Focused ultrasound solid–liquid extraction of perfluorinated compounds from sewage sludge

A method for the determination of perfluorocarboxylic acids (PFCAs) and perfluorooctanesulfonic acid (PFOS) in sewage sludge based on focused ultrasound solid–liquid extraction (FUSLE) and reverse-phase ultra-performance liquid chromatography (UPLC) coupled to quadrupole-time of flight mass spectrometry (QTOFMS) has been developed. FUSLE is a fast, low-cost and efficient extraction technique based on the application of high power focused ultrasonic waves using a micro-tip immersed directly in the extraction mixture. e method development, the extraction solvent was studied and afterwards the factors affecting the extraction efficiency were optimised by means of a central composite design. Optimal FUSLE conditions were: 8 mL of acetonitrile as extraction solvent and an ultrasonic irradiation power of 65% for only 20 s. Two extraction cycles were enough for the quantitative extraction of PFCs from sewage sludge. Limits of detection below 0.2 ng g−1 (dry sewage sludge), relative standard deviation values less than 8% and recovery values between 69 and 104% were found for the target analytes. Finally, the method was applied to the analysis of sewage sludge samples from several wastewater treatment plants of La Rioja.