Simultaneous determination of pesticides, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in seawater and interstitial marine water samples, using stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry

A method for the simultaneous determination of semi-volatile organic contaminants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, organochlorine and organophosphorus pesticides) in marine samples has been developed, for the first time, using the stir bar sorptive extraction technique (SBSE) and thermal desorption coupled to capillary gas chromatography–mass spectrometry (SBSE-TD-GC–MS). Polydimethyl siloxane (PDMS) was used for the extraction of the selected analytes and two procedures have been optimised and validated, one for seawater samples (100 mL) and another for interstitial water samples (10 mL), using PDMS stir bars of 20 mm and 10 mm size, respectively. The extraction and analytical conditions, such as extraction time, matrix effects, sample volume and desorption time, were optimised. The proposed methods are sensitive, simple and show good linearity and detection limits lower than 1 ng L−1 with seawater and lower than 10 ng L−1 with interstitial marine water for the majority of compounds tested. Repeatability and reproducibility, expressed as relative standard deviation, have values lower than 20% for the majority of analytes considered. The recoveries for both sample volume procedures are higher than 60 and 70% for 10 and 100 mL, respectively, except for the more apolar (some PAHs and PCBs) and the more polar (some triazines) analytes which present lower values. The present SBSE/GC/MS method was applied for the analysis of trace organic contaminants in seawater and interstitial water samples from Cadiz Bay (SW of Spain). Terbutylazine, DDX and some PAHs were found at several seawater sampling points at ng L−1 levels, and some PAHs in interstitial water too.