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L. Brown et al.
solutes, and high costs of chromatography columns, partially due to their limited
lifetimes. In LLC, the range of solvent systems that can be considered includes a
narrow range of molecular solvents, such as water, methanol, ethanol, butanol, ethanenitrile, ethyl ethanoate, dichloromethane, trichloromethane, poly(ethylene) oxide
(PEO), and hexane, mixed in varying proportions to result in the formation of a
biphasic solvent system [6]. Additionally, if compounds are not soluble or react with
the stationary or mobile phase, they are unsuitable for LLC. From a safety standpoint,
the solvent systems can have high vapor pressures from the use of volatile organic
compounds (VOCs) [7]. This limitation is avoided with ionic liquids, which have
negligible vapor pressures [8].
In the last ten years, ionic liquids have become widely used in solvent extraction
[9, 10]. The potential of ionic liquids in both countercurrent chromatography (CCC)
[11] and centrifugal partition chromatography (CPC) [11, 12] has been evaluated
by Berthod and was found to have a number of problems [13]. The instrumentation
available at that time was not able to cope with high backpressures due to the high
viscosities of many ionic liquids. After this study, ionic liquids have been found to
be useful in separations in CCC and CPC by a number of authors [14a, b]. A customdesigned countercurrent chromatography instrument was manufactured that allowed
ionic liquids to be used as the stationary phase or mobile phase [15]. This new type of
instrument was utilized for industrially relevant separations, including the separation
and isolation of transition metal salts, monosaccharides from disaccharides, alkanes
from aromatics, and the refining of essential oils [14a, 16].
7.2 Chromatographic Separations
Chromatography techniques operate through the distribution of analytes between
different phases (gas, liquid, solid). Figure 7.1 shows the various forms of liquid
chromatography.
For liquid–liquid chromatography, two immiscible liquids are used, and the separations are based on the distribution ratio of solutes between the two liquid solvents
[17].
7.3 Countercurrent Chromatography
There are various implementations of CCC that are in use [18], and these have been
applied in separations on a large scale [19]. HPCCC (high-performance countercurrent chromatography) [19] is one of the forms of the instrumentation available
currently. In CCC, the stationary and mobile phases used must be immiscible liquids.
The main principle on which a CCC instrument works involves one fluid mixing and
separating from a second fluid, often in a column or coiled pipe. This column comprises an open-ended tube coiled around a bobbin. In HPCCC, the bobbin is rotated
L. Brown et al.
solutes, and high costs of chromatography columns, partially due to their limited
lifetimes. In LLC, the range of solvent systems that can be considered includes a
narrow range of molecular solvents, such as water, methanol, ethanol, butanol, ethanenitrile, ethyl ethanoate, dichloromethane, trichloromethane, poly(ethylene) oxide
(PEO), and hexane, mixed in varying proportions to result in the formation of a
biphasic solvent system [6]. Additionally, if compounds are not soluble or react with
the stationary or mobile phase, they are unsuitable for LLC. From a safety standpoint,
the solvent systems can have high vapor pressures from the use of volatile organic
compounds (VOCs) [7]. This limitation is avoided with ionic liquids, which have
negligible vapor pressures [8].
In the last ten years, ionic liquids have become widely used in solvent extraction
[9, 10]. The potential of ionic liquids in both countercurrent chromatography (CCC)
[11] and centrifugal partition chromatography (CPC) [11, 12] has been evaluated
by Berthod and was found to have a number of problems [13]. The instrumentation
available at that time was not able to cope with high backpressures due to the high
viscosities of many ionic liquids. After this study, ionic liquids have been found to
be useful in separations in CCC and CPC by a number of authors [14a, b]. A customdesigned countercurrent chromatography instrument was manufactured that allowed
ionic liquids to be used as the stationary phase or mobile phase [15]. This new type of
instrument was utilized for industrially relevant separations, including the separation
and isolation of transition metal salts, monosaccharides from disaccharides, alkanes
from aromatics, and the refining of essential oils [14a, 16].
7.2 Chromatographic Separations
Chromatography techniques operate through the distribution of analytes between
different phases (gas, liquid, solid). Figure 7.1 shows the various forms of liquid
chromatography.
For liquid–liquid chromatography, two immiscible liquids are used, and the separations are based on the distribution ratio of solutes between the two liquid solvents
[17].
7.3 Countercurrent Chromatography
There are various implementations of CCC that are in use [18], and these have been
applied in separations on a large scale [19]. HPCCC (high-performance countercurrent chromatography) [19] is one of the forms of the instrumentation available
currently. In CCC, the stationary and mobile phases used must be immiscible liquids.
The main principle on which a CCC instrument works involves one fluid mixing and
separating from a second fluid, often in a column or coiled pipe. This column comprises an open-ended tube coiled around a bobbin. In HPCCC, the bobbin is rotated