7 Ionic Liquid–Liquid Chromatography: A Novel Separation Method
173
corrosive compounds (concentrated acids/bases), titanium, or polytetrafluoroethylene (PTFE). Additionally, the centrifuge must be capable of running at up to 50 °C,
which can dramatically improve the ILLC separation performance [15, 26].
The inherent tunability (“designer solvents”) of ionic liquids allows control over
their physicochemical properties: viscosity, hydrophobicity, hydrophilicity, density,
and corrosivity. Moreover, and of vital importance, the distribution ratios of a solute
between an ionic liquid phase and a second phase (either an organic solvent or
another ionic liquid) can be controlled. Indeed, ionic liquids can dissolve materials
which are conventionally considered to be insoluble, such as kerogens [37]. As
will be demonstrated here, this versatility will enable a generic methodology for a
wide range of potential separations to be developed, especially the ones that were
previously thought to be difficult to implement, for instance, bio-polymers, proteins,
saccharides, polysaccharides, metal salts, and petrochemicals. Moreover, the ionic
liquids are easily recyclable and can be used for multiple separations, which justifies
the initial higher costs of using ionic liquid media.
To some extent, the early publications stating that ionic liquids could not be easily
utilized with CCC and CPC [13] may have held back the development of ionic liquid
solvent systems in CCC and CPC. AECS-QuikPrep Ltd./Quattro CCC (UK), in collaboration initially with the QUILL Research Centre within the Queen’s University
of Belfast (UK), were able to successfully employ biphasic ionic liquid-based solvent systems in CCC [14a]. Here, ionic liquid-based solvent systems were utilized
in the separation of a mixture of CoCl 2 , NiCl 2 , and CuCl 2 , the separation of two
monosaccharides form a disaccharide, and the extraction of cumene from hexane
[14a]. By the use of a hexane/ionic liquid solvent system, the separation of hydrocarbons from oxygenated hydrocarbons in vetiver oil was achieved [16]. In addition,
ionic liquid solvent systems have been studied in the countercurrent chromatographic
separation of nonpolar lipids [38]. Cao et al. have used dilute solutions of ionic liquids in CCC in the determination of Alternaria mycotoxins and the determination
of chlorophenols in red wine [14b, 39]. Also, four patents have been published on
the use of ionic liquids in CCC solvent systems in general [15], in bio-organic [26b],
in organic [26a], and in inorganic separations [26c]. Two examples of chiral separations by CCC are in the use of solutions of chiral salts [40] (similar to an ionic
liquid), derived from cinchona alkaloid, in the separation of N-(3,5-dinitrobenzoyl)(±)-leucine (Fig. 7.5). Similarly, cyclodextrin and a chiral copper complex have been
used in the enantioseparation of naringenin (Fig. 7.5) by CCC [41].
7.6 ILLC and ILLE Instrumentation
The Quattro IL-Prep™ ILLC instrument that we are using at QUILL (Fig. 7.6)
incorporates four coils, as shown in Table 7.1 and Fig. 7.7, and has been tested
for several separations, in order to evaluate the effectiveness of ILLC for various
mixtures. Here, we concentrate on four examples of ionic liquid biphasic systems
based on two or three components.
173
corrosive compounds (concentrated acids/bases), titanium, or polytetrafluoroethylene (PTFE). Additionally, the centrifuge must be capable of running at up to 50 °C,
which can dramatically improve the ILLC separation performance [15, 26].
The inherent tunability (“designer solvents”) of ionic liquids allows control over
their physicochemical properties: viscosity, hydrophobicity, hydrophilicity, density,
and corrosivity. Moreover, and of vital importance, the distribution ratios of a solute
between an ionic liquid phase and a second phase (either an organic solvent or
another ionic liquid) can be controlled. Indeed, ionic liquids can dissolve materials
which are conventionally considered to be insoluble, such as kerogens [37]. As
will be demonstrated here, this versatility will enable a generic methodology for a
wide range of potential separations to be developed, especially the ones that were
previously thought to be difficult to implement, for instance, bio-polymers, proteins,
saccharides, polysaccharides, metal salts, and petrochemicals. Moreover, the ionic
liquids are easily recyclable and can be used for multiple separations, which justifies
the initial higher costs of using ionic liquid media.
To some extent, the early publications stating that ionic liquids could not be easily
utilized with CCC and CPC [13] may have held back the development of ionic liquid
solvent systems in CCC and CPC. AECS-QuikPrep Ltd./Quattro CCC (UK), in collaboration initially with the QUILL Research Centre within the Queen’s University
of Belfast (UK), were able to successfully employ biphasic ionic liquid-based solvent systems in CCC [14a]. Here, ionic liquid-based solvent systems were utilized
in the separation of a mixture of CoCl 2 , NiCl 2 , and CuCl 2 , the separation of two
monosaccharides form a disaccharide, and the extraction of cumene from hexane
[14a]. By the use of a hexane/ionic liquid solvent system, the separation of hydrocarbons from oxygenated hydrocarbons in vetiver oil was achieved [16]. In addition,
ionic liquid solvent systems have been studied in the countercurrent chromatographic
separation of nonpolar lipids [38]. Cao et al. have used dilute solutions of ionic liquids in CCC in the determination of Alternaria mycotoxins and the determination
of chlorophenols in red wine [14b, 39]. Also, four patents have been published on
the use of ionic liquids in CCC solvent systems in general [15], in bio-organic [26b],
in organic [26a], and in inorganic separations [26c]. Two examples of chiral separations by CCC are in the use of solutions of chiral salts [40] (similar to an ionic
liquid), derived from cinchona alkaloid, in the separation of N-(3,5-dinitrobenzoyl)(±)-leucine (Fig. 7.5). Similarly, cyclodextrin and a chiral copper complex have been
used in the enantioseparation of naringenin (Fig. 7.5) by CCC [41].
7.6 ILLC and ILLE Instrumentation
The Quattro IL-Prep™ ILLC instrument that we are using at QUILL (Fig. 7.6)
incorporates four coils, as shown in Table 7.1 and Fig. 7.7, and has been tested
for several separations, in order to evaluate the effectiveness of ILLC for various
mixtures. Here, we concentrate on four examples of ionic liquid biphasic systems
based on two or three components.