Current Trends in Liquid-Liquid Microextraction for Analysis of Pesticide Residues in Food and Water

Since the middle of last century, the use of organic synthetic pesticides became a widespread practice, in order to better prevent, control and destroy pests. Despite their usefulness in the increment of food production, the extensive use of pesticides during production, processing, storage, transport or marketing of agricultural commodities can led to environmental contamination and to the presence of residues in food. Real and perceived concerns about pesticide toxicity have promoted their strict regulation in order to protect consumers, environment and also the users of pesticides. Thus, reliable and accurate analytical methods are essential to protect human health and to support the compliance and enforcement of laws and regulations pertaining to food safety. The first analytical methods for pesticide analysis were developed in the years 1960s, employing an initial extraction with acetone, followed by a partitioning step upon addition of a non-polar solvent and salt; these methods involved complex and solvent-intensive cleanup steps. Moreover, the instruments available for analysis of the target compounds had a relative low selectivity and sensitivity. The development of technology and robotic in the 1990s allied to the aim to reduce manual interference and to allow sample preparation during non-working time, has boosted the development of automated sample preparation techniques such as supercritical fluid extraction and pressure liquid extraction. Though initially very promising, these techniques have not succeeded in the field of pesticides analysis for various reasons, namely high price and low reliability of the instruments, and inability to extract different pesticide classes in foods with the same efficiency, often requiring separate optimization for different analytes. Later, a successful simplification of “traditional” solvent sample preparation, QuEChERS (quick, easy, cheap, effective, rugged, and safe) was presented by Lehotay and collaborators (Anastassiades et al., 2003). This procedure, involving a simple extraction/partition using acetonitrile and salts followed by a simple dispersive cleanup, has been adopted for the analysis of many pesticide residues in food (Cunha et al, 2010). Two similar QuEChERS methods achieved the status of Official Method of the AOAC International (Lehotay, 2007) and European Committee for Standardization (CEN) standard method EN 15662 (Standard Method EN 15662). Unfortunately, the analysis of QuEChERS extracts in acetonitrile by GC-MS is not totally straightforward. Several facts can occur: degradation of the GC column by the polar solvent,