187
liquid-phase microextraction and solid-phase microextraction techniques will be
described, and their applications using deep eutectic solvents as extraction solvents
will be presented.
6.2.1 Liquid-Phase Microextraction
In the liquid-phase microextraction techniques, the sample solution containing the
target analyte is designated as the donor phase and the extraction solvent as the
acceptor phase. These techniques consist on adding few microliters of the solvent
into the aqueous sample followed by the collection of the extraction solvent containing the target analytes (Yilmaz and Soylak 2018). Different liquid-phase microextraction techniques exist such as single-drop microextraction, hollow-fiber
liquid-phase microextraction, and dispersive liquid-liquid microextraction.
Single-Drop Microextraction
This method consists of a solvent drop suspended at the end of the needle of a
microsyringe. Single-drop microextraction can be distinguished in two different
techniques: headspace single-drop microextraction or direct immersion single-drop
microextraction. Figure 6.1 presents schematically these two techniques.
Headspace single-drop microextraction is applied for the extraction of volatile or
semi-volatile compounds from a complex matrix because the suspended solvent
drop is exposed only to the headspace of the sample. Table 6.1 presents examples of
extractions processes via the headspace single-drop microextraction technique
using deep eutectic solvents as extraction solvents.
Tang et al. (2014) applied headspace single-drop microextraction method to
extract terpenoids using the optimal deep eutectic solvent choline chloride/ethylene
glycol (1:4 molar ratio) because it showed the best extraction efficiency. This
method showed a pronounced advantage compared to other conventional methods
(ultrasonication and heat reflux extraction) using methanol as extraction solvent
(Tang et al. 2014). Also, Yousefi et al. (2018) validated the efficacy of this method
in the extraction of aromatic hydrocarbons using a new type of hydrophobic deep
eutectic solvent-magnetic bucky gel. The solvent drop was formed by mixing the
optimal deep eutectic solvent (choline chloride/chlorophenol 1:2 molar ratio) with
magnetic multiwalled carbon nanotubes. This mixture made the solvent drop more
stable. Therefore, the heating temperature and the stirring rates were increased,
which allowed to decrease the extraction time (Yousefi et al. 2018).
Direct immersion single-drop microextraction is applied for the extraction of
nonvolatile compounds and polar analytes. Herein, the acceptor solvent should be
immiscible with the donor phase as the solvent drop is immersed in it. Gu et al.
(2014) used this method for the extraction of phenolic compounds (phenol, p- cresol,
and β-naphthol) from crude oils with 10 μL of choline chloride/ethylene glycol (1:3
6 Methods for Extraction of Bioactive Compounds from Plant and Animal Matter…
liquid-phase microextraction and solid-phase microextraction techniques will be
described, and their applications using deep eutectic solvents as extraction solvents
will be presented.
6.2.1 Liquid-Phase Microextraction
In the liquid-phase microextraction techniques, the sample solution containing the
target analyte is designated as the donor phase and the extraction solvent as the
acceptor phase. These techniques consist on adding few microliters of the solvent
into the aqueous sample followed by the collection of the extraction solvent containing the target analytes (Yilmaz and Soylak 2018). Different liquid-phase microextraction techniques exist such as single-drop microextraction, hollow-fiber
liquid-phase microextraction, and dispersive liquid-liquid microextraction.
Single-Drop Microextraction
This method consists of a solvent drop suspended at the end of the needle of a
microsyringe. Single-drop microextraction can be distinguished in two different
techniques: headspace single-drop microextraction or direct immersion single-drop
microextraction. Figure 6.1 presents schematically these two techniques.
Headspace single-drop microextraction is applied for the extraction of volatile or
semi-volatile compounds from a complex matrix because the suspended solvent
drop is exposed only to the headspace of the sample. Table 6.1 presents examples of
extractions processes via the headspace single-drop microextraction technique
using deep eutectic solvents as extraction solvents.
Tang et al. (2014) applied headspace single-drop microextraction method to
extract terpenoids using the optimal deep eutectic solvent choline chloride/ethylene
glycol (1:4 molar ratio) because it showed the best extraction efficiency. This
method showed a pronounced advantage compared to other conventional methods
(ultrasonication and heat reflux extraction) using methanol as extraction solvent
(Tang et al. 2014). Also, Yousefi et al. (2018) validated the efficacy of this method
in the extraction of aromatic hydrocarbons using a new type of hydrophobic deep
eutectic solvent-magnetic bucky gel. The solvent drop was formed by mixing the
optimal deep eutectic solvent (choline chloride/chlorophenol 1:2 molar ratio) with
magnetic multiwalled carbon nanotubes. This mixture made the solvent drop more
stable. Therefore, the heating temperature and the stirring rates were increased,
which allowed to decrease the extraction time (Yousefi et al. 2018).
Direct immersion single-drop microextraction is applied for the extraction of
nonvolatile compounds and polar analytes. Herein, the acceptor solvent should be
immiscible with the donor phase as the solvent drop is immersed in it. Gu et al.
(2014) used this method for the extraction of phenolic compounds (phenol, p- cresol,
and β-naphthol) from crude oils with 10 μL of choline chloride/ethylene glycol (1:3
6 Methods for Extraction of Bioactive Compounds from Plant and Animal Matter…