Exceeding 5000-fold concentration of dilute analytes in micellar electrokinetic chromatography.

When a neutral analyte zone is injected into a charged pseudostationary phase, the length of the zone is predicted to be narrowed by 1/(1 + k), where k is the retention factor. The conditions for zone narrowing to occur assume negligible electroosmotic flow, a relatively constant electric field along the capillary column, and no pseudostationary phase in the injected analyte mixture. The theoretically expected concentration enhancement was demonstrated experimentally. Consequently, the detection sensitivity of analytes in micellar electrokinetic chromatography (MEKC) can be improved significantly. For example, 9 to 18 parts per billion of an environmentally important racemic herbicide spiked in lake water was separated by MEKC and detected by ultraviolet absorption.