Article pubs.acs.org/jced
Equilibrium Data and Physical Properties of Aqueous Two Phase Systems Formed by PEG (1500 and 4000) g·mol−1 + Sodium Sulfate + Water at Different Temperatures and pH 2 Ada A. Barbosa,† Renata C. F. Bonomo,† Cristiane V. Martins,† Rafael C. I. Fontan,† Evaldo C. Souza Júnior,*,† Luis A. Minim,‡ and Michelle C. Pignata† †
Departamento de Tecnologia Rural e Animal, Universidade Estadual do Sudoeste da Bahia, Praça Primavera 40, Bairro Primavera, 45700-000 Itapetinga, Bahia, Brasil ‡ Departamento de Tecnologia de Alimentos, Universidade Federal de Viçosa, Campus Universitário s/n, Centro, 36570-900 Viçosa, Minas Gerais, Brasil ABSTRACT: Liquid−liquid equilibrium data and phase diagrams of aqueous two phase systems (ATPS) composed of polyethylene glycol (PEG) of molar mass (1500 and 4000) g·mol −1 + sodium sulfate + water were determined at temperatures of 293.15, 303.15, 313.15, and 323.15 K at pH 2. Temperature had no significant effect on the biphasic region, indicating a small enthalpic contribution in the phase separation process. The change in temperature however caused an increase in the tie line slope because water molecules were transferred from the upper phase to the lower phase. Increasing the molar mass of the polymer led to an increase in the biphasic region of the phase diagram. In determining the physical properties of the systems studied, it was observed that the increase in concentration increased the viscosity and the refraction index; while relative to temperature, the viscosity, refraction index, and density decreased.
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INTRODUCTION In aqueous two phase systems (ATPS) when the chemical species (polyelectrolytes, polymers, ionic liquids, etc.) are mixed at certain compositions and temperatures, they divide into two phases with different compositions, with thermodynamic equilibrium. The phases present intensive thermodynamic properties, such as the refraction index, composition, and density. These phases are separated by an interface, the region where the intensive thermodynamic properties of each phase transmit different values, always tending toward the value of that property in the other phase at equilibrium.1The main component of these systems is water. Biphasic systems have been formed by aqueous polymer solutions with inorganic salts or other structurally different hydrophilic polymers and more recently by mixing inorganic salts and ionic liquids. As such they are widely used in biotechnology to separate and purify biomaterials.2The polymer-salt system presents large advantages, such as lower viscosity, and therefore less phase separation time and lower cost compared to polymer−polymer systems.13 To employ aqueous two phase systems in the biocompound partition it is necessary to evaluate the behavior of these systems at different compositions, temperatures, and pH conditions. Since then research in this area has become deeper, making ATPS a tool in the partitioning and concentrating of diverse types of solutes, including cellular organelles,3,4proteins,5 DNA,6nanoparticles,7ions,8−10and dyes.11,12 © 2015 American Chemical Society
Various studies on equilibrium data for the polyethylene glycol and sodium sulfate systems are available in the literature.13−17References to studies on sodium sulfate systems at different temperatures and pH 2 were not found, however, necessitating the study of systems where biomolecules present stability at low pH such as the anthocyanins that are more stable under acidic conditions and have been added to the anthocyanin food products due to their antioxidant and antiinflammatory qualities. The objective of this study was to determine phase equilibrium experimental data for ATPSs composed of PEG (1500 and 4000) g·mol−1 + sodium sulfate + water at pH 2. For each of these systems, equilibrium data were determined at four temperatures (293.15, 303.15, 313.15, and 323.15 K). The effects of temperature and PEG molar mass on the behavior of the equilibrium data are discussed, and physical properties, such as density, viscosity, and refraction index, are determined.
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EXPERIMENTAL SECTION Materials. PEG with media molar mass of 1500 g·mol −1 and 4000 g·mol −1 and sodium sulfate were acquired from VETEC (Brazil). All other reagents were of analytical grade, with a minimum purity of 99%. Received: September 16, 2014 Accepted: November 16, 2015 Published: December 14, 2015 3
DOI: 10.1021/je5008586 J. Chem. Eng. Data 2016, 61, 3−11
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Figure 1. Phase diagram at the temperatures 293.15, 303.15, 313.15, and 323.15 K, pH 2: a) PEG 1500 + sodium sulfate + water and b) PEG 4000 + sodium sulfate + water.
