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 chro matography (RM-MEKC) using 50 mM sodium dodecyl sulfate, 50 mM phosphoric a cid, and 15 mM gamma-cyclodextrin. Three on-line concentration techniques a re then evaluated to increase the detection sensitivity of the RM-MEKC syst em. Stacking with reverse migrating micelles (SRMM, water as the sample sol vent) provided the best results among the focusing techniques studied. Usin g 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 bil lion of each herbicide spiked in tap or pond water was detected by MEKC aft er SPE and SRMM. (C) 2000 Elsevier Science B.V. All rights reserved.