A simplified HPLC procedure for the determination of glyphosate in soybeans employing postcolumn fluorescence labeling

An analytical procedure for residues of the herbicide glyphosate [N-phospho nomethylglycine] in soybeans is described. Extraction of soybeans is perfor med with 20 mmol/L berate buffer solution. Cleanup is achieved by an ortho- phthalaldehyde-mercaptoethanol (OPA-MERC) reaction followed by application to a dual mini-cartridge column (graphite and octadecyl-bonded silica gel) system, and determination is performed by ion-pair mode high-performance li quid chromatography employing postcolumn fluorescence labeling of the appro priate primary amine with OPA-MERC. Conversion of glyphosate to a primary a mine (presumably ammonia and/or glycine) is achieved postcolumn by oxidatio n with sodium hypochlorite. Residues can easily be measured at the 0.05 ppm level with recoveries greater than 74%. The efficiency of the purification and the simplicity of the procedure allow for high sample throughput compa red to existing procedures.