Recebido em 16/4/07; aceito em 26/10/07; publicado na web em 1/9/08 ATOMIC SPECTROMETRY AND THE DETERMINATION OF METALS IN POLYMERIC MATERIALS. Polymeric materials are widely used in the chemical industry and are part of our daily lives. Inorganic species may be added to them as additives, anti-oxidizing agents, stabilizers, plasticizers, colorants and catalysts and may be present in a wide range of concentrations. Their determination demands the development of analytical methods considering different kinds of polymeric materials, their composition and the final use of the material. Although many different analytical techniques may be used, this review emphasizes those based on atomic absorption and emission spectrometry. Solid sampling techniques and digestion methods are described and discussed and compared considering published results.Keywords: polymers; inorganic constituents; polymer dissolution. INTRODUÇÃOOs polímeros constituem um importante grupo de materiais de engenharia pela sua facilidade de produção e variadas aplicações. Esses materiais incluem desde líquidos de baixa viscosidade e borrachas elásticas até sólidos rígidos. 1,2Com a finalidade de melhorar as propriedades físicas dos polímeros, especialmente as mecânicas e térmicas, são adicionados compostos denominados aditivos, que podem ser: estabilizador, plastificante, carga, corante e pigmento, lubrificante, catalisador etc. Muitos destes aditivos são compostos inorgânicos e com o crescente uso dos polímeros, principalmente os plásticos, nas indústrias de alimentos (embalagens) e de brinquedos existe uma necessidade crescente de métodos para determinação de íons de metais, em especial aqueles que podem apresentar caráter tóxico. 3,4 A escolha de uma técnica analítica adequada para a determinação de elementos metálicos em polímeros depende de vários fatores: preparo de amostra, limite de detecção das técnicas disponíveis, precisão, exatidão, faixa de concentração, interferências e tempo de análise. Esses fatores serão discutidos ao longo deste trabalho, que avalia o uso de técnicas espectroanalíticas, baseadas nos fenômenos de absorção e emissão atômica. A espectrometria de absorção atômica com chama (FAAS) ou com atomização eletrotérmica (ETAAS e, especialmente GF AAS, espectrometria de absorção atômica com forno de grafite) e a espectrometria de emissão óptica em plasma com acoplamento indutivo (ICP OES) são técnicas bem estabelecidas e bastante utilizadas em laboratórios de pesquisa, desenvolvimento e prestação de serviços. A técnica de espectrometria de massas com plasma acoplado indutivamente (ICP-MS), a espectrometria de emissão com plasma induzido por laser (LIBS), a fluorescência de Raios-X (XRF) e a aná-lise por ativação com nêutrons (NAA) também são utilizadas, porém em menor escala, devido a diferentes fatores como complexidade da técnica, custo operacional, limite de detecção, etc.A determinação de elementos metálicos em material polimérico só recentemente despertou o interesse da comunidade científica mundial e, no Brasil, poucos gr...
An acid microwave closed vessel digestion method was used for the determination of inorganic contaminants (Sb, As, Pb, Cd, Cr, Co, Cu, Ni and Hg) in polyamide raw materials (pellets) and textiles by inductively coupled plasma optical emission spectrometry (ICP OES). The initial tests were carried out with samples of polyamide pellets, which is the main raw material used to manufacture sport textiles. The recovery factors obtained were 94.4-105.7% with relative standard deviation (RSD) of 0.5-2.2%. The proposed method was evaluated by addition and recovery tests and also using certified reference materials (ERM-BCR680 and ERM-BCR681) showing good accuracy. The residual acidity was about 4% HNO(3) (w/w) and the quantification limits were from 0.1 to 6.6 mg kg(-1). After the development of these parameters for the raw material, the method was applied to textile samples from different sport fabrics obtained from three different brands. The residual carbon after sample digestion was 0.2% (w/w) and the most significant result was obtained for chromium, 901 mg kg(-1), in black fabric. Lixiviation tests using synthetic sweat and temperature were carried out on two black samples, showing that only 0.3% of the initial concentration migrated to the solution.
Neste trabalho estão descritos alguns métodos para a digestão de amostras de emulsão aquosa de acetato de polivinila visando à determinação de As, B, Cd, Cr, Cu, Fe, Hg, Ni, Pb e Sb por espectrometria de emissão óptica em plasma com acoplamento indutivo (ICP OES). Foram estudados métodos clássicos como calcinação, digestão ácida (a baixa temperatura e a alta temperatura) em chapa de aquecimento e também a digestão assistida por microondas (MW). Nas condições otimizadas (MW) obteve-se apenas 0,1% de conteúdo de carbono residual (RCC), recuperações das espécies estudadas entre 100 e 107 %, com RSD entre 0,5 e 2,5 % e limites de quantificação entre 0,003 e 0,29 mg kg -1 Digestion method for the determination of As, B, Cd, Cr, Cu, Fe, Hg, Ni, Pb and Sb by inductively coupled plasma optical emission spectrometry (ICP OES) in samples of polyvinyl acetate water emulsions were developed. A comparison between classical methods like calcination, acid digestion (low temperature and high temperature) on a heating plate and microwave digestion (MW) was made. Under optimum conditions, using the MW procedure, only 0.1% of residual carbon content (RCC) was found as residue and recoveries between 100 and 107%, with RSD between 0.5 and 2.5% and quantification limits between 0.003 and 0.29 mg kg -1 were obtained.
A closed vessel method using a microwave oven was developed for the determination of As, B, Ba, Bi, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, Sn and Sb by Inductively Coupled Argon Plasma Optical Emission Spectrometry (ICP OES). The method was applied to samples of polyvinyl acetate-based glue in water emulsions. Parameters such as wavelength, nebulization pressure and RF power were optimized and the residual acidity after the digestion process was determined. The addition of internal standards was evaluated and the accuracy of the proposed method was verified with addition and recovery experiments and also with certified reference materials, achieving good results. Using a nebulization flow rate of 0.73 L min(-1)and a RF power of 1200 W it was possible to obtain adequate values for limit of detection and limit of quantification as well as recovery values in the range of 80-106%, for all the analytes. The analysis of coloured glue samples (white, black, blue, yellow, red and green), widely used by children, showed no contamination by the elements studied.
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