Biphasic Aqueous System. To build the biphasic aqueous systems, PEG-salt-water compound stock solutions were prepared with PEG in water and salt in water. The PEG solution concentration was 50% w/w, and the saline sodium sulfate solution concentration was 22% w/w. Both solutions had pH 2, obtained via adjustment with the conjugate and sulfuric acids and confirmed with a pH meter. Equilibrium data were determined for systems formed by PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water. All systems were analyzed at temperatures of 293.15, 303.15, 313.15, and 323.15 K. The solutions and dilutions were prepared using an analytical balance (GEHAKA, model AG-200) with uncertainty of ±0.1 mg. The binodal curves were determined by the turbidimetric method (ALBERTSSON, 1985), which indicates the start of the biphasic region. The procedure consists of weighing 1 g of the stock polymer solution in glass tubes to better visualize the turbidity. The tube containing the polymer solution was taken to a thermostatic bath (TECNAL, Tec-4MC), where it was left for 10 min to reach thermal equilibrium. Ten μL aliquots of the salt solution were added with an automatic pipet and kept in manual agitation in a tube in the water bath, the mixture was kept for 3 min at the desired temperature, until system turbidity occurred and the solution had a whitish appearance, and then the final mass of the systems was obtained. Distilled water was titrated in the system until it became clear, and the quantity of water necessary for the system to remain homogeneous was noted the same and was kept for 3 min, until cleaning the system was confirmed. The procedure was done repeatedly until the necessary points for making the curve were obtained. The tielines used to construct the diagrams were obtained based on the turbidimetric curve, with the global points above the curve where the biphasic region was found. Five global points were used for each PEG-salt system. The systems were formed by adding an adequate quantity of PEG stock solution, salt, and water for a total system mass of 50 g in graduated centrifuge tubes with conical bottoms. The resulting mixture was agitated in a vortex agitator (PHOENIX, model AP-56) for approximately 3 min and centrifuged at 3000g (SP LABOR, model Sp-701) for 20 min to accelerate the formation of the two phases. The phases were kept at rest for 24 h in a B.O.D. incubator (LONGEN SCIENTIFC, model LG340 FT220) at
the studied temperatures. Thermodynamic equilibrium was considered obtained when the phases were totally clear. After reaching equilibrium, an aliquot of the samples from the upper and lower phases was collected in duplicate to determine the composition of each phase. The upper phase was collected with the help of a syringe, with the needle left in this phase until the layer was approximately 5 mm above the interface. This procedure aimed to ensure the interface was not perturbed. After collecting the upper phase, a syringe was carefully inserted (with a 5 cm needle) into the cell of equilibrium, perturbing the interface as little as possible. After 1 h at rest, equilibrium was re-established, and the plunger of the syringe was pulled vigorously until a 5 mm layer of the lower phase remained in the cell. The phases were collected in covered containers and refrigerated until all analyses were done. System components were quantified in each phase, and equilibrium diagrams were constructed. Phase Composition Determination. The PEG concentration was determined by means of liquid−liquid extraction, using chloroform as the solvent. Initially, approximately 2 g of each phase was weighed in 15 mL tubes. Three mL of chloroform was added, then agitated with a vortex, and centrifuged at 4000g (BIOSYSTEMS, model MPW-350) for 5 min. The PEG-containing lower phase was collected and stored in tubes which had previously been dried and weighed. The upper phase was subjected to two more extractions so all PEG could be extracted. The tubes containing PEG + chloroform were placed in an incubator at 105 °C for 12 h to evaporate the chloroform, and the PEG mass was obtained by subtracting the weight of the dry tubes. The standard pattern of PEG quantification was ±0.0067% of mass. The water concentration was determined by the lyophilization technique using the equipment (LV2000 TERRONI). This method consists of weighing of the sample under controlled and standardized conditions before and after drying according to Silva et al.18The standard deviation of the water quantification was ±0.0037% of mass. The sodium sulfate concentration in the phases was determined with the use of conductivity measurements (TECNAL, Tec-4MC) with full scale accuracy of ±0.01, as described by Regupathi et al.19 All analytic measurements were done in duplicate. The standard deviation of the salt quantification was ±0.0034% of mass. The experimental data 4
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Figure 2. Liquid−liquid equilibrium for systems composed of PEG 1500 + sodium sulfate + water, at pH 2 at temperatures a) 292.15, b) 303.15, c) 313.15, and d) 323.15 K.
