- Email: [email protected]
Liquid–liquid equilibria of aqueous two-phase systems composed of TritonX-100 and sodium citrate or magnesium sulfate salts
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 34 (2010) 81–83
Contents lists available at ScienceDirect
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad
Liquid–liquid equilibria of aqueous two-phase systems composed of TritonX-100 and sodium citrate or magnesium sulfate salts Alireza Salabat ∗ , Somayeh Tiani Moghadam, Mina Rahmati Far Chemistry Department, Arak University, P.O. Box 38156-879, Arak, Iran
article
info
Article history: Received 29 August 2009 Received in revised form 20 December 2009 Accepted 20 December 2009 Available online 5 January 2010 Keywords: Aqueous two-phase system Surfactant-based ATPS TritonX-100 Magnesium sulfate Sodium citrate
abstract Liquid–liquid phase diagrams of surfactant-based aqueous two-phase systems (ATPS) composed of TritonX-100, as a non-ionic surfactant, and two different salts have been studied at 298.15 K. The salts used were an inorganic salt, magnesium sulfate (MgSO4 ), and an organic salt, sodium citrate (Na3 C6 H5 O7 ). The results show that the salt MgSO4 is more capable of inducing ATPS formation than the salt Na3 C6 H5 O7 . The experimental liquid–liquid equilibrium data were correlated using a modified virial model. Good agreement was obtained with the experimental data. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction Aqueous two-phase systems (ATPS) have been utilized very extensively in many different industries such as the biotechnology, petroleum, paint, adhesives and pharmaceuticals ones. In particular, aqueous two-phase systems have attracted considerable attention in relation to the large-scale recovery and purification of bioproducts [1–3]. Four kinds of ATPS have been developed so far; they are polymer–polymer ATPS, polymer–salt ATPS, ionic liquid (IL)-based ATPS and surfactant-based ATPS. Due to the higher content of water in both phases and the lower interface tension in comparison with the other cases, surfactant-based ATPS have greater advantages, such as lower cost, experimental convenience, ease of waste disposal and consequently shorter time for phase separation. The surfactant ATPS are especially suitable for use in hydrophobic membrane protein separation [4]. Despite the polymer–polymer and polymer–salt ATPS studies, thermodynamic data for IL-based and surfactant-based ATPS in the literature are scarce. More recently some thermodynamic investigations and their applications in biotechnology have been reported for surfactant-based ATPS [4–7] and for IL-based ATPS [8–12]. In our previous paper we have reported LLE data for some new surfactant-based ATPS composed of nonylphenyl ethoxylate (NP-9) [13]. Non-ionic surfactants containing polyoxyethylene functional groups are known to form neutral adducts with a variety of
reagents [5]. TritonX-100, which is considered a comparatively mild detergent, is often used in biochemical applications to solubilize proteins. Many enzymes remain active in the presence of TritonX-100 [14]. It can be concluded that this non-ionic surfactant forms a gentle environment for some biomolecules and is thus suitable for use in extraction and purification systems. In continuation of our previous work, we report LLE data for surfactant-based aqueous two-phase systems composed TritonX100 and MgSO4 or Na3 C6 H5 O7 salts at 298.15 K. The experimental results obtained as regards the phase diagrams were correlated using a modified virial-type model. 2. Experimental 2.1. Materials The non-ionic surfactant TritonX-100 (octylphenol polyethoxylene) was purchased from Acros Organics Co., and used without further purification. The average number of ethylene oxide (EO) units per molecule, the average molecular weight and the critical micelle concentration (CMC) of TritonX-100 are about 10, 646.85 g mol−1 and 130 mg L−1 , respectively. Magnesium sulfate (GR, min. 99.5%) and sodium citrate (GR, min. 99.5%) were obtained from Merck. 2.2. Apparatus and procedure
∗
Corresponding author. Tel.: +98 861 2767314; fax: +98 861 2774031. E-mail addresses: [email protected], [email protected] (A. Salabat).
