Focused ultrasound solid-liquid extraction and selective pressurised liquid extraction to determine bisphenol A and alkylphenols in sewage sludge by gas chromatography-mass spectrometry

A new method for determining endocrine disrupter compounds (EDCs) in sewage sludge is described in this paper. EDCs studied were bisphenol A (BPA) and alkylphenols (APs). In order to obtain a fast and simple method, selective pressurised liquid extraction (SPLE) and focused ultrasound solid-liquid extraction (FUSLE) were tested. Best results for SPLE were obtained using Florisil as clean-up sorbent and dichloromethane as extraction solvent, while temperature was the only significant variable. Analyte extraction by SPLE was completed in only one extraction cycle of 1 min at 130 °C. FUSLE was carried out in one step of 20 s at 75% power (0.5 cycles) and with 8 mL of ethyl acetate. Although the optimised FUSLE process was faster, simpler and cheaper, SPLE provided higher recovery values (ranging from 81 to 105%) and therefore SPLE-based method was selected and validated. The SPLE and GC-MS method showed an LOD of 10.7 ng/g for BPA and LODs between 1.2 and 41.6 ng/g for APs. Relative standard deviation values lower than 6% were obtained for all analytes. As a result, an efficient, fast and simple method based on SPLE and GC-MS for the determination of BPA and APs in sewage sludge is proposed.