Qualitative screening and quantitative determination of pesticides and contaminants in animal feed using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

A method has been developed for the target analysis of over 100 pesticides and contaminants in a complex feed matrix. The method is based on extraction with ethyl acetate, cleanup by gel permeation chromatography (GPC) and dispersive solid-phase extraction (SPE) with primary secondary amine phase (PSA), and analysis by comprehensive two-dimensional gas chromatography with full scan time-of-flight mass spectrometric detection (GC × GC–TOF-MS). Parameters studied during method development included a dispersive SPE cleanup step after GPC, large volume injection into the GC system and the GC × GC separation. Qualitative and quantitative performance of the GC × GC system was evaluated by analyzing spiked extracts in the range equivalent to 1–100 μg/kg in feed. At levels of 50 μg/kg and higher, all compounds targeted for could be identified fully automatically by the software based on their mass spectra. At lower levels the hit rate decreased with the concentration. System linearity was excellent in solvent and only slightly affected by matrix (correlation coefficients r ≥ 0.995 for 90% of the compounds). Limits of quantification were in the 1–20 μg/kg range for most compounds. The overall method was validated for 106 compounds at the 10 and 100 μg/kg level. Recoveries between 70% and 110% and RSDs below 20% were obtained for the majority of the compounds.