Comparison of Three Types of Mass Spectrometer for High-Performance Liquid Chromatography/Mass Spectrometry Analysis of Perfluoroalkylated Substances and Fluorotelomer Alcohols

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Abstract
The performance of three different types of mass spectrometer (MS) coupled to high performance liquid chromatography (HPLC), was compared for trace analysis of perfluoroalkylated substances (PFAS) and fluorotelomer alcohols (FTOHs). An ion trap MS in the full-scan and product-ion mass spectrometry (MS2) mode, time-of-flight (ToF) high-resolution MS and quadrupole MS in the selected ion mode, as well as triple quadrupole tandem MS were tested. Electrospray ionisation in the negative-ion mode [ESI(–)] was best suited for all instruments and compounds. PFAS could only be separated by a buffered mobile phase, but the presence of buffer suppressed the ionisation of FTOHs. Therefore, two independent chromatographic methods were developed for the two compound classes. Mass spectra and product-ion spectra obtained by in-source and collision-induced dissociation fragmentation are discussed, including ion adduct formation. Product ion yields of PFAS were only in the range of 0.3 to 12%, independent of the applied MS instrument. Ion trap MS2 gave product ion yields of 20 to 62% for FTOHs, whereas only 4.1 to 5.8% were obtained by triple quadrupole tandem MS. Ion trap MS was best suited for qualitative analysis and structure elucidation of branched isomeric structures of PFAS. Providing typical detection limits of 5 ng injected in MS2 mode, it was not sensitive enough for selective trace amount quantification. ToF high-resolution MS was the only technique combining high selectivity and excellent sensitivity for PFAS analysis (detection limits of 2 to 10 pg), but lacked the possibilities of MS/MS. Triple-quadrupole tandem MS was the method of choice for quantification of FTOHs with detection limits in the low pg range. It is also well suited for the determination of PFAS, although its detection limits of 10 to 100 pg in tandem MS mode are about one order of magnitude higher than for ToF MS.