Switchable solvent-based micro-extraction of pesticides in food and environmental samples.

Switchable solvents are new generation solvents that are environmentally friendly and can be used for the effective pre-concentration of pesticide residues in food and environmental matrices. They have physico-chemical properties that can be switched abruptly and reversibly between two opposite forms. The common switchable solvents used commonly during pesticide pre-concentration involve polarity switch. Such solvent switch between hydrophobic and hydrophilic forms during pesticide pre-concentration. Secondary and tertiary amines are typical switchable hydrophilicity solvents. The amines are hydrophobic but they abruptly and reversibly switch to their hydrophilic forms on addition of CO2 to them. The application of amine-based switchable solvents during pre-concentration of pesticide residue in food and environmental samples are discussed in this paper. Medium-chain fatty acids can also be used as switchable solvents. Their switch between hydrophobic and hydrophilic forms is usually triggered by pH changes. Applications of fatty acid-based switchable solvents during pre-concentration of pesticide residues are reviewed in this paper. Switchable solvent-based micro-extraction can be combined with other pre-concentration techniques to enhance selectivity resulting in clean chromatograms. This paper has a section dedicated to the application of hyphenated switchable solvent-based micro-extraction techniques during pre-concentration of pesticides in food and environmental samples. In addition, the challenges associated with the use of switchable solvents during micro-extraction of pesticide residues are also discussed.