SIMULTANEOUS DETERMINATION OF THE HERBICIDES GLYPHOSATE, GLUFOSINATE AND BIALAPHOS AND THEIR METABOLITES BY CAPILLARY GAS-CHROMATOGRAPHY ION-TRAP MASS-SPECTROMETRY

A sensitive gas chromatographic (GC)-ion-trap mass spectrometric (IT-MS) method has been developed to determine simultaneously the herbicides glyphosate, glufosinate and bialaphos and their major metabolites. A single-step derivatization is achieved at 80-degrees-C for 30 min with the reagent N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide in dimethylformamide, which introduces the tert.-butyldimethylsilyl group at active hydrogens and gives only a single peak for each compound. The derivatives of three herbicides, their metabolites and nineteen amino acids were simultaneously chromatographed and well separated in a single run on a DB-1 fused-silica capillary column. Each tert.-butyldimethylsilylated derivative produces an easily interpretable mass spectrum dominated by unique M - 15, M - 57, M - 85 and M - 159 fragment ions. The limits of detection were estimated to be 10-20 ng for glyphosate and glufosinate and their metabolites, and 500 ng for bialaphos, by GC-IT-MS. On the other hand, using GC analysis with flame ionization - detection, glyphosate and glufosinate and their metabolites were detectable at levels of approximately 100 ng, but bialaphos could not be detected at a level of 5000 ng.