Reversed migration micellar electrokinetic chromatography with off-line and on-line concentration analysis of phenylurea herbicides

Three environmentally important phenylurea herbicides (monuron, isoproturon, diuron) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 50 mM sodium dodecyl sulfate, 50 mM phosphoric acid, and 15 mM gamma-cyclodextrin. Three on-line concentration techniques are then evaluated to increase the detection sensitivity of the RM-MEKC system. Stacking with reverse migrating micelles (SRMM, water as the sample solvent) provided the best results among the focusing techniques studied. Using a z-shaped detection cell, more than 500-fold increase in peak height is obtained. As a sample preparation and off-line concentration method, solid-phase extraction (SPE) that further improved detection sensitivity was used in the analysis of spiked tap and pond water. For example, 1 parts per billion of each herbicide spiked in tap or pond water was detected by MEKC after SPE and SRMM.