uncertainty of ±0.01. This equipment was connected to a Brookfield TC-500 thermostatic bath (Brookfield Engineering Laboratories, Massachusetts, USA), accurate to 0.1 K, with an uncertainty of ±0.05 K. Approximately 9 mL of sample was used for each measurement. The angular velocity was 100 rpm with 6 measurements with the SC4-31 spindle.
were used to assemble the tie line length model, according to eq 1 TLL = [(w2T − w2B)2 + (w3T − w3B)2 ]1/2
(1)
where wT2 , wT3 , wB2 , and wB3 are the top (T) and bottom (B) equilibrium mass fractions of PEG (2) and sodium sulfate (3). The tie-line-length (TLL) was expressed in terms of mass fractions (%). Density Measurements, Refraction Index, and Viscosity. To determine the density, a Digital Densimeter DMA 5000 M (ANTON PAAR) was used, with accuracy of ±5 × 10−6 g·cm−3 and repeatability of ±1 × 10−6 g·cm−3 in an operating range from 0 to 3 g·cm−3. The equipment temperature ranges from 273.15 K to 363.15 K with an accuracy of +0.01 K and repeatability of +0.001 K. For the refraction index, digital refractometer was used (ATAGO, Brazil, accuracy 0.2%, with an uncertainty of ±0.01). This machine was connected to a thermostatic bath (TECNAL, Te184), which allowed temperature control with an accuracy of 0.1 K, with an uncertainty of ±0.05 K. The equipment was properly calibrated with distilled water at the studied temperatures, and a sample was placed on the refractometer prism to perform a direct reading. Viscosity was measured with a rotational viscometer, Brookfield, model DVII+Pro, made by Brookfield Engineering Laboratories, Inc., USA, with an
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RESULTS AND DISCUSSION Binodal Curves. The diagrams presented in Figure 1represented a binodal curve for the ATPS composed of PEG (1500, 4000) g·mol−1 + sodium sulfate, obtained by the turbidimetric method at temperatures of 293.15, 303.15, 313.15, and 323.15 K and pH 2. The biphasic region of the PEG 1500 + sodium sulfate + water systems did not vary with increased temperature (Figure 1 a). This indicates insignificant variation in the calorific capacity of the phases and, consequently, low enthalpic variation associated with the separation process. Regarding the PEG 4000 + sodium sulfate + water systems, as the polymer concentration decreases and the salt concentration increases, there is an increase in the biphasic regions with increased temperature (Figure 1 b). This occurs because the PEG-salt interaction in ATPS formation is endothermic, i.e. increased temperature favors ATPS formation. A similar tendency was reported by various authors for other ATPSs studied at different temperatures, e.g. by Murugeran and 5
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Figure 3. Liquid−liquid equilibrium for systems composed of PEG 4000 + sodium sulfate + water, at pH 2 at temperatures a) 292.15, b) 303.15, c) 313.15, and d) 323.15 K.
