Determination of linear alkylbenzene sulfonates and their polar carboxylic degradation products in sewage treatment plants by automated solid-phase extraction followed by capillary electrophoresis-mass spectrometry

Abstract

Linear alkylbenzene sulfonates (LAS) were determined by solid-phase extraction (SPE), followed by capillary electrophoresis and mass spectrometry detection (CE-MS). The linear range of the proposed method varied from 33 to 316 and from 215 to 2057 μg L⁻¹, depending on the compound, with limits of detection ranging from 4.4 to 23 μg L⁻¹ when 200 ml of wastewater were preconcentrated. The analysis and confirmation of the polar carboxylic metabolites of LAS, the sulfophenyl carboxylic acids (SPC) was also achieved, and their presence was detected in both, influent and effluents of the sewage treatment plant (STP). [M − H]⁻ ions were used for CE-MS confirmation and quantification. CE-MS diagnostic ions were the same ones used in LC-electrospray (ESI)-MS and corresponded to m/z 297, 311, 325 and 339 for C10LAS, C11LAS, C12LAS and C13LAS, respectively. For SPC identification, diagnostic ions corresponded to m/z 215 to 369 (with 14 mass unit steps) for C2 to C13SPC, respectively. LAS were determined in wastewater samples of the influent and effluent of three sewage treatment plants (STP), two of them using biological treatment with secondary settlement and receiving mainly domestic wastewater whereas one of the plants was operated with physicochemical treatment and received mainly industrial wastewater. The concentration levels of total LAS varied from 1000 to 1900 μg L⁻¹ in the influents of STP, whereas in the effluents the concentrations varied from 125 to 360 μg L⁻¹.