174
synthetic dyes (Ravandi and Fat’hi 2018; Faraji 2019) in food and/or water samples
and nitrite in water and biological samples (Zhang et al. 2019). The isolation of
antibiotics from environmental water (Tang et al. 2018) and determination of trace
polycyclic aromatic hydrocarbons in simulated environmental water samples
(Yousefi et al. 2018) have both been described using a [N 8881 ]Cl/1-octanol deep
eutectic solvent. In addition, zwitterionic components combined with fluorinated
alcohols (e.g., hexafluoroisopropanol) which increase hydrophobicity have been
reported for microextraction of pyrethroid insecticides from tea and fruit juices
(Deng et al. 2019), while liquid-liquid microextraction for the pre-concentration of
pyrethroid (Liu et al. 2019) with hydrophobic quaternary phosphonium salt/straight
chain carboxylic acid deep eutectic solvents has also been reported.
The use of choline chloride/phenol mixtures as deep eutectic solvents for preconcentration and analysis of ionic and organomercury species water and freshwater fish samples after complexation with dithizone (for ionic mercury) or direct
extraction (organomercury species) has been described (Thongsaw et al. 2019).
Detection limits for Hg
2+
and [CH 3 Hg]
+
were 0.073 and 0.091 ng mL
−1
and enrichment factors were 34.0 and 18.3, respectively. Microextraction for concentration
and detection of trace concentrations of nickel in water samples (Rad et al. 2019)
has employed a related choline chloride/bromophenol deep eutectic solvent, while
other choline chloride/phenolic mixtures have been applied to microextraction of
amphetamine and methamphetamine from human blood plasma and pharmaceutical
wastewater using a choline chloride/2-phenylethanol deep eutectic solvent (Rajabi
et al. 2018). Rajabi et al. also reported the use of hollow fiber microextraction with
choline chloride/1-phenylethanol deep eutectic solvent for the concentration and
detection of antiarrhythmic agents in biological and environmental samples (Rajabi
et al. 2019). However, it is important to note that although these deep eutectic solvents form aqueous biphases, there is no data currently available on the leaching
levels of either components of these deep eutectic solvents. While it is known that
choline chloride is inherently hygroscopic and that phenol has been found to leach
in small amounts into an aqueous phase from a trioctylphosphine oxide-based
hydrophobic eutectic (Gilmore et al. 2018a), it is likely that extensive leaching of
one or both components may occur.
Hydrophobic deep eutectic solvents comprised of nonionic components have
also been applied to a number of microextractions. A DL-menthol/phenyl salicylate
mixture has been used to concentrate nitroaromatic explosive compounds in the
deep eutectic solvent phase, removing them from aqueous solution (Nedaei et al.
2018). Hydrophobic magnetic ferrofluids, prepared by dispersing magnetic nanoparticles in DL-menthol/carboxylic acid hydrophobic deep eutectic solvents, have been
reported as extractants for explosive residues from soil and water samples and for
mefenamic acid, an anti-inflammatory analgesic, from urine samples (Zarei et al.
2018; Dil et al. 2019). Finally, these nonionic component-based hydrophobic deep
eutectic solvents have been utilized in combination with hydrophilic deep eutectic
solvents in biphasic deep eutectic solvent systems consisting of hydrophilic and
hydrophobic deep eutectic solvents, i.e., (−)-menthol/L(+)-lactic acid and choline
chloride/urea, respectively, for enantiomeric separation in chiral extraction of
E. L. Byrne et al.
synthetic dyes (Ravandi and Fat’hi 2018; Faraji 2019) in food and/or water samples
and nitrite in water and biological samples (Zhang et al. 2019). The isolation of
antibiotics from environmental water (Tang et al. 2018) and determination of trace
polycyclic aromatic hydrocarbons in simulated environmental water samples
(Yousefi et al. 2018) have both been described using a [N 8881 ]Cl/1-octanol deep
eutectic solvent. In addition, zwitterionic components combined with fluorinated
alcohols (e.g., hexafluoroisopropanol) which increase hydrophobicity have been
reported for microextraction of pyrethroid insecticides from tea and fruit juices
(Deng et al. 2019), while liquid-liquid microextraction for the pre-concentration of
pyrethroid (Liu et al. 2019) with hydrophobic quaternary phosphonium salt/straight
chain carboxylic acid deep eutectic solvents has also been reported.
The use of choline chloride/phenol mixtures as deep eutectic solvents for preconcentration and analysis of ionic and organomercury species water and freshwater fish samples after complexation with dithizone (for ionic mercury) or direct
extraction (organomercury species) has been described (Thongsaw et al. 2019).
Detection limits for Hg
2+
and [CH 3 Hg]
+
were 0.073 and 0.091 ng mL
−1
and enrichment factors were 34.0 and 18.3, respectively. Microextraction for concentration
and detection of trace concentrations of nickel in water samples (Rad et al. 2019)
has employed a related choline chloride/bromophenol deep eutectic solvent, while
other choline chloride/phenolic mixtures have been applied to microextraction of
amphetamine and methamphetamine from human blood plasma and pharmaceutical
wastewater using a choline chloride/2-phenylethanol deep eutectic solvent (Rajabi
et al. 2018). Rajabi et al. also reported the use of hollow fiber microextraction with
choline chloride/1-phenylethanol deep eutectic solvent for the concentration and
detection of antiarrhythmic agents in biological and environmental samples (Rajabi
et al. 2019). However, it is important to note that although these deep eutectic solvents form aqueous biphases, there is no data currently available on the leaching
levels of either components of these deep eutectic solvents. While it is known that
choline chloride is inherently hygroscopic and that phenol has been found to leach
in small amounts into an aqueous phase from a trioctylphosphine oxide-based
hydrophobic eutectic (Gilmore et al. 2018a), it is likely that extensive leaching of
one or both components may occur.
Hydrophobic deep eutectic solvents comprised of nonionic components have
also been applied to a number of microextractions. A DL-menthol/phenyl salicylate
mixture has been used to concentrate nitroaromatic explosive compounds in the
deep eutectic solvent phase, removing them from aqueous solution (Nedaei et al.
2018). Hydrophobic magnetic ferrofluids, prepared by dispersing magnetic nanoparticles in DL-menthol/carboxylic acid hydrophobic deep eutectic solvents, have been
reported as extractants for explosive residues from soil and water samples and for
mefenamic acid, an anti-inflammatory analgesic, from urine samples (Zarei et al.
2018; Dil et al. 2019). Finally, these nonionic component-based hydrophobic deep
eutectic solvents have been utilized in combination with hydrophilic deep eutectic
solvents in biphasic deep eutectic solvent systems consisting of hydrophilic and
hydrophobic deep eutectic solvents, i.e., (−)-menthol/L(+)-lactic acid and choline
chloride/urea, respectively, for enantiomeric separation in chiral extraction of
E. L. Byrne et al.