Efficiencies of Different Methods for Determination of Organophosphate Pesticide Residues in Fermented Wheat Substrate

In the present work, the efficiencies of three different sample preparation methods for GC/MS determination of pirimiphos-methyl and chlorpyrifos-methyl residues in wheat (Triticumspelta) samples fermented by Lactobacillus plantarum were compared. All three methods werebased on methanol:acetone=1:1 extraction, while further purification of the obtained sampleswas altered. First purification was through a column containing a mixture of aluminiumoxide and activated charcoal slurry-packed and eluted with dichlormethane, the second waspurification on a florisil column slurry-packed and eluted with ethyl acetate:acetone=4:1, whilethe third was based on a combination of the former two methods, i.e. clean-up through columnsfilled with a mixture of aluminum oxide and activated charcoal slurry-packed and elutedwith ethyl acetate:acetone=4:1. The second method was found the most effective for obtainingsatisfactory recoveries at four fortification levels. For pirimiphos-methyl, recoveries werein the range of 91.3-96.0% and had good reproducibility, i.e. RSD ranging from 2.2-4.1%, whilethe corresponding range for chlorpyrifos-methyl was 81.6-88.2%, and the RSD range 2.5-5.4%.The chosen method was further optimized in order to establish the optimum volume of elutionsolvent used during the clean-up procedures. The highest recoveries of 93.7±3.5% for pirimiphos-methyl and 85.3±2.5% for chlorpyrifos-methyl were obtained after elution with 25 mlvolume of solvent. Considering all, simple, efficient and reliable GC/MS detection of pirimiphosmethyland chlorpyrifos-methyl residues in wheat grain substrate altered by fermentation withL. plantarum was achieved by the two-steps extraction with 25 ml of methanol:acetone=1:1solvent mix for 30 min, followed by a clean-up procedure through a glass column with florisilcoupled with elution by 25 ml of ethyl acetate:acetone=4:1.