Comparison of different solid-phase-extraction cartridges for a fatty acid cleanup of the ethyl acetate/cyclohexane based multi-pesticide residue method EN 12393.

SPE cartridges of different anion exchange materials and florisil were compared regarding their efficiency to remove free fatty acids from ethylacetate/cyclohexane (1:1) extracts, their elution profiles and recovery rates for 38 representative pesticides, their contribution to an elevated background during gas chromatography-mass spectrometry (GC-MS), and on possible matrix effects caused by the cartridge material itself. From the seven tested cartridges, only Varian PSA (PSA) and Silicycle SiliaPrep Diamine (SPD) were very well able to retain fatty acids from ethylacetate/cyclohexane solutions and provided satisfying recoveries and elution profiles for the tested pesticides. Thus, with both cartridges a fast and simple cleanup was developed and tested with 86 pesticides as well as with EN 12393 GPC extracts of oat flour. The SPE cleanup clearly improved the identification of pesticides and reduced false negative findings due to retention time shifts and superimpositions of quantifier and/or qualifier ions. As compared with dispersive SPE it was shown, that depending on the amount of sorbent the cleanup efficiency was comparable, but recoveries were generally better for cartridge SPE procedures.