica com forno de grafite (GFAAS). A exatidao foi avaliada por comparacao dos resultados usando outros dois procedimentos de preparo de amostra e por analise de materiais de referencia certificados. Nao houve diferenca significativa entre os resultados obtidos, em um nivel de confianca de 95%. Os limites de deteccao para Ca, Cu, Fe e Mg foram 45,0, 0,2, 16,0 e 0,3 µg g -1 , respectivamente. A espectrometria de absorcao atomica de alta resolucao com fonte continua em forno de grafite (HR-CS GFAAS) foi empregada para avaliar as interferencias espectrais na determinacao de Cu. Entretanto, nenhuma interferencia foi encontrada. O metodo proposto e simples, rapido e confiavel para analise de produtos carneos e nao requer o uso de equipamentos especiais nem de acidos 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.

Evaluation of the Use of a Reflux System for Sample Preparation of Xanthan Gum and Subsequent Determination of Ca, Cu, K, Mg, Na and Zn by Atomic Spectrometry Techniques

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.

USE OF MIP OES AND F AAS/AES FOR DETERMINATION OF Ca, K, Na AND Mg IN BRAZILIAN CREAM CHEESE

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.

DETERMINAÇÃO DE Cd E Pb EM AMOSTRAS DE GOMA XANTANA POR GF AAS

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.

New Design of Mini PTFE Vessels for Sample Preparation in Micro Scale: Determination of Cd, K, Mg and Na in Biological Sample

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.

DETERMINAÇÃO DE METAIS POR TÉCNICAS DE ESPECTROMETRIA ATÔMICA EM AMOSTRAS DE CARVÃO MINERAL E CINZAS UTILIZANDO METODOLOGIA DE SUPERFÍCIE DE RESPOSTA

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.