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[Insight] Quality control: Determination of pesticides present in cultivated products using the QuEChERS procedure

In most cases, the pesticides used during cultivation disappear due to the effect of external agents, such as wind and rain. However, sometimes pesticides can be absorbed by the surface of the plant, remaining retained in the leaves and fruit, to later be ingested by the consumer. Because long-term exposure to pesticides has been linked to various acute and chronic human health problems, it is especially important to ensure that pesticides do not exceed the optimal limits in the final product of the production chain; process known as quality control.

The analysis of pesticides for the quality control of the cultivated products consists of two steps: extraction of pesticides and detection using analysis instruments like GC-MS (gas chromatography – mass spectrometry) or LC-MS (liquid chromatography – mass spectrometry).

For the extraction, the most used method is the “QuEChERS” (Quick, Easy, Cheap, Effective, Rugged, and Safe) method. This process requires a centrifuge that allows working with 15 and 50 ml samples, reaching RCF of more than 3000 xg, such as our Bioprocen 22 R.

For this process, approximately 8-15g of homogenized sample is resuspended in 10-15mL of water in a 50mL tube. Then 10-15mL of ACN (acetonitrile) are added, which is the organic solvent used for the extraction. After shaking the tube, the QuEChERS salts, which are composed of MgSO4, NaCl, and citrate buffer, are added. The tube is shaken again and then centrifuged for 5 minutes at > 3000 XG.

As a result of this centrifugation, the components of the sample are separated into phases based on their density and their affinity to the different solutions of the mixture. Pesticides are concentrated in the upper phase, made up of ACN. Thus, the next step consists of washing the sample, taking the ACN phase and transferring it to a 15mL tube containing dSPE (dispersive solid phase extraction).

The tube is centrifuged for 5 minutes at> 3000 G, after which two phases form in the tube: a dSPE pellet containing the proteins, lipids, and chlorophyll; and an ACN supernatant containing the pesticides. Finally, the supernatant is transferred to an appropriate vial for analysis by GC-MS or LC-MS.