Simultaneous determination of diquat and paraquat residues in various matrices by capillary zone electrophoresis with diode array detection

The separation of diquat and paraquat by CZE has been investigated. The addition of acetonitrile (10 %, v/v) to a phosphate buffer (100 mM, pH 4.0) is necessary for effective separation of both herbicides at an optimum applied voltage of around 12 kV; the current and migration times were stable and reproducible under these conditions. The method was validated for linearity and reproducibility. The detection level calculated for diquat and paraquat was 30 and 40 nM, respectively in the injection solution. By use of stacking, these detection levels were improved by a factor of 120. The method is suitable for the determination of both herbicides in samples such as herbicidal formulations, water, soil, potatoes, urine and serum. Photodiode-array detection permitted the rapid identification of both compounds.