SIMULTANEOUS DETERMINATION OF RESIDUES OF PARAQUAT AND DIQUAT IN POTATOES USING HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS WITH ULTRAVIOLETDETECTION

A method was developed to separate and simultaneously determine paraqu at and diquat residues in potatoes by high-performance capillary elect rophoresis (HPCE) separation with UV detection. The potato samples are chopped into fine pieces and sonicated with 6 N HCl solution for 30 m in. After the mixture settles, the herbicides are isolated using a sil ica gel Sep-Pak cartridge. Following the addition of an internal stand ard (N,N'-tetramethylene-2,2'-bipyridinium dibromide), the extract is analyzed using a 50 cm x 50 mu m Bio-Rad HPCE column or a 60 cm x 75 m u m in-house coated column and with UV detection at 200 nm. The method achieves mean recoveries of over 70.0% and is repeatable with overall coefficients of variation of 9.8% and 10.6% (n = 20) for paraquat and diquat, respectively, at 0.05-1.0 ppm fortification levels. The limit of detection calculated as 3x standard deviation at 0.05 ppm fortific ation level is 0.01 ppm for-both paraquat and diquat. The HPCE separat ion technique demonstrates the absence of interferences from coextract ives, low migration times of 5.77, 5.93, and 6.74 min, respectively, f or paraquat, diquat, and the internal standard, and a high separation efficiency generating over 4 X 10(5) theoretical plates per meter and giving total resolution of paraquat and diquat peaks in the electrophe rogram.