AUTOMATED-DETERMINATION OF PHENYLCARBAMATE HERBICIDES IN ENVIRONMENTAL WATERS BY ONLINE TRACE ENRICHMENT AND REVERSED-PHASE LIQUID-CHROMATOGRAPHY DIODE-ARRAY DETECTION

A fully automated liquid chromatographic method using on-line trace-en richment, gradient elution and diode array detection is described for the trace-level determination of several phenylcarbamate herbicides, s uch as carbetamide, propham, desmedipham, phenmedipham, chlorbufam and chlorpropham, in environmental water samples. In this work, two diffe rent enrichment pre-columns have been assayed, a 5.8x4.6 mm I.D., 10 m u m ODS Prelute cartridge and a 10x2 mm I.D. cartridge filled with 10 mu m PRP-1 polymer, both coupled to a 150x4.6 mm I.D. analytical colum n filled with 5 mu m ODS. Using the C-18 pre-column, up to 50 ml of wa ter sample could be percolated without peak broadening of any compound . However, a lack of reproducibility was observed in the case of carbe tamide, the most polar analyte, after performing recovery experiments by percolating drinking and surface water samples spiked at several le vels (0.5 and 4 mu g l(-1))(.) On the other hand, the PRP-1 pre-column allowed the enrichment up to 100 ml of water sample with satisfactory results for every compound, including carbetamide. The procedure was validated by recovery experiments in environmental water samples spike d at 0.2 and 1 mu g l(-1) yielding average recoveries between 84-108% with relative standard deviations in the range 2-12%. Detection limits as low as 0.04 mu g l(-1) were achieved. It was observed that desmedi pham and phenmedipham degraded rapidly in the environmental water samp les as showed the degradation studies performed along 24 h in drinking and surface waters spiked at 4 mu g l(-1). Although the standard mixt ure, prepared in HPLC water, was stable for around one week, in the en vironmental water matrices more than 95% of each herbicide degraded af ter 6 h, and new chromatographic peaks corresponding to the degradatio n products were detected. (C) 1998 Elsevier Science B.V. All rights re served.