POSSIBLE USES OF MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY ANDHIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY FOR THE CHIRAL DISCRIMINATION OF SOME PYRETHROIDS

Micellar electrokinetic capillary chromatography (MECC) and highperfor mance liquid chromatography (HPLC) were used for the separation of ste reoisomers of the lipophilic uncharged pyrethroids cypermethrin, alpha methrin, permethrin, and fenpropathrin. Different kinds of cyclodextri n (beta-cyclodextrin, hydroxypropyl-beta-cyclodextrin, dimethyl-beta-c yclodextrin, and gamma-cyclodextrin), surfactants (sodium dodecyl sulp hate [SDS] and cetyltrimethylammonium bromide [CTAB]), and cations of background electrolyte (sodium, ammonium, TRIS, and Ammediol) were tes ted. Optimized conditions (background electrolyte: 50 mmol/l sodium ph osphate, pH = 2.5, 150 mmol/l SDS, 150 mg/ml gamma-cyclodextrin) allow ed the separation of alphamethrin, the eight cypermethrin stereoisomer s being eluted in seven peaks and the separation of two enantiomers of fenpropathrin with resolution R-s = 10 and with n approximate to 500, 000 theoretical plates. Different experimental conditions, e.g., mobil e phase composition, temperature, injected amount, and flow rate, were also optimized in HPLC experiments. The optimal conditions (stationar y phase: ChiraDex, 5 mu m; mobile phase: 150 mmol triethylamine/l with H2SO4 in water (pH = 3.5) with methanol or acetonitrile; now rate: 0. 8 or 0.6 ml/min; temperature: ambient or 30 degrees, 20 degrees, or 10 degrees C; experimental conditions were modified according to the typ e of analysis) allow chiral discrimination of alphamethrin enantiomers and analysis of permethrin stereoisomers. MECC offers higher efficien cy and shorter analysis time than HPLC, but under tested conditions it was shown that the methods complement each other. (C) 1997 Wiley-Liss , Inc.