Abstract 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 iso- lated by solid-phase extraction (SPE) with the polymeric phase Isolute ENV, then determined by liquid chromatog- raphy–electrospray mass spectrometry (LC–ESI–MS). The method enabled unequivocal identification of C 10 –C 13 LAS by monitoring the ion at m/z 183 and the base peak corre- sponding 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 –1 to 1.5 μg L –1 when 200 mL waste water were preconcentrated. For sewage sludge, recoveries var- ied 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 –1 when 2.5 g sewage sludge was extracted. Un- equivocal identification and determination of some metabo- lites of the LAS, the sulfophenyl carboxylate compounds (SPC), was achieved by monitoring [M–H] – ions. Introduction Linear alkylbenzene sulfonates (LAS) are the most com- monly used anionic surfactants. Of the 6 million tons of surfactants produced throughout the world in 1994, almost 2.4 million tons were LAS [1]. Commercially available LAS are mixtures of secondary isomers, with alkyl chain lengths of 10–13 carbon atoms. After use, LAS are dis- charged into domestic or industrial waste waters. Routine determination of LAS in surface waters involves the use of solid-phase extraction (SPE), then derivatization and determination by gas chromatography–mass spectrometry (GC–MS) [2, 3]. Such methods are tedious, because of the derivatization step. A method involving continuous-flow fast-atom bombardment MS has also been developed; this enabled the direct determination of LAS in waste water and river samples [4]. Methods based on liquid chromatog- raphy are also used routinely and usually employ either UV or fluorescence detection [5]. We have previously reported [5] the use of LC–electrospray (ESI)–MS to identify LAS and a few of their metabolites, polar sulfophenyl carboxyl- ate compounds (SPC), in coastal waters; a two-step SPE method, employing, first, a hydrophobic C 18 minicolumn then a strong anion exchanger (SAX), was used for sam- ple-preparation. Other authors have used graphitized car- bon black with multiple steps [6]. In general, isolation of LAS from sewage influent and effluent generally requires multiple steps if clean extracts are to be obtained. Field reported a simpler method involving in-vial C 18 Empore disk derivatization [7]. Because of the properties of LAS, which contain sulfonic acid groups, and our experience in this field [8, 9], it was envisaged that LC–MS could be used for the trace determination of LAS in complex influ- ent and effluent water samples. Despite all the advanced chromatographic–MS meth- ods available for the determination of LAS [10], their rou- tine analysis in official laboratories involved in water-pol- lution control is still achieved by means of the non-spe- cific method for anionic surfactants based on the determi- nation of methylene blue-active substances (MBAS) [11]. This routine method is commonly used by water authori- ties in Europe to measure the presence of anionic surface- active substances in different waters. In the work described in this paper we investigated the functioning of five STP, three using biological treatment and two with physicochemical treatment, located in Cat- alonia (North East Spain). Of the five STP studied, three receive substantial important amounts of industrial waste water and two receive basically domestic waste water. These five STP were previously investigated for other compounds [8]. The objectives of the current work were: J. Riu · E. Martínez · D. Barceló · A. Ginebreda · LL. Tirapu LC–MS determination of linear alkylbenzene sulfonates and their carboxylic degradation products in influent and effluent water samples and sludges from sewage-treatment plants Fresenius J Anal Chem (2001) 371 : 448–455 DOI 10.1007/s002160101052 Received: 19 January 2001 / Revised: 10 July 2001 / Accepted: 18 July 2001 / Published online: 2 October 2001 SPECIAL ISSUE PAPER J. Riu · E. Martínez · D. Barceló (✉) Department of Environmental Chemistry, IIQAB -CSIC, Jordi Girona 18–26, 08034 Barcelona, Spain e-mail: dbcqam@cid.csic.es A. Ginebreda · LL. Tirapu Catalan Water Agency (Agencia Catalana de l’Aigua), Provença 204, 08036 Barcelona, Spain © Springer-Verlag 2001