Perumalsamy20for PEG 2000 + sodium citrate, Sadeghi and Golabiazar21for PEG 6000 + sodium tungstate systems, Regupathi et al.22for PEG 6000 + triammonium citrate, Oliveira et al.23for PEG 4000 + zinc sulfate, and Carvalho et al.1for PEG 4000 + sodium sulfate. The effect of the polymer molar mass on the binodal curve is shown in Figures 2 and 3. An increase in the biphasic region was observed in the diagrams formed by polymers of larger mass. At all temperatures studied, the PEG 4000 presented a larger biphasic region than the other polymers. It is therefore understood that increased polymer molar mass caused an increase in hydrophobicity, contributing to the segregation process that occurs with lower quantities of salt and polymer. The binodal curves become more asymmetric and shift to lower concentrations of PEG and salt with the increasing molar mass of the polymer for salt at the studied temperatures. This behavior is attributed to the reduced solubility of PEG in water, which increases with the molar mass increase. For this reason, lower concentrations are required for phase separation. The PEG-rich phase saturated at relatively low concentrations with the increase of the polymer molar mass. This tendency is in accordance with the experimental results found in the literature.2,23,24
Equilibrium Data. The equilibrium compositions of the ATPSs formed by PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water at different temperatures and pH 2 are presented in Tables 1 and 2, where the data referring to the phase components are expressed in terms of mass fraction (w/w %). Five tielines corresponding to the systems that contain PEG (1500 and 4000) and sodium sulfate were determined and are represented in Figures 2 and 3, all as a function of the temperature. With the results presented, an exclusionary relationship between the polymer and the salt forming systems was confirmed, independent of the temperature. This exclusion is common in all biphasic aqueous systems formed by polymers and salt, since the upper phase is mainly composed of polymers and water and the lower phase is mainly composed of salt and water. TLL values for each system studied are shown (Tables 1 and 2). TLL increased with the increase in temperature, when compared to the temperature data from 293.15 to 323.15 K for all systems studied (Figure 4). TLL is dependent on the difference in salt and polymer concentrations in the upper and lower phases. According to Sousa et al.25the TLL is associated with the selectivity of the system and global composition data of the system. When it is shorter the biomolecule partitioning 6
DOI: 10.1021/je5008586 J. Chem. Eng. Data 2016, 61, 3−11
TLL
= 293.15 K 25.12 32.51 36.47 41.70 45.40 = 303.15 K 21.02 27.14 35.79 41.64 44.99 = 313.15 K 27.99 32.48 36.50 40.69 44.41 = 323.15 K 31.13 35.63 40.57 44.81 46.48
TL
T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5
8.00 9.00 10.00 11.00 12.00
15.00 16.00 17.00 18.00 19.00
8.00 9.00 10.00 11.00 12.00
8.00 9.00 10.00 11.00 12.00
15.00 16.00 17.00 18.00 19.00
14.00 15.00 16.00 17.00 18.00
9.00 9.91 11.00 12.00 13.00
100w2
14.00 14.86 16.00 17.00 18.00
100w1
78.00 76.00 74.00 72.00 70.00
77.00 75.00 73.00 71.00 69.00
77.00 75.00 73.00 71.00 69.00
77.00 75.23 73.00 71.00 69.00
100w3
global composition
30.92 34.69 38.39 41.92 43.39
28.54 32.15 34.98 38.06 40.87
21.00 26.00 32.81 38.00 41.00
24.81 30.18 33.72 38.00 40.50
100w1
0.28 0.62 0.54 0.58 0.66
0.66 0.30 0.26 0.34 0.54
0.17 0.23 0.13 0.42 0.31
0.67 0.49 0.19 0.58 0.61
deviation %
3.21 2.75 2.42 1.38 1.37
4.13 3.90 3.42 2.89 2.47
5.00 4.52 3.00 2.00 2.00
4.00 3.40 3.15 2.36 2.00
100w2
0.30 0.06 0.01 0.03 0.26
0.22 0.33 0.32 0.05 0.29
0.01 0.26 0.19 0.34 0.04
0.03 0.25 0.08 0.28 0.27
deviation %
upper phase
64.16 60.79 58.36 56.03 54.78
67.98 63.66 62.39 59.29 56.30
72.59 66.44 62.66 59.67 59.63
69.64 65.47 62.98 60.11 57.47
100w3
0.14 0.21 0.29 0.35 0.15
0.17 0.37 0.14 0.29 0.24
0.07 0.01 0.08 0.01 0.09
0.02 0.22 0.00 0.01 0.20
deviation %
1.00 0.75 0.12 0.10 0.56
1.83 1.21 0.62 0.12 0.07
2.00 1.41 0.39 0.21 0.22
1.77 0.21 0.61 0.21 0.03
100w1
0.02 0.05 0.10 0.67 0.32
0.01 0.49 0.18 0.04 0.00
0.30 0.11 0.02 0.02 0.06
0.02 0.02 0.27 0.09 0.04
deviation %
11.82 13.59 15.89 17.49 19.43
12.48 13.78 15.73 17.62 20.00
14.00 16.00 18.17 19.50 21.00
14.00 16.00 18.45 20.00 22.58
100w2
0.40 0.24 0.27 0.33 0.31
0.24 0.26 0.35 0.15 0.17
0.01 0.04 0.25 0.04 0.05
0.02 0.26 0.15 0.29 0.28
deviation %
lower phase
87.90 83.37 84.57 82.29 80.30
83.37 85.89 82.47 80.79 79.12
83.59 83.36 81.94 80.61 78.81
83.24 81.17 72.26 79.31 77.38
100w3
Table 1. Equilibrium Data of the Polyethylene Glycol System 1500 g/mol (w1), Sodium Sulfate (w2), and Water (w3) at 293.15, 303.15, 313.15, 323.15 K; pH 2
0.15 0.37 0.36 0.03 0.16
0.37 0.34 0.18 0.23 0.03
0.28 0.01 0.05 0.27 0.36
0.06 0.32 0.22 0.35 0.14
deviation %
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TLL
= 293.15 K 31.23 34.89 37.49 40.48 42.95 = 303.15 K 22.73 26.98 31.10 34.98 38.86 = 313.15 K 22.00 27.09 32.48 36.52 40.27 = 323.15 K 23.30 32.28 37.75 40.68 42.80
TL
T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5
6.00 7.00 8.00 9.00 10.00
16.00 17.00 18.00 19.00 20.00
6.00 7.00 8.00 9.00 12.20
6.00 7.00 8.00 9.00 10.00
17.00 18.00 19.00 20.00 21.00
15.00 16.00 17.00 18.00 19.00
7.00 8.14 9.00 10.00 11.00
100w2
17.00 18.40 19.00 20.00 21.00
100w1
79.00 77.00 75.00 73.00 68.80
78.00 76.00 74.00 72.00 70.00
77.00 75.00 73.00 70.99 69.00
76.00 73.46 72.00 70.00 68.00
100w3
global composition
24.26 31.37 36.14 38.32 40.11
20.84 25.03 30.00 32.99 35.27
21.16 24.09 27.06 29.94 34.00
29.37 32.53 34.63 36.55 38.76
100w1
0.03 0.06 1.40 0.08 0.03
0.02 0.29 0.30 0.36 0.37
0.19 0.34 0.36 0.27 0.27
0.33 0.33 0.25 0.31 0.17
deviation %
3.77 2.80 2.17 1.89 1.71
4.36 3.14 2.79 2.05 1.86
4.41 3.56 3.13 2.99 2.56
2.29 2.66 2.47 2.34 2.32
100w2
0.04 0.13 0.26 0.35 0.29
0.30 0.12 0.18 0.31 0.01
0.17 0.01 0.13 0.18 0.33
0.12 0.17 0.13 0.24 0.18
deviation %
upper phase
70.82 64.67 60.98 59.21 57.92
75.39 66.87 66.01 65.60 62.54
70.86 68.92 69.32 61.57 63.06
67.91 63.04 61.29 57.48 55.12
100w3
0.07 0.17 0.37 0.35 0.34
0.29 0.35 0.18 0.65 0.33
0.25 0.37 0.18 0.13 0.24
0.30 0.22 0.29 0.25 0.17
deviation %
1.83 0.45 0.21 0.04 0.39
0.54 0.31 0.25 0.26 0.04
0.56 0.34 0.14 0.10 0.82
0.45 0.12 0.08 0.1 0.06
100w1
0.01 0.00 0.00 0.00 0.01
0.28 0.06 0.08 0.13 0.04
0.03 0.01 0.01 0.02 0.03
0.01 0.02 0.01 0.07 0.02
deviation %
10.09 12.09 13.76 15.64 17.64
12.85 14.21 15.83 18.26 21.35
14.01 16.37 18.70 21.24 22.79
14.08 15.58 17.04 19.95 20.96
100w2
0.02 0.08 0.24 0.31 0.33
0.29 0.17 0.33 0.20 0.33
0.04 0.20 0.04 0.22 0.29
0.13 0.19 0.11 0.20 0.27
deviation %
lower phase
88.23 87.67 89.17 84.77 81.94
84.37 86.82 85.23 83.54 79.96
86.83 84.86 78.88 80.85 81.73
85.47 83.04 86.79 79.3 77.61
100w3
0.12 0.04 0.37 0.28 0.03
0.36 0.05 0.02 0.17 0.05
0.31 0.22 0.31 0.20 0.20
0.33 0.26 0.15 0.27 0.27
deviation %
Table 2. Equilibrium Data of the Polyethylene Glycol System 4000 g/mol (w1), Sodium Sulfate (w2), and Water (w3) at 293.15, 303.15, 313.15, and 323.15 K; pH 2
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Figure 4. Effect of temperature on the equilibrium phase compositions for the PEG (a) 1500 and (b) 4000 + sodium sulfate + water system. Observed data at (▼) 293.15 K and (○) 323.15 K; tie lines obtained at () 293.15 K and (- - -) 323.15 K.
