Electrically Driven Microseparation Methods for Pesticides and Metabolites: I. Micellar Electrokinetic Capillary Chromatography of Carbamate Insecticides with MEGA-Borate and SDS Surfactants

Abstract

Abstract The migration behavior of some representative carbamate insecticides in micellar electrokinetic capillary chromatography (MECC) was investigated over a wide range of elution conditions, including the nature and concentration of the surfactant and the concentration of added urea in the running electrolyte. Decanoyl-N-methylglucamide (MEGA 10) surfactant was compared with the traditionally used sodium dodecyl sulfate (SDS) surfactant for separation of the carbamate insecticides under investigation. The MEGA 10 micellar system is based on the complexation of MEGA 10 with borate, yielding an in situ charged micelle (i.e., MEGA 10-borate micelle), whose surface charge density can be readily manipulated by varying the pH and the concentrations of borate and MEGA 10 in the running electrolyte. This flexibility, in turn, allowed the modulation of the migration time window and, consequently, the analysis time. Because of its relatively weaker hydrophobic character, the MEGA 10-borate micellar system permitted the resolution of 9 different carbamate insecticides in about 12 min. Conversely, with the SDS micellar system, whose hydrophobicity is higher, the separation of all 9 solutes necessitated the addition of 4.0M urea, a condition that brought about a doubling of the analysis time. In addition, the MEGA 10-borate micellar system produced twice as many plates per min as did the SDS micellar system. Because MEGA 10-borate yielded results superior to those of the SDS micellar system, on-column preconcentration of the carbamate insecticides was attempted in MEGA 10-borate by using the concept of field-amplified sample stacking (FASS). Thus far, only a few attempts have been made toward the application of FASS in MECC of neutral compounds such as carbamate insecticides.