A combination of ultrasonic assisted extraction with LC–MS/MS for the determination of organophosphorus pesticides in sludge

A method has been developed for the analysis of a wide polarity range of the currently used organophosphorus pesticides (OPs) and their metabolites in sewage sludge samples. Extraction was carried out using ultrasonic assisted extraction (UAE) with different solvents. The levels of OPs in sludge were determined by liquid chromatography-tandem mass spectrometry (LC–MS/MS) using electrospray ionization (ESI) in positive or negative ion mode. Extraction with acetonitrile containing 1% acetic acid gave the best results with recoveries between 83.2% and 106.4% and RSD ≤ 8.7%. Evaluation of matrix effect showed high ion suppression for OPs of intermediate polarity, which decreased to approximately 50% by matrix dilution to an equivalent of 0.5 g of sludge per millilitre; however, for polar OPs, the matrix effect was negligible at the same concentration. Therefore, matrix-matched standards were used for OPs quantification. The limits of quantification were in the range of 1–14 ng g−1. This method was successfully applied to real sludge samples collected from Madrid Province and chlorpyrifos along with its metabolite TCPY were the OPs found in sludge at the highest levels, 113–344 ng g−1 and 33–307 ng g−1, respectively.