Monitoring the supercritical fluid extraction of pyrethroid pesticides using capillary electrochromatography

Capillary electrochromatography (CEC) is reported for monitoring the extraction of the pyrethroid pesticides fenpropathrin, fenvalerate and fluvalinate by SFE using supercritical CO₂. The optimum SFE conditions obtained for the pyrethroid pesticides from spiked cellulose matrix, were for fenpropathrin 300 atm and 70°C, fenvalerate 300 atm and 60°C and for fluvalinate 200 atm and 75°C. Extracts collected in methanol were subjected to analysis by CEC on a 30 cm x 75 μm i.d. fused silica capillary packed with 5 μm Hypersil ODS (21 cm packed length). Electrochromatograms of the three pyrethroid pesticides were obtained in order of elution thiourea (as the EOF marker), fenpropathrin, fenvalerate and fluvalinate, with mobile phase ACN-25 mM NaH₂PO₄ pH 8.3 (85:15), voltage 25 kV, electrokinetic injection 5 kV, 3 sec and detection at 200 nm. The SFE recoveries were > 80% for all three solutes. In addition, enantioseparation of the pyrethroid pesticides was investigated using Me-β-CD and HP-β-CD as chiral additives. The enantioseparation of fenpropathrin was optimised to a methanol-25 mM Tris pH 8.3 mobile phase (75:25) containing 70 mM Me-β-CD.