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A method for the simultaneous determination of 10 sulfonyl- and phenylurea herbicides (chlorsulfuron, triasulfuron, fenuron, monuron, fluometuron, chlorotoluron, isoproturon, diuron, metobromuron, linuron) and one of their most common degradation products (3-chloro-4-methylphenyl urea) has been developed. Liquid chromatography with diode array UV detection (LC-DAD UV) and positive ion electrospray mass spectrometry (LC-ESI-MS) were used for the separation, identification and quantification of these analytes. In the LC-DAD UV method, chromatographic separation was achieved in about 27 min; however, analysis time can be reduced to less than 13 min when LC-MS is applied, since no complete separation of the chromatographic peaks was required.

A preconcentration step based on solid-phase extraction was applied for the simultaneous extraction of sulfonylureas (acidic in nature) and phenylureas (neutral compounds) from water samples. Different types of sorbents were evaluated: silica-based C-18 and two polymeric sorbents, Oasis HLB and LiChrolut EN. The best results were obtained with Oasis HLB, a co-polymer of poly(divinylbenzene-co-N-vinylpyrrolidone). Other parameters, such as the elution solvent and sample volume, were optimised in order to maximise extraction efficiency; the recoveries obtained varied between 70 and 95% for the acidic and neutral herbicides extracted jointly without acidification of the sample.

Both procedures, SPE LC-DAD UV and SPE-LC-MS, were applied to spiked river waters and were compared in terms of selectivity and sensitivity. The detection limits obtained in river water samples were below 50 ng L-1 for both procedures. (C) 2004 Elsevier B.V. All rights reserved.