leads to an increase in polymer concentration in the upper phase and a small dilution in the lower phase and, consequently, an increased TLS. In the systems formed by PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water presented in Figure 4, TLS increased with increased temperature when compared to the data at the temperatures of 293.15 to 323.15 K. This increase reached 79% in the PEG 4000 + sodium sulfate + water system in tielines 2 and 3. This behavior was expected because the polymer concentration increase caused increased hydrophobicity in the upper phase. Thus, the increase in TLS happened by virtue of the transfer of water from the upper phase to the lower phase, resulting in a reduced salt concentration in the lower phase and an increased PEG concentration in the upper phase. The relationship of the tie line increase as a function of the temperature was the same for all systems. Similar behavior was observed by Zafarani-Moattar and Sadeghi,2who verified that the slope and length of the tielines increased with elevated temperature. Similar results were obtained by Voros et al.26and Mishima et al.,27when studying systems containing PEG and salt. According to Da Silva and Loh28the interaction between the salt ions and the polymer in ATPs formation occurred with the absorption of energy, i.e. an endothermic interaction. Thus, favoring the salt-PEG interaction lead to a decrease in the necessary quantity of salt added to the systems for ATPs formation to occur, hence shifting the binodal curve for the region closest to the axis of the equilibrium diagram. Thus, entropic analysis of system behavior should be done. With the temperature increase, the conformational entropy of the polymer increased because of the folding process of the chain and consequent decrease in water solubility. In this way, water is transferred from the upper phase to the lower phase, reducing the salt concentration in the lower phase and increasing the ILA. With this observation, the predominance of entropy influencing the behavior of the ATPs was confirmed. Density, Refraction Index, and Viscosity. The physical properties of the upper and lower phases in ternary systems present distinct characteristics in relation to composition and temperature. This information is necessary for design and increased scale for production and extraction processes. Therefore, in Tables 4and 5the experimental values of viscosity (η/mPa·s), density (ρ/kg·m−3), and refraction index (Nd) are
coefficient value of interest will be closer to 1 and therefore less selective to extraction. With the increase of TLL, however, the protein transfer tends toward one of the phases; that is, the value of the partitioning coefficient becomes increasingly more distant from 1, more or less. This behavior results from the increase in the compositional difference between the phases and consequently generates increasing entropic and enthalpic contributions in the transfer of the protein to one of the phases. Table 3 shows the values of the tieline slope (TLS) of the systems at all temperatures. The TLS is defined as the ratio Table 3. Influence of Temperature on the Tie Line Slopes for the PEG System temperature (K) tie lines
293.15
303.15
PEG 1500 + Sodium Sulfate + Water 1 −2.30 −2.11 2 −2.38 −2.14 3 −2.16 −2.13 4 −2.14 −2.15 5 −1.96 −2.14 PEG 4000 + Sodium Sulfate + Water 1 −2.45 −2.14 2 −2.51 −1.85 3 −2.31 −1.72 4 −2.07 −1.63 5 −2.07 −1.64
313.15
323.15
−3.20 −3.13 −2.79 −2.57 −2.32
−3.47 −3.13 −2.84 −2.59 −2.37
−2.38 −2.23 −2.28 −2.01 −1.80
−3.55 −3.32 −3.10 −2.78 −2.49
