Determination of parts per trillion level of carboxylic degradation products of linear alkylbenzenesulfonates in coastal water by solid-phase extraction followed by liquid chromatography ionspray mass spectrometry using negative ion detection

Long-chain sulfophenyl carboxylate compounds (SPC) with more than five carbon atoms, which are degradation products of linear alkylbenzenesulfonates (LAS), have been isolated by solid-phase extraction (SPE) followed by identification with liquid chromatography / ionspray - mass spectrometry (LC/ISP-MS). The isolation procedure involved extraction in a C-18 minicolumn and subsequently in a strong anionic exchange (SAX) column, the final determination was accomplished by Negative Ion LC/ISP/MS using a two step approach. First, a chromatographic run at a cone voltage of 80 V was performed. At this voltage the major fragment ion corresponded either to mit 183 (C11 SPC and LAS) or to m/z 170 (C6SPC to C10SPC), and permitted the confirmation of LAS and SPC. The second step involved an extraction cone voltage of 20 V In this case [M-H](-) ion was the base peak for all the studied compounds (LAS and SPC) and was used as a quantitative ion. The linear range of the proposed method varied from 0.4 to 10 ppb with a limit of detection ranging from 2-20 ppt when 250mL of coastal water were preconcentrated. The present method represents an important advancement for the unequivocal trace determination of the polar degradation products of LAS, SPC, since current established protocols involve either the use of derivatization/gas chromatography-mass spectrometry and/or liquid chromatography with UV detection. By using the protocol described the direct confirmation and quantitative trace determination of both LAS and their polar metabolites SPC is feasible.