Alpha,beta-unsaturated sulfophenylcarboxylates as degradation intermediates of linear alkylbenzenesulfonates: evidence for omega-oxygenation followed by beta-oxidations by liquid chromatography-mass spectrometry.

Liquid chromatography with an electrospray interface to a mass spectrometer (LC-ES-MS) and LC-ES coupled to a tandem MS (LC-ES-MS/MS) were used to detect and identify intermediates excreted transiently during the aerobic degradation of linear alkylbenzenesulfonates (LAS) in fixed-bed bioreactors (FBBR). The inoculum for the FBBR was the microflora of the River Rhine, Germany. Two major phenomena were observed on the addition of 100 mg/L LAS to the system, sorption and then biodegradation. Disappearance due to sorption was followed in an inhibited FBBR. Biodegradation of LAS started on day 7 and was accompanied by the transient excretion of intermediates, which were later largely degraded. We detected not only the sulfophenylcarboxylates (SPCs) observed previously but also the alpha,beta-unsaturated SPCs (SPC-2H), which have not been reported before. Experiments with the (4-sulfophenyl)dodecanes (C12-LAS), which had minor contaminants of C11-LAS, showed C12-, C10-, C8-, C6-, and C4-SPCs when LAS was degraded as well as traces of C9-, C7-, and C5-SPCs. Signals from the SPC-2H species were usually some 10% of those from the corresponding SPCs. Samples from these experiments were also examined by gas chromatography-mass spectrometry (GC-MS), but no desulfonated intermediates were detected. We interpret the data to mean that the only attack on LAS was by (omega-oxygenation; there was no visible initial desulfonation. The products of omega-oxygenation were oxidized to the corresponding SPC and subject to beta-oxidation, as evidenced not only by the pattern of C-2 units in the excreted SPCs but also in the corresponding series of SPC-2H, representing the intermediates in beta-oxidation.