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Reality

Since its introduction, the QuEChERS method has been readily accepted by many pesticide residue analysts. Some modifications to the originally published method had to be introduced to ensure efficient extraction of pH-dependent compounds (e.g. phenoxyalcanoic acids), to minimize degradation of susceptible compounds (e.g. pesticides labile under alkaline and acidic conditions) and to expand the spectrum of matrices covered. Buffering with citrate salts has been introduced in the first extraction/partitioning step to adjust the pH to a compromise value of 5 to 5.5, where most pesticides labile under acidic or alkaline conditions are sufficiently stabilized. To improve stability of alkaline-labile compounds after PSA clean-up the final sample extracts are slightly acidified by adding a small amount of formic acid. Acidic pesticides are directly analysed from the raw extract before PSA clean-up. For samples with high chlorophyll content, a mixture of PSA and GCB (Graphitized Carbon Black) is used for clean-up at amounts, where some residual chlorophyll still remains in the final extract. Dry commodities such as cereals, dried fruits or tea require the addition of water prior to extraction to weaken interactions of pesticides with the matrix and to ensure adequate partitioning. Even commodities with a high lipid load, such as avocados or plant oils are amenable to this procedure. However, due to a partition to the lipid phase, highly non-polar pesticides give relatively low but typically consistent recoveries (< 70%). Co-extracted lipids in the extracts can be removed to a high degree by a freezing-out step or a C18 clean-up.

USA
AOAC Official Method 2007.01
Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate.

Europe
prEN 15662 Version 2007-10-24
Foods of Plant Origin—Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-up by Dispersive SPE (QuEChERS-method).



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last update: 2011-05-15