avoiding pyrethroid isomerization. However, the sensitivity of LC is lower than that
of the GC, and this needs to be considered when working at residue levels. Thus,
pre-concentration and cleanup procedures are necessary to be applied to comply with
tolerance levels. LC separation has been performed on a 250 Â 4.6 mm i.d. Water
symmetry C18 column (5 μm particle size) coupled by quadrupole MS with an
electrospray ionization (ESI) interface [20]. Acetonitrile was the solvent A and
ammonium formate 50 mM, 5% of acetonitrile, pH 3.5, the solvent B. ILODs
were found in the range 0.3–0.5 μg/L [20]. LC techniques have been used also
coupled to photochemically induced fluorimetry (PIF) for derivatization (pyrethroids
do not display native fluorescence; thus, they were photolyzed into strongly fluorescent photoproducts) and a fluorescence detector (FD) [21, 50]. The FD is very
selective, overcoming matrix interference [68]. LC separation was performed on a
3.5 μm symmetry C18. Acetonitrile water was used as mobile phase
[21, 50]. Valverde et al. showed that in LC-ESI-MS (positive ion mode),
deltamethrin and the two diastereoisomers of tralomethrin were efficiently separated,
whereas, under GC conditions, both insecticides elute at the same retention time and
give the same mass spectra [61]. This is probably due to the transformation of the
two isomers of tralomethrin into deltamethrin in the GC injector port by elimination
of a molecule of bromine. The LC separation was carried out on LiChroCART
Superspher 100 RP-18 column using isocrated elution with acetonitrile/water
(80:20) as eluent [61]. For HPLC determination, the analytical column employed
was C18 stationary phase (150 Â 4.6 mmI.D., 5.0 m), and the mobile phase was
water-methanol (20:80, v/v). The detection was performed with an UV-Vis detector
working at wavelength of 220 nm [17]. Liu et al. employed a Spursil C18 column
(5, 4.6, 250 mm) with a Spursil C18 Guard Cartridges (5, 2.1, 10 mm) [45]. The
mobile phase was an acetonitrile/water mixture (83/17, v/v). The detector was
variable wavelength detector (VWD) with wavelength set at 230 nm [45]. Parilla
Vazquez et al. performed liquid separation on a column of 250 Â 4.6 mm id packed
with 3.5 μm Symmetry C18 [21, 50]. The mobile phase was a programmed gradient
with acetonitrile/water. The detector was PIF-FD operating with a programmed
excitation and emission wavelengths of 283 and 330 nm [21, 50].
4 Enantioselective Separation
Chiral pollutants as pyrethroids are receiving growing environmental concern due to
differential biological activities of their enantiomers. Liu et al. reported enantiomeric
separation of cis-bifenthrin, permethrin, cypermethrin, and cyfluthrin using LC with
variable wavelength UV detection for quantification and a laser polarimetric detection for the identification of the direction of optical rotation of the separated
stereoisomers [62, 69]. The separation of the stereoisomers of cis-bifenthrin, cispermethrin, and trans-permethrin was achieved on a 25 cm Sumichiral OA-2500-I
column using hexane/1,2-dichloroethane (500:1, v/v) as eluent, whereas isomer
separation for cypermethrin and cyfluthrin was obtained on two 25 cm Chirex
38
M. L. Feo
of the GC, and this needs to be considered when working at residue levels. Thus,
pre-concentration and cleanup procedures are necessary to be applied to comply with
tolerance levels. LC separation has been performed on a 250 Â 4.6 mm i.d. Water
symmetry C18 column (5 μm particle size) coupled by quadrupole MS with an
electrospray ionization (ESI) interface [20]. Acetonitrile was the solvent A and
ammonium formate 50 mM, 5% of acetonitrile, pH 3.5, the solvent B. ILODs
were found in the range 0.3–0.5 μg/L [20]. LC techniques have been used also
coupled to photochemically induced fluorimetry (PIF) for derivatization (pyrethroids
do not display native fluorescence; thus, they were photolyzed into strongly fluorescent photoproducts) and a fluorescence detector (FD) [21, 50]. The FD is very
selective, overcoming matrix interference [68]. LC separation was performed on a
3.5 μm symmetry C18. Acetonitrile water was used as mobile phase
[21, 50]. Valverde et al. showed that in LC-ESI-MS (positive ion mode),
deltamethrin and the two diastereoisomers of tralomethrin were efficiently separated,
whereas, under GC conditions, both insecticides elute at the same retention time and
give the same mass spectra [61]. This is probably due to the transformation of the
two isomers of tralomethrin into deltamethrin in the GC injector port by elimination
of a molecule of bromine. The LC separation was carried out on LiChroCART
Superspher 100 RP-18 column using isocrated elution with acetonitrile/water
(80:20) as eluent [61]. For HPLC determination, the analytical column employed
was C18 stationary phase (150 Â 4.6 mmI.D., 5.0 m), and the mobile phase was
water-methanol (20:80, v/v). The detection was performed with an UV-Vis detector
working at wavelength of 220 nm [17]. Liu et al. employed a Spursil C18 column
(5, 4.6, 250 mm) with a Spursil C18 Guard Cartridges (5, 2.1, 10 mm) [45]. The
mobile phase was an acetonitrile/water mixture (83/17, v/v). The detector was
variable wavelength detector (VWD) with wavelength set at 230 nm [45]. Parilla
Vazquez et al. performed liquid separation on a column of 250 Â 4.6 mm id packed
with 3.5 μm Symmetry C18 [21, 50]. The mobile phase was a programmed gradient
with acetonitrile/water. The detector was PIF-FD operating with a programmed
excitation and emission wavelengths of 283 and 330 nm [21, 50].
4 Enantioselective Separation
Chiral pollutants as pyrethroids are receiving growing environmental concern due to
differential biological activities of their enantiomers. Liu et al. reported enantiomeric
separation of cis-bifenthrin, permethrin, cypermethrin, and cyfluthrin using LC with
variable wavelength UV detection for quantification and a laser polarimetric detection for the identification of the direction of optical rotation of the separated
stereoisomers [62, 69]. The separation of the stereoisomers of cis-bifenthrin, cispermethrin, and trans-permethrin was achieved on a 25 cm Sumichiral OA-2500-I
column using hexane/1,2-dichloroethane (500:1, v/v) as eluent, whereas isomer
separation for cypermethrin and cyfluthrin was obtained on two 25 cm Chirex
38
M. L. Feo