Pressurized liquid extraction followed by liquid chromatography–mass spectrometry for the determination of alkylphenolic compounds in river sediment

A new methodology based on pressurized liquid extraction (PLE) followed by LC–MS is presented for the simultaneous and unequivocal determination of alkylphenol ethoxylates (APEOs) and their degradation products, alkylphenols (APs) and alkylphenoxy carboxylates (APECs), in sediment samples. The protocol, applicable to a full range of APEO oligomers and degradation products, permits the sensitive and selective determination of APEOs (nEO=1–15), APECs (nEO=0–1) and APs at low ppb levels (LODs=1–5 μg/kg) in sediment samples. Optimization of the operational parameters of PLE clearly demonstrates that significant thermal losses of APs occur during extraction at elevated temperatures. The loss of octylphenol (OP) at 100 °C was 61.2% and of nonylphenol (NP) 40.0%, whereas other compounds were completely recovered. Thus, to avoid losses due to the volatility of alkylphenols, a low extraction temperature should be applied. The conditions that gave the best results for all target compounds were as follows: extraction solvent mixture, methanol–acetone (1:1, v/v); temperature, 50 °C; pressure, 1500 p.s.i.; two static cycles. Using PLE and a subsequent clean-up with solid-phase extraction (SPE), the simultaneous extraction of APEOs, APs and APECs from sediment samples was achieved yielding recoveries >70% and producing low MS background noise. The developed methodology was applied on a routine basis to the analysis of alkylphenolic compounds in sediment samples. APEOs and their persistent degradation products were detected in significant concentrations in sediments from Portuguese rivers, especially at sites situated in the proximity of industrial plants (mainly the textile industry). The total concentration of alkylphenolic compounds (APEOs+APs+APECs) ranged from 155 to 2400 μg/kg. Of all the alkylphenolic compounds, NP comprised 40 to 50% with concentrations up to 1172 μg/kg.