A new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) prepared via a double-imprinting process was developed for the recognition and preconcentration of Pb(2+) from water samples. The sorbent was characterized by FT-IR, SEM, TGA and textural data. The maximum dynamic sorption capacity of Pb(2+) was 42.04 mg Pb(2+) g(-1) of the double-imprinted polymer. The sorption kinetics data were described by a pseudo-second-order model. The double-imprinted polymer exhibited a higher sorption efficiency of Pb(2+) than the blank polymer (non-imprinted polymer). The preconcentration procedure involved the loading of a Pb(2+) solution at pH 7.25 through 40.0 mg of the double-imprinted polymer packed in a mini-column at 5.0 mL min(-1). The selective efficiency of proposed method for the Pb(2+) preconcentration was assured by competitive sorption using different proportions of Pb(2+)/cations and Pb(2+)/anions. An analytical curve was obtained in the range 0.0-300.0 μg L(-1) (r=0.999) and a limit of detection of 2.46 μg L(-1) was obtained. The preconcentration factor was found to be 21, the consumptive index 0.95 mL and the concentration efficiency 5.25 min(-1). The preconcentration method was successfully applied to the Pb(2+) ions determination in different kinds of water samples with high recovery values (91.3-108.9%).

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A novel poly(methacrylic acid) material (IIP/CTAB) was prepared by a hierarchical double-imprinting process with Ni2+ ion and cationic surfactantcetyltrimethylammonium bromide (CTAB) as templates, and it was employed to adsorb Ni2+ ions from aqueous medium. Other poly(methacrylic acid) materials single-imprinted (IIP/no CTAB) and nonimprinted (NIP/no CTAB) were investigated in adsorption studies. All the synthesized polymers were characterized by FTIR, SEM, and nitrogen adsorption–desorption isotherm. The maximum Ni2+ adsorption capacities of IIP/CTAB and NIP/no CTAB were found to be 33.31 and 18.64 mg g–1, respectively, at pH 7.25. The relative selectivity coefficient (k′) values for Ni2+/Cu2+, Ni2+/Mn+, Ni2+/Co2+ and Ni2+/Pb2+ systems were higher than 1, thus confirming the significant improvement in the selectivity of the polymer. The kinetic data were described very well by the pseudo-second-order model, thereby confirming the chemical nature of the Ni2+ adsorption (chemisorption), whereas the dual-site Langmuir–Freundlich equation provided the best fit to the isotherm data, suggesting the existence of two kinds of adsorption sites (with low and high binding energies) on the polymer surface. The high chemical stability of IIP/CTAB was verified with 300 Ni2+ adsorption–desorption cycles using 1.0 mol L–1 HNO3 as stripping agent.

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, by preconcentrating 12.0 and 24.0 mL of sample, respectively. The method was applied for copper determination in water samples, synthetic saliva, guarana powder, tea samples and soft drinks and the accuracy was assessed by analyzing the certified reference materials Dogfish Liver (DOLT-4) and Lobster Hepatopancreas (TORT-2).Keywords: cloud point preconcentration; copper; DMIT [4,5-dimercapto-1,3-dithyol-2-thionate]. INTRODUÇÃOA extração no ponto nuvem é uma técnica que se baseia no fenômeno de turbidez de uma solução aquosa contendo surfactante acima da concentração micelar crítica, ocasionado pela adição de alguma substância apropriada (sais ou ácidos) ou por alteração de suas propriedades, como temperatura ou pressão. Quando a solução se torna turva diz-se que o surfactante atinge o ponto nuvem, devido ao decréscimo de sua solubilidade no meio aquoso, e a solução se separa em duas fases isotrópicas, sendo uma rica em surfactante e de pequeno volume contendo os compostos extraídos da solução original, e outra, de grande volume contendo pequena quantidade de surfactante, denominada de fase pobre, que deve ser descartada.1,2 Devido à partição líquido-líquido dos compostos na fase rica em agregados micelares, bem como pelo caráter atóxico dos surfactantes e elevados fatores de pré-concentração usualmente obtidos, a técnica de extração no ponto nuvem tem sido bastante empregada na pré-concentração de metais e moléculas orgânicas em detrimento da extração convencional líquido-líquido com solventes orgânicos.3,4 A pré-concentração de íons metálicos no ponto nuvem é comumente realizada na forma de quelato metálico altamente hidrofóbico em meio aquoso, para que o mesmo possa ser retido no interior das estruturas micelares constituídas de cadeias alquílicas.5 Assim, a adoção adequada do ligante e surfactante pode conferir elevada sensibilidade e seletividade ao método de pré-concentração. Métodos espectrométricos de absorção e emissão atômica associados com a etapa de pré-concentração no ponto nuvem são tradicionalmente relatados na literatura, visando a determinação de metais e/ou especiação em amostras de interesse ambiental, alimentício e clínico.6 Cita-se, por exemplo, a determinação de chumbo, cobre e cobalto por espectrometria de absorção atômica em chama (FAAS) em amostras de águas e alimentos após complexação com 1-feniltiossemicarbazida (1-PTSC) em pH 9,0 e pré-concentração no ponto nuvem.7 Em trabalho prévio, 8 os autores desenvolveram um método de pré-concentração no ponto nuvem para determinação de cobre, níquel e cobalto em amostras biológicas, águas naturais e efluentes, solos e amostras de sangue. Neste trabalho foi utilizado o ligante metil-2-piridilcetona (MPKO) cuja reação de complexação ocorreu em pH 10. Dentre outros ligantes utilizados na pré-concentração no ponto nuvem é relatado o uso de 1,2-di-hidroxiantraquinona-

The present study proposes a new method for cloud point preconcentration of Pb 2+ ions based on complex formed with [4,5-dimercapto-1,3-dithyol-2-thionate] and posterior determination by flame atomic absorption spectrometry (FAAS). The preconcentration of Pb 2+ was carried at pH 5.0 under following conditions: time and temperature of batch at 15 min. and 70 o C, respectively, 0.1% (v/v) Triton X-114, 0.003 mol L-1 acetate/acetic acid buffer solution, 1.0 x 10-5 mol L-1 DMIT and 0.5% (m/v) NaCl. Under the best analytical conditions the method provided a limit of detection of 2.85 μg L-1 by preconcentrating 10.0 mL of sample and calibration curve ranging from 0 up to 650 μg L-1 (r = 0.99945). The applicability of proposed method for Pb 2+ determination in natural waters without interferences was checked through addition/recovery tests.