between the difference of the polymer concentration and the salt concentration in the upper and lower phases, as presented by eq 2 TLS = (Cpu − Cpl)/(Csu − Csl)
(2)
where Cpu and Cpl are the polymer concentrations in the upper and lower phases, and Csu and Csl are the salt concentrations in the upper and lower phases. Table 3 shows that the TLS becomes more negative with increased temperature. This behavior was expected, since the TLS variation is caused by increased hydrophobicity, which is intensified by the temperature increase and causes water molecules of the solvating polymer to migrate from the upper phase to the lower phase. The reduction of water molecules 9
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Table 4. Density Values (ρ), Refraction Index (nD), and Viscosity (η) for the Upper and Lower Phases of the System Composed of PEG 1500 + Sodium Sulfate + Water at 293.15, 303.15, 313.15, and 323.15 K upper phase TL T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5
ρ/kg·m
−3
= 293.15 K 1078.361 1080.296 1083.042 1085.866 1086.406 = 303.15 K 1076.995 1078.803 1080.585 1081.026 1081.943 = 313.15 K 1072.479 1073.291 1073.304 1074.818 1074.905 = 323.15 K 1061.175 1063.413 1066.416 1067.996 1071.928
nD
Table 5. Density Values (ρ), Refraction Index (nD), and Viscosity (η) for the Upper and Lower Phases of the Systems Composed of PEG 4000 + Sodium Sulfate + Water at 293.15, 303.15, 313.15, and 323.15 K
lower phase η/mPa·s
ρ/kg·m
−3
nD
upper phase η/mPa·s
1.366 1.370 1.368 1.385 1.374
8.848 12.497 15.147 18.746 24.195
1137.345 1159.921 1175.624 1194.085 1213.742
1.355 1.357 1.353 1.357 1.362
3.549 3.699 3.749 3.849 3.899
1.358 1.373 1.376 1.369 1.369
5.849 8.898 10.398 17.146 19.447
1117.777 1137.763 1153.150 1182.438 1194.884
1.354 1.355 1.353 1.359 1.361
2.999 3.149 3.299 3.399 3.599
1.353 1.359 1.370 1.358 1.356
6.449 7.998 8.248 10.948 11.997
1125.385 1143.312 1151.069 1177.620 1190.331
1.352 1.351 1.355 1.354 1.346
2.100 2.399 2.449 2.499 2.549
1.358 1.354 1.357 1.354 1.359
5.048 6.948 8.642 9.348 10.398
1100.540 1117.033 1133.645 1157.681 1169.459
1.346 1.348 1.351 1.333 1.351
1.650 1.850 2.399 2.399 2.649
LA T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5 T 1 2 3 4 5
ρ/kg·m
−3
= 293.15 K 1078.144 1080.819 1087.268 1088.198 1090.945 = 303.15 K 1071.487 1075.533 1079.572 1081.384 1084.344 = 313.15 K 1048.047 1066.802 1069.402 1073.751 1078.539 = 323.15 K 1057.593 1060.976 1063.447 1072.382 1078.965
lower phase
nD
η/mPa·s
1.376 1.372 1.370 1.378 1.383
25.045 34.643 40.391 57.188 65.536
1.369 1.374 1.370 1.365 1.380
ρ/kg·m
−3
nD
η/mPa·s
1149.029 1159.059 1178.408 1196.385 1203.422
1.355 1.353 1.355 1.360 1.361
2.699 3.599 3.749 3.749 3.899
13.497 23.145 27.444 35.242 45.940
1110.344 1130.190 1148.422 1173.374 1197.008
1.354 1.350 1.352 1.356 1.355
3.599 3.599 3.599 3.299 4.049
1.354 1.379 1.374 1.359 1.366
10.698 17.796 23.645 30.993 41.991
1132.455 1109.013 1132.141 1142.887 1186.546
1.353 1.349 1.351 1.352 1.356
2.499 3.149 3.299 3.499 3.850
1.348 1.347 1.372 1.357 1.367
7.148 12.497 18.196 25.844 31.693
1079.030 1093.508 1107.898 1140.012 1196.175
1.345 1.345 1.351 1.351 1.342
2.100 2.250 2.100 2.399 2.699
lower phase. According to Saravanan et al.,29the high difference in viscosity between the phases is ideal in operational terms, since it reduces the separation time. According to Kalaivani et al.,30 studying systems composed of PEG + ammonium hydrogen citrate, the density and viscosity increased with the concentration and molar mass of the constituents of the system. Thus, for the process of extracting the ATPS, lower viscosity values are ideal, since they are highly beneficial in industrial processes by favoring biomolecule mass transfer between the two phases and improved handling. Selecting the more efficient system will depend on the characteristics of the extraction solute, however. Regarding the refraction index of the PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water systems at all temperatures, there was an insignificant decrease. The upper phase presented higher values than the lower phase because of its increased density, which makes light propagation more difficult.31
