Application of on-site solid-phase microextraction in aquatic dissipation studies of profoxydim in rice

The application of a manual operated solid-phase microextraction (SPME)–HPLC interface is discussed for the analysis of thermally labile analytes in aqueous matrices. The technique has been applied on-site at a flooded rice field to demonstrate its potential for real time extraction of the herbicide profoxydim. Thus, compounds which would otherwise easily degrade in the aqueous matrices within hours or days could be determined more accurately. The fibers were shipped back to the laboratory with express delivery where the target analyte was desorbed from the fiber and determined by HPLC–UV analysis. The SPME method was characterized by significant ruggedness where conventional techniques such as liquid–liquid extraction and solid-phase extraction require additional shipping and handling costs and time-consuming multiple sample preparation steps. In general, any delay in shipping the aqueous samples to the laboratory has the potential for sample degradation and a loss in accuracy when using non on-site extraction techniques. Fifty μm Carbowax–templated resin coatings were most suitable for coupling SPME to HPLC in order to achieve a high sensitivity for polar analytes. The SPME technique was characterized by a good sensitivity and a precision less than 10% RSD. The SPME–LC–UV method was linear over at least three orders of magnitude while achieving a limit of detection in the lower μg/l range. The on-site SPME method has shown significantly increased accuracy. Profoxydim was determined at concentrations of ca. 180 μg/l 3 h after an application on a flooded bare soil field.