Analytical Methods For The Determination Of Polyfluoroalkyl Sulfonates And Alternatives In Water Samples

Per- and polyfluoroalkyl substances are a family of typical Persistant Organic Pollutants (POPs) that could hardly be degraded and undergo a long distance transportation globally. Furthermore, they can accumulate through food chains and have potential toxicity on humans. Consequently, they have aroused wide social concerns. They were enormously produced and utilized in our daily necessities, leading to their release into environment through direct or indirect ways. In 2009, perfluorooctane sulfonate was added to the list of Stockhelm Convention on Persistent Organic Pollutants (POPs). The prohibition of PFOS boosted the emergence of alternatives such as fluorotelomer sulfonates (FTSs) and chlorinated polyfluoroalkyl ether sulfonates (Cl-PFAES). In this paper, two methods were developed for simultaneous qualitative and quantitative analysis of perfluoroalkane sulfonates (PFSAs), FTSs and Cl-PFAES in environmental samples.Thirteen riverine samples were collected from the main river estuaries in China. Solid phase extraction (SPE) was selected for sample pre-treatment and three kinds of cartridges including Sep-Pak C18, Oasis HLB, Oasis WAX were compared to determine which one was more efficient. Meanwhile, influential factors such as pH value, wash buffer ratio and eluent volume were optimized to ensure the best conditions for SPE. The results indicated that Oasis WAX cartridges behaved better than the other two ones thus was selected for SPE. The pH values of water samples were adjusted to about 6.0 before loaded onto the cartridges. After the loading process, the cartridges were washed with 4 mL methanol to remove more environmental matrices. After dried under vacuum for about 30 min,6 mL alkaline methanol solution (0.1% NH4OH) was applied to elute target analytes from the cartridges. Satisfactory recoveries were obtained for all analytes with a range of 92.4-110.7% except perfluorodecane sulfonate (PFDS) with a relatively low recovery of 56.5%.Two instrumental analysis methods were established for simultaneously qualitative and quantitative analysis of PFSAs, FTSs and Cl-PFAES. One of them was by ultra-high performance liquid chromatography coupled with triple quadruple mass spectrometry (UHPLC-MS/MS). The other one was ultra-high performance liquid chromatography combined to orbitrap tribrid high resolution mass spectrometry (UHPLC-Orbitrap Tribrid HRMS). Comparison was conducted between UHPLC-MS/MS and UHPLC-Orbitrap Tribrid HRMS methods involving selectivity, linearity, method detection limits and quantification limits (MDLs and MQLs), trueness, precision and matrix effects. Results demonstrated that the two methods were all effective tools for the qualitative and quantitative analysis of PFS As and the alternatives. For qualitative analysis, UHPLC-Orbitrap Tribrid HRMS took advantage of chromatographic retention time along with the mass deviation of precursor ions and fragmentation ions. Generally, the ions could be identified with a mass tolerance less than 5 ppm. Good results were available for all analytes with mass deviations less than 0.8 ppm for precursor ions and 3.3 ppm for fragmentation ions respectively. As for UHPLC-MS/MS, a ratio between two fragmentations of the same precursor ion was necessary for analytes identification besides chromatographic retention time. Relatively, UHPLC-Orbitrap Tribrid HRMS method was much more believable in analytes identification because of its high resolution. Because under low concentrations, the signal of fragmentation ions was unstable, making ratios between two fragmentation ions inaccurate for UHPLC-MS/MS method. In terms of quantitative analysis, UHPLC-Orbitrap Tribrid HRMS made its way under full-scan mass spectrum (MS) and data-dependent MS2 (Full scan/DDA) mode. While UHPLC-MS/MS conducted quantification using the transition between the precursor ion and one of its fragmentation ions under multiple reaction monitoring (MRM) mode. UHPLC-MS/MS method was much more beneficial because it could avoid more interferents, thus diminishing matrix effects. The method validation results were as follows:linearity (r>0.998), MDLs (12-54 pg·L-1), accuracy (90.9-127%), precision (0.2-9.9%), matrix effects (96.4-104%) for UHPLC-MS/MS method; linearity (r>0.999), MDLs (7.1-62 pg·L-1), accuracy (88.2-118%), precision (0.1-11.3%), matrix effects (88.8-151%) for UHPLC-Orbitrap Tribrid HRMS method.The established methods were applied for the trace analysis of PFSAs and alternatives in thirteen riverine samples from east China. For UHPLC-MS/MS method, the quantitative results for PFSAs, FTSs and 6:2 Cl-PFAES were in a range of 0.11-424 ng·L-1,0.1-0.3 ng·L-1,0.1-0.3 ng·L-1 respectively. While the results by UHPLC-Orbitrap Tribrid HRMS method were 0.19-440 ng·L-1,0.2-0.4 ng·L-1 and 2.0-44.2 ng·L-1 respectively for PFSAs, FTSs and 6:2 Cl-PFAES. The quantitative results by UHPLC-MS/MS method were in good accordance with those by UHPLC-Orbitrap Tribrid HRMS method (r>0.99), indicating that both methods could be used for the analysis of PFSAs and alternative pollutants in riverine samples.