The most important part in a complete pesticide analysis for any sample type is the sample preparation. The goal is to get a homogenized sample from which the targeted pesticide is easy to extract.
The first step in sample preparation is cutting and homogenization. Care must be taken to avoid analyte degradation because of heat during the milling process. It's recommended to have cooled milling for that purpose. To have a better extraction, the particle size of the sample should be reduced to less than 1mm.
The second step is extraction of the pesticide using a suitable organic solvent. The purity of the selected solvent should be chosen according to the analytical technique which will be used in the quantification phase. Other parameters such as sample processing, temperature, pH, and time can also affect the stability and extraction of analyte.
One of the most commonly used techniques for extraction and clean-up of extract is the Solid Phase Extraction (SPE) method. By this method, an extract containing the targeted analyte is passed through a column filled with a suitable sorbent which is previously prepared. Another way is having a suitable solvent pass through a column filled with sorbent and added prepared sample. By using selective sorbents, the other end of the column will elute an extract containing the targeted pesticides.
The third and final step is the concentration of extract. This is done by evaporation of the solvent at some level to obtain a more concentrated analyte. To avoid losing any analyte, the technique for evaporation must be chosen according to the analyte’s physical and chemical properties.
Đurović, R., & Đorđević, T. (2011). Modern Extraction Techniques for Pesticide Residues Determination in Plant and Soil Samples. In Pesticides in the Modern World - Trends in Pesticides Analysis. InTech.