Simultaneous determination of phenyl- and sulfonylurea herbicides in water by solid-phase extraction and liquid chromatography with UV diode array or mass spectrometric detection

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-chloro4-methyl-phenyl 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 C18 and two polymeric sorbents, Oasis HLB and LiChrolut EN. The best results were obtained with Oasis HLB, a co-polymer of poly(divinylbenzene-co-Nvinylpyrrolidone). 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.