Determination of chlorophenoxy herbicides in waters by capillary gas chromatography with ion trap detection

Abstract

A method for the determination of 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in water samples is reported. Methyl esterification with boron trifluoride-methanol (BF 3-CH 3OH) and mass spectrometric detection in the electron ionization mode (EI-MS) have been evaluated. The use of mass spectrometry detection places less pressure on the need for a very efficient clean-up procedure. Further, herbicides positively identified in samples are automatically confirmed without resorting to a mass spectrometer. In this procedure we can avoid the clean-up procedure and the use of anhydrous sodium sulfate as a drying agent. The water samples were acidified to pH<1 and the herbicides were extracted with methylene chloride. After methylation with boron trifluoride, the esters were determined by gas chromatography-ion trap spectrometry with a SE-54 fused-silica capillary column, over the mass range 60–430 amu. The method was successfully validated for herbicide concentration as low as 0.04 μg/l for MCPA and 2,4-D and 0.05 μg/l for 2,4,5-T. Recoveries from water samples spiked with the 3 herbicides at 0.05 to 0.25 μg/l ranged from 63.5 to 92.0%.