Detection of seven pesticides in cucumbers using hollow fibre-based liquid-phase microextraction and ultra-high pressure liquid chromatography coupled to tandem mass spectrometry.

A liquid-phase microextraction (LPME) methodology based on the use of porous polyvinylidene fluoride (PVDF) hollow fibres was developed for extracting seven pesticides from cucumbers. The seven pesticides include propoxur, carbofuran, atrazine, cyanatryn, metolachlor, prometryn and tebuconazole. The PVDF hollow fibre provides higher extraction efficiency due to its higher porosity and better solvent compatibility. A new desorption methodology was developed since some pesticides were absorbed by the wall pore of the PVDF. Ultra-high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS) was used for pesticide analysis. In order to obtain high recoveries and enrichment factors of the analytes, several parameters such as method of sealing, acceptor phase (organic solvents), stirring speed, extraction time, salting out effect, desorption mode and time were optimized. A fast, simple method for closing fibre ends was practiced by using mechanical crimping. Pesticides were extracted from the sample to the organic solvent and then desorbed in a mixture of methanol:water (1:1 v/v) prior to chromatographic analysis. Limits of detection (LOD) for the multi-reaction-monitoring (MRM) mode of the method varies from 0.01 to 0.31 μg/kg with optimized sample preparation. Calibration curves are linear with R² ≥ 0.991. Enrichment factor of the hollow fibre LPME ranges from 100 to 147. Matrix effect has been considered and is in the range of 76-122%. The relative recoveries from cucumber samples are between 63% and 119% with the relative standard deviation (RSD, n=6) lower than 20%.