Expanding the Commodity Spectrum Covered by QuEChERS

The original QuEChERS procedure only focused on high water and low fat containing commodities such as fruits, vegetables, and juices (group A in Table I). 

Especially challenging are commodihes with intermediate or high fat content. 

According to our experiments, the solubility of vegetable oil in raw QuEChERS extracts is -4 mg/mL (-40 mg in 10 mb). In the presence of water, the solubility is slightly lower ( 2 mg/mL). Due to this low solubility, excess lipids form an additional layer into which highly lipophilic pesticides tend to parhhon. The parhtioning rate depends on the peshcide s Hpophilicity, the lipid/acetonitrile raho as well as on the presence or absence of water, which obviously modifies the polarity of the acetonitrile phase, making it less receptive for lipophilic compounds. 

The sample weights suggested in Table I constitute a compromise between the recoveries of the lipophilic pesticides, the limits of detection, and the subsampling variability. For the commodity groups A-E, the sample weights given in the table ensure HCB-recoveries 70%. For the commodity groups F-H, 

As the QuEChERS-extracts are solved in acetonitrile, they are directly amenable to GC- and LC-applications. However, since acetonitrile is rather difficult to handle by GC using split/splitless inlets, the use of a PTV with solvent vent possibility is highly recommended. Should a PTV not be available and the desired pesticide detection limits cannot be achieved using the split/splitless technique, extract concentration followed by a solvent exchange, if necessary, may be considered. If GC-MSD is employed, a simple evaporative concentration of the extracts by a factor of four should be sufficient. To achieve this, e.g., a 4-mL extract (acidified to pH 5) is transferred into a test tube and reduced to ca. 1 mL at 40 °C using 

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