A extração no ponto nuvem (CPE) foi realizada em duas etapas seqüenciais para a determinação de elementos traço em soro humano, sangue animal e dieta alimentar por espectrometria de massas com fonte de plasma indutivamente acoplado. A primeira CPE foi realizada adicionando dietil-ditiofosfato, Triton ® X-114 seguida de aquecimento a 40 °C, centrifugação e esfriamento a 0 °C. A fase rica em surfactante foi separada para determinar Cd, Pb e Cu pela técnica de quantificação por diluição isotópica. As medidas das razões isotópicas foram caracterizadas por RSD < 0.7%. O pH da solução empobrecida em surfactantante foi ajustado entre 4 e 5 antes da adição de 4-(2-pirilidazo)resorcinol, Triton ® X-114 e seguiram-se os procedimentos para atingir o ponto nuvem. Na segunda fase rica em surfactante extraída foram quantificados Co e Ni pelo método de adições de padrão com RSD < 2%. Recuperações entre 85 a 96% foram obtidas para todos os elementos. A exatidão foi aferida pela análise de materiais de referência com valores recomendados e certificados.A two-step sequential cloud point extraction (CPE) of trace elements from small sample volumes of human serum, animal blood, and food diet is proposed to gain analytical information in the analysis by inductively coupled plasma mass spectrometry. The first CPE was attained by adding O,O-diethyldithiophosphate, the non ionic surfactant Triton ® X-114 followed by heating at 40 °C, centrifugation and cooling at 0 °C. The resulting surfactant-rich phase was separated to determine Cd, Pb and Cu by isotope dilution. Isotope ratio measurements presented RSD < 0.7%. The residual surfactant-poor phase solution had the pH adjusted in the range 4 to 5 before the chelating reagent, 4-(2-pyridylazo) resorcinol plus surfactant Triton ® X-114 were added followed by the sequence to attain the CPE. Co and Ni were quantified in the second extracted surfactantrich phases by standard additions method with RSD < 2%. Recoveries from 85 to 96% were obtained for all elements. Analyzing reference materials with certified and recommended values assessed accuracy.Keywords: sequential cloud point extraction, CPE, inductively coupled plasma mass spectrometry, isotope dilution, biological samples, trace elements
IntroductionSurfactant mediated phase separation constitutes the basis for the approach known as cloud point extraction 1 which is a liquid-liquid extraction alternative to that of organic solvents. The main parameter to attain a surfactant monomer agglomeration in a micelle-rich phase is the surfactant concentration at the cloud point temperature. The temperature-concentration phase diagram is specific for each surfactant. 2 The effect of additives such as salts and other surfactants also has to be considered. 1,3 The first application of cloud point extraction for analytical purposes described the micelle aggregation of hydrophobic anionic metal complexes. 2 The ability of surfactant micelles to bind organic compounds separated by CPE was applied for pre-concentration of organic Sequential Cloud Poin...