RESUMEN
A method using off-line supercritical fluid extraction (SFE) and micro liquid chromatography (microLC) with UV detection at 260 nm, was developed for selective determination of fenpyroximate in apple samples. The packed capillary liquid chromatography method utilises 20 microl injection volumes with on-column focusing. A 350x0.32 mm capillary column packed with Kromasil 100-C18 of 5 microm particle size was used with a mobile phase of acetonitrile-10 mM ammonium acetate (85:15, v/v) at a flow of 5 microl/min. A two-step SFE procedure was used to extract fenpyroximate selectively in 2 g apple samples, with Hydromatrix (HMX) added as a water absorbent at a 1:1 (w:w) ratio. Fenpyroximate was extracted at 200 bar and 90 degrees C for 15 min using carbon dioxide at a flow of 2 ml/min, and solvent trapping collection in 10 ml acetonitrile. The volume of the acetonitrile extract was reduced by evaporation and water was added to a final composition of acetonitrile-water (40:60, v/v). The resulting 2.0 ml solution was filtered using a 0.45 microm poly(vinylidene difluoride) syringe filter before microLC analysis. Validation of the method was accomplished with apple samples spiked with fenpyroximate, covering the range of 0.1 to 1.0 microg/kg. The within-day and between-day repeatabilities were in the range 4-18% relative standard deviation. Accuracy, measured as recovery, was found to be approximately 60%. Apple samples from a field treated with fenpyroximate were analysed. None of the samples contained fenpyroximate above the quantification level.