0364-5916/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2009.12.004
The experimental apparatus and the aqueous two-phase equilibrium experiment were described previously [15]. The
82
A. Salabat et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 34 (2010) 81–83
experiments were performed in a 30 ml glass bottle. Aqueous twophase systems were prepared from liquid surfactant and different salts containing magnesium sulfate or sodium citrate in triply distilled water. The total weight of these components for each sample was about 20 g. The mixtures were shaken for about 30 min and then placed in a thermostat at 298.15 K for at least 24 h to ensure complete equilibration, as indicated by the absence of turbidity in each phase. After equilibration of the systems, the samples of the upper and lower phase were taken out carefully for analysis using syringes. The concentration of MgSO4 was determined by magnesium analysis using atomic absorption spectroscopy (AAS). This measurement was carried out with a Shimadzu Atomic Absorption Spectrophotometer AA-670G. The concentration of Na3 C6 H5 O7 was determined using atomic emission spectroscopy with a flame photometer (Perkin-Elmer). A double-beam Perkin-Elmer Lambda 15 UV–visible spectrophotometer was used for determination of the TritonX-100 concentration in the top and bottom phases. The absorbance of the samples was measured at λ = 283 nm. Determinations of the salt and triton mass percentages were carried out for solutions of known concentrations to determine the suitability and uncertainty of the methods. The mean uncertainties of the salt and TritonX-100 mass percentages were obtained as less than ±0.2 and ±0.3, respectively.
Table 1 Liquid–liquid equilibrium data for the TritonX-100 (1) + salt (2) + water (3) aqueous two-phase system at 298.15 K. Total phase 100w1
Top phase 100w2
100w1
Bottom phase
STL
100w2
100w1
100w2
1.6 1.2 0.9 0.7 0.6 0.3
0.0 0.0 0.0 0.0 0.0 0.0
10.7 13.0 13.7 16.3 19.1 20.4
4.9 4.5 4.2 3.7 3.3 3.1
3.3 2.6 1.5 1.1 0.7
0.0 0.0 0.1 0.1 0.1
12.5 13.7 17.9 21.8 24.9
4.1 4.1 3.4 2.9 2.7
TritonX-100 + MgSO4 + H2 O 20.3 20.9 21.4 23.5 24.6 25.7
6.5 7.1 8.3 9.4 11.3 11.9
44.7 48.8 53.3 57.3 61.0 63.0
TritonX-100 + Na3 C6 H5 O7 + H2 O 20.0 21.0 23.1 25.0 27.0
7.5 9.0 11.2 13.2 15.0
37.2 46.1 56.0 59.7 65.3
3. The thermodynamic framework In this work, the experimental liquid–liquid equilibrium data were correlated using a modified virial model [16,17]. For aqueous electrolyte solutions the excess Gibbs energy is often written as the sum of two contributions, one accounting for short-range and the other for long-range interactions: GE = GE ,LR + GE ,SR .
(1)
In this model the short-range term for the excess Gibbs energy is given by 1000 GE ,SR nw Mw RT
=
XX i
Aij mi mj
(2)
j
Fig. 1. Experimental and calculated phase diagram of the TritonX-100 + MgSO4 + H2 O system; solid lines: experimental tie-lines, dotted lines: calculated tie-lines; curve: binodal.
where Mw is the molecular mass of water (in g mol−1 ), nw is the number of moles of water, Aij is the second virial coefficient or interaction parameter related to species i and j and m is the molality of species i or j. The long-range term is a modified Debye–Hückel term written as 1000 GE ,LR nw Mw RT
=−
4Aγ I b
√
ln(1 + b I )
(3)
where b is a constant equal to 1.2 kg1/2 mol−1/2 and Ar for the solvent water at 298.15 K is 0.3914 kg1/2 mol−1/2 . The ionic strength I is calculated as I =
1X 2
mi Zi2
(4)
i
where Zi is the charge of ion i. Using the following expression, the activity coefficient for salt, surfactant and water can be obtained: ln γi =
1 RT
∂G ∂ ni
E P ,T ,ni6=j
.
Fig. 2. Experimental and calculated phase diagram of the TritonX-100 + Na3 C6 H5 O7 + H2 O system; solid lines: experimental tie-lines, dotted lines: calculated tie-lines; curve: binodal.
