Sample preparation of polymers for halogen determination requires special attention because they are difficult to bring into solution and due to the risk of analyte losses when using acid digestion. A method using microwave-induced combustion (MIC) was optimized for accurate determination of halogens in polymeric parts obtained in waste of electrical and electronic equipment. Results were compared with those by using microwave-assisted extraction (MAE) with alkaline solution and microwave-assisted wet digestion (MAWD) using concentrated nitric acid, which are common choices for sample preparation. In this particular case, the MAE method was not suitable and underestimated results were obtained, showing the necessity for the complete digestion. Even with the use of MAWD under high temperature and pressure, incomplete digestion and high acid content were obtained, which were unsuitable for analysis and resulted in poor recovery. Only by using MIC (diluted ammonia as absorbing solution) acceptable recoveries (95 to 104%) and agreement with certified values for the certified reference materials (CRMs) of polymers were obtained. Thus, a suitable method for all halogen to be determined by ion chromatography (IC) or inductively coupled plasma mass spectrometry (ICP-MS), with the exception of F, was obtained in agreement with the requirements by the Restriction of the Use of Certain Hazardous Substances (RoHS) European directive.

A method for digestion of plastics from waste of electrical and electronic equipment (WEEE) was developed using the microwave-assisted wet digestion in single reaction chamber (MAWD-SRC). The determination of As, Cd, Co, Cr, Cu, Ni, Pb, Sb and Zn by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP OES) was carried out after sample digestion. Mercury was determined by flow-injection cold vapor generation coupled to inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS). Results obtained using MAWD-SRC for sample preparation were compared with those obtained using microwave-assisted wet digestion (MAWD) at high pressure. Acid mixtures (HNO3 or HNO3 + HCl) were evaluated and feasibility for further inorganic contaminants determination by ICP-MS and ICP OES was demonstrated. Sample preparation by MAWD-SRC using HNO3 + HCl mixture resulted in better digestion efficiency in comparison to MAWD. In addition, lower limits of quantification were obtained using MAWD-SRC due to the higher sample mass that can be digested (500 mg). The combination of HNO3 and HCl for digestion showed to be crucial for quantitative recovery of some elements, as Cr and Sb. Agreement with certified values was better than 96%.

A method for digestion of crude oil distillation residues (atmospheric residue, AR and vacuum residue, VR) using microwave-induced combustion (MIC) was developed for simultaneous determination of metals (Ba, Co, Fe, Mg, Mn, Ni and V) and sulfur by inductively coupled plasma optical emission spectrometry (ICP-OES). Samples were wrapped in polyethylene films and combusted using 20 bar of oxygen. Nitric acid solutions were evaluated using 5 min of reflux after combustion. Accuracy was evaluated using certified reference material and comparison with the results obtained by microwave-assisted wet digestion (MAWD). No statistical difference was observed between the certified values and those obtained using MIC as well as between the values obtained using MAWD or MIC. In spite of both methods have been apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using 3 mol L-1 HNO3 as absorbing solution. Furthermore, it is important to notice that using MIC, C content in digests was lower than 10 mg L-1, preventing interferences in ICP-OES. In addition, the simultaneous digestion of eight samples was possible in less than 30 min and without using concentrated acids and/or longer heating times, making the proposed method well-suited for routine analysis.

In this work, a method using microwave-induced combustion (MIC) was optimized in order to obtain a fast, simple, efficient and greener sample preparation method for coal digestion and further determination of sulfur by inductively coupled plasma optical emission spectrometry (ICP OES). Accuracy was evaluated by comparison of the results with those obtained using elemental analysis by UV-fluorescence, microwave-assisted acid digestion with determination by ICP OES and by analysis of certified reference materials of coal. Some parameters that influence MIC method, such as the type and concentration of absorbing solution, the necessity of using a reflux step as well as the cooling time were carefully optimized. No statistical difference was observed for combustion without reflux followed by 5 min of cooling, in comparison to the reference values obtained by elemental analysis. Complete digestion was obtained with this fast and simple method (total digestion program required only 6 min) and using a diluted acid solution for quantitative recovery. The feasibility of digests for sulfur determination as sulfate by ion chromatography (IC) with conductivity detection was also demonstrated. The possibility of determining other elements, commonly monitored in coals, is another advantage of this high-efficiency digestion method (MIC) combined with the multielemental capacity of ICP OES or IC instruments.

A determinação de Al, Cd, Co, Cr, Cu, Mg, Mn e Pb em nanotubos de carbono (CNTs) foi realizada por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta de sólidos (DSS-ET AAS, corretor de fundo com fonte de deutério). Foram avaliados os parâmetros de aquecimento, uso de Pd como modificador químico, possibilidade de calibração com soluções aquosas e massa máxima de amostra. Para comparação dos resultados as amostras foram analisadas por espectrometria de massa com plasma indutivamente acoplado (ICP-MS) e espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) após decomposição por via úmida em sistema de alta pressão assistida por micro-ondas e também por combustão iniciada por micro-ondas. Não foram observadas diferenças significativas entre os resultados obtidos pelo método proposto e pelas outras técnicas. A exatidão também foi avaliada por comparação com resultados de análise por ativação neutrônica (NAA). A calibração foi possível com soluções de referência aquosas. Os sinais de fundo foram sempre inferiores a 0,02 (altura de pico) e o uso de modificador químico não foi necessário. O método proposto possibilitou a determinação de todos os analitos, com menores limites de detecção quando comparados com as outras técnicas.

Metal impurities (Al, Cd, Co, Cr, Cu, Mg, Mn and Pb) were determined in carbon nanotubes (CNTs) by direct solid sampling electrothermal atomic absorption spectrometry (DSS-ET AAS, deuterium lamp background corrector). Parameters as pyrolysis and atomization temperatures, use of Pd as chemical modifier, feasibility of calibration using aqueous standard solutions and maximum sample mass were investigated. Results obtained by the proposed method were compared with those obtained by neutron activation analysis (NAA) and also by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP OES) after high-pressure microwave assisted wet digestion and microwave-induced combustion methods. No significant differences were observed between the results obtained by DSS-ET AAS, ICP-MS and ICP OES after both digestion methods and also by NAA. Calibration was performed using aqueous standards. Background signals were always lower than 0.02 (peak height) and no chemical modifier was used. The proposed method allowed the determination of all elements in CNTs with lower limits of detection in comparison with other techniques.