DETERMINATION OF TRACE LEVELS OF HERBICIDES IN ESTUARINE WATERS BY GAS AND LIQUID-CHROMATOGRAPHIC TECHNIQUES

A screening procedure based on a two-step liquid-liquid extraction with dichloromethane was used for the isolation of two fractions, one neutral containing molinate, trifluralin, atrazine, simazine, alachlor, metolachlor, isoproturon, chlortoluron and linuron and the other acidic containing bentazone, 2,4-D and 4-chloro-o-tolyloxyacetic acid. Recoveries varying from 60 to 100% with a relative standard deviation of 10% were achieved for most of the herbicides added to 1-4 ml water samples at levels varying from 2.5 to 25-mu-g/l. Exceptions were the acidic herbicides 2,4-D and MCPA, for which low recoveries up to 40% were obtained. Determinations were usually carried out by gas chromatography with nitrogen-phosphorus detection, allowing the determination of herbicides at the 5-10 ng/l level with further confirmation by gas chromatography-mass spectrometry with electron impact ionization. Liquid chromatography with diode-array detection permitted the characterization of herbicides at levels of 0.1-0.5-mu-g/l. Although liquid chromatography-diode-array detection was much less sensitive than gas chromatography-nitrogen-phosphorus detection determinations, its usefulness was demonstrated for direct characterization of acidic herbicides without derivatization. Illustrative examples of the determination of several herbicides in estuarine water samples from the Ebro Delta (Tarragona, Spain) are shown. Atrazine, simazine, molinate, alachlor, metolachlor and bentazone were the most common herbicides found with concentrations levels varying from 5 ng/l to 5-mu-g/l.