(5)
4. Results and discussion The experimental liquid–liquid equilibrium results for the TritonX-100 + salts + H2 O two-phase systems at 298.15 K are
reported in Table 1. In this table, wi represents the mass fraction of solute i. The experimental phase diagrams for these systems are also shown in Figs. 1 and 2. In each system, the upper layer was the surfactant-rich, salt-poor phase, and the lower layer was the water-rich, salt-rich phase.
A. Salabat et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 34 (2010) 81–83
83
Table 2 Interaction parameters, Aij , of the modified virial model and the average deviation for TritonX-100 (1) + salts (2) + H2 O (3) systems at 298.15 K. Salt
A22
A12
A11
δ1
δ2
MgSO4 Na3 C6 H5 O7
19.87 36.38
26.69 25.27
7.11 2.29
0.5 1.8
0.04 0.5
‘‘exp.’’ and ‘‘cal.’’ indicate the experimental and calculated values, respectively. On the basis of the deviations obtained, it can be concluded that the modified virial model is a suitable model for the correlation of LLE data for such systems. The comparison of the experimental tie-line data with those calculated from the model is shown in Figs. 1 and 2. 5. Conclusion Fig. 3. Effect of salt on the LLE behavior of TritonX-100 + salts + H2 O; ∗MgSO4 , Na3 C6 H5 O7 .
The tie-lines are determined by connecting each corresponding bottom and top phase point. The binodal curves were drawn through the top and bottom phase points. The effect of salt on the phase equilibrium curves is given in Fig. 3. The results presented demonstrate that the salting-out powers of the salts are such that MgSO4 > Na3 C6 H5 O7 , because they depress the binodal to lower surfactant concentrations (Fig. 3). This means that the salt MgSO4 is more capable of inducing ATPS formation than the salt Na3 C6 H5 O7 . The effect of salt on the phase equilibrium composition can be analyzed through the slope of the tie-lines (STL) that are reported in Table 1. The STL is defined as the following ratio: STL =
1wTriton 1wsalt
XXX p
l
exp. 2
. mcal p,l,i − mp,l,i
(7)
i
where mp,l,i is the molality of the component i in the phase p for the lth tie-line. The liquid–liquid equilibrium data of Table 1 for TritonX-100 + salts + H2 O systems were correlated using the parameters obtained and the following equilibrium condition:
(mi γi )top = (mi γi )bot .
(8)
The fitting parameters obtained for the model along with the corresponding average deviation, calculated using Eq. (9), are listed in Table 2.
δi =
N 1 X
N i=1
Acknowledgement Financial support from the Arak University research group is gratefully acknowledged.
(6)
where 1wTriton and 1wsalt are the differences between the compound concentrations in the two coexisting phases. A change in slope indicates that the composition of the equilibrium phases is affected by salt. The STL results confirm that MgSO4 has a better salting-out effect than Na3 C6 H5 O7 . The model surfactant–surfactant (A11 ), surfactant–salt (A12 ) and salt–salt (A22 ) interaction parameters were estimated by minimizing the following objective function: OF =
In the present work, we have measured the LLE data for two ternary surfactant-based ATPS systems of TritonX-100 + salts + H2 O at 298.15 K. The salts used for investigation of the salt effect are MgSO4 and Na3 C6 H5 O7 . The results show that the saltingout power of MgSO4 is more than that of Na3 C6 H5 O7 in these systems. The experimental results relating to the phase diagrams were correlated using the modified virial model. The calculated average deviation between the experimental and calculated phase diagrams revealed that the modified virial model is a good model for the correlation and calculation of the LLE data for such systems.
w cal. − w exp. i i
(9)
where N is the number of experimental points and the superscripts
Appendix. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.calphad.2009.12.004. References [1] P.-A. Albertsson, Partition of Cell Particles and Macromolecules, third ed., Wiley, New York, 1986. [2] H. Walter, D. Brooks, D. Fisher, Partitioning in Aqueous Two-Phase Systems: Theory, Methods, Uses, and Applications to Biotechnology, Academic press, New York, 1985. [3] H. Hustedt, K.-H. Kroner, M.-R. Kula, in: H. Walter, D. Brooks, D. Fisher (Eds.), Partitioning in Aqueous Two-Phase Systems, Academic Press, New York, 1985, pp. 529–587. [4] H. Tani, T. Kamidate, H. Watanabe, Anal. Sci. 14 (1998) 875–888. [5] W.J. Horvath, C.W. Huie, Talanta 39 (1992) 487–492. [6] J.X. Xiao, U. Sivars, F. Tjerneld, J. Chromatogr. B 743 (2000) 327–338. [7] H.G. Xie, Y.J. Wang, M. Sun, Process. Biochem. 41 (2006) 689–696. [8] K.E. Gutowski, G.A. Broker, H.D. Willauer, J.G. Huddleston, R.P. Swatloski, J.D. Holbrey, R.D. Rogers, J. Am. Chem. Soc. 125 (2003) 6632–6633. [9] C. He, S. Li, H. Liu, K. Li, F. Liu, J. Chromatogr. A 1082 (2005) 143–149. [10] S. Li, C. He, H. Liu, K. Li, F. Liu, J. Chromatogr. B 826 (2005) 58–62. [11] M.T. Zafarani, S. Hamzezadeh, J. Chem. Eng. Data 57 (2007) 1686–1692. [12] S. Dreyera, P. Salimb, U. Kragl, Biochem. Eng. J. 46 (2009) 176–185. [13] A. Salabat, M. Alinoori, CALPHAD 32 (2008) 611–614. [14] M.D. Womack, D.A. Kendall, R.C. MacDonald, Biochem. Biophys. Acta 733 (1983) 210–216. [15] A. Salabat, Fluid Phase Equilib. 187–188 (2001) 489–498. [16] E. Edmond, A.G. Ogston, Biochem. J. 109 (1968) 569–574. [17] L.H. Haraguchi, R.S. Mohamed, W. Loh, P.A. Pessoa Filho, Fluid Phase Equilib. 215 (2004) 1–5.
Contents lists available at ScienceDirect
CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad
Liquid–liquid equilibria of aqueous two-phase systems composed of TritonX-100 and sodium citrate or magnesium sulfate salts Alireza Salabat ∗ , Somayeh Tiani Moghadam, Mina Rahmati Far Chemistry Department, Arak University, P.O. Box 38156-879, Arak, Iran
article
info
Article history: Received 29 August 2009 Received in revised form 20 December 2009 Accepted 20 December 2009 Available online 5 January 2010 Keywords: Aqueous two-phase system Surfactant-based ATPS TritonX-100 Magnesium sulfate Sodium citrate
abstract Liquid–liquid phase diagrams of surfactant-based aqueous two-phase systems (ATPS) composed of TritonX-100, as a non-ionic surfactant, and two different salts have been studied at 298.15 K. The salts used were an inorganic salt, magnesium sulfate (MgSO4 ), and an organic salt, sodium citrate (Na3 C6 H5 O7 ). The results show that the salt MgSO4 is more capable of inducing ATPS formation than the salt Na3 C6 H5 O7 . The experimental liquid–liquid equilibrium data were correlated using a modified virial model. Good agreement was obtained with the experimental data. © 2010 Elsevier Ltd. All rights reserved.
