Gas chromatographic determination of acid herbicides in surface water samples with electron-capture detection and mass spectrometric confirmation

The development of a multi-residue method for the determination of eight polar acidic herbicides (MCPA, MCPB, mecoprop, 2,4-D, dichlorprop, bentazone, dicamba and dikegulac) in surface water is described. The method involves an off-line solid-phase extraction (SPE) procedure prior to instrumental analysis. The herbicides are isolated on an SPE C,, column and derivatized with pentafluorobenzyl bromide. After clean-up of the obtained solution on a disposable silica gel cartridge, the herbicide derivatives are determined by capillary gas chromatography with electron-capture detection and confirmed by capillary gas chromatography with mass selective detection using negative chemical ionization. The detection limits for the herbicides are in the range of 0.02-0.05 μg per litre surface water. The average recovery is 93%. A few hundreds of water samples were successfully analysed with this method