cleanup. Recoveries were of 90–135% and MLODs of 0.2–1.5 ng/g [31]. Sonication
has been also used for the extraction of pyrethroids from sediment samples. Xue
et al. used methanol/acetonitrile (50/50 volume/volume) as extraction solvent and
performed the cleanup of the extracts on a Florisil column using dichloromethane/
hexane (20/80 v/v) as eluent [19]. They found recoveries of 71–103% and MLODs
of 3.0 Â 10
À5
–1.5 Â 10
À3 ng/g [19]. However, Feo et al. used hexane/
dichloromethane (2:1) as extraction solvent in a sonicator for 15 min at room
temperature and performed the cleanup with Florisil cartridge (2 g/15 mL). Ethyl
acetate was used as eluent. Recoveries were of 51–105% and MLODs were of
2.6–62.4 pg/g [6]. In the last years, new extraction techniques have been developed
for solid samples (such as supercritical fluid extraction, solid-phase microextraction,
microwave-assisted extraction, pressurized fluid extraction) with the intent to reduce
the volume of the organic solvent used for the extraction and the time of the analysis.
Pressurized fluid extraction (PFE), which consists of using organic solvents, pumped
into an extraction cell containing the sample and brought to an elevated temperature
and pressure [57], has been used for extraction of pyrethroids from sediments
[15]. PFE was followed by cleanup with gel permeation (GP) (size exclusion), and
dichloromethane was used as eluent. Recoveries were 84–108% with 0.5–4 ng/g
MLODs [15]. Supercritical fluid extraction consists of using supercritical fluids
(normally water or carbon dioxide), as extraction agents. Supercritical fluids exhibit
a liquid-like density, while their viscosity and diffusivity remain between gas-like
and liquid-like values. Thus, supercritical fluids have lower viscosity and higher
diffusivity compared to organic solvents. The applicability of supercritical fluid
extraction (SFE) for multi-residue analysis was studied for soil samples. The best
efficiency was achieved at 400 bar using methanol as modifier at 60
C. Cleanup was
carried out using C18 cartridge and dichloromethane/hexane (50:50 v/v) as eluent.
Recoveries were 70–97% with MLODs <0.01 mg/kg [33]. A simple solvent-free
method based on headspace SPME (HS-SPME) was developed in order to determine
pyrethroids in agricultural soils [34]. Factors (e.g., extraction temperature, matrix
modification by addition of water, salt addition, and fiber coating) were considered
in optimizing the procedure. The results showed that temperature and fiber coating
were the most significant variables affecting extraction efficiency. Good sensitivity
for all investigated compounds was achieved at 100
C by extracting soil samples
wetted with 0.5 mL of ultrapure water (0% NaCl) employing a polyacrylate coating
fiber. Recoveries were 81–122% with MLODs less than 0.004–1.2 ng/g [34]. Microwave-assisted extraction (MAE) was performed by Esteve et al. for the determination of synthetic pyrethroids in soil using toluene as extraction solvent and an
irradiation of 700 W for 9 min [32]. Cleanup was performed with 2 g of Florisil
and elution with 20 mL ethyl acetate/hexane 33% (v/v). Recoveries were of
97–106% and MLODs of 0.3–2 μg/L [32]. However, the author observed that
different chemical forms of pyrethroids respond differently at low irradiation
power (between 350 and 700 W) and irradiation time (between 3 and 12 min).
Thus, different extraction conditions are needed to be set for individual pyrethroids
during MAE. The stability of pyrethroids under MAE-optimized conditions still
needed further studies. QuEChERS method was used for the extraction of pesticides
32
M. L. Feo
has been also used for the extraction of pyrethroids from sediment samples. Xue
et al. used methanol/acetonitrile (50/50 volume/volume) as extraction solvent and
performed the cleanup of the extracts on a Florisil column using dichloromethane/
hexane (20/80 v/v) as eluent [19]. They found recoveries of 71–103% and MLODs
of 3.0 Â 10
À5
–1.5 Â 10
À3 ng/g [19]. However, Feo et al. used hexane/
dichloromethane (2:1) as extraction solvent in a sonicator for 15 min at room
temperature and performed the cleanup with Florisil cartridge (2 g/15 mL). Ethyl
acetate was used as eluent. Recoveries were of 51–105% and MLODs were of
2.6–62.4 pg/g [6]. In the last years, new extraction techniques have been developed
for solid samples (such as supercritical fluid extraction, solid-phase microextraction,
microwave-assisted extraction, pressurized fluid extraction) with the intent to reduce
the volume of the organic solvent used for the extraction and the time of the analysis.
Pressurized fluid extraction (PFE), which consists of using organic solvents, pumped
into an extraction cell containing the sample and brought to an elevated temperature
and pressure [57], has been used for extraction of pyrethroids from sediments
[15]. PFE was followed by cleanup with gel permeation (GP) (size exclusion), and
dichloromethane was used as eluent. Recoveries were 84–108% with 0.5–4 ng/g
MLODs [15]. Supercritical fluid extraction consists of using supercritical fluids
(normally water or carbon dioxide), as extraction agents. Supercritical fluids exhibit
a liquid-like density, while their viscosity and diffusivity remain between gas-like
and liquid-like values. Thus, supercritical fluids have lower viscosity and higher
diffusivity compared to organic solvents. The applicability of supercritical fluid
extraction (SFE) for multi-residue analysis was studied for soil samples. The best
efficiency was achieved at 400 bar using methanol as modifier at 60
C. Cleanup was
carried out using C18 cartridge and dichloromethane/hexane (50:50 v/v) as eluent.
Recoveries were 70–97% with MLODs <0.01 mg/kg [33]. A simple solvent-free
method based on headspace SPME (HS-SPME) was developed in order to determine
pyrethroids in agricultural soils [34]. Factors (e.g., extraction temperature, matrix
modification by addition of water, salt addition, and fiber coating) were considered
in optimizing the procedure. The results showed that temperature and fiber coating
were the most significant variables affecting extraction efficiency. Good sensitivity
for all investigated compounds was achieved at 100
C by extracting soil samples
wetted with 0.5 mL of ultrapure water (0% NaCl) employing a polyacrylate coating
fiber. Recoveries were 81–122% with MLODs less than 0.004–1.2 ng/g [34]. Microwave-assisted extraction (MAE) was performed by Esteve et al. for the determination of synthetic pyrethroids in soil using toluene as extraction solvent and an
irradiation of 700 W for 9 min [32]. Cleanup was performed with 2 g of Florisil
and elution with 20 mL ethyl acetate/hexane 33% (v/v). Recoveries were of
97–106% and MLODs of 0.3–2 μg/L [32]. However, the author observed that
different chemical forms of pyrethroids respond differently at low irradiation
power (between 350 and 700 W) and irradiation time (between 3 and 12 min).
Thus, different extraction conditions are needed to be set for individual pyrethroids
during MAE. The stability of pyrethroids under MAE-optimized conditions still
needed further studies. QuEChERS method was used for the extraction of pesticides
32
M. L. Feo