be the coating of the inner walls of the capillary, a filling of particles or packed fibers,
or a monolithic bed [97]. The sample is aspirated and expelled from the capillary
until equilibrium is reached. It has the advantage that the process of extraction and
final determination can be automated. It is very convenient for HPLC [55, 97]. The
extracted analytes are desorbed statically or dynamically [104]. The extraction
efficiency depends on the nature and thickness of the sorbent and the length and
internal diameter of the capillary [55].
There are large amounts of fibers and polymeric sorbents for the extraction and
concentration of molecules by SPME. The most commonly used fiber is fused silica
[90, 104]. The polymer coating includes polydimethylsiloxane (PDMS) [58, 59, 97]
and polyacrylate (PA) [58, 59, 90, 97, 104], the first polymeric sorbents used in
SPME. PDMS is less efficient for NSAID extraction than PA [90, 104]. Further
development of combinations, such as PDMS-divinylbenzene (PDMS-DVB)
[59, 90, 97, 104], carbowax-DVB (CW-DVB) [59, 90, 104], PA-PDMS [93], and
carboxeno-PDMS (CAR-PDMS) [59, 97], have improved extraction efficiencies.
Nanostructured materials, such as carbon nanotubes (CNT) [60], graphene oxide
(GO) [95], iron oxide (Fe 3 O 4 ) nanoparticles [92], molecularly printed polymers
(MIP) with specific recognition sites for the target molecules [45, 98, 115], and
others, have facilitated development of SPME sorbents. These materials are characterized by porous structures, high specific surface areas, and high thermal and
mechanical stabilities. The selection of one or the other depends on the polarity,
volatility, hydrophilicity, size of the analyte to be extracted, and the interference to
be eliminated [98, 104].
Variants of static SPME can be executed in three modes of extraction: (1) by
direct immersion of the sorbent in the solution (DI-SPME) [59, 90, 96–98, 104, 115,
124]; (2) in the free volume of the vial containing the sample (head space
microextraction [HS-SPME]) [58]; and (3) with a protective membrane, in which a
semipermeable membrane is placed around the fiber to avoid being damaged by
compounds of high molecular weight that could be present in the matrix. It is used
for heavily contaminated matrices [96]. The most commonly used variants of LPME
for the concentration of NSAIDs in water samples are those with a hollow fiber
liquid membrane (HF-LPME, which is used in dynamic mode called CHF-LPME)
[82, 94] and the dispersive (DLLME) [61, 103, 119].
HF-LPME uses porous hollow fibers, composed of a hydrophobic polypropylene
polymer whose pores are impregnated with a small volume of organic solvent
(usually 1-octanol). After the pores are filled with the solvent, the hollow fiber is
sealed and introduced into the aqueous solution containing the analyte, supported in
the cannula of a syringe [42, 94, 95, 99], or in a Teflon microtube [82]. Extraction
and preconcentration can be easily performed [42, 82, 94, 99]. If an aqueous phase is
also introduced into the fiber in addition to the organic phase, it is then possible to
re-extract previously extracted analytes. In this case, the technique is called
HF-LLLME [42, 82, 99]. An interesting variant of HF-LPME, proposed by
Rezafeizar et al. [95], reinforces the acceptor organic phase (1-octanol) with a
nanocomposite of functionalized graphene oxide with hyperbranched polyglycerol
(BPH). This modification increases the extraction efficiency even more. The
94
K. Isaac-Olivé et al.
or a monolithic bed [97]. The sample is aspirated and expelled from the capillary
until equilibrium is reached. It has the advantage that the process of extraction and
final determination can be automated. It is very convenient for HPLC [55, 97]. The
extracted analytes are desorbed statically or dynamically [104]. The extraction
efficiency depends on the nature and thickness of the sorbent and the length and
internal diameter of the capillary [55].
There are large amounts of fibers and polymeric sorbents for the extraction and
concentration of molecules by SPME. The most commonly used fiber is fused silica
[90, 104]. The polymer coating includes polydimethylsiloxane (PDMS) [58, 59, 97]
and polyacrylate (PA) [58, 59, 90, 97, 104], the first polymeric sorbents used in
SPME. PDMS is less efficient for NSAID extraction than PA [90, 104]. Further
development of combinations, such as PDMS-divinylbenzene (PDMS-DVB)
[59, 90, 97, 104], carbowax-DVB (CW-DVB) [59, 90, 104], PA-PDMS [93], and
carboxeno-PDMS (CAR-PDMS) [59, 97], have improved extraction efficiencies.
Nanostructured materials, such as carbon nanotubes (CNT) [60], graphene oxide
(GO) [95], iron oxide (Fe 3 O 4 ) nanoparticles [92], molecularly printed polymers
(MIP) with specific recognition sites for the target molecules [45, 98, 115], and
others, have facilitated development of SPME sorbents. These materials are characterized by porous structures, high specific surface areas, and high thermal and
mechanical stabilities. The selection of one or the other depends on the polarity,
volatility, hydrophilicity, size of the analyte to be extracted, and the interference to
be eliminated [98, 104].
Variants of static SPME can be executed in three modes of extraction: (1) by
direct immersion of the sorbent in the solution (DI-SPME) [59, 90, 96–98, 104, 115,
124]; (2) in the free volume of the vial containing the sample (head space
microextraction [HS-SPME]) [58]; and (3) with a protective membrane, in which a
semipermeable membrane is placed around the fiber to avoid being damaged by
compounds of high molecular weight that could be present in the matrix. It is used
for heavily contaminated matrices [96]. The most commonly used variants of LPME
for the concentration of NSAIDs in water samples are those with a hollow fiber
liquid membrane (HF-LPME, which is used in dynamic mode called CHF-LPME)
[82, 94] and the dispersive (DLLME) [61, 103, 119].
HF-LPME uses porous hollow fibers, composed of a hydrophobic polypropylene
polymer whose pores are impregnated with a small volume of organic solvent
(usually 1-octanol). After the pores are filled with the solvent, the hollow fiber is
sealed and introduced into the aqueous solution containing the analyte, supported in
the cannula of a syringe [42, 94, 95, 99], or in a Teflon microtube [82]. Extraction
and preconcentration can be easily performed [42, 82, 94, 99]. If an aqueous phase is
also introduced into the fiber in addition to the organic phase, it is then possible to
re-extract previously extracted analytes. In this case, the technique is called
HF-LLLME [42, 82, 99]. An interesting variant of HF-LPME, proposed by
Rezafeizar et al. [95], reinforces the acceptor organic phase (1-octanol) with a
nanocomposite of functionalized graphene oxide with hyperbranched polyglycerol
(BPH). This modification increases the extraction efficiency even more. The
94
K. Isaac-Olivé et al.