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 carb on atoms, which are degradation products of linear alkylbenzenesulfonates ( LAS), have been isolated by solid-phase extraction (SPE) followed by identi fication with liquid chromatography / ionspray - mass spectrometry (LC/ISP- MS). The isolation procedure involved extraction in a C-18 minicolumn and s ubsequently in a strong anionic exchange (SAX) column, the final determinat ion was accomplished by Negative Ion LC/ISP/MS using a two step approach. F irst, a chromatographic run at a cone voltage of 80 V was performed. At thi s voltage the major fragment ion corresponded either to mit 183 (C11 SPC an d LAS) or to m/z 170 (C6SPC to C10SPC), and permitted the confirmation of L AS 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 propo sed 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 met hod represents an important advancement for the unequivocal trace determina tion of the polar degradation products of LAS, SPC, since current establish ed protocols involve either the use of derivatization/gas chromatography-ma ss spectrometry and/or liquid chromatography with UV detection. By using th e protocol described the direct confirmation and quantitative trace determi nation of both LAS and their polar metabolites SPC is feasible.