α, β‐Unsaturated sulfophenylcarboxylates as degradation intermediates of linear alkylbenzenesulfonates: Evidence for Ω‐oxygenation followed by β‐oxidations by liquid chromatography‐mass spectrometry

Abstract 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 α, β‐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 ω‐oxygenation; there was no visible initial desulfonation. The products of ω‐oxygenation were oxidized to the corresponding SPC and subject to β‐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 β‐oxidation.