The Impact of Pesticides - Academy Publish

Pressurised Liquid Extraction (PLE)PLE has received numerous names, such as accelerated solvent extraction (ASE),pressurized fluid extraction (PFE), pressurised hot solvent extraction (PHSE),subcritical solvent extraction (SSE) and hot H 2 O extraction (HWE) (Carabias-Martinez et al., 2005). This technique utilizes solvents that are raised to the nearsupercritical region, where they show better extraction properties. At hightemperatures, the rate of extraction increases because the viscosity and the surfacetension decreases, while its solubility and diffusion rate into the sample increase.Pressure keeps the solvent below its boiling point and forces its penetration into thepores of the sample (Beyer and Biziuk, 2008). The combined use of high pressures(500-3000 psi) and temperatures (50-200 °C) provides a faster extraction process (5-10 min) that requires smaller amounts of solvent compared with traditionalextraction, thus decreasing the dilution of the sample (Richter et al., 1996). The timerequired for extraction is practically independent of the sample mass and theefficiency of extraction is mainly dependent on temperature (Beyer and Biziuk,2008).PLE can be performed in both static and dynamic (flowthrough) modes, or acombination of both. In static mode, the sample is enclosed in a stainless steel vesselfilled with an extraction solvent, and following extraction the remaining solvent ispurged with N 2 into a collection vial. Flow-through systems continuously pumpsolvent through the sample, but this has the disadvantage of using larger volumes ofsolvent and of diluting the extract. A desiccant, such as sodium sulphate,diatomaceous earth or cellulose can be added directly to the extraction cell orsorbent materials can be used to provide in situ clean-up. The extraction conditionsmust be optimised and this can be done using statistical “experimental design”procedures to minimize the number of experiments (Pallaroni and von Holst, 2003;von Holst et al., 2005).Comparing PLE to LLE or Soxhlet extraction, the advantage of reducing solventconsumption and extraction time contrast with the disadvantage of using veryexpensive and specialized equipment. However, the major problem with fattymatrices is the presence of large amounts of co-extracted lipids, which means thatpost-clean-up of the extract is required to carry out lipid elimination (Beyer andBiziuk, 2008).Frenich et al. (2006a) optimized and validated a method for the simultaneousdetermination of residues of organochlorine (OCPs) and organophosphorus (OPPs)pesticides in meat samples from chicken, pork and lamb. The method is based in theextraction of homogenized meat mixed with sodium sulphate and ethyl acetate inpolytron, although accelerated solvent extraction (ASE) and the determination wasperformed by gas chromatography (GC) coupled to a triple quadrupole (QqQ) massspectrometry (MS) detection system. Recoveries and precision values were 70.0–90.0% and 15%, respectively, for the bulk majority of pesticides. Values of LOD