Immunoassays for pyraclostrobin analysis in processed food products using novel monoclonal antibodies and QuEChERS-based extracts

Strobilurins are a family of synthetic natural-derived pesticides widely used for fungi control in many crops. As part of a larger research project, a collection of monoclonal antibodies to one of the most relevant strobilurins, i.e. pyraclostrobin, has been generated using functionalized haptens with the spacer arm located at different sites. The toxophore aliphatic moiety, as observed with other strobilurins, and the planar aromatic two-ring system characteristic of this molecule were revealed as the best tethering sites for high-affinity monoclonal antibody production. A central derivatization position did not generate a good immune response, but such derivatives were useful as heterologous competitors in order to improve assay sensitivity. Direct and indirect assays were characterized in terms of solvent influence, pH, and ionic strength. Immunoassays with limits of detection below 0.1 μg/L were developed. A QuEChERS-based procedure was applied to the extraction of blueberry, strawberry, raspberry, peach, apricot, and plum jams. Clean acetonitrile extracts were properly diluted in water and analyzed by both optimized immunoassays with good accuracy and precision at levels covering the European maximum residue limits for those fruits.