presented for the phases of the systems composed of PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water at the temperatures 293.15, 303.15, 313.15, and 323.15 K at pH 2. For both phases, the standard deviations of density, refraction index, and viscosity were less than 7.12 kg·m−3, 0.001 mPa·s, and 0.12 mPa·s. The density of the upper and lower phases of the system composed of PEG 1500 + sodium sulfate + water at the temperature 293.15 K varied from 1078.361 kg· m−3 to 1086.406 kg·m−3 and 1137.345 kg·m−3 to 1213.742 kg· m−3 (Table 4). By means of data analysis, an increase in density with increased concentrations of system constituents was confirmed in both the upper and lower phases. Moreover, it was determined that the lower phase, composed mainly of salt and water, was more dense that the upper phase, which is rich in PEG and water; therefore phase formation will be faster mainly because of the greater constituent density of the lower phase. These observations may also be made at the temperatures 303.15, 313.15, and 323.15 K. The same behavior was verified for the other systems composed of PEG 4000 + sodium sulfate + water at the studied temperatures (Table 5). It was observed that the PEG-rich upper phase is more viscous than the salt-rich lower phase. Evaluating the increase in the constituent concentrations of the tie lines, an increase in the viscosity of the systems composed of PEG 1500 + sodium sulfate + water and PEG 4000 + sodium sulfate + water was observed at the studied temperatures (Tables 4 and 5). It was shown that the system temperature increase leads to decreased viscosity in the solutions, with greater impact on the polymeric solution. In the PEG 1500 + sodium sulfate + water system on tie line 5, the difference in viscosity was 620% between the upper and
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CONCLUSION Diagrams were constructed composed of PEG 1500 + sodium sulfate and PEG 4000 + sodium sulfate + water at temperatures of 293.15, 303.15, 313.15, and 323.15 K at pH 2. The effect of the temperature on the systems did not present large variations in the biphasic region. There was an increase in the tie line slope because of the increased temperature, however, leading to the conclusion that water molecules were transferred from the upper phase to the lower phase. It is also possible that the increased molar mass causedan increase in the biphasic region at all studied temperatures. 10
DOI: 10.1021/je5008586 J. Chem. Eng. Data 2016, 61, 3−11
Journal of Chemical & Engineering Data
Article
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Values of viscosity, density, and refraction index were determined experimentally for all systems studied. Physical properties, viscosity, and density are influenced by concentration, and there was an increase thereof with the increase of system components, both during the phase of polymer and salt. The refraction index however was not significantly affected by increased concentration.
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AUTHOR INFORMATION
Corresponding Author
*Phone: 55-77-3261-8659. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/je5008586 J. Chem. Eng. Data 2016, 61, 3−11
