Separation of the insecticidal pyrethrin esters by capillary electrochromatography

A simple, rapid technique for the direct separation and quantification of the six insecticidally active pyrethrin esters in typical extracts and commercial formulations by capillary electrochromatography (CEC) has been described. The separation of the pyrethrin esters was achieved by optimizing several parameters including the length of stationary phase, the mobile phase composition and column temperature. The mobile phase composition had the most pronounced effect toward resolving these structurally similar compounds. A ternary mobile phase composed of acetonitrile–aqueous buffer–tetrahydrofuran (55:35:10) provided the elutropic solvent strength needed to resolve the six esters from an extract mixture in under 16 min. A 25 cm packed bed of Hypersil 3 μm C18 stationary phase was used with the ternary mobile phase at 25°C and 30 kV voltage. These conditions also yielded excellent separation of the pyrethrin esters in two different commercially available insecticidal formulations. In addition, the developed CEC method was shown to be a fast and easy way of quantifying the amount of these esters in typical pyrethrin formulations.