Phase separation in aqueous systems for realizing virtually significant extractions

Abstract

Polyvinylpyrrolidone (PVP) forms aqueous biphasic systems with tri-block co-polymers, surfactants and salts. The phase diagrams of PVP–salt and PVP–surfactant systems were constructed by a turbidometric titration method at 296 K. Density measurements of the phase forming solutions at this temperature also led to an attractive outcome of the formation of two tri-phasic systems among the components of our study (Na-tartrate + PVP + Triton-X-100 and Na-tartrate + PVP + PPG–PEG–PPG). We also constructed a spreadsheet reflecting the relationship between miscibility and the possibility of phase separation between the components, consisting of the seven phase forming solutions to open up different possibilities of ABS formation. Some completely new biphasic systems were obtained as well as the process of gel formation of a PVA solution in the presence of salt and polymer solutions was also observed. The applications of some of the developed ABSs are described for the recovery of an antibiotic drug, amoxicillin and a catalyst, molybdenum disulphide.

---

Introduction

Environmental concerns and sustainability requirements have led to a demanding research field with unconventional solvents and extraction techniques. Aqueous biphasic systems (ABSs) provide an alternative which is an efficient and clean technique and has a wide spectrum of applications. The mixing of certain mutually incompatible aqueous solutions of polymers, or of a polymer and a salt or two solutions of salts above certain critical thermodynamic conditions leads to the formation of distinctly separable phases.^1–3 Both phases are composed predominantly of water, and each is richer in one of the components over the other. As both the phases are aqueous solutions, they may form a single phase initially upon mixing, which becomes more and more impossible as the concentrations of both the solutes increase and finally result in a separation of the two phases. Depending on the components of the biphase and their compositions several types of mechanisms have been suggested for this in the literature, like salting out, hydrophilic and hydrophobic interactions, etc.⁴ In case of ionic liquid–salt and polymer–salt biphasic systems, salting out phenomenon in assistance with hydrophobic interactions have been demonstrated.^5,6 Whilst for a polymer–polymer ABS, the hydrophobic interactions, difference in polarity of the components and hydrogen bond orientation in the two phases are described as the main reasons behind biphase formation.⁷ Moreover, if a solute is added to this biphasic system it will distribute unevenly between the two phases depending upon various hydrophobic or electrostatic interactions of the solute with the solvent. Conventional polymer-based ABSs have been largely explored since the 1980's. These are mainly composed of two incompatible polymers or a polymer and a salt having a salt-out inducing effect. In 2003, Rogers and co-workers reported a new alternative, pointing towards the possible creation of ABS by the addition of inorganic salts to aqueous solutions of ionic liquids⁵ and since then considerable effort has been given towards the development of hydrophilic ionic liquids for replacing the polymer-rich phases.^8–10 ABS formed from ionic liquids in conjunction with different kosmotropic salts, carbohydrates, amino acids and different polymers along with their applications have been discussed in a very recent review.⁴ Due to the inherent aqueous environment, ABSs are recognized as biocompatible systems for cells, cell organelles and biologically active substances in downstream processing.^11,12 It is suitable for the separation and purification of a broad array of biomolecules, metal species, dyes, drug molecules and small organic moeities.^13,14 Furthermore, the low cost, high capacity, ease to scale-up, possibility of direct application to fermentation broths and use of environmentally benign green solvents are the obvious advantages.

Phase separation in solutions containing polymer mixtures is very familiar phenomenon.^7,15 In aqueous solutions most hydrophilic polymer pairs can form a biphase and the driving force for the demixing process is the enthalpy associated with the interactions of the components, which is opposed by the loss in entropy associated with the segregation of the components during phase separation.¹⁶ Water, as a universal solvent, is capable to engage in different non-covalent interactions with the polymer. Such interactions increase with the molecular size of the polymers. The phase separation in such polymer–polymer biphasic systems occur at very low polymer concentrations because of the large size of the polymers and consequently small loss in entropy upon demixing.^17–19 However, in case of polymer–salt two-phase systems the salt-out inducing capacity of the salts takes a crucial role for the phase separation process.

Antibiotic compounds are normally procured from aqueous environments, which require further separation and purification steps. These steps involve large production cost. Thus, improvement of the separation and purification methods can make significant savings to the overall manufacturing costs. On the other hand, the issue of the remnants of antibiotic in the environment is a matter of scientific attention in the recent years. A range of separation methods such as conventional solvent extraction, ion-exchange, chromatography, crystallization, or a combination of these methods have been used for the recovery of antibiotics.^20–22 However, most of the times the separation techniques are time consuming as is the case for ion-exchange, chromatography and crystallization. The solvent extraction methods need expensive solvents and are not free from solvent contamination.

Molybdenum disulfide (MoS₂) is an effective co-catalyst for desulfurization in petrochemistry and it is completely insoluble in water and most of the organic solvents. To improve the efficacy of the MoS₂ as a catalyst, trace amounts of metal like cobalt or nickel is doped into it. Such catalysts are generated by treating molybdate/cobalt or nickel-impregnated alumina with H₂S or other equivalent reagent. Regeneration of the catalyst in an uncontaminated form after its chemical activities is very crucial. Even for heterogeneous systems, minute amounts of the material are lost in each step. A comparative study of catalyst regeneration methods have been reported in the literature.²³ ABS assisted regeneration may reduce this loss because of entrapment of the fine particles of the powdery material inside the micellar matrix of the polymer rich phase. In addition, MoS₂ has important contributions in the field of energy conversion and energy storage. It has been identified as promising catalyst for electrocatalytic or photoelectrocatalytic hydrogen evolution. MoS₂ and its composites also find application as electrode materials in Li ion batteries.²⁴

In our present work we have explored polyvinylpyrrolidone (PVP) based aqueous two-phase systems with different aqueous solutions of polymer, tri-block co-polymer, surfactant and salt and also the possibility of ABS formation of one of these with the other. In literature, some PVP–salt ABSs are reported.^25–28 However, none of the systems were analyzed for the possibility of their applications. PVP being a biocompatible polymer, has the potential to be applied for sustainable extractions. In fact they are used as drug excipients in pharmaceutical sciences.

Keeping this in mind and realizing several other possibilities of PVP solution to form biphasic systems, we explored the new possibilities of their ABS formation. In this work, we have characterized the two-phase systems consisting of polymer–salt [PVP (40%) + Na-tartrate (1.8 M)] and polymer–surfactant [PVP (30%) + Triton-X-100 (30%)] and established the possibility of their applications in separating amoxicillin and MoS₂ which are of immense practical importance.

Experimental

Materials

Polyvinylpyrrolidone (PVP) [(C₆H₉NO)_n] (MW = 40 000) (Spectrochem), di-sodium tartrate dihydrate (Merck, 99%), Triton-X-100 (TX) (octylphenol polyethoxylene, C₃₄H₆₂O₁₁) (Spectrochem), poly(propyleneglycol)-block-poly(ethyleneglycol)-block-poly(propyleneglycol) (PPG–PEG–PPG) (MW = 2000) (Sigma Aldrich), poly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol) (PEG–PPG–PEG) (MW = 5800) (Sigma Aldrich), poly(vinylalcohol) (PVA) (MW = 89 000–98 000) (Sigma Aldrich), polyethylene glycol (PEG) (MW = 6000) (Merck), amoxicillin (Wyeth), molybdenum disulphide (MoS₂) (Loba Chemie, 98%).

Apparatus

The UV visible spectra were obtained using an Agilent 8453 diode array spectrophotometer. Absorbance values are measured up to fifth decimal place. Centrifugation was done using Hermle microprocessor controlled universal refrigerated high speed table top centrifuge (model Z 36 K) operated on 230 V/50 Hz with an adjustable speed range of (200 to 30 000) rpm. The density was measured using a Mettler Toledo portable density meter (model 30PX). Density values were measured precisely up to fourth place of decimal. A BOD incubator shaker NOVA model: SHCI 10(D) was used to maintain the temperature at 296 ± 0.5 K. A Mettler Toledo digital balance correct up to fourth decimal place was used for measuring the weights.

Construction of the phase diagrams

The phase diagrams of our proposed PVP-based ABSs were constructed by the simple turbidometric titration method.^25,29–33 Binodal curves were obtained for the biphasic compositions of PVP (40%)/Na-tartrate (1.8 M) and PVP (30%)/TX (30%) systems. For this purpose, the initial weight of the blank centrifuge tube was recorded. Experimental sets with different weight fractions were prepared keeping the final weight 3 g in each case. Now the mixtures were shaken uniformly for 5 min in BOD shaker at 296 K. The solutions were then centrifuged for 5 min at 4500 rpm at the same temperature. Two distinct phases were observed, and the weight of the tube was taken. Water was added dropwise to the biphasic solution, and the same procedure was repeated until the system turned clear; that is, a single phase was formed. The final weight of the centrifuge tube was noted and the amount of water added just prior to mono-phase formation was noted. Now after calculating the system composition of the phase forming components, their resulting compositions were determined considering the amount of water added in different sets. Weight percentages of PVP/Na-tartrate and PVP/TX, for variable sets were plotted, and two binodals were obtained. By convention, the component predominantly in the bottom phase was plotted in the abscissa (Na-tartrate and PVP respectively in the two systems), and the component predominantly in the top phase was plotted as the ordinate (PVP and TX).

Determination of the tie-lines

The experimental binodal curves were further fitted by the following equation proposed by Merchuk et al.³⁴

Y = A exp[(BX^0.5) − (CX³)] (1)

where, Y and X are the mass fraction of the two components respectively. A, B, and C are constants obtained by the regression of the experimental binodal data. The tie-lines associated with the phase diagrams were obtained by a simple gravimetric method.⁵ Ternary mixtures composed of PVP + Na-tartrate + water and PVP + TX + water at the biphasic region were gravimetrically prepared, strongly agitated, and left to equilibrate for 24 h at (296 ± 0.5) K, for a complete separation of the coexisting phases. Both phases were then carefully separated and individually weighed.

Each TL was determined by the lever-arm rule through the relationship between the top phase composition and the overall system composition and for which the following system of four equations (eqn (2)–(5)) and four unknown factors were solved.

Y_T = A exp[(B × X_T^0.5) − (C × X_T³)] (2)

Y_B = A exp[(B × X_B^0.5) − (C × X_B³)] (3)

where T, B, and M, designate the top phase, the bottom phase and the mixture, respectively; X and Y represent the weight fraction percentage of the phase forming components of PVP/Na-tartrate and PVP/TX respectively; is the ratio between the mass of the top phase and the total mass of the mixture. Each tie-line length (TLL) and slope of the tie-lines (STL) could be obtained using the following equation:

STL = (Y_T − Y_B)/(X_T − X_B) (7)

where T, B, and M, represent the top phase, the bottom phase and the mixture, respectively; and X and Y represent the equilibrium weight fraction percentages of the phase forming components.

Density measurements and tri-phase formation

The densities of the biphase forming solutions of different concentrations were measured at 296 K. Now considering the density values we can easily determine the compositions/concentrations where the existence of the biphase would be logical and the potential working area of the two-phase system can be achieved. The density values are tabulated in Table 1. However, from the density values of PVP (30% and 40%), TX (30%), Na-tartrate (1.8 M) and PPG–PEG–PPG (80%), it is evident that there is a possibility of tri-phase formation which would be a very interesting outcome.

Table 1 Density values (ρ) of different solutions (S) at different concentrations (C) at temperature T = 296 K and pressure p = 0.1 MPa

S	C	ρ (g cm^−3)
PVP	30%	1.045
PVP	40%	1.061
Na-tartrate	1.8 M	1.180
Triton-X-100	30%	1.028
PPG–PEG–PPG	80%	1.072
PEG–PPG–PEG	30%	1.015

---

The possibility of different biphasic systems

In our present work, we have explored a series of ABSs with polymers, surfactant and salt in combination with each other. Solutions of each of the components with different concentrations were checked for their possibility to form an ABS with the other members of the series. All the possibilities were explored to find new ABSs originating from these precursors.

Application in extraction of amoxicillin

3 capsules of Wymox (500 mg) were dissolved in 6 mL triple-distilled water. The solution was then centrifuged at 4500 rpm for 20 minutes and filtered with a Whatman 40 filter paper to remove the binder material. Considering this as a standard amoxicillin solution a calibration was done in the PVP medium using its absorbance spectra. The absorbance maximum of the amoxicillin solution was at the wavelength λ_max = 360 nm. For the extraction purpose, we took two of our newly designed aqueous-two phase systems, PVP/tartrate and PVP/TX. To the biphasic system containing PVP (3 mL) + Na-tartrate (3 mL), 0.3 mL of the amoxicillin solution was added, shaken well for 5 minutes in BOD shaker and centrifuged for 5 minutes at 4500 rpm at 296 K. Both the phases were separated out and absorbance of the PVP rich phase was measured. Same procedure was followed for the PVP/TX system also. The percentage extractions of Amoxicillin were calculated using the following equation:where, [x]_{top phase} was the concentration of a particular component in the top phase and [x]_{bottom phase} was the concentration of the particular component in the bottom phase.

Application in extraction of molybdenum disulphide

We performed an extraction study of MoS₂ in our proposed PVP/Na-tartrate and PVP/TX ABSs. A broad absorption peak was obtained for MoS₂ both in PVP and TX medium at the wavelength 560 nm. A calibration was done using increasing concentrations of MoS₂ in PVP medium. A known amount of MoS₂ was taken in the ABS and extractions were performed in the usual way. The PVP rich phase was separated and analyzed for its absorbance. The percent extraction was calculated as before using eqn (8).

Results and discussion

Phase diagram and the tie-lines

The construction of phase diagram is very important to obtain the biphasic region and to ascertain the preliminary partitioning. The phase diagram demarcates the active working area for a particular biphasic system. By plotting the weight compositions of the two components a binodal curve is obtained, which separates a zone of component concentrations that will form two immiscible aqueous phases (the region above the curve) from those that will form a homogenous single phase (the region at and below the curve). The phase diagrams of the PVP/Na-tartrate and PVP/TX systems were obtained at 296 K (Fig. 1 and 2) and the details of system compositions and final compositions are tabulated in Table 2 and 3 respectively.

Fig. 1 Phase diagram of PVP + Na-tartrate aqueous two phase drawn at 296 K. Abscissa shows the weight fraction of Na-tartrate and ordinate shows the weight fraction of PVP.

Fig. 2 Phase diagram of PVP + TX aqueous two phase drawn at 296 K. Abscissa shows the weight fraction of PVP and ordinate shows the weight fraction of TX.

Table 2 Experimental (liquid + liquid) equilibrium mass fractions (binodal curve data) for the system Na-tartrate (x₁) + PVP (x₂) in water at temperature T = 296 K, pressure p = 0.1 MPa

System composition		Final composition
x1	x2	x1	x2
14.7	28	14.4	27.6
15.1	27	14.7	26.4
15.4	25	15.0	24.8
16.0	24	15.5	23.0
18.0	23	15.9	21.0
19.0	21	16.4	18.8
20.0	20	17.0	17.0
21.0	19	17.4	15.7
22.0	18	18.0	14.3

---

Table 3 Experimental (liquid + liquid) equilibrium mass fractions (binodal curve data) for the system PVP (x₁) + Triton-X-100 (x₂) in water at temperature T = 296 K, pressure p = 0.1 MPa

System composition		Final composition
x1	x2	x1	x2
10	20	8.0	16.1
11	19	8.8	15.3
12	18	9.7	14.4
13	17	10.4	13.6
14	16	11.1	12.7
15	15	12.0	12.0
16	14	12.8	11.2
17	13	14.0	10.7
18	12	14.8	9.9
19	11	15.8	9.2

---

The ternary phase diagrams of PVP + water + Na-tartrate and PVP + water + TX along with the respective tie lines are shown in Fig. 3 and 4 respectively. By connecting two nodes on these plots we get tie-lines, each point on the tie line represents the final concentrations of phase components in the top and bottom phases. Any point on the tie-line coordinates represent systems with varying total compositions and volume ratios, but the same final concentration of the phase components in the top and bottom phases. All the tie line lengths were calculated using eqn (2)–(5) and are presented in Table 4 and 5 for PVP/tartrate and PVP/TX systems respectively. Fitting parameters, A, B, C and R² values are given in Table 6. Phase diagram is a characteristic feature unique to the particular ABS under set conditions of component concentration, pH and temperature.

Fig. 3 Ternary phase diagram of water–PVP–Na-tartrate system drawn at 296 K. Weight fractions of Na-tartrate, water and PVP are shown in the three coordinates.

Fig. 4 Ternary phase diagram of water–PVP–TX system drawn at 296 K. Weight fractions of PVP, water and TX are shown in the three coordinates.

Table 4 Experimental (liquid + liquid) equilibrium data for the system Na-tartrate (x₁) + PVP (x₂) in water for mass fractions and Tie-line Length (TLL) at the temperature T = 296 K, pressure p = 0.1 MPa

Feed composition		Top phase		Bottom phase		TLL	STL
x1	x2	x1	x2	x1	x2
16.1	20	13.94	30.30	19.38	10.78	20.27	−3.58
17.18	18.67	12.97	36.35	20.83	8.08	29.34	−3.60

---

Table 5 Experimental (liquid + liquid) equilibrium data for the system PVP (x₁) + Triton-X-100 (x₂) in water for mass fractions and Tie-line Length (TLL) at the temperature T = 296 K, pressure p = 0.1 MPa

Feed composition		Top phase		Bottom phase		TLL	STL
x1	x2	x1	x2	x1	x2
15	15	2.75	26.87	26.22	4.12	32.68	−0.97
14	16	2.77	26.81	26.42	4.05	32.83	−0.96
13	17	2.73	26.92	26.39	4.06	32.89	−0.97

---

Table 6 Fitting parameters of the binodal curves

ABS	A	B	C × 10^−5	R^2
PVP + TX	54.143	−0.4228	2.287	0.996
PVP + Na-tartrate	2395.747	−1.12657	6.097	0.998

---

Density measurements and tri-phase formation

The two aqueous phases of the biphasic systems organize spontaneously according to their densities. As water is the common component in the two phases, the interfacial surface energy between the phases of an ABS is extremely low.^35,36 Moreover, water being the common solvent in phase-separated systems enables the analysis of biological mixtures. Now if three solutions X, Y and Z have different densities and binary mixtures of these phases form X/Y, Y/Z and X/Z two-phase systems, then there is a fair possibility that a mixture of components X/Y/Z would produce a three-phase system. This has been actually observed using our current aqueous solutions. From the combinations we observe two triphase systems, one consisting of Na-tartrate (bottom layer) + PVP (middle layer) + TX (top layer) [salt + polymer + surfactant] and another one consisting of Na-tartrate (bottom layer) + PVP (middle layer) + PPG–PEG–PPG (top layer) [salt + polymer + tri block copolymer]. These tri-phasic systems might be highly applicable for minute analytical separations, selective extractions and recovery of biomolecules, drugs, catalysts, etc. Fig. 5 shows the two tri-phasic systems.

Fig. 5 Triphasic systems.

The possibility of different biphasic systems

We have constructed a spreadsheet reflecting the relationship between miscibility and possibility of phase separation between the components, consisting of the seven phase forming solutions. We observed a broad array of aqueous two-phase systems composed of polymer–salt, polymer–surfactant, and polymer-block copolymer solutions. However, PVP forms single phase with polyethylene glycol (PEG) and poly vinylalcohol (PVA). So, all the probable combinations for ABSs resulting out of the above phase forming solutions were sorted. These result in the formation of some completely new aqueous two-phase systems as well as some interesting outcomes like gel formation of PVA solution in presence of Na-tartrate,³⁷ PEG and co-polymer PPG–PEG–PPG solutions were observed. The systems are represented pictorially in Fig. 6.

Fig. 6 Aqueous biphasic systems comprising of polymers, salt, block copolymer and surfactant. Two-component mixtures produced three outcomes: no phase separation (miscible, red), formation of gel (incompatible, yellow), or phase separation (immiscible, green). (1) PVP (40%); (2) Na-tartrate (1.8 M); (3) TX (30%); (4) PPG–PEG–PPG (80%); (5) PEG–PPG–PEG (30%); (6) PEG (50%); (7) PVA (5%).

Application in extraction of amoxicillin

Amoxicillin is an oral medicine frequently used as antibiotic drug. Extraction and separation of this drug from various matrices have been reported using various methods like solid phase extraction^38,39 and micellar extraction.⁴⁰ Solid phase extractions involving molecularly imprinted polymers,³⁸ and reverse phase column chromatographic methods³⁹ are reported in the literature. However, the main difficulty with the solid phase extraction is the regeneration of the compound by desorption which is time consuming and eluant dependent. Additionally, the reported extraction percentages using the two methods are 75% and 78.2% respectively which definitely need further improvements. In micellar extraction (90–95% efficiency), mixed AOT-TWEEN 85 reverse micelles were used for extraction of amoxicillin.⁴⁰ The method involves a series of forward and backward extractions and has the disadvantage of surfactant medium which needs to be removed from the drug for its proper regeneration. Amoxicillin is water soluble and so recovery of this drug in ABS is easy to scale up. The advantage of using PVP as the matrix lies in the fact that PVP itself acts as a binder and a drug excipient which need not be removed further. We performed the extraction study of amoxicillin using two of our newly designed PVP based aqueous two phase systems (PVP + Na-tartrate and PVP + Triton-X-100). After phase separation, UV-visible spectra of both the phases were obtained. A typical absorbance spectrum of amoxicillin used for its calibration is shown in Fig. S1† which agrees with the literature⁴¹ in having a λ_max ≈ 360 nm pertaining to the π → π* transition arising out of the delocalized π orbitals of the benzene ring present in amoxicillin. We found that amoxicillin was exclusively extracted in PVP rich phase. The percentage extraction of the drug in the PVP rich phase of the two biphasic systems were calculated using suitable calibration curves and is presented in Fig. 7. The reason behind the extraction of amoxicillin in PVP rich phase in both the cases may be attributed to the intermolecular nitrogen–sulphur nonbonding interactions between the N atom of PVP and S containing moiety of amoxicillin. Such N–S nonbonding interactions have proven effect on chemical systems.⁴² The absence of nitrogen in both TX and sodium tartrate has facilitated the quantitative extraction of the drug in PVP phase alone.

Fig. 7 Extraction profile of amoxicillin in PVP medium against Na-tartrate and TX phase of aqueous two-phase systems.

Application in extraction of molybdenum disulfide

MoS₂ functions as an effective natural lubricant and is completely insoluble in water and other organic solvents. The catalyst does not react to most of the acids except aqua-regia and hot concentrated sulfuric acid, hydrochloric acid and nitric acid. So regeneration of this catalyst is quite difficult to carry out. In addition, the problem with most heterogeneous catalysts is its poisoning that occurs due to the blockage of active sites by the products and side products present in the medium. Therefore it is necessary to regenerate the catalyst by removing the poisons as completely as possible. H₂ treatment at high temperatures is a common practice to attain this. These reactions in turn are often exothermic.^43,44

In polymeric solution the catalyst forms a suspension in the micellar medium at tracer concentrations. If the reaction occurs in aqueous medium, it would not be difficult to wash off the poisons from the catalyst surface and extract in the PVP phase of ABS. So we dissolved MoS₂ in PVP solution at millimolar concentration and extracted it using our proposed biphasic system. In the polymeric matrix of PVP, MoS₂ shows a double humped broad spectrum which shows gradually increasing absorbance value with increasing concentration (Fig. S2†). This spectrum resembles with that reported in the literature for crystalline MoS₂.⁴⁵

The typical broad humped nature and slight changes in the peak positions are attributed to the particle size distribution of MoS₂ in the dispersed state depending on the nature of the medium. In agreement with the literature, the spectra consist of a well-defined shoulder at ∼530 nm, and low-intensity long-wave absorption at λ_max > 600 nm. In case of PVP/Na-tartrate system we found that MoS₂ was exclusively extracted in PVP medium which was confirmed by absorbance measurement (Fig. 8). The preference of MoS₂ for PVP may again be attributed to weak N–S nonbonding interactions which allows the catalyst to get extracted in the PVP rich phase. However, if the biphasic system containing MoS₂ is allowed to settle for a few hours, it accumulates as dust at the PVP/Na-tartrate biphasic interface and from there the catalyst can be easily separated out. In PVP/TX ABS, MoS₂ is alienated in the PVP rich phase (bottom phase) and can be regenerated properly. In this case also an initial N–S nonbonding interaction seems to be responsible for the extraction of MoS₂ in the PVP rich phase as before. However, if allowed to settle for a longer time, the MoS₂ particles aggregate and gradually settle down.

Fig. 8 Extraction profile of MoS₂ in PVP medium against Na-tartrate and TX phase of aqueous two-phase systems.

Conclusion

Some potential aqueous biphasic systems were designed involving PVP, Na-tartrate, Triton X-100, PEG, PVA and the block copolymers, PPG–PEG–PPG and PEG–PPG–PEG. A range of some new two phase systems was obtained upon combining these solutions at particular concentrations. Well defined phase diagrams with suitable tie lines were obtained for two-phase systems consisting of polymer–salt [PVP (40%) + Na-tartrate (1.8 M)] and polymer–surfactant [PVP (30%) + Triton-X-100 (30%)] at 296 K. These two ABSs were also found to be potentially suitable for separation and regeneration of antibiotic drug amoxicillin and catalyst MoS₂. PVP being a biocompatible water soluble polymer, is most suited for drug delivery action. Once the antibiotic is extracted in PVP rich phase it needs no further preconcentration or separation indicating its suitability both as an extracting and pharmaceutical reagent. The regeneration method of MoS₂ will be yet another contribution to the field of catalysis relevant to chemical synthesis. The present work may form the directive of solving several separation-based analytical problems and that too using an environmentally benign and sustainable technique.

Acknowledgements

We gratefully acknowledge Department of Science and Technology (Fast Track Sanction no. SR/FT/CS-105/2011) for funding. One of the authors, AC thanks DST Fast Track for providing necessary fellowship.

References

1. W. J. Fawcett, E. J. Haxby and D. A. Mal, Br. J. Anaesth., 1999, 83, 302–320.
2. D. Das and K. Sen, J. Ind. Eng. Chem., 2012, 18, 855–859.
3. J. G. Huddleston, H. D. Willauer and R. D. Rogers, J. Chem. Eng. Data, 2003, 48, 1230–1236.
4. M. G. Freire, A. F. M. Cláudio, J. M. M. Araújo, J. A. P. Coutinho, I. M. Marrucho, J. N. C. Lopesac and L. P. N. Rebelo, Chem. Soc. Rev., 2012, 41, 4966–4995.
5. K. E. Gutowski, G. A. Broker, H. D. Willauer, J. G. Huddleston, R. P. Swatloski, J. D. Holbrey and R. D. Rogers, J. Am. Chem. Soc., 2003, 125, 6632–6633.
6. L. A. Ferreira and J. A. Teixeira, J. Chem. Eng. Data, 2011, 56, 133–137.
7. M. L. Moody, H. D. Willauer, S. T. Griffin, J. G. Huddleston and R. D. Rogers, Ind. Eng. Chem. Res., 2005, 44, 3749–4376.
8. F. J. Deive, A. Rodríguez, A. B. Pereiro, J. M. M. Araújo, M. A. Longo, M. A. Z. Coelho, J. N. Canongia Lopes, J. M. S. S. Esperanc, L. P. N. Rebelo and I. M. Marrucho, Green Chem., 2011, 13, 390–396.
9. X. Lin, Y. Wang, X. Liu, S. Huang and Q. Zeng, Analyst, 2012, 137, 4076–4085.
10. M. G. Freire, C. L. S. Louros, L. P. N. Rebelo and J. A. P. Coutinho, Green Chem., 2011, 13, 1536–1545.
11. P. Å. Albertsson, Partition of cell particles and macromolecules, ed. John Wiley & Sons Inc., New York, 1971.
12. Partitioning in Aqueous Two-Phase Systems: Theory, Methods, Use, and Applications to Biotechnology, ed. H. Walter, D. E. Brooks and D. Fisher, Academic Press, Orlando, FL, 1985.
13. B. Y. Zaslavsky, Aqueous two-phase partitioning, Marcel Dekker Inc, New York, 1995.
14. A. Frerix, P. Geilenkirchen, M. Muller, M.-R. Kula and J. Hubbuch, Biotechnol. Bioeng., 2007, 96, 57.
15. F. L. C. Machado, J. S. R. Coimbra, A. D. G. Zuniga, A. R. Costa and J. P. Martins, J. Chem. Eng. Data, 2012, 57, 1984–1990.
16. M. G. Freire, F. M. Claudio, J. M. M. Araujo, J. A. P. Coutinho, I. M. Marrucho, J. N. C. Lopes and L. P. N. Rebelo, Chem. Soc. Rev., 2012, 41, 4966–4995.
17. Partition in Aqueous Two-phase Systems. Theory, Methods, Uses and Applications to Biotechnology, ed. H. Walter, D. E. Brooks and D. Fisher, Academic, Orlando, FL, 1985.
18. J. N. Baskir, T. A. Hatton and U. W. Suter, Biotechnol. Bioeng., 1991, 34, 541–558.
19. N. L. Abbot, D. Blankschtein and T. A. Hatton, Bioseparation, 1990, 1, 191–225.
20. M. Setapar and S. Hamidah, Liquid–liquid separation of antibiotic with reverse micelles, inAdvances in Separation Processes, Penerbit UTM, Johor, 2007, pp. 154–171.
21. D. G. Rao, Introduction to Biochemical Engineering, Tata McGraw Hill, New Delhi, India, 2nd edn, 2010.
