Acidic and non-acidic products from the photo-oxidation of the crude oil component dibenzothiophene dissolved in seawater Original Research Article

A solution of dibenzothiophene in membrane-filtered natural seawater was exposed to sunlight in a quartz vessel. The same solution in an amber glass vessel served as the dark control. Acidic photoproducts were isolated, identified and quantified from seawater, employing solid phase extraction and HPLC in ion-pair mode. This extraction procedure allows the determination of aromatic sulphonic as well as carboxylic acids in the low ppb-range in seawater and makes a separation between these two substance classes possible. 2-Sulphobenzoic acid and benzothiophene-2,3-dicarboxylic acid were identified as the main products. The two isomeric benzothiophenemonocarboxylic acids as well as an isomer of thiophenetricarboxylic acid were also detected by GC–MS analysis in significant concentrations after methylation. Non-acidic products were also isolated and analysed by gas chromatography using the atomic emission detector and GC–MS.