Determination of Toxic Elements in Nuts by Inductively Coupled Plasma Mass Spectrometry after Microwave-Induced Combusti
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Determination of Toxic Elements in Nuts by Inductively Coupled Plasma Mass Spectrometry after Microwave-Induced Combustion Aline L. H. Muller & Cristiano C. Muller & Fernanda Lyra & Paola A. Mello & Marcia F. Mesko & Edson I. Muller & Erico M. M. Flores
Received: 13 November 2011 / Accepted: 13 February 2012 # Springer Science+Business Media, LLC 2012
Abstract Microwave-induced combustion (MIC) of nuts in closed vessels was evaluated as a sample preparation method for further determination of As, Cd, and Pb by inductively coupled plasma mass spectrometry (ICP-MS) and Hg by flow injection cold vapor generation coupled to ICP-MS (FI-CVG– ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels was also used for results comparison. Samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 μl of 6 mol l−1 ammonium nitrate as aid for ignition. Sample masses up to 500 mg of hazelnuts, almonds, cashew nuts, Brazil nuts, and walnuts were combusted using 7 mol l−1 HNO3 as absorbing solution. Accuracy was evaluated using certified reference materials and an agreement better than 96% was obtained for all analytes. Using MIC, it was possible to obtain lower limits of detection (LODs) in comparison with those obtained by MW-AD. The LOD obtained using MIC was 3, 2, and 6 ng g−1 for As, Cd, and Pb, respectively. The LOD for Hg by FI-CVG–ICP-MS was 7 ng g−1. Residual carbon content obtained after decomposition by MW-AD and MIC was 20% and lower than 1.5%, respectively, showing the high efficiency of MIC and allowing the determination of toxic elements in samples with high fat content. With the use of MIC up to eight samples could be processed simultaneously and only diluted A. L. H. Muller : C. C. Muller : F. Lyra : P. A. Mello : E. I. Muller : E. M. M. Flores (*) Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, Rio Grande do Sul, Brazil e-mail: [email protected] M. F. Mesko Instituto de Química e Geociências, Universidade Federal de Pelotas, 96010-610 Pelotas, Rio Grande do Sul, Brazil
nitric acid was required minimizing physical interferences, reagent consumption, and waste generation. Keywords Nuts . Toxic elements . ICP-MS . Sample preparation . MIC
Introduction Nuts are considered as one of the most economically available foods in the world, and they are largely consumed due to their flavor and nutritional properties (Momen et al. 2007). They are complex plant foods that are not only rich sources of unsaturated fat but also contain several nonfat constituents as antioxidants, vitamins, minerals, carbohydrates, and other beneficial nutrients (oil content ranges between 36% and 61%) (Plessi et al. 1999). Nuts contain favorable fatty acid profiles and have received particular attention due to protection for coronary heart disease (Kris-Etherton et al. 2001; Jenkins et al. 2002). The mineral composition of nuts is influenced by a number of factors such as climate, soil characteristics (content of organic matter, pH, and clay minera
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