1. Introduction Aqueous two-phase systems (ATPS) have been utilized very extensively in many different industries such as the biotechnology, petroleum, paint, adhesives and pharmaceuticals ones. In particular, aqueous two-phase systems have attracted considerable attention in relation to the large-scale recovery and purification of bioproducts [1–3]. Four kinds of ATPS have been developed so far; they are polymer–polymer ATPS, polymer–salt ATPS, ionic liquid (IL)-based ATPS and surfactant-based ATPS. Due to the higher content of water in both phases and the lower interface tension in comparison with the other cases, surfactant-based ATPS have greater advantages, such as lower cost, experimental convenience, ease of waste disposal and consequently shorter time for phase separation. The surfactant ATPS are especially suitable for use in hydrophobic membrane protein separation [4]. Despite the polymer–polymer and polymer–salt ATPS studies, thermodynamic data for IL-based and surfactant-based ATPS in the literature are scarce. More recently some thermodynamic investigations and their applications in biotechnology have been reported for surfactant-based ATPS [4–7] and for IL-based ATPS [8–12]. In our previous paper we have reported LLE data for some new surfactant-based ATPS composed of nonylphenyl ethoxylate (NP-9) [13]. Non-ionic surfactants containing polyoxyethylene functional groups are known to form neutral adducts with a variety of
reagents [5]. TritonX-100, which is considered a comparatively mild detergent, is often used in biochemical applications to solubilize proteins. Many enzymes remain active in the presence of TritonX-100 [14]. It can be concluded that this non-ionic surfactant forms a gentle environment for some biomolecules and is thus suitable for use in extraction and purification systems. In continuation of our previous work, we report LLE data for surfactant-based aqueous two-phase systems composed TritonX100 and MgSO4 or Na3 C6 H5 O7 salts at 298.15 K. The experimental results obtained as regards the phase diagrams were correlated using a modified virial-type model. 2. Experimental 2.1. Materials The non-ionic surfactant TritonX-100 (octylphenol polyethoxylene) was purchased from Acros Organics Co., and used without further purification. The average number of ethylene oxide (EO) units per molecule, the average molecular weight and the critical micelle concentration (CMC) of TritonX-100 are about 10, 646.85 g mol−1 and 130 mg L−1 , respectively. Magnesium sulfate (GR, min. 99.5%) and sodium citrate (GR, min. 99.5%) were obtained from Merck. 2.2. Apparatus and procedure
∗
Corresponding author. Tel.: +98 861 2767314; fax: +98 861 2774031. E-mail addresses: [email protected], [email protected] (A. Salabat).
0364-5916/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2009.12.004
The experimental apparatus and the aqueous two-phase equilibrium experiment were described previously [15]. The
82
A. Salabat et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 34 (2010) 81–83
experiments were performed in a 30 ml glass bottle. Aqueous twophase systems were prepared from liquid surfactant and different salts containing magnesium sulfate or sodium citrate in triply distilled water. The total weight of these components for each sample was about 20 g. The mixtures were shaken for about 30 min and then placed in a thermostat at 298.15 K for at least 24 h to ensure complete equilibration, as indicated by the absence of turbidity in each phase. After equilibration of the systems, the samples of the upper and lower phase were taken out carefully for analysis using syringes. The concentration of MgSO4 was determined by magnesium analysis using atomic absorption spectroscopy (AAS). This measurement was carried out with a Shimadzu Atomic Absorption Spectrophotometer AA-670G. The concentration of Na3 C6 H5 O7 was determined using atomic emission spectroscopy with a flame photometer (Perkin-Elmer). A double-beam Perkin-Elmer Lambda 15 UV–visible spectrophotometer was used for determination of the TritonX-100 concentration in the top and bottom phases. The absorbance of the samples was measured at λ = 283 nm. Determinations of the salt and triton mass percentages were carried out for solutions of known concentrations to determine the suitability and uncertainty of the methods. The mean uncertainties of the salt and TritonX-100 mass percentages were obtained as less than ±0.2 and ±0.3, respectively.
Table 1 Liquid–liquid equilibrium data for the TritonX-100 (1) + salt (2) + water (3) aqueous two-phase system at 298.15 K. Total phase 100w1
Top phase 100w2
100w1
Bottom phase
STL
100w2
100w1
100w2
1.6 1.2 0.9 0.7 0.6 0.3
0.0 0.0 0.0 0.0 0.0 0.0
10.7 13.0 13.7 16.3 19.1 20.4
4.9 4.5 4.2 3.7 3.3 3.1
3.3 2.6 1.5 1.1 0.7
0.0 0.0 0.1 0.1 0.1
12.5 13.7 17.9 21.8 24.9
4.1 4.1 3.4 2.9 2.7
TritonX-100 + MgSO4 + H2 O 20.3 20.9 21.4 23.5 24.6 25.7
6.5 7.1 8.3 9.4 11.3 11.9
44.7 48.8 53.3 57.3 61.0 63.0
TritonX-100 + Na3 C6 H5 O7 + H2 O 20.0 21.0 23.1 25.0 27.0
7.5 9.0 11.2 13.2 15.0
37.2 46.1 56.0 59.7 65.3
3. The thermodynamic framework In this work, the experimental liquid–liquid equilibrium data were correlated using a modified virial model [16,17]. For aqueous electrolyte solutions the excess Gibbs energy is often written as the sum of two contributions, one accounting for short-range and the other for long-range interactions: GE = GE ,LR + GE ,SR .
