Determination of low concentrations of acetochlor in water by automated solid-phase extraction and gas chromatography with mass-selective detection

A sensitive and reliable gas chromatographic/mass spectrometric (GC/MS) method for determining acetochlor in environmental water samples was developed, The method involves automated extraction of the herbicide from a filtered 1 L water sample through a C-18 solid-phase extraction column, elution from the column with hexane-isopropyl alcohol (3 + 1), and concentration of the extract with nitrogen gas, The herbicide is quantitated by capillary/column GC/MS with selected-ion monitoring of 3 characteristic ions, The single-operator method detection limit for reagent wafer samples is 0.0015 mu g/L. Mean recoveries ranged from about 92 to 115% for 3 water matrixes fortified at 0.05 and 0.5 mu g/L. Average single-operator precision, over the course of 1 week, was better than 5%.