Investigation of Chlorpyrifos and Its Transformation Products in Fruits and Spices by Combining Electrochemistry and Liquid Chromatography Coupled to Tandem Mass Spectrometry

The identification of transformation products (TPs) of pesticides in food is a crucial task difficult to tackle, due to the lack of standards. In this work, we present a novel methodology to synthesize five main TP standards of the insecticide chlorpyrifos (CPF) and to investigate their occurrence in selected fruits and spices. TPs were electrochemically (EC) synthesized using a boron-doped diamond electrode (BDD) and identified by EC coupled online to mass spectrometry, LC-MS/MS, and high-resolution mass spectrometry. CPF and its TPs were analyzed in the food samples by LC-MS/MS on multiple reaction monitoring (MRM) after dispersive solid-phase extraction. A good recovery of 83–103% for CPF and 65–85% for TPs was obtained. Matrix effects, which cause signal suppression, ranged between 81 to 95% for all targeted analytes. The limit of detection and quantification for CPF were 1.6–1.9 and 4.9–5.7 μg/kg, respectively. Among investigated samples, CPF was determined in fresh lemon (104 μg/kg), fenugreek seed (40 μg/kg), and black pepper (31 μg/kg). CPF content in all samples was lower than the EU maximum residue level (MRL). The most frequently detected TPs were diethylthiophosphate and diethylphosphate. Other TPs, CPF oxon and trichloropyridinol, were also detected. Hence, EC is a versatile tool to synthesize TP standards which enables the determination of contaminants and residues in foodstuffs even if no commercial standards are available.