Freely dissolved concentrations of anionic surfactants in seawater solutions: Optimization of the non-depletive solid-phase microextraction method and application to linear alkylbenzene sulfonates

A solid-phase microextraction method (SPME) has been optimized for the analysis of freely dissolved anionic surfactants, namely linear alkylbenzene sulfonates (LAS), in seawater. An effect of the thermal conditioning treatment on the polyacrylate fiber coating was demonstrated for both uptake kinetics and sorption isotherm linearity. Thermal conditioning at 120 °C yielded linear sorption isotherms and reproducible SPME measurements for several individual LAS compounds, with detection limits at the low microgram per liter range. Sorption of LAS to the conditioned SPME fiber was independent of LAS co-solutes in mixtures. The method has been applied to study the precipitation of LAS in seawater, and solubility data for a wide range of individual LAS constituents is presented for the first time. Hence, the developed SPME method for the anionic LAS has shown to be a useful tool in complex matrices. The advantage of the SPME analyses in complex matrices is, besides its simplicity, that it also leads to clean extracts for chromatographic analyses.