Communicating Confidence of Per- and Polyfluoroalkyl Substance Identification via High-Resolution Mass Spectrometry

Abstract

Per- and polyfluoroalkyl substances (PFASs) are important environmental contaminants, yet relatively few analytical reference standards exist for this class. Nontarget analyses performed by means of high-resolution mass spectrometry (HRMS) are increasingly common for the discovery and identification of PFASs in environmental and biological samples. The certainty of PFAS identifications made via HRMS must be communicated through a reliable and harmonized approach. Here, we present a confidence scale along with identification criteria specific to suspect or nontarget analysis of PFASs by means of nontarget HRMS. Confidence levels range from level 1a—“Confirmed by Reference Standard,” and level 1b—“Indistinguishable from Reference Standard,” to level 5—“Exact Masