Aqueous two-phase system

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Aqueous biphasic systems (ABS) or aqueous two-phase systems (ATPS) are clean alternatives for traditional organic-water solvent extraction systems.

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ABS are formed when either two polymers, one polymer and one kosmotropic salt, or two salts (one chaotropic salt and the other a kosmotropic salt) are mixed at appropriate concentrations or at a particular temperature. The two phases are mostly composed of water and non volatile components, thus eliminating volatile organic compounds. They have been used for many years in biotechnological applications as non-denaturing and benign separation media. Recently, it has been found that ATPS can be used for separations of metal ions like mercury and cobalt, [1] carbon nanotubes, [2] [3] [4] environmental remediation, metallurgical applications and as a reaction media.

Introduction

In 1896, Beijerinck first noted an 'incompatibility' in solutions of agar, a water-soluble polymer, with soluble starch or gelatine. [5] Upon mixing, they separated into two immiscible phases.

Subsequent investigation led to the determination of many other aqueous biphasic systems, of which the polyethylene glycol (PEG) - dextran system is the most extensively studied. Other systems that form aqueous biphases are: PEG - sodium carbonate or PEG and phosphates, citrates or sulfates. Aqueous biphasic systems are used during downstream processing mainly in biotechnological and chemical industries.

The two phases

It is a common observation that when oil and water are poured into the same container, they separate into two phases or layers, because they are immiscible. In general, aqueous (or water-based) solutions, being polar, are immiscible with non-polar organic solvents (cooking oil, chloroform, toluene, hexane etc.) and form a two-phase system. However, in an ABS, both immiscible components are water-based.

The formation of the distinct phases is affected by the pH, temperature and ionic strength of the two components, and separation occurs when the amount of a polymer present exceeds a certain limiting concentration (which is determined by the above factors).

PEG–dextran system

The "upper phase" is formed by the more hydrophobic polyethylene glycol (PEG), which is of lower density than the "lower phase," consisting of the more hydrophilic and denser dextran solution.

Although PEG is inherently denser than water, it occupies the upper layer. This is believed to be due to its solvent 'ordering' properties, which excludes excess water, creating a low density water environment. [6] The degree of polymerization of PEG also affects the phase separation and the partitioning of molecules during extraction.[ citation needed ]

Advantages

ABS is an excellent method to employ for the extraction of proteins/enzymes and other labile biomolecules from crude cell extracts or other mixtures. Most often, this technique is employed in enzyme technology during industrial or laboratory production of enzymes.

Specificity may be further increased by tagging ligands specific to the desired enzyme, onto the polymer. This results in a preferential binding of the enzyme to the polymer, increasing the effectiveness of the extraction.

One major disadvantage, however, is the cost of materials involved, namely high-purity dextrans employed for the purpose. However, other low-cost alternatives such as less refined dextrans, hydroxypropyl starch derivatives and high-salt solutions are also available.

Thermodynamic Modeling

Besides the experimental study, it is important to have a good thermodynamic model to describe and predict liquid-liquid equilibrium conditions in engineering and design. To obtain global and reliable parameters for thermodynamic models usually, phase equilibrium data is suitable for this purpose. As there are polymer, electrolyte and water in polymer/salt systems, all different types of interactions should be taken into account. Up to now, several models have been used such as NRTL, Chen-NRTL, Wilson, UNIQUAC, NRTL-NRF and UNIFAC-NRF. It has been shown that, in all cases, the mentioned models were successful in reproducing tie-line data of polymer/salt aqueous two-phase systems. In most of the previous works, excess Gibbs functions have been used for modeling. [7]

Related Research Articles

<span class="mw-page-title-main">Phase (matter)</span> Region of uniform physical properties

In the physical sciences, a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air is a third phase over the ice and water. The glass of the jar is another separate phase.

<span class="mw-page-title-main">Solution (chemistry)</span> Homogeneous mixture of a solute and a solvent

In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. These surrounded solute particles then move away from the solid solute and out into the solution. The mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution usually has the state of the solvent when the solvent is the larger fraction of the mixture, as is commonly the case. One important parameter of a solution is the concentration, which is a measure of the amount of solute in a given amount of solution or solvent. The term "aqueous solution" is used when one of the solvents is water.

<span class="mw-page-title-main">Solubility</span> Capacity of a substance to dissolve in a solvent in a homogeneous way

In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.

<span class="mw-page-title-main">Separatory funnel</span> Laboratory glassware

A separatory funnel, also known as a separation funnel, separating funnel, or colloquially sep funnel, is a piece of laboratory glassware used in liquid-liquid extractions to separate (partition) the components of a mixture into two immiscible solvent phases of different densities. Typically, one of the phases will be aqueous, and the other a lipophilic organic solvent such as ether, MTBE, dichloromethane, chloroform, or ethyl acetate. All of these solvents form a clear delineation between the two liquids. The more dense liquid, typically the aqueous phase unless the organic phase is halogenated, sinks to the bottom of the funnel and can be drained out through a valve away from the less dense liquid, which remains in the separatory funnel.

Liquid–liquid extraction (LLE), also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar). There is a net transfer of one or more species from one liquid into another liquid phase, generally from aqueous to organic. The transfer is driven by chemical potential, i.e. once the transfer is complete, the overall system of chemical components that make up the solutes and the solvents are in a more stable configuration. The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called the raffinate. LLE is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment called as mixer settlers. This type of process is commonly performed after a chemical reaction as part of the work-up, often including an acidic work-up.

Microemulsions are clear, thermodynamically stable isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt(s) and/or other ingredients, and the "oil" may actually be a complex mixture of different hydrocarbons. In contrast to ordinary emulsions, microemulsions form upon simple mixing of the components and do not require the high shear conditions generally used in the formation of ordinary emulsions. The three basic types of microemulsions are direct, reversed and bicontinuous.

Partition equilibrium is a special case of chemical equilibrium. The most common chemical equilibrium systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such as two liquids that do not mix. Partition equilibria are described by Nernst's distribution law.

A multiphasic liquid is a mixture consisting of more than two immiscible liquid phases. Biphasic mixtures consisting of two immiscible phases are very common and usually consist of an organic solvent and an aqueous phase.

See Patented via Nth Cycle for metal electro-extraction process.

The distribution constant (KD) is the equilibrium constant for the distribution of an analyte in two immiscible solvents.

Countercurrent distribution is an analytical chemistry technique which was developed by Lyman C. Craig in the 1940s. Countercurrent distribution is a separation process that is founded on the principles of liquid–liquid extraction where a chemical compound is distributed (partitioned) between two immiscible liquid phases according to its relative solubility in the two phases. The simplest form of liquid-liquid extraction is the partitioning of a mixture of compounds between two immiscible liquid phases in a separatory funnel. This occurs in five steps: 1) preparation of the separatory funnel with the two phase solvent system, 2) introduction of the compound mixture into the separatory funnel, 3) vigorous shaking of the separatory funnel to mix the two layers and allow for mass transfer of compounds in and out of the phases, 4) The contents of the separatory funnel are allowed to settle back into two distinct phases and 5) the two phases are separated from each other by draining out the bottom phase. If a compound is insoluble in the lower phase it will distribute into the upper phase and stay in the separatory funnel. If a compound is insoluble in the upper phase it will distribute into the lower phase and be removed from the separatory funnel. If the mixture contains one or more compounds that are soluble in the upper phase and one or more compounds that are soluble in the lower phase, then an extraction has occurred. Often, an individual compound is soluble to a certain extent in both phases and the extraction is, therefore, incomplete. The relative solubility of a compound in two phases is known as the partition coefficient.

<span class="mw-page-title-main">Miscibility</span> Ability of two substances to form a homogeneous solution when mixed regardless of concentration

Miscibility is the property of two substances to mix in all proportions, forming a homogeneous mixture. The term is most often applied to liquids but also applies to solids and gases. An example in liquids is the miscibility of water and ethanol as they mix in all proportions.

<span class="mw-page-title-main">Temperature-responsive polymer</span> Polymer showing drastic changes in physical properties with temperature

Temperature-responsive polymers or thermoresponsive polymers are polymers that exhibit drastic and discontinuous changes in their physical properties with temperature. The term is commonly used when the property concerned is solubility in a given solvent, but it may also be used when other properties are affected. Thermoresponsive polymers belong to the class of stimuli-responsive materials, in contrast to temperature-sensitive materials, which change their properties continuously with environmental conditions. In a stricter sense, thermoresponsive polymers display a miscibility gap in their temperature-composition diagram. Depending on whether the miscibility gap is found at high or low temperatures, either an upper critical solution temperature (UCST) or a lower critical solution temperature (LCST) exists.

<span class="mw-page-title-main">Extraction (chemistry)</span> Separation of a desired substance from other substances in the sample

Extraction in chemistry is a separation process consisting of the separation of a substance from a matrix. The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly how the analyte moves from the initial solvent into the extracting solvent. The term washing may also be used to refer to an extraction in which impurities are extracted from the solvent containing the desired compound.

<span class="mw-page-title-main">Centrifugal extractor</span>

A centrifugal extractor—also known as a centrifugal contactor or annular centrifugal contactor—uses the rotation of the rotor inside a centrifuge to mix two immiscible liquids outside the rotor and to separate the liquids in the field of gravity inside the rotor. This way, a centrifugal extractor generates a continuous extraction from one liquid phase into another liquid phase.

<span class="mw-page-title-main">Countercurrent chromatography</span>

Countercurrent chromatography is a form of liquid–liquid chromatography that uses a liquid stationary phase that is held in place by inertia of the molecules composing the stationary phase accelerating toward the center of a centrifuge due to centripetal force and is used to separate, identify, and quantify the chemical components of a mixture. In its broadest sense, countercurrent chromatography encompasses a collection of related liquid chromatography techniques that employ two immiscible liquid phases without a solid support. The two liquid phases come in contact with each other as at least one phase is pumped through a column, a hollow tube or a series of chambers connected with channels, which contains both phases. The resulting dynamic mixing and settling action allows the components to be separated by their respective solubilities in the two phases. A wide variety of two-phase solvent systems consisting of at least two immiscible liquids may be employed to provide the proper selectivity for the desired separation.

