LC–MS determination of linear alkylbenzene sulfonates and their carboxylic degradation products in influent and effluent water samples and sludges from sewage-treatment plants

Linear alkylbenzene sulfonates (LAS) have been determined in samples of the influent and the effluent, and in the sludge, from sewage-treatment plants (STP). LAS and sulfophenyl carboxylate compounds (SPC) were isolated by solid-phase extraction (SPE) with the polymeric phase Isolute ENV, then determined by liquid chromatography–electrospray mass spectrometry (LC–ESI–MS). The method enabled unequivocal identification of C₁₀–C₁₃LAS by monitoring the ion at m/z 183 and the base peak corresponding to the [M–H]–ion. Average recoveries varied from 77–93% and the linear range of the method varied from 0.2 to 10 µg L–¹, with a limit of detection ranging from 10 ng L–¹to 1.5 µg L–¹when 200 mL waste water were preconcentrated. For sewage sludge, recoveries varied from 58 to 90% and the linear range was between 0.2 and 100 µg L–¹, with a detection limit ranging from 0.4 to 120 µg kg–¹when 2.5 g sewage sludge was extracted. Unequivocal identification and determination of some metabolites of the LAS, the sulfophenyl carboxylate compounds (SPC), was achieved by monitoring [M–H]–ions.