in a comparison with conventional methods such as Soxhlet, ASE is favored by time
and by the reduction of the volume of solvent. However, compared to other more
sustainable techniques such as MAE, USE, and QuEChERS, ASE may no longer be
considered in terms of time or cost savings, but in some cases, it can provide better
efficiency, reproducibility, and robustness. Therefore, ASE is a choice of interest for
the development of analytical methods to determine pharmaceutical products from
the soil (Table 2).
4.2 Ultrasound Solvent Extraction (USE)
Different extraction solvents were employed for pharmaceutical extraction from soil
with ultrasonication, such as acidified aqueous solutions, EDTA solutions, and
phosphate and McIlvaine buffers, mixed with organic solvent. Acetonitrile, methanol, and ethyl acetate are the main organic solvents employed with sonication
methods (solvent selection depends on its viscosity). Na 2 EDTA (disodium ethylenediaminetetraacetate) is a chelating agent and is used extensively to prevent
pharmaceutical products such as tetracyclines and fluoroquinolones from forming
chelated complexes with soil matrix (such as metal ions present in the soil).
Sulfonamides are amphoteric and are best extracted in an acid medium, while
tetracyclines are better extracted with a McIlvaine buffer. However, a combination
of buffer and organic solvent has been used for the simultaneous extraction of
multiple pharmaceutical residues. Hu and colleagues used potassium phosphate
buffer with ACN (1/1, v/v, pH ¼ 3.2) with 0.4 g of Na 2 EDTA in order to obtain
the best recoveries for fluoroquinolones, tetracyclines, and sulfonamides [75]
(Table 3).
The sonication time and the number of cycles are important parameters and
should be optimized so as to obtain the maximum recovery of the target analytes
with a minimum matrix that interferes with the compounds (this can be explained by
the distribution coefficients of pharmaceutical products rather than by the kinetics of
desorption process). The sonication time ranged from 10 to 30 min, and the number
of cycles ranged from 1 to 4 cycles at maximum. The temperature of the ultrasonic
bath was not controlled in most studies. However, USE extraction was always
performed at room temperature.
4.3 Microwave-Assisted Extraction (MAE)
In MAE, extraction parameters such as time, power, solvent (type and volume),
pressure, temperature, number of cycles, and sample size are important parameters
that require vigorous optimization to obtain the maximum recovery yield. The
extraction solvents for MAE should be capable of absorbing microwaves, with
permanent dipole leading (polar), although the combination of solvents with and
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
447
and by the reduction of the volume of solvent. However, compared to other more
sustainable techniques such as MAE, USE, and QuEChERS, ASE may no longer be
considered in terms of time or cost savings, but in some cases, it can provide better
efficiency, reproducibility, and robustness. Therefore, ASE is a choice of interest for
the development of analytical methods to determine pharmaceutical products from
the soil (Table 2).
4.2 Ultrasound Solvent Extraction (USE)
Different extraction solvents were employed for pharmaceutical extraction from soil
with ultrasonication, such as acidified aqueous solutions, EDTA solutions, and
phosphate and McIlvaine buffers, mixed with organic solvent. Acetonitrile, methanol, and ethyl acetate are the main organic solvents employed with sonication
methods (solvent selection depends on its viscosity). Na 2 EDTA (disodium ethylenediaminetetraacetate) is a chelating agent and is used extensively to prevent
pharmaceutical products such as tetracyclines and fluoroquinolones from forming
chelated complexes with soil matrix (such as metal ions present in the soil).
Sulfonamides are amphoteric and are best extracted in an acid medium, while
tetracyclines are better extracted with a McIlvaine buffer. However, a combination
of buffer and organic solvent has been used for the simultaneous extraction of
multiple pharmaceutical residues. Hu and colleagues used potassium phosphate
buffer with ACN (1/1, v/v, pH ¼ 3.2) with 0.4 g of Na 2 EDTA in order to obtain
the best recoveries for fluoroquinolones, tetracyclines, and sulfonamides [75]
(Table 3).
The sonication time and the number of cycles are important parameters and
should be optimized so as to obtain the maximum recovery of the target analytes
with a minimum matrix that interferes with the compounds (this can be explained by
the distribution coefficients of pharmaceutical products rather than by the kinetics of
desorption process). The sonication time ranged from 10 to 30 min, and the number
of cycles ranged from 1 to 4 cycles at maximum. The temperature of the ultrasonic
bath was not controlled in most studies. However, USE extraction was always
performed at room temperature.
4.3 Microwave-Assisted Extraction (MAE)
In MAE, extraction parameters such as time, power, solvent (type and volume),
pressure, temperature, number of cycles, and sample size are important parameters
that require vigorous optimization to obtain the maximum recovery yield. The
extraction solvents for MAE should be capable of absorbing microwaves, with
permanent dipole leading (polar), although the combination of solvents with and
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
447