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This study describes an in-depth investigation of the parameters involved in the solid-phase extraction performance of perfluoroalkylated compounds (seven carboxylates and one sulfonate), particularly with sea water samples. The two most popular sorbents, Oasis WAX and Oasis HLB, were considered and it was observed that the high ionic strength of sea water may impair solid-phase extraction recoveries. In the final protocol, Oasis HLB cartridges were selected, incorporating a 10% methanol clean-up step before elution with methanol, since less matrix effects were obtained. The proposed method allows successful recoveries, higher than 71%, and relative standard deviations lower than 20%. It also provides excellent limits of detection values between 0.01 and 0.21 ng/L. Finally, the method was applied to fresh and sea water samples, where several perfluoroalkylated compounds were found at concentrations ranging between 0.16 and 64 ng/L. In the case of perfluorooctane sulfonate, recently included in the Water Frame Directive, its concentration reached the highest values among the perfluoroalkylated compounds measured (64 ng/L in river samples).