Solvent impregnated resins (SIRs) are commercially available (macro)porous resins impregnated with a solvent/an extractant. In this approach, a liquid extractant is contained within the pores of (adsorption) particles. Usually, the extractant is an organic liquid. Its purpose is to extract one or more dissolved components from a surrounding aqueous environment. The basic principle combines adsorption, chromatography and liquid-liquid extraction.

Thermoresponsive polymers can be used as stationary phase in liquid chromatography. Here, the polarity of the stationary phase can be varied by temperature changes, altering the power of separation without changing the column or solvent composition. Thermally related benefits of gas chromatography can now be applied to classes of compounds that are restricted to liquid chromatography due to their thermolability. In place of solvent gradient elution, thermoresponsive polymers allow the use of temperature gradients under purely aqueous isocratic conditions. The versatility of the system is controlled not only through changing temperature, but through the addition of modifying moieties that allow for a choice of enhanced hydrophobic interaction, or by introducing the prospect of electrostatic interaction. These developments have already introduced major improvements to the fields of hydrophobic interaction chromatography, size exclusion chromatography, ion exchange chromatography, and affinity chromatography separations as well as pseudo-solid phase extractions.

<span class="mw-page-title-main">Heather Willauer</span> American analytical chemist and patents holder

Heather D. Willauer (born 1974) is an American analytical chemist and inventor working in Washington, D.C., at the United States Naval Research Laboratory (NRL). Leading a research team, Willauer has patented a method for removing dissolved carbon dioxide (CO2) from seawater, in parallel with hydrogen (H2) recovered by conventional water electrolysis. Willauer is also searching to improve the catalysts required to enable a continuous Fischer–Tropsch process to recombine carbon monoxide (CO) and hydrogen gases into complex hydrocarbon liquids to synthesize jet fuel for Navy aircraft.

The advanced reprocessing of spent nuclear fuel is a potential key to achieve a sustainable nuclear fuel cycle and to tackle the heavy burden of nuclear waste management. In particular, the development of such advanced reprocessing systems may save natural resources, reduce waste inventory and enhance the public acceptance of nuclear energy. This strategy relies on the recycling of major actinides and the transmutation of minor actinides in appropriate reactors. In order to fulfill this objective, selective extracting agents need to be designed and developed by investigating their complexation mechanism.

References

  1. ↑ Hamta, Afshin; Reza Dehghani, Mohammad (2017). "Application of polyethylene glycol based aqueous two-phase systems for extraction of heavy metals". Journal of Molecular Liquids. 231: 20–24. doi:10.1016/j.molliq.2017.01.084.
  2. ↑ Khripin, Constantine Y.; Fagan, Jeffrey A.; Zheng, Ming (2013-05-08). "Spontaneous Partition of Carbon Nanotubes in Polymer-Modified Aqueous Phases". Journal of the American Chemical Society. 135 (18): 6822–6825. doi:10.1021/ja402762e. ISSN   0002-7863. PMID   23611526.
  3. ↑ Li, Han; Gordeev, Georgy; Garrity, Oisin; Reich, Stephanie; Flavel, Benjamin S. (2019-01-28). "Separation of Small-Diameter Single-Walled Carbon Nanotubes in One to Three Steps with Aqueous Two-Phase Extraction". ACS Nano. 13 (2): 2567–2578. doi:10.1021/acsnano.8b09579. ISSN   1936-0851. PMID   30673278.
  4. ↑ Turek, Edyta; Shiraki, Tomohiro; Shiraishi, Tomonari; Shiga, Tamehito; Fujigaya, Tsuyohiko; Janas, Dawid (2019). "Single-step isolation of carbon nanotubes with narrow-band light emission characteristics". Scientific Reports. 9 (1): 535. Bibcode:2019NatSR...9..535T. doi:10.1038/s41598-018-37675-4. ISSN   2045-2322. PMC   6345979 . PMID   30679809.
  5. ↑ Beijerinck, M.W. (1896). Zentralblatt für Bakteriologie, Parasiten und Infektionskrankenheiten . 2: 697–699.{{cite journal}}: CS1 maint: untitled periodical (link)
  6. ↑ Chaplin, Martin. "Aqueous Biphasic Systems". Archived from the original on 2006-09-24. Retrieved 2006-09-06.
  7. ↑ Hamta, Afshin; Mohammadi, Asma; Dehghani, Mohammad Reza; Feyzi, Farzaneh (2018). "Liquid–Liquid Equilibrium and Thermodynamic Modeling of Aqueous Two-Phase System Containing Polypropylene Glycol and NaClO4 at T = (288.15 and 298.15) K". Journal of Solution Chemistry. 47: 1–25. doi:10.1007/s10953-017-0704-x. S2CID   103996286.

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