Pesticide residues in chicken eggs - A sample preparation methodology for analysis by gas and liquid chromatography/tandem mass spectrometry

A sample preparation method was developed for the analysis of chicken eggs to determine 97 GC and 81 LC amenable residues, including organophosphates, organochlorines, pyrethroids, triazoles, carboxyl-containing compounds, and the indicator PCBs. Hereby, considerations were given to the recoveries of the analytes, the method's suitability for routine analysis, and the assessment of the clean-up effect, for which a simple thin layer chromatography was implemented to visualize the most important lipid classes. The procedure consisted of (I) the extraction by matrix solid phase dispersion, and the clean-up by means of (II) small-scale gel permeation chromatography (GPC) and (III) two different solid phase extractions (SPE) for GC and LC amenable analytes, as well as (IV) the quantification using GC-MS/MS and LC-MS/MS. Cyclohexane/ethyl acetate was chosen as extraction solvent due to its suitability for extracting strong non-polar but also more polar analytes. The classical GPC was scaled down to ensure a 50% lower solvent consumption. The comprehensive investigation of conventional and modern zirconium-oxide-coated SPE materials resulted in the selection of octadecyl-modified silica (C18) combined with primary secondary amine using acetonitrile as elution solvent for GC amenable analytes and pure C18 in combination with acidified methanol for LC amenable pesticides. Compared to the currently established EN 1528 method the sample preparation proposed offered a higher sample throughput and a lower solvent consumption. Furthermore, for the first time the clean-up effectiveness of the sample preparation steps was documented as shown by means of thin-layer chromatography. The validation of chicken eggs proved the fulfillment of the quality control criteria for 164 of the 178 analytes tested, mostly at the lowest validated level of 5μg/kg for pesticides and 0.5μg/kg for the single indicator PCBs. However, the analysis of strongly polar analytes was still problematic, which could be attributed to the extraction and the GPC step. Nevertheless, the successful investigation of EU proficiency test materials (EUPT AO 07-09) confirmed the comparability of the results with the currently established sample preparation procedures and demonstrated the potential of the applicability of the presented method to other matrices as exemplified for lean poultry meat and fatty liquid cream.