Assessing the performance of various sorbents in micro-solid phase extraction cartridges for pesticide residue analysis in feed

Newly designed micro-solid phase extraction cartridges are now available, reflecting the increasing shift towards laboratory automation, especially in the clean-up step for the analysis of pesticide residues in food and feed. In the present study, the introduction of different sorbents on the newly designed PAL µSPE CTC cartridges was investigated for the removal of matrix interferents and the recovery of pesticides. Eight cartridges containing different sorbent combinations and different amounts were used including EMR-lipid (not activated), Z-sep, chitin, C18, PSA, and GCB. The evaluation of co-extractive removal for each cartridge showed that the optimal choice for removing fatty acids was the cartridges containing PSA and Z-sep as clean-up sorbents. However, the presence of C18 and EMR-lipid was still required for the removal of sterols and tocopherols. Two grams of sample, fish feed (FF) and rapeseed cake (RSC) were extracted using QuEChERS citrate buffer, followed by a freeze-out step. The recoveries and repeatability of QuEChERS using µ-SPE clean-up were evaluated for 216 pesticide residues (112 compounds analyzed by GC-MS/MS and 143 compounds by LC-MS/MS, from which 39 compounds were analyzed using both techniques). The best results, with recovery between 70 and 120% and RSD <20%, were achieved when FF samples were cleaned-up with 15 mg EMR-lipid and 20 mg MgSO₄. This was achieved for 94% of GC-amenable compounds and 86% of LC-amenable compounds. In the case of RSC, the best results were seen when samples were cleaned-up with the cartridge containing only 20 mg Z-sep and 20 mg MgSO₄. This was achieved for 88% of GC-amenable compounds and 90% of LC-amenable compounds. Although these cartridges yielded optimal results in terms of recovery, their use could require more instrument maintenance, especially for GC-MS/MS, due to the lower removal of co-extractives.