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6.3 Influence of Deep Eutectic Solvent Properties
on the Extraction Efficiency
The properties of deep eutectic solvent highly influence the extraction efficiency of
the analytes (Tang et al. 2014). These properties depend both on the physicochemical properties of each component and on the interactions between the two constituents of the deep eutectic solvent. While deep eutectic solvent melting point, density,
viscosity, and compatibility with instrumental detection systems may control the
extraction process feasibility, the extraction efficiency is mainly influenced by the
deep eutectic solvent solubilizing capacities and by its cell structures disruption
ability. Since the majority of the bioactive compounds are being extracted from a
medium containing large amount of water, deep eutectic solvent properties can be
influenced by the presence of water. Accordingly, El Achkar et al. (2019) discussed,
in a recent review, the effect of water on the main physicochemical properties of
deep eutectic solvents; the water content should be considered in the analysis of the
extraction efficiency by deep eutectic solvent (El Achkar et al. 2019).
6.3.1 Melting Point
As it was mentioned above, deep eutectic solvents are characterized by a lower
melting point than that of any of its individual components. For example, choline
chloride has a melting point of 302 °C and urea 113 °C; when mixing these two
compounds, a eutectic mixture with a melting point of 12 °C is obtained (Zhang
et al. 2012). This melting point depression is due to an interaction between the
halide anion Cl
−
and urea via hydrogen bonds, and consequently charge delocalization occurs. This indicates that the melting point is dependent on the nature of
hydrogen bond acceptor and hydrogen bond donor and is highly in correlation with
the hydrogen bond strength. The molar ratio of the deep eutectic solvent components also affects the melting point (Zhang et al. 2012). So it is considered when
choosing the temperature in the extraction procedure.
6.3.2 Density
Most of deep eutectic solvents possess higher density values than water, with levels
ranging from 1.041 to 1.63 g.cm
−3
. Density differences between deep eutectic solvents are explained by their molecular organization and packing (Zhang et al. 2012).
Deep eutectic solvent density is higher than the individual components densities
because of the “hole theory”: the radius of the existing holes decreases after mixing.
Deep eutectic solvent’s density is a highly important property when separating
phases in the extraction process especially in dispersive liquid-liquid
L. Nakhle et al.
6.3 Influence of Deep Eutectic Solvent Properties
on the Extraction Efficiency
The properties of deep eutectic solvent highly influence the extraction efficiency of
the analytes (Tang et al. 2014). These properties depend both on the physicochemical properties of each component and on the interactions between the two constituents of the deep eutectic solvent. While deep eutectic solvent melting point, density,
viscosity, and compatibility with instrumental detection systems may control the
extraction process feasibility, the extraction efficiency is mainly influenced by the
deep eutectic solvent solubilizing capacities and by its cell structures disruption
ability. Since the majority of the bioactive compounds are being extracted from a
medium containing large amount of water, deep eutectic solvent properties can be
influenced by the presence of water. Accordingly, El Achkar et al. (2019) discussed,
in a recent review, the effect of water on the main physicochemical properties of
deep eutectic solvents; the water content should be considered in the analysis of the
extraction efficiency by deep eutectic solvent (El Achkar et al. 2019).
6.3.1 Melting Point
As it was mentioned above, deep eutectic solvents are characterized by a lower
melting point than that of any of its individual components. For example, choline
chloride has a melting point of 302 °C and urea 113 °C; when mixing these two
compounds, a eutectic mixture with a melting point of 12 °C is obtained (Zhang
et al. 2012). This melting point depression is due to an interaction between the
halide anion Cl
−
and urea via hydrogen bonds, and consequently charge delocalization occurs. This indicates that the melting point is dependent on the nature of
hydrogen bond acceptor and hydrogen bond donor and is highly in correlation with
the hydrogen bond strength. The molar ratio of the deep eutectic solvent components also affects the melting point (Zhang et al. 2012). So it is considered when
choosing the temperature in the extraction procedure.
6.3.2 Density
Most of deep eutectic solvents possess higher density values than water, with levels
ranging from 1.041 to 1.63 g.cm
−3
. Density differences between deep eutectic solvents are explained by their molecular organization and packing (Zhang et al. 2012).
Deep eutectic solvent density is higher than the individual components densities
because of the “hole theory”: the radius of the existing holes decreases after mixing.
Deep eutectic solvent’s density is a highly important property when separating
phases in the extraction process especially in dispersive liquid-liquid
L. Nakhle et al.