The Impact of Pesticides - Academy Publish

of application, with some still scarce but promising results (García-Lopez et al.,2008). Automation of the whole extraction process, miniaturization (with theconsequent reduction of sample, sorbent, and solvent consumption), and the use ofcost-effective and harmless solvents are also current trends, which will keep ongoing.Instrumental-based Sample Extraction TechniquesAn important step in the preparation of food samples prior to final analysis isisolation and/or enrichment. The procedures consist of the transfer of analytes fromthe primary matrix into the secondary one with a concurrent purging of interferingsubstances (isolation) and increasing the analytes concentrations to a level above thedetection limit for a given analytical technique (enrichment) (Beyer and Biziuk,2008).A number of instrumental-based extraction procedures have been developed toisolate pesticides residues from food of animal origin, including microwave-assistedextraction (MAE), supercritical fluid extraction (SFE), pressurised liquid extraction(PLE), solid-phase extraction (SPE) and solid-phase micro-extraction (SPME)systems. Advantages in using such technology include the potential for automation,more selective isolation of residues through tuning of instrument parameters and onlineclean-up of samples. Disadvantages include the limited number ofcommercially available instruments, additional extraction costs and instrumentaldowntime (Kinsella et al., 2009).Microwave-Assisted Extraction (MAE)MAE uses microwave energy to cause molecular movement and liquid rotation withpermanent dipole, leading to very fast heating of the solvent and the sample in orderto partition analytes of interest from sample matrix into the solvent (Beyer andBiziuk, 2008; Kinsella et al., 2009). Using microwave energy allows the solvent tobe heated rapidly: an average extraction takes 15 to 30 min (Camel, 2001). MAEoffers high sample throughput (several samples can be extracted simultaneously)with low solvent consumption (10 to 30 mL) (Kinsella et al., 2009). This techniqueis only applicable to thermally stable compounds due to the increase in temperatureduring extraction. As non-polar solvents do not absorb microwave energy, at leastsome polar solvent, such as water, must be used (Ridgway et al., 2007).MAE systems can operate in two modes, open (focused MAE) or closed(pressurized MAE) vessels. Open vessels operate at atmospheric pressure, whileclosed vessels are sealed and operate under higher pressures. Closed vessel MAEoperates somewhat like PLE, since the temperature of the solvent can be increasedby increasing the pressure (Kinsella et al., 2009).The main advantages of microwave pretreatment are the low temperaturerequirement, high extraction rate, automation and the possibility of simultaneouslyextracting different samples at the same time without interferences (Camel, 2000).However, solvent choice is limited, care must be taken not to overheat the sample,AcademyPublish.org - The Impact of Pesticides362