Rapid method based on immunoassay for determination of paraquat residues in wheat, barley and potato

The detection of bipyridine herbicides residues in food samples is hampered due to their particular physico-chemical features, which requires the application of specific extraction and analytical procedures, which disqualifies them from being incorporated into the multi-residue methods (MRMs). There is a need for alternative robust and efficient analytical screening methods, and in this respect, we present here a fast and reliable immunochemical analytical procedure for the detection of paraquat (PQ) residues in food samples, particularly potato, barley and wheat. The procedure involves the extraction with 1 N HCl:MeOH at 80 °C, followed by centrifugation and filtration, and the extracts can be directly measured by a microplate-based ELISA without any other sample treatment or clean-up, except from buffering the solution and adjusting the pH. Selective polyclonal antibodies, were raised against N-(4-carboxypent-1-yl)-N′-methyl bipyridilium acid (hapten PQ1), and used to establish a high sensitive immunochemical analytical assay, able to measure simultaneously many samples. Under these conditions the accuracy is very good, with almost quantitative recoveries. The non-specific interferences caused by the matrix are negligible for the case of potato and wheat, while for barley it is necessary to further dilute the extract or using a negative certified extract to build the standard calibration curve. The method of extraction consisted in acidic extraction and after a dilution is able to be measured. The analysis method results simply, achieving good detectabilities. The limits of detection (LODs) achieved were between 0.037 ± 0.01 μg kg−1 in wheat, 0.71 ± 0.3 μg kg−1 in barley and 0.56 ± 0.10 μg kg−1 in potatoes, values that are far below the Maximum Residue Level (20 μg kg−1) established by the EU policies for paraquat residues in these foodstuff products. The results demonstrate the high potential of these methods as screening tools for food safety and inspection controls.