radiations generate a great number of tiny bubbles in liquid media (the extraction
solvent added to the sample in the centrifuge tube) and mechanical erosion of solids
(soil and crops samples); thus, particles rupture [11]. However, USE does not always
reach high efficiency as efficiencies reached by other methods. Additionally, ultrasonic irradiation enhances the release of matrix components simultaneously with the
analytes, hence an important matrix effect.
For a maximum pharmaceuticals’ recovery, several parameters should be optimized such as type of solvent, irradiation conditions (temperature and amplitude of
sonication), sonication time, number of cycles, and sample amount. Generally, to
obtain the highest extraction efficiency with the lowest matrix interferences, several
extraction cycles are employed, each with a fresh and small solvent volume
[12]. Thus, solvents from the different extraction cycles are combined and processed
to the following step, usually clean-up step, unless it is skipped to analysis.
Several ultrasound devices are available, such as the water bath, probes,
sonireactors, or microplate horn [13]. Yet, an ultrasonic water bath was always
employed for soil and crop analysis, which is also known to be the cheapest and
the most available [14–16]. An important aspect is that these types of devices are
almost always available in every laboratory. Finally, USE is an environment-friendly
technique, less solvent consumer, and energy and time saving.
2.3 Microwave-Assisted Extraction (MAE)
MAE is also called microwave-assisted solvent extraction (MASE). In this technique, microwave energy is used to directly heat the solvent in contact with the
sample, thus achieving the partition of target analytes from the sample to the solvent
and accelerating the speed of extraction. The microwave energy released is
nonionizing radiation that causes molecular motion by migration of ions and rotation
of dipoles [12]. The efficiency of MAE depends strongly on the nature of the solvent
and the matrix [17]. Solvents used for MAE should be able to absorb microwaves. In
other words, solvent should have dipole leading (polar). However, a combination of
polar and non-polar solvents has extended MAE usage [10].
It is an automated green extraction technique offering many advantages such as
less solvent consumption and short extraction times, even less than USE technique
[17, 18]. Additionally, several samples can be extracted simultaneously, hence
increasing the number of samples analyzed daily. It also offers protection for
thermolabile compounds. Further, the equipment for MAE is relatively expensive,
which probably is the main reason why a small number of studies are dealing with
MAE. Finally, several factors should be optimized in order to obtain the best
efficiency, such as solvent selection, temperature, and extraction time.
422
R. Manasfi et al.
solvent added to the sample in the centrifuge tube) and mechanical erosion of solids
(soil and crops samples); thus, particles rupture [11]. However, USE does not always
reach high efficiency as efficiencies reached by other methods. Additionally, ultrasonic irradiation enhances the release of matrix components simultaneously with the
analytes, hence an important matrix effect.
For a maximum pharmaceuticals’ recovery, several parameters should be optimized such as type of solvent, irradiation conditions (temperature and amplitude of
sonication), sonication time, number of cycles, and sample amount. Generally, to
obtain the highest extraction efficiency with the lowest matrix interferences, several
extraction cycles are employed, each with a fresh and small solvent volume
[12]. Thus, solvents from the different extraction cycles are combined and processed
to the following step, usually clean-up step, unless it is skipped to analysis.
Several ultrasound devices are available, such as the water bath, probes,
sonireactors, or microplate horn [13]. Yet, an ultrasonic water bath was always
employed for soil and crop analysis, which is also known to be the cheapest and
the most available [14–16]. An important aspect is that these types of devices are
almost always available in every laboratory. Finally, USE is an environment-friendly
technique, less solvent consumer, and energy and time saving.
2.3 Microwave-Assisted Extraction (MAE)
MAE is also called microwave-assisted solvent extraction (MASE). In this technique, microwave energy is used to directly heat the solvent in contact with the
sample, thus achieving the partition of target analytes from the sample to the solvent
and accelerating the speed of extraction. The microwave energy released is
nonionizing radiation that causes molecular motion by migration of ions and rotation
of dipoles [12]. The efficiency of MAE depends strongly on the nature of the solvent
and the matrix [17]. Solvents used for MAE should be able to absorb microwaves. In
other words, solvent should have dipole leading (polar). However, a combination of
polar and non-polar solvents has extended MAE usage [10].
It is an automated green extraction technique offering many advantages such as
less solvent consumption and short extraction times, even less than USE technique
[17, 18]. Additionally, several samples can be extracted simultaneously, hence
increasing the number of samples analyzed daily. It also offers protection for
thermolabile compounds. Further, the equipment for MAE is relatively expensive,
which probably is the main reason why a small number of studies are dealing with
MAE. Finally, several factors should be optimized in order to obtain the best
efficiency, such as solvent selection, temperature, and extraction time.
422
R. Manasfi et al.