COMPARISON OF CAPILLARY ELECTROPHORESIS AND REVERSED-PHASE ION-PAIR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY FOR THE DETERMINATION OF PARAQUAT, DIQUAT AND DIFENZOQUAT

The conditions were established for the simultaneous determination of paraquat, diquat and difenzoquat by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). For the HPLC separation, the use of a reversed phase, heptanesulphonate as ion-pairing agent and an aqueous-acetonitrile mobile phase with stepwise elution from 93:7 to 70:30 was adopted. Acetic acid-sodium acetate (pH 4.0) with 100 mM sodium chloride as running buffer and electrokinetic injection were used in CE. The figures of merit were calculated and the two techniques were compared. Detection limits (signal-to-noise ratio = 3:1) ranged from 2.9 to 5.5 mu g l(-1) and were similar for both techniques when standards were dissolved in water, but when CE was used the response was greatly affected by the nature of the sample matrix. The run-to-run and day-to-day reproducibilities and the analysis times were similar for both techniques. However, CE did not require preconditioning and a long stabilization period was needed in ion-pair HPLC. The methods were applied to the determination of the herbicides in crop waters.