soil, MeOH, ACN, and water are the most used solvents for the extraction procedure.
Different mixtures have been reported in order to achieve the optimum polarity
conditions to extract the targeted compounds and avoiding interferences from the
matrix plant [40, 74, 130]. Additionally, buffer mixtures such as citric acid and
NaOH are included providing the properly pH into the mixture and enhancing the
extraction efficiency. The most used extraction solvent, MeOH, provided good
results in carrot and potato, coming to detect ten PhACs in a single analysis [40]
but also in wheat [129] and in cucumber [126]. Using water as extractant solvent
helped Azanu et al. to extract tetracycline and amoxicillin from lettuce and carrot
[39]. On the other hand, Cortés et al. managed to extract four pharmaceuticals from
soybean and wheat using buffered water (0.01 M NaOH) [131]. It is worth to
mention that the greenest method consists of using water as a unique extraction
solvent.
Up to 15 different plant matrices were studied under ASE methodology in only
9 reports (Table 6), indicating the versatility of ASE. Moreover, lettuce and carrot
were the matrices most studied (three reports for each matrix). Reports showed the
capability to develop one method for the detection of PhACs in several matrices
[39, 130].
5.2 Ultrasound Solvent Extraction (USE)
The USE methodology is certainly the most widely performed extraction method in
the environmental field. The base of the USE is centered in the formation of small
cavities inside the sample by means of ultrasound, for a subsequent penetration of
the solvent causing a greater contact surface between the sample and the extraction
solvent, enhancing PhACs extraction [132]. A further comminution of the samples
could occur due to the increase in collisions between the particles due to the
vibration of ultrasound and to the disturbances created for cavitation [132]. Dispersant agents such as sand are commonly employed to help the formation of cavities
into the samples by impact of sand particles into the sample [133]. USE is known to
be an easy extraction method but also for the use of low quantities of solvent.
However, the heat that is usually generated by particle collisions on the one hand
could facilitate the release of some classes of target compounds; in the case of
PhACs, it could lead to negative effects due to a possible thermal degradation. The
sonication time and the number of cycles are parameters that must be optimized to
ensure good extraction performance. Normally, the sonication time varied from 10 to
30 min, and 1 to 4 cycles are performed [112]. The organic solvents most used in the
extraction of PhACs from plants are mainly the same as previously seen as MeOH,
ACN, and water, used individually or in different mixtures [41, 134]. In particular,
the ACN/water mixture has been used successfully for the extraction of pharmaceutical residues in radish, ryegrass, Pisum sativum, lettuce, spinach, and rocket with
satisfactory results [31, 41, 43, 133]. Buffered mixtures containing NaHCO 3 , formic
acid, or NH 4 OH were also used providing an adequate pH for a better extraction
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
463
Different mixtures have been reported in order to achieve the optimum polarity
conditions to extract the targeted compounds and avoiding interferences from the
matrix plant [40, 74, 130]. Additionally, buffer mixtures such as citric acid and
NaOH are included providing the properly pH into the mixture and enhancing the
extraction efficiency. The most used extraction solvent, MeOH, provided good
results in carrot and potato, coming to detect ten PhACs in a single analysis [40]
but also in wheat [129] and in cucumber [126]. Using water as extractant solvent
helped Azanu et al. to extract tetracycline and amoxicillin from lettuce and carrot
[39]. On the other hand, Cortés et al. managed to extract four pharmaceuticals from
soybean and wheat using buffered water (0.01 M NaOH) [131]. It is worth to
mention that the greenest method consists of using water as a unique extraction
solvent.
Up to 15 different plant matrices were studied under ASE methodology in only
9 reports (Table 6), indicating the versatility of ASE. Moreover, lettuce and carrot
were the matrices most studied (three reports for each matrix). Reports showed the
capability to develop one method for the detection of PhACs in several matrices
[39, 130].
5.2 Ultrasound Solvent Extraction (USE)
The USE methodology is certainly the most widely performed extraction method in
the environmental field. The base of the USE is centered in the formation of small
cavities inside the sample by means of ultrasound, for a subsequent penetration of
the solvent causing a greater contact surface between the sample and the extraction
solvent, enhancing PhACs extraction [132]. A further comminution of the samples
could occur due to the increase in collisions between the particles due to the
vibration of ultrasound and to the disturbances created for cavitation [132]. Dispersant agents such as sand are commonly employed to help the formation of cavities
into the samples by impact of sand particles into the sample [133]. USE is known to
be an easy extraction method but also for the use of low quantities of solvent.
However, the heat that is usually generated by particle collisions on the one hand
could facilitate the release of some classes of target compounds; in the case of
PhACs, it could lead to negative effects due to a possible thermal degradation. The
sonication time and the number of cycles are parameters that must be optimized to
ensure good extraction performance. Normally, the sonication time varied from 10 to
30 min, and 1 to 4 cycles are performed [112]. The organic solvents most used in the
extraction of PhACs from plants are mainly the same as previously seen as MeOH,
ACN, and water, used individually or in different mixtures [41, 134]. In particular,
the ACN/water mixture has been used successfully for the extraction of pharmaceutical residues in radish, ryegrass, Pisum sativum, lettuce, spinach, and rocket with
satisfactory results [31, 41, 43, 133]. Buffered mixtures containing NaHCO 3 , formic
acid, or NH 4 OH were also used providing an adequate pH for a better extraction
Development of Methods for the Determination of PhACs in Soil/Earthworm/Crop. . .
463