22. M. Chun-hong, W. Wang Liang, Y. Yong-sheng, C. Guang-bo, Y. Yan-su, W. Ren-zhang and L. Dong-ying, Chem. Res. Chin. Univ., 2009, 25, 832–835.
23. M. Sheintuch and Y. I. M. Meytal, Catal. Today, 1999, 53, 73–80.
24. Y. Zhao, Y. Zhang, Z. Yang, Y. Yan and K. Sun, Sci. Technol. Adv. Mater., 2013, 14, 043501–043513.
25. R. Sadeghi, Fluid Phase Equilib., 2006, 246, 89–95.
26. B. Y. Zaslavsky, A. U. Mahmudov, T. O. Bagirov, A. A. Borovskaya, G. Z. Gasanova, N. D. Gulaeva, V. Y. Levin, N. M. Mestechkina, L. M. Miheeva and M. N. Rodnikova, Colloid Polym. Sci., 1987, 265, 548–552.
27. R. Sadeghi, Fluid Phase Equilib., 2005, 237, 40–47.
28. M. T. Zafarani-Moattar and R. Sadeghi, Fluid Phase Equilib., 2005, 238, 129–135.
29. R. Hatti-Kaul, Methods in Biotechnology: Aqueous Two Phase Sytems, Methods and Protocol, Humana Press, Totowa New Jersey, 2000, p. 11.
30. P. G. Tello, F. Camacho, G. Blázquez and F. J. Alarcon, J. Chem. Eng. Data, 1996, 41, 1333–1336.
31. F. Rashimpour and A. R. Baharvand, World Acad. Sci. Eng. Tech., 2009, 35, 150–155.
32. G. Blázquez, G. Camacho, P. González-Tello and F. J. Alarcón, Biochim. Biophys. Acta, Gen. Subj., 1998, 1379, 191–197.
33. A. Chakraborty and K. Sen, J. Chem. Eng. Data, 2014, 59, 1288–1294.
34. J. C. Merchuk, B. A. Andrews and J. A. Asenjo, J. Chromatogr. B: Biomed. Sci. Appl., 1998, 711, 285–293.
35. C. R. Mace, O. Akbulut, A. A. Kumar, N. D. Shapiro, R. Derda, M. R. Patton and G. M. Whitesides, J. Am. Chem. Soc., 2012, 134, 9094–9097.
36. P.-Å. Albertsson, Partition of Cell Particles and Macromolecules, Wiley Interscience, New York, 1986.
37. P. Samaddar and K. Sen, J. Sol-Gel Sci. Technol., 2014 in press.
38. A. Beltran, R. M. Marcé, P. A. Cormack, D. C. Sherrington and F. Borrull, J. Sep. Sci., 2008, 31, 2868–2874.
39. T. F. Kuo, Y. K. Wang, S. Y. Sheu, M. H. Chang and J. H. Wang, Taiwan Vet. J., 2009, 35, 66–74.
40. S. C. Chuo, S. H. Mohd-Setapar, S. N. Mohamad-Aziz and V. M. Starov, Colloids Surf., A, 2014, 460, 137–144.
41. G. Tiwari, R. Tiwari, B. Srivastava, A. K. Rai and K. Pathak, Asian J. Res. Chem., 2008, 1, 91–94.
42. S. Lin, S. T. Wrobleski, J. Hynes Jr, S. Pitt, R. Zhang, Y. Fan, A. M. Doweyko, K. F. Kish, J. S. Sack, M. F. Malley, S. E. Kiefer, J. A. Newitt, M. McKinnon, J. Trzaskos, J. C. Barrish, J. H. Dodd, G. L. Schieven and K. Leftheris, Bioorg. Med. Chem. Lett., 2010, 20, 5864–5868.
43. Handbook of Heterogeneous Ca-talysis, ed. D. L. Trimm, G. Ertl, H. Knozinger and J. Weit-kamp, Wiley-VCH, Weinheim, 1997, vol. 3.
44. H. Hiller, et al., Gas Production, in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2006, vol. A12.
45. I. V. Klimenko, A. S. Golub, T. S. Zhuravleva, N. D. Lenenko and Y. N. Novikov, Russ. J. Phys. Chem. A, 2009, 83, 276–280.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra06798c

---