The effect of operating variables in microemulsion electrokinetic capillary chromatography

Abstract

Microemulsion electrokinetic capillary chromatography (MEEKC) is similar to micellar electrokinetic chromatography (MEKC) in that it separates neutral solutes based on their chromatographic retention factors. In MEEKC solutes partition between the aqueous phase and oil droplets, which are moving through the solution. The background to MEEKC is described including novel approaches to method development and optimisation. In this case water-immiscible octane forms minute oil droplets that are coated with SDS and butan-1-ol. The effects were evaluated using a test-mixture containing nine components of insoluble and soluble acids, bases and neutrals. Selectivity has been adjusted by use of a large number of factors including organic solvent, co-surfactant, urea, temperature, cyclodextrins, ion-pair reagent. Previous reports on the selectivity in MEEKC have concentrated only on neutral solutes. Separation selectivity was drastically changed with addition of alcohol such as butan-1-ol, propan-2-ol, cyclodextrin or using a low pH buffer. Microemulsion preparation process or filtration of the buffer did not affect the separation. The separation was largely unaffected by the use of methanol or acetonitrile, surfactant concentration, buffer type, oil type, sample diluent or type of the counter-ion. Migration times were dramatically altered with the use of ion-pair reagent and buffer concentration. It was also demonstrated that temperature variations alter the migration time but not the selectivity.