Method for the determination of sub-ppm concentrations of perfluoroalkylsulfonate anions in water

Abstract

The determination of sub-ppm concentrations of aqueous perfluoroalkylsulfonate (PFS) anions, including perfluorooctylsulfonate (PFOS), has been accomplished with a relatively simple mass spectrometric procedure that does not require extraction of the analytes into an organic solvent or a chromatographic separation prior to injection into the negative-ion electrospray ionization mass spectrometer. Sample pretreatment was minimized and consisted of dilution of the aqueous samples of groundwater, surface water, tap water, and distilled water with acetonitrile, addition of dodecylsulfate (DDS) as an internal standard, and, in some cases, addition of known amounts of perfluorobutylsulfonate (PFBS) or PFOS for standard-addition experiments. The linear-response range for PFOS is 25.0 µg L⁻¹ to 2.5 mg L⁻¹. The lower limit of this range is three orders of magnitude lower than an equally straightforward chromatographic method. The relative errors for standard aqueous solutions containing only 25.0 µg L⁻¹ and 2.5 mg L⁻¹ PFOS are ±14% and ±7%, respectively, with 133 µg L⁻¹ DDS as the internal standard. The detection limit and quantification limit for PFOS in these standards are 5.0 µg L⁻¹ and 25.0 µg L⁻¹, respectively. Six different PFS anions, containing three to eight carbon atoms, were identified and quantified in an aqueous film-forming foam (AFFF) formulation using the method of standard additions. Two alkylsulfate anions and two perfluoroalkylcarboxylate anions were also identified in the AFFF formulation.