Negative-ion atmospheric pressure ionisation of semi-volatile fluorinated compounds for ultra-high-performance liquid chromatography tandem mass spectrometry analysis
In this work, the feasibility of negative-ion atmospheric pressure chemical ionisation (APCI) and atmospheric pressure photoionisation (APPI) for ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) determination of fluorotelomer alcohols (FTOHs), fluorinated octanesulfonamides (FOSAs) and fluorinated octanesulfonamido-ethanols (FOSEs) was evaluated. The study of the effect of mobile phase composition on the atmospheric pressure ionisation of these compounds indicated that methanol/water mixtures provided the best responses in APCI, while acetonitrile/water with a post-column addition of toluene as dopant was the most appropriated mixture in APPI. Under the optimal working conditions, most of the target compounds produced the ion [M–H]− as base peak, although in-source collision-induced dissociation fragment ions in APCI and APPI and superoxide adduct ions [M+O2]−• in APPI were also present. These ions proved to be more useful as precursor ions for MS/MS determination than the adduct ions generated in electrospray. Although the UHPLC-APCI-MS/MS method allowed the determination of these semi-volatile compounds at low concentration levels, the analysis by UHPLC-APPI-MS/MS provided the lowest limits of detection and it was applied to the analysis of water samples in combination with solid-phase extraction. Quality parameters demonstrated the good performance of the proposed method, providing low method limits of detection (0.3–6 ng L−1), good precision (RSD % < 5%) and an accurate quantification (relative error % < 14%). Among the river water samples analysed by the developed method, 4:2 FTOH and N-EtFOSA were determined at 30 and 780 ng L−1, respectively.
KeywordsFluorotelomer alcohols Fluorinated sulfonamides Fluorinated sulfonamido-ethanols Atmospheric pressure chemical ionisation Atmospheric pressure photoionisation Liquid chromatography tandem mass spectrometry
The authors acknowledge the financial support received from the Spanish Ministry of Economy and Competitiveness under the project CTQ2015-63968-C2-1-P and also from the Generalitat of Catalonia under the project 2018-SGR-310. Juan F. Ayala-Cabrera also thanks the Spanish Ministry of Education, Culture and Sports for the PhD FPU fellowship and the Water Research Institute (IdRA) from University of Barcelona for the PhD research financial assistance.
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Conflict of interest
The authors declare that they have no conflict of interest.
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