range 0.12–0.43 ng/mL [24]. A one-step microwave-assisted headspace solid-phase
microextraction (MA-HS-SPME) has been applied to be a pretreatment step in the
analysis of aqueous pyrethroid residuals by GC analysis [25]. Microwave heating
was applied to accelerate the vaporization of pyrethroids into the headspace and then
being absorbed directly on a SPME fiber under the controlled conditions. Extraction
of pyrethroids from aqueous (at pH 4) was achieved with the use of a 100 m PDMS
fiber, microwave irradiation of 157 W, and sampling at 30
C for 10 min. Recoveries
were between 88.5 and 115.5%, and MLODs were 0.2–2.6 ng/L [25]. The method
was applied to groundwater samples [25]. Van Hoeck et al. developed an SBSE
method for the enrichment of pyrethroids from unfiltered water samples [4]. The
method consists of adding the stir bar in the water sample (10 mL) together with
methanol to minimize wall adsorption. The SBSE method is followed to thermal
desorption (TD) in classical GC split/splitless inlet equipped with a flip top inlet
sealing system. The extraction was performed at room temperature, with stirring at
900 rpm. Recoveries were of 40–80% and MLODs of 0.02–1.4 ng/L [4]. Sequential
SBSE followed by thermal desorption (TD)-low thermal mass (LTM) gas chromatography mass spectrometer (GC-MS) was developed by Ochai et al. [26, 27]. The
usage of dual SBE was to provide more uniform enrichment over the entire polarity/
volatility range for organic pollutants at ultra-trace levels in water. In a first experiment, two stir bars were added to the unfiltered water, the extraction was performed
at room temperature, and then, pyrethroids were desorbed from the two stir bars
directly in the glass desorption liner. Recoveries were low (17–33%) and MLODs
were 3–100 ng/L [26]. In a second experiment, the authors first added one stir bar to
the sample without modifier and then a second stir bar to the same sample after
adding 30% NaCl. The first extraction with unmodified sample was mainly to target
for solutes with high Kow (log Kow > 4.0); and the second extraction with modified
sample solution (containing 30% NaCl) was targeted at solutes with low and
medium Kow (log Kow < 4.0). After the extraction, the two bars were placed in a
single glass desorption liner and were simultaneously desorbed. Recoveries were
82–113% with low MLODs (>10 ng/L) [27]. Molecularly imprinted solid-phase
extraction (MI-SPE) based on selective molecularly imprinted polymers (MIPs) has
been used for the isolation and cleanup of pyrethroid insecticides in aquaculture
seawater [30]. Recoveries were 86–96% and MLODs were 16.6–37.0 ng/L [30].
2.2 Extraction from Soil and Sediment Samples
The interaction between pyrethroids and soil/sediment matrix is much stronger than
it is in water due to the hydrophobic character of pyrethroids [5] and to the
consequently formation of bound residues in soil/sediment [56]. Thus, more exhaustive extraction procedures are required to liberate pyrethroids from the solid matrix.
Conventional methods as Soxhlet extraction have been used for pyrethroid extraction from sediments although the method is time-consuming and requires a large
amount of solvents. Dichloromethane was used as solvent and by Florisil for the
Analytical Methods for Determining Pyrethroid Insecticides in Environmental and. . .
31
microextraction (MA-HS-SPME) has been applied to be a pretreatment step in the
analysis of aqueous pyrethroid residuals by GC analysis [25]. Microwave heating
was applied to accelerate the vaporization of pyrethroids into the headspace and then
being absorbed directly on a SPME fiber under the controlled conditions. Extraction
of pyrethroids from aqueous (at pH 4) was achieved with the use of a 100 m PDMS
fiber, microwave irradiation of 157 W, and sampling at 30
C for 10 min. Recoveries
were between 88.5 and 115.5%, and MLODs were 0.2–2.6 ng/L [25]. The method
was applied to groundwater samples [25]. Van Hoeck et al. developed an SBSE
method for the enrichment of pyrethroids from unfiltered water samples [4]. The
method consists of adding the stir bar in the water sample (10 mL) together with
methanol to minimize wall adsorption. The SBSE method is followed to thermal
desorption (TD) in classical GC split/splitless inlet equipped with a flip top inlet
sealing system. The extraction was performed at room temperature, with stirring at
900 rpm. Recoveries were of 40–80% and MLODs of 0.02–1.4 ng/L [4]. Sequential
SBSE followed by thermal desorption (TD)-low thermal mass (LTM) gas chromatography mass spectrometer (GC-MS) was developed by Ochai et al. [26, 27]. The
usage of dual SBE was to provide more uniform enrichment over the entire polarity/
volatility range for organic pollutants at ultra-trace levels in water. In a first experiment, two stir bars were added to the unfiltered water, the extraction was performed
at room temperature, and then, pyrethroids were desorbed from the two stir bars
directly in the glass desorption liner. Recoveries were low (17–33%) and MLODs
were 3–100 ng/L [26]. In a second experiment, the authors first added one stir bar to
the sample without modifier and then a second stir bar to the same sample after
adding 30% NaCl. The first extraction with unmodified sample was mainly to target
for solutes with high Kow (log Kow > 4.0); and the second extraction with modified
sample solution (containing 30% NaCl) was targeted at solutes with low and
medium Kow (log Kow < 4.0). After the extraction, the two bars were placed in a
single glass desorption liner and were simultaneously desorbed. Recoveries were
82–113% with low MLODs (>10 ng/L) [27]. Molecularly imprinted solid-phase
extraction (MI-SPE) based on selective molecularly imprinted polymers (MIPs) has
been used for the isolation and cleanup of pyrethroid insecticides in aquaculture
seawater [30]. Recoveries were 86–96% and MLODs were 16.6–37.0 ng/L [30].
2.2 Extraction from Soil and Sediment Samples
The interaction between pyrethroids and soil/sediment matrix is much stronger than
it is in water due to the hydrophobic character of pyrethroids [5] and to the
consequently formation of bound residues in soil/sediment [56]. Thus, more exhaustive extraction procedures are required to liberate pyrethroids from the solid matrix.
Conventional methods as Soxhlet extraction have been used for pyrethroid extraction from sediments although the method is time-consuming and requires a large
amount of solvents. Dichloromethane was used as solvent and by Florisil for the
Analytical Methods for Determining Pyrethroid Insecticides in Environmental and. . .
31