Abstract: As great quantities of quaternary ammonium herbicides were used in agricultural production. In this article, conditions have been optimized for simultaneous determination of paraquat (PQ)、diquat (DQ) and difenzoquat(DF)by sweeping-MEKC with diode array detector (DAD) after their preconcentration by solid phase extraction(SPE). The influence of concentration of buffer,pH,concentration of SDS and organic modifier,separation voltage and injection time on the separation of quaternary ammonium herbicides were studied. An optimal separation condition was obtained by using background buffer containing 40 mmol/L SDS,50 mmol/L NaH₂PO₄ and 20% acetonitrile at pH2.6 with 20 ℃,the separation voltage at -22 kV,the sample injection time for 160 s at 6.895 kPa and 198 nm detection. The calibration curves showed good linearities in the range of 0.2~100 μg/L for paraquat,0.15~100 μg/L for diquat and 0.05~100 μg/L for difenzoquat,the limits of detections(S/N=3)for PQ, DQ and DF were 0.07, 0.05 and 0.02 μg/L respectively. The relative recoveries of the three quaternary ammonium herbicides ranged from 89.3% to 107.1% with relative standard deviation ranging from 4.5% to 11.4%. The method can be applied in the detection of quaternary ammonium herbicides in the agricultural pond water.

Key words: capillary electrophoresis, Sweeping-MEKC, pond water, solid phase extraction, quaternary ammonium herbicides