3 Sample Preparation
Sample preparation concept is to convert a field matrix to a sample suitable for
analysis. It is a crucial and important step especially for food and environmental
matrices such as crops and soil, which are characterized by their complexity, besides
the presence of pharmaceuticals in these matrices in trace amounts [29]. This step
also allows to weaken the interactions established between pharmaceuticals and
matrices, which is highly dependent on the physical and chemical properties of
both pharmaceuticals and matrices. Further these interactions affect the applicability
of different extraction methods, their factor conditions, as well as their efficiency and
reproducibility.
Additionally, sample pretreatment is needed to assure its homogeneity and a good
contact with the solvent during the extraction process. On the other hand, most of the
analytical devices are unable to handle those matrices directly, which requires a
pretreatment step before extraction for any matrix. In general, soil preparation
includes three steps [12]: the first step is drying of sample, either by the use of the
oven, by air-drying, or by lyophilization. However, sample exposure to elevated
temperature may risk analyte degradation and alteration. Whenever lyophilization is
employed, analytes are neither degraded nor evaporated, and the drying time is
shorter. Generally, lyophilization is the most advantageous drying technique
[30]. The second step consists in the homogenization and finely grounding of the
soil samples generally using a mortar. The third and last step is soil sieving at 2 mm
to remove coarse particles to increase sample homogeneity. Thereafter, soil samples
are stored at À20
C or +4
C in the dark until analysis.
To perform ASE, from 0.5 to 20 g (Table 2) of soil are placed in a stainless-steel
extraction cell (33 mL extraction cell volume is the most commonly used) and
capped with filters at both ends. Soil sample is usually mixed with a cell matrix
(dispersant) before loading in the cell, to enhance the extraction efficiency. Finally,
the extraction cell is placed in the oven, and the system automatically starts setting
the desired temperature and pressure. For MAE, 0.2–3 g (Table 4) were used, and no
common step was found between the reported studies; they differ largely according
to the MAE procedure employed. Finally, USE and QuEChERS are the easiest,
where soil samples in both methods were introduced in centrifuge tubes. For USE
0.5–5 g (Table 3) of soil were used, the extraction solvent is therefore added, and the
tube is placed in the sonication bath. While from 1 to 10 g (Table 5) of soil were used
for QuEChERS, the extraction solvent and salts were added and the tube was
immediately vortexed and hand shacked.
Plants are normally harvested when they have reached commercial size. When
treating branched root plants, care should be taken, while their extraction from soil is
done in order to preserve the root part completely. Once samples are recollected,
they are handwashed and rinsed with tap water in order to remove residues such as
the remaining soil and other interferences [7]. When plant samples are composed of a
root part and a vegetative part or fruits, normally each part is treated differently due
to its great difference between them [31]. Plant sample pretreatments also consist of
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
425
Sample preparation concept is to convert a field matrix to a sample suitable for
analysis. It is a crucial and important step especially for food and environmental
matrices such as crops and soil, which are characterized by their complexity, besides
the presence of pharmaceuticals in these matrices in trace amounts [29]. This step
also allows to weaken the interactions established between pharmaceuticals and
matrices, which is highly dependent on the physical and chemical properties of
both pharmaceuticals and matrices. Further these interactions affect the applicability
of different extraction methods, their factor conditions, as well as their efficiency and
reproducibility.
Additionally, sample pretreatment is needed to assure its homogeneity and a good
contact with the solvent during the extraction process. On the other hand, most of the
analytical devices are unable to handle those matrices directly, which requires a
pretreatment step before extraction for any matrix. In general, soil preparation
includes three steps [12]: the first step is drying of sample, either by the use of the
oven, by air-drying, or by lyophilization. However, sample exposure to elevated
temperature may risk analyte degradation and alteration. Whenever lyophilization is
employed, analytes are neither degraded nor evaporated, and the drying time is
shorter. Generally, lyophilization is the most advantageous drying technique
[30]. The second step consists in the homogenization and finely grounding of the
soil samples generally using a mortar. The third and last step is soil sieving at 2 mm
to remove coarse particles to increase sample homogeneity. Thereafter, soil samples
are stored at À20
C or +4
C in the dark until analysis.
To perform ASE, from 0.5 to 20 g (Table 2) of soil are placed in a stainless-steel
extraction cell (33 mL extraction cell volume is the most commonly used) and
capped with filters at both ends. Soil sample is usually mixed with a cell matrix
(dispersant) before loading in the cell, to enhance the extraction efficiency. Finally,
the extraction cell is placed in the oven, and the system automatically starts setting
the desired temperature and pressure. For MAE, 0.2–3 g (Table 4) were used, and no
common step was found between the reported studies; they differ largely according
to the MAE procedure employed. Finally, USE and QuEChERS are the easiest,
where soil samples in both methods were introduced in centrifuge tubes. For USE
0.5–5 g (Table 3) of soil were used, the extraction solvent is therefore added, and the
tube is placed in the sonication bath. While from 1 to 10 g (Table 5) of soil were used
for QuEChERS, the extraction solvent and salts were added and the tube was
immediately vortexed and hand shacked.
Plants are normally harvested when they have reached commercial size. When
treating branched root plants, care should be taken, while their extraction from soil is
done in order to preserve the root part completely. Once samples are recollected,
they are handwashed and rinsed with tap water in order to remove residues such as
the remaining soil and other interferences [7]. When plant samples are composed of a
root part and a vegetative part or fruits, normally each part is treated differently due
to its great difference between them [31]. Plant sample pretreatments also consist of
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
425