the removal of the water content and also a crushing process in order to obtain fine
powder samples [32]. Although not all the studies have decided to eliminate the
sample moisture, water content removal could provide more stabilization to the
sample when stored [33, 34]. Besides, working with wet matrices makes it necessary
to work with a higher amount of sample than working with dry samples. Commonly,
freeze-drying process is performed ensuring a complete water removal. On the other
hand, the crushing process is performed to ensure homogenization of the sample, but
it also improves the subsequent extraction process. Depending on the extraction
method performed and the use of dry or wet samples, the quantity of sample required
varies. In general, 0.1 to 15 g of samples are used for analysis. Small quantities up to
5 g are used for dry samples [35], while larger amounts are required when wet
samples are analyzed [36]. Freeze-drying samples, apart from preserving the stability
of compounds of interest, allows to store in a small space originally voluminous
samples. Lyophilization is the most common freeze-drying technique used [37] due
to its rapidity but also the certainty of not wasting sample during the process [38].
As before-mentioned, sample quantity strongly depends on the extraction method
used. Similar sample weights are used for the extraction of pharmaceutical products
from plant tissues. From 0.1 to 8 g samples [39, 40] were used to perform ASE as its
methodology is mainly focused on parameters such as solvent, temperature, and
pressure, while sample amount plays a secondary role. In the case of USE, weights
between 0.1 and 10 g sample were used [41–44]. However, compared to ASE, less
quantity of sample is needed when USE was employed. Little amount of sample
enhances the extraction efficiency due to the need to create cavities inside the matrix
that are easily formatted when lower amount of sample is analyzed. On the other
hand, ASE is not as sensitive to this factor owing to other parameters such as
temperature and pressure which could help in the creation of these cavities inside
the sample. Finally, as regards the QuEChERS method, several authors used weight
ranges from 0.5 to 15 g [7, 36, 45, 46]. Looking at the original method developed by
Anastassiades et al. [19], the established weight was 10 g of wet sample. This
quantity was established on the basis of the amount of salts used by the QuEChERS
methodology. It has to be noted that, depending on the nature of the analyzed sample
(low-fat samples, high-fat samples, low water amount samples, etc.), different
weights and hydration volumes should be applied in order to achieve a successful
extraction performance. When 10 g of fruits between 25 and 80% of water content
are analyzed, the amount of hydration water added varies depending on its water
content. For example, for fruit with 60% water content, 4 mL of water should be
added. On the other hand, 5 g of cereals and honey requires 10 mL of hydration
water, while fruits with a water content above 80% do not need any amount of water
hydration [47]. All these considerations are based on pesticide extraction though;
extraction variations could be observed when PhACs are the target analytes.
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
443
powder samples [32]. Although not all the studies have decided to eliminate the
sample moisture, water content removal could provide more stabilization to the
sample when stored [33, 34]. Besides, working with wet matrices makes it necessary
to work with a higher amount of sample than working with dry samples. Commonly,
freeze-drying process is performed ensuring a complete water removal. On the other
hand, the crushing process is performed to ensure homogenization of the sample, but
it also improves the subsequent extraction process. Depending on the extraction
method performed and the use of dry or wet samples, the quantity of sample required
varies. In general, 0.1 to 15 g of samples are used for analysis. Small quantities up to
5 g are used for dry samples [35], while larger amounts are required when wet
samples are analyzed [36]. Freeze-drying samples, apart from preserving the stability
of compounds of interest, allows to store in a small space originally voluminous
samples. Lyophilization is the most common freeze-drying technique used [37] due
to its rapidity but also the certainty of not wasting sample during the process [38].
As before-mentioned, sample quantity strongly depends on the extraction method
used. Similar sample weights are used for the extraction of pharmaceutical products
from plant tissues. From 0.1 to 8 g samples [39, 40] were used to perform ASE as its
methodology is mainly focused on parameters such as solvent, temperature, and
pressure, while sample amount plays a secondary role. In the case of USE, weights
between 0.1 and 10 g sample were used [41–44]. However, compared to ASE, less
quantity of sample is needed when USE was employed. Little amount of sample
enhances the extraction efficiency due to the need to create cavities inside the matrix
that are easily formatted when lower amount of sample is analyzed. On the other
hand, ASE is not as sensitive to this factor owing to other parameters such as
temperature and pressure which could help in the creation of these cavities inside
the sample. Finally, as regards the QuEChERS method, several authors used weight
ranges from 0.5 to 15 g [7, 36, 45, 46]. Looking at the original method developed by
Anastassiades et al. [19], the established weight was 10 g of wet sample. This
quantity was established on the basis of the amount of salts used by the QuEChERS
methodology. It has to be noted that, depending on the nature of the analyzed sample
(low-fat samples, high-fat samples, low water amount samples, etc.), different
weights and hydration volumes should be applied in order to achieve a successful
extraction performance. When 10 g of fruits between 25 and 80% of water content
are analyzed, the amount of hydration water added varies depending on its water
content. For example, for fruit with 60% water content, 4 mL of water should be
added. On the other hand, 5 g of cereals and honey requires 10 mL of hydration
water, while fruits with a water content above 80% do not need any amount of water
hydration [47]. All these considerations are based on pesticide extraction though;
extraction variations could be observed when PhACs are the target analytes.
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
443