A highly sensitive pre-column derivatization HPLC method for simultaneous determination of glyphosate (GLYP) and its major metabolite aminomethylphosphonic acid (AMPA) in soybean samples was developed. The analytes were labeled with a novel fluorescent labeling reagent 3,6-dimethoxy-9-phenyl-9H-carbazole-1-sulfonyl chloride (DPCS-Cl) at 70 C for 25 min. The optimized concentration of DPCS-Cl was 25 mg mL À1 and the molar ratio of analytes to DPCS-Cl was 1 : 4.2. The derivatives were separated

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... a reversed-phase column by gradient elution and were monitored with fluorescence detection at 318 nm (excitation) and 440 nm (emission). The method linearity, calculated for GLYP and AMPA, had a correlation coefficient greater than 0.999. The detection limits for GLYP and AMPA were 0.02 ng mL À1 and 0.01 ng mL À1 (S/N ¼ 3), respectively. In addition, a simple sample pretreatment for the soybean samples was developed to extract GLYP and AMPA. The recovery of extraction was more than 95%. Then, this method gave the detection limits of 0.002 mg kg À1 for GLYP and 0.001 mg kg À1 for AMPA in soybean samples. This HPLC method was applied to the determination of glyphosate and AMPA in soybean samples with its merits of simplicity in pretreatment, rapidity in derivatization, stability of the derivatives and high sensitivity.