1. Aim and Scope
This manuscript describes a method for the analysis of pesticide residues in produce with a low fat content, such as fruits, vegetables, cereals as well as processed products including dried fruit.
2. Short Description
The homogeneous and representative subsample is extracted in frozen condition with the help of acetonitrile. After addition of magnesium sulfate, sodium chloride and buffering citrate salts (pH 5-5.5), the mixture is shaken intensively and centrifuged for phase separation. An aliquot of the organic phase is cleaned-up by dispersive SPE employing bulk sorbents (e.g. PSA, GCB) as well as MgSO4 for the removal of residual water. PSA treated extracts are acidified by adding a small amount of formic acid, to improve the storage stability of certain base-sensitive pesticides. The final extract can be directly employed for GC- and LC-based determinative analysis. Quantification is performed using an internal standard, which is added to the extract after the initial addition of acetonitrile. Samples with a low water content (<80%) require the addition of water before the initial extraction to get a total of ca. 10 mL water. When dealing with samples containing <25% water (e.g. cereals, dried fruit, honey, spices) the size of the analytical sample may have to be reduced (e.g. 1-5 g) depending on the load of matrix-co-extractives expected in the final extracts. A brief overview of the method is shown in the flowchart at the end of this document.