Simultaneous extraction of several persistent organic pollutants in sediment using focused ultrasonic solid-liquid extraction.

Focused ultrasonic solid-liquid extraction (FUSLE) has been optimised for simultaneous analysis of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalate esters (PEs), and nonylphenols (NPs) in sediment samples. Optimisation was performed using naturally polluted freeze-dried sediment samples. The variables studied during the optimisation process were: percentage of maximum power (10-60%), extraction time (10-300 s), number of cycles (1-9), composition of the extraction solvent (acetone-n-hexane, 10:90-90:10), and sample mass (0.1-1 g). The volume of the extractant was constant (10 mL) and the extraction was performed at 0 degrees C in an ice-bath during the optimisation process. All these variables were studied using an experimental design approach by means of The Unscrambler software. The extraction time and the operational variables (number of cycles and power) had no statistically significant effect in the extraction and they were held at 2 min, 20% power, and seven cycles, respectively. The mass and the addition of non-polar solvent (n-hexane) had a negative effect in the extraction yield and, thus, the mass was held at 0.5 g and pure acetone was used as extraction solvent. After those variables were optimised, the effect of the extraction temperature (0 degrees C or room temperature) was also studied. The validation of the extraction method was performed using NIST-1944 reference material in the case of PAHs and PCBs. Because no certified reference sediment is available for PEs and NPs, the results obtained for FUSLE were compared with those obtained for microwave-assisted extraction (MAE) under conditions optimised elsewhere. In all the cases the analysis were performed by gas chromatography-mass spectrometry (GC-MS). Good accuracy were achieved in all cases. The limits of detection (LODs) obtained were between 0.10 and 1.70 ng g(-1) for PAHs (except for naphthalene 5.33 ng g(-1)), 0.02 and 0.16 ng g(-1) for PCBs, 46 and 188 ng g(-1) for PEs, and 0.6 and 12.4 microg g(-1) for NPs. The precision was around 5-10% for most of the PAHs and PCBs and around 2-10% for most of the PEs and NPs.