(1)
In this model the short-range term for the excess Gibbs energy is given by 1000 GE ,SR nw Mw RT
=
XX i
Aij mi mj
(2)
j
Fig. 1. Experimental and calculated phase diagram of the TritonX-100 + MgSO4 + H2 O system; solid lines: experimental tie-lines, dotted lines: calculated tie-lines; curve: binodal.
where Mw is the molecular mass of water (in g mol−1 ), nw is the number of moles of water, Aij is the second virial coefficient or interaction parameter related to species i and j and m is the molality of species i or j. The long-range term is a modified Debye–Hückel term written as 1000 GE ,LR nw Mw RT
=−
4Aγ I b
√
ln(1 + b I )
(3)
where b is a constant equal to 1.2 kg1/2 mol−1/2 and Ar for the solvent water at 298.15 K is 0.3914 kg1/2 mol−1/2 . The ionic strength I is calculated as I =
1X 2
mi Zi2
(4)
i
where Zi is the charge of ion i. Using the following expression, the activity coefficient for salt, surfactant and water can be obtained: ln γi =
1 RT
∂G ∂ ni
E P ,T ,ni6=j
.
Fig. 2. Experimental and calculated phase diagram of the TritonX-100 + Na3 C6 H5 O7 + H2 O system; solid lines: experimental tie-lines, dotted lines: calculated tie-lines; curve: binodal.
(5)
4. Results and discussion The experimental liquid–liquid equilibrium results for the TritonX-100 + salts + H2 O two-phase systems at 298.15 K are
reported in Table 1. In this table, wi represents the mass fraction of solute i. The experimental phase diagrams for these systems are also shown in Figs. 1 and 2. In each system, the upper layer was the surfactant-rich, salt-poor phase, and the lower layer was the water-rich, salt-rich phase.
A. Salabat et al. / CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry 34 (2010) 81–83
83
Table 2 Interaction parameters, Aij , of the modified virial model and the average deviation for TritonX-100 (1) + salts (2) + H2 O (3) systems at 298.15 K. Salt
A22
A12
A11
δ1
δ2
MgSO4 Na3 C6 H5 O7
19.87 36.38
26.69 25.27
7.11 2.29
0.5 1.8
0.04 0.5
‘‘exp.’’ and ‘‘cal.’’ indicate the experimental and calculated values, respectively. On the basis of the deviations obtained, it can be concluded that the modified virial model is a suitable model for the correlation of LLE data for such systems. The comparison of the experimental tie-line data with those calculated from the model is shown in Figs. 1 and 2. 5. Conclusion Fig. 3. Effect of salt on the LLE behavior of TritonX-100 + salts + H2 O; ∗MgSO4 , Na3 C6 H5 O7 .
The tie-lines are determined by connecting each corresponding bottom and top phase point. The binodal curves were drawn through the top and bottom phase points. The effect of salt on the phase equilibrium curves is given in Fig. 3. The results presented demonstrate that the salting-out powers of the salts are such that MgSO4 > Na3 C6 H5 O7 , because they depress the binodal to lower surfactant concentrations (Fig. 3). This means that the salt MgSO4 is more capable of inducing ATPS formation than the salt Na3 C6 H5 O7 . The effect of salt on the phase equilibrium composition can be analyzed through the slope of the tie-lines (STL) that are reported in Table 1. The STL is defined as the following ratio: STL =
1wTriton 1wsalt
XXX p
l
exp. 2
. mcal p,l,i − mp,l,i
(7)
i
where mp,l,i is the molality of the component i in the phase p for the lth tie-line. The liquid–liquid equilibrium data of Table 1 for TritonX-100 + salts + H2 O systems were correlated using the parameters obtained and the following equilibrium condition:
(mi γi )top = (mi γi )bot .
