organophosphate pesticides, acylanilides, imidazolinones, phenoxypropanoic acid
herbicides and triazoles with HPLC separation techniques. In recent years, the list of
available methods for the trace level determination of pesticide enantiomers continued to grow in line with the continuous development of the available analytical
methods.
The enantiomer-selective transformation and up-take of the triazole fungicide
hexaconazole was studied in vegetables and agricultural soil. These results were
presented in a recent report (Li et al. 2013). A new enantiomer-selective HPLC
separation method with tandem mass spectrometry (LC-MS/MS) was developed and
validated for measuring hexaconazole enantiomers in tomato, cucumber and soil.
The enantiomer separation was performed on an RP-phase Chiralcel OD-RH column
(CSP see above), under isocratic conditions (mobile phase: acetonitrile-2 mM
ammonium acetate in water (60/40, v/v), flow rate of 0.4 mL/min.). This analytical
method was used for the investigation of the enantiomeric signature of rachexaconazole in vegetables and soil. The enantiomer-selective transformation of
the two hexaconazole enantiomers was confirmed but the velocity and kinetics seem
matrix dependent: The (+)-enantiomer showed a faster transformation in plants,
while the (À)-enantiomer dissipated faster in field soil, resulting in relative enrichment of the opposite enantiomer.
Today, the enantiomer specific multi-compound analysis is the favourable
attempt to cope with ever increasing potential contaminant numbers. A Chinese
study recently reported the simultaneous enantiomer-selective determination of
18 currently used chiral pesticides (CUPs) both in solid and liquid environmental
samples (Zhao et al. 2018a, b, c). In this study modified carbon nanotube amended
enantioselective liquid chromatography was applied to reach the required chromatographic resolution. For the environmental measurements, samples were collected in
Shenyang (Liaoning province, PRC). River water and sediment from the Hunhe
River were taken for enantiomer-selective analysis. The analysis was performed on
UHPLC/QqQ in positive and negative ESI, simultaneously. The commercially
available ChiralPak IG CSP (separation condition: acetonitrile/water in 5-mM
ammonium ethanoate and 0.05% methanoic acid) was used for the simultaneous
enantiomer-selective separation (producer Chiral Technology, West Chester, PA).
Most of the target compounds were identified in the (waste-) water samples analysed
with trans-2R,4R-(+)-defenoconazole in the highest levels (46 ng/L) in influent
wastewater. In river water, however, paclobutrazol E1 (stereo-specific structure
unknown yet) was found in the highest concentrations (9 ng/L).
Ulrich et al. examined the enantiomer distribution of five CUPs in aquatic
systems (Ulrich et al. 2018). The here-performed survey was a part of an ongoing
US-EPA monitoring. Previously optimised enantiomer-selective methods were
applied to the enantiomer determination of five chiral CUPs (fipronil, cis-bifenthrin,
cis- and trans-permethrin, cypermethrin and cyfluthrin) in 90 aqueous samples.
Enantiomer fractions were found for fipronil, bifenthrin and cis-permethrin target
compounds. However, 98% of fipronil, 82% of bifenthrin and 43% of cis-permethrin
EF measured (n ¼ 75) were racemic indicating minor biotransformation potential.
166
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
herbicides and triazoles with HPLC separation techniques. In recent years, the list of
available methods for the trace level determination of pesticide enantiomers continued to grow in line with the continuous development of the available analytical
methods.
The enantiomer-selective transformation and up-take of the triazole fungicide
hexaconazole was studied in vegetables and agricultural soil. These results were
presented in a recent report (Li et al. 2013). A new enantiomer-selective HPLC
separation method with tandem mass spectrometry (LC-MS/MS) was developed and
validated for measuring hexaconazole enantiomers in tomato, cucumber and soil.
The enantiomer separation was performed on an RP-phase Chiralcel OD-RH column
(CSP see above), under isocratic conditions (mobile phase: acetonitrile-2 mM
ammonium acetate in water (60/40, v/v), flow rate of 0.4 mL/min.). This analytical
method was used for the investigation of the enantiomeric signature of rachexaconazole in vegetables and soil. The enantiomer-selective transformation of
the two hexaconazole enantiomers was confirmed but the velocity and kinetics seem
matrix dependent: The (+)-enantiomer showed a faster transformation in plants,
while the (À)-enantiomer dissipated faster in field soil, resulting in relative enrichment of the opposite enantiomer.
Today, the enantiomer specific multi-compound analysis is the favourable
attempt to cope with ever increasing potential contaminant numbers. A Chinese
study recently reported the simultaneous enantiomer-selective determination of
18 currently used chiral pesticides (CUPs) both in solid and liquid environmental
samples (Zhao et al. 2018a, b, c). In this study modified carbon nanotube amended
enantioselective liquid chromatography was applied to reach the required chromatographic resolution. For the environmental measurements, samples were collected in
Shenyang (Liaoning province, PRC). River water and sediment from the Hunhe
River were taken for enantiomer-selective analysis. The analysis was performed on
UHPLC/QqQ in positive and negative ESI, simultaneously. The commercially
available ChiralPak IG CSP (separation condition: acetonitrile/water in 5-mM
ammonium ethanoate and 0.05% methanoic acid) was used for the simultaneous
enantiomer-selective separation (producer Chiral Technology, West Chester, PA).
Most of the target compounds were identified in the (waste-) water samples analysed
with trans-2R,4R-(+)-defenoconazole in the highest levels (46 ng/L) in influent
wastewater. In river water, however, paclobutrazol E1 (stereo-specific structure
unknown yet) was found in the highest concentrations (9 ng/L).
Ulrich et al. examined the enantiomer distribution of five CUPs in aquatic
systems (Ulrich et al. 2018). The here-performed survey was a part of an ongoing
US-EPA monitoring. Previously optimised enantiomer-selective methods were
applied to the enantiomer determination of five chiral CUPs (fipronil, cis-bifenthrin,
cis- and trans-permethrin, cypermethrin and cyfluthrin) in 90 aqueous samples.
Enantiomer fractions were found for fipronil, bifenthrin and cis-permethrin target
compounds. However, 98% of fipronil, 82% of bifenthrin and 43% of cis-permethrin
EF measured (n ¼ 75) were racemic indicating minor biotransformation potential.
166
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants