Equilibrium Data of the Biphasic System Poly(ethylene oxide) 4000 + Copper Sulfate + Water at (5, 10, 35, and 45) °C Rosana Moura de Oliveira, † Jane Se ´lia dos Reis Coimbra,* ,† Kelly Roberta Francisco, ‡ Luis Antonio Minim, † Luis Henrique Mendes da Silva, ‡ and Edwin Elard Garcia Rojas § Department of Food Technology and Department of Chemistry, Federal University of Vic ¸osa (UFV), P. H. Rolfs Avenue, s/n, Zip Code 36570-000, Vic ¸osa - MG, Brazil, and Department of Agribusiness and Administration Engineering, Federal University Fluminense (UFF), Trabalhadores Av., 420, Zip Code 27225-250, Volta Redonda - RJ, Brazil Phase equilibrium data of an aqueous two-phase system composed of poly(ethylene oxide) 4000 + copper sulfate + water were determined at four temperatures, (5, 10, 35, and 45) °C. The phase separation was entropically driven as can be seen by the small influence of temperature on the phase diagram. However, the rise in temperature increased both the tie line length and the slope of the tie line. Introduction Aqueous two-phase systems (ATPS) are an alternative method for liquid-liquid extraction, which has been used for the extraction and purification of metallic ions 1 and biological materials such as cells and proteins. 2 These systems are formed by adding two water-soluble polymers, or a water-soluble polymer and a component of low molar mass, such as inorganic salts. For industrial applications, polymer + salt systems are preferred to the polymer + polymer systems, since they present lower viscosity and costs. Additionally, the phase separation in such systems occurs relatively fast. Data on the composition and properties of biphasic systems are necessary for the design of extraction processes using ATPS and also for the development of thermodynamic and mass transfer models of extractive processes. Albertsson 3 and Zaslavsky 4 reported phase equilibrium diagrams for different types of ATPS. Nevertheless, experimental data of poly(ethylene oxide) (PEO) + salts systems are still needed. Several authors have focused on the measurement of liquid-liquid equilibrium data of biphasic PEO with different molar masses and salt systems, as presented in Table 1. However, equilibrium data of PEO 4000 + copper sulfate aqueous systems are scarce in the literature. 15 Thus, the aim of this work was to obtain phase equilibrium data of the PEO 4000 + CuSO 4 + water system at (5, 10, 35, and 45) °C. Experimental Section Materials. The analytical grade reagents used were PEO (M ) 4000 g · mol -1 , ISOFAR, Brazil) and copper sulfate (NUCLEAR, Brazil) with a minimum purity of 98 %. The water was deionized (Milli-Q, Millipore, USA; conductivity ) 18.2 MΩ · cm). All chemicals were used without further purification. Experimental Procedure. Stock solutions of PEO 4000 (w ) 0.50) and copper sulfate (w ) 0.28, pH ) 2.37) were used in the experiments. Aqueous biphasic systems with a total mass of 40 g were prepared in 50 cm 3 centrifuge tubes by weighing appropriate quantities of water and stock solutions of PEO 4000 and copper sulfate on an analytical balance with ( 0.1 mg precision (Denver Instruments, M-310, USA). After sufficient mixing, the tubes were centrifuged (Centrifuge Eppendorf 5804, Germany) at 716g for 20 min to accelerate phase separation and then allowed to settle for 24 h at the desired temperature. When equilibrium was achieved, phases were withdrawn using syringes and needles. The top phase was carefully sampled, and a layer of solution of approximately 0.5 cm was left above the interface. The bottom phase was then withdrawn using a syringe with a long needle. Densities of both phases were determined using a 10 mL pycnometer and a balance with readings of ( 0.1 mg, im- mediately after each sample was withdrawn. The concentrations of copper sulfate in the top and bottom phases were determined by copper analysis using atomic absorption spectroscopy (AAS) (Varian Spectr AA-200, Aus- tralia). The concentration of PEO was determined by refractive index measurements at 30 °C using a refractometer (Analytic Jena AG Abbe refractometer 09-2001, Germany). Since the refractive index of phase samples is dependent on PEO and salt concentrations, the PEO concentration was obtained by subtract- ing the salt concentration measured by AAS from the total solution composition. The water concentration was determined by the freeze-drying technique (Freezone 4.5 s LABCONCO, USA). Salt and PEO content measurements were performed in triplicate and water content in duplicate. * To whom correspondence should be addressed. E-mail: jcoimbra@ufv.br. Fax: + 55-31-3899-2208. Phone: + 55-31-3899-1618. † Department of Food Technology, UFV. ‡ Department of Chemistry, UFV. § Department of Agribusiness and Administration Engineering, UFF. Table 1. ATPS Composed of Poly(ethylene oxide) with Different Molar Masses and Salts polymer salt ref PEO 4000 NaNO 3 5 PEO 4000 K 2 HPO 4 6, 7 PEO 4000 Na 2 SO 4 6, 12 PEO 4000 Cs 2 CO 3 8 PEO 4000 Li 2 SO 4 9, 12 PEO 4000 ZnSO 4 10 PEO 4000 Na 3 C 6 H 5 O 7 11 PEO 4000 K 2 HPO 4 /KH 2 PO 4 12 PEO 1500 Li 2 SO 4 , MgSO 4 , Na 2 SO 4 13 PEO 4000 Cs 2 SO 4 14 PEO 20000 CuSO 4 15 J. Chem. Eng. Data 2008, 53, 1571–1573 1571 10.1021/je800111j CCC: $40.75  2008 American Chemical Society Published on Web 06/19/2008