(8)
The fitting parameters obtained for the model along with the corresponding average deviation, calculated using Eq. (9), are listed in Table 2.
δi =
N 1 X
N i=1
Acknowledgement Financial support from the Arak University research group is gratefully acknowledged.
(6)
where 1wTriton and 1wsalt are the differences between the compound concentrations in the two coexisting phases. A change in slope indicates that the composition of the equilibrium phases is affected by salt. The STL results confirm that MgSO4 has a better salting-out effect than Na3 C6 H5 O7 . The model surfactant–surfactant (A11 ), surfactant–salt (A12 ) and salt–salt (A22 ) interaction parameters were estimated by minimizing the following objective function: OF =
In the present work, we have measured the LLE data for two ternary surfactant-based ATPS systems of TritonX-100 + salts + H2 O at 298.15 K. The salts used for investigation of the salt effect are MgSO4 and Na3 C6 H5 O7 . The results show that the saltingout power of MgSO4 is more than that of Na3 C6 H5 O7 in these systems. The experimental results relating to the phase diagrams were correlated using the modified virial model. The calculated average deviation between the experimental and calculated phase diagrams revealed that the modified virial model is a good model for the correlation and calculation of the LLE data for such systems.
w cal. − w exp. i i
(9)
where N is the number of experimental points and the superscripts
Appendix. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.calphad.2009.12.004. References [1] P.-A. Albertsson, Partition of Cell Particles and Macromolecules, third ed., Wiley, New York, 1986. [2] H. Walter, D. Brooks, D. Fisher, Partitioning in Aqueous Two-Phase Systems: Theory, Methods, Uses, and Applications to Biotechnology, Academic press, New York, 1985. [3] H. Hustedt, K.-H. Kroner, M.-R. Kula, in: H. Walter, D. Brooks, D. Fisher (Eds.), Partitioning in Aqueous Two-Phase Systems, Academic Press, New York, 1985, pp. 529–587. [4] H. Tani, T. Kamidate, H. Watanabe, Anal. Sci. 14 (1998) 875–888. [5] W.J. Horvath, C.W. Huie, Talanta 39 (1992) 487–492. [6] J.X. Xiao, U. Sivars, F. Tjerneld, J. Chromatogr. B 743 (2000) 327–338. [7] H.G. Xie, Y.J. Wang, M. Sun, Process. Biochem. 41 (2006) 689–696. [8] K.E. Gutowski, G.A. Broker, H.D. Willauer, J.G. Huddleston, R.P. Swatloski, J.D. Holbrey, R.D. Rogers, J. Am. Chem. Soc. 125 (2003) 6632–6633. [9] C. He, S. Li, H. Liu, K. Li, F. Liu, J. Chromatogr. A 1082 (2005) 143–149. [10] S. Li, C. He, H. Liu, K. Li, F. Liu, J. Chromatogr. B 826 (2005) 58–62. [11] M.T. Zafarani, S. Hamzezadeh, J. Chem. Eng. Data 57 (2007) 1686–1692. [12] S. Dreyera, P. Salimb, U. Kragl, Biochem. Eng. J. 46 (2009) 176–185. [13] A. Salabat, M. Alinoori, CALPHAD 32 (2008) 611–614. [14] M.D. Womack, D.A. Kendall, R.C. MacDonald, Biochem. Biophys. Acta 733 (1983) 210–216. [15] A. Salabat, Fluid Phase Equilib. 187–188 (2001) 489–498. [16] E. Edmond, A.G. Ogston, Biochem. J. 109 (1968) 569–574. [17] L.H. Haraguchi, R.S. Mohamed, W. Loh, P.A. Pessoa Filho, Fluid Phase Equilib. 215 (2004) 1–5.