Sample stacking with matrix removal for the determination of paraquat, diquat and difenzoquat in water by capillary electrophoresis

Conditions for the simultaneous determination of paraquat, diquat and difen zoquat by capillary zone electrophoresis using a stacking technique in a ch emically modified capillary have been established. To apply the stacking me thod with sample matrix removal for the analysis of cations, an anodic elec troosmotic flow is mandatory. For quats, 50 mM acetic acid-ammonium acetate (pH 4.0) with 5% (v/v) methanol as electrophoretic buffer and the addition of 0.8 mM cetyltrimethylammonium bromide as wall capillary organic modifie r was proposed. Field polarity reversal time was optimised fur several samp le matrices. Detection was carried out at 220 and 255 nm. Detection limits, based on a signal-to-noise ratio of 3:1, were lower than 15 mug 1(-1) for standards in Milli-Q water and two to ten times higher for drinking water s amples. Run-to-run and day-to-day reproducibility have been established. Th e method was successfully applied to the determination of the three herbici des in spiked drinking water. (C) 2001 Elsevier Science B.V. All rights res erved.