ANALYSIS OF MULTIPLE HERBICIDES IN SOYBEANS USING PRESSURIZED LIQUID EXTRACTION AND CAPILLARY ELECTROPHORESIS

Several herbicides commonly used on soybeans are often difficult to ex tract, isolate, and quantify from the complex soybean matrix at low co ncentrations. Typical analytical methods for herbicide residues in soy beans are single analyte procedures using HPLC or GC after chemical de rivatization. In this study, method development for the analysis of si x polar herbicides in soybeans was performed using pressurized liquid extraction (PLE), which is also known by the trade name, Accelerated S olvent Extraction, and capillary electrophoresis (CE). In CE, a 50 mM ammonium acetate running buffer, pH 4.75, was able to separate imazaqu in (Scepter), chlorimuron-ethyl (Classic), thifensulfuron-methyl (Harm ony), acifluorfen (Blazer), bentazon (Basagran), and 2,4-dichloropheno xyacetic acid in a 75 mu m i.d., 83 cm capillary (65 cm to detector) w ithin 30 min at 17 kV applied voltage. Chlorsulfuron (Glean) was used as an internal standard in the analysis, and detection was by UV absor bance at 240 nm in a high-sensitivity optical cell. PLE extracts requi red extensive cleanup prior to CE/UV analysis. Several cleanup techniq ues were investigated and compared, including liquid-liquid partitioni ng, gel-permeation chromatography, semipreparative HPLC, and solid-pha se extraction with a variety of stationary and mobile phase combinatio ns. A combination of techniques that provided the most efficient clean up was selected in the final method. Four of the six herbicides could be determined by the method in samples fortified at tolerance levels w ith average recoveries of 71% and relative standard deviation (RSD) of 11%. At a higher spiking level, all of the herbicide recoveries were > 70% with %RSDs < 10%, except for acifluorfen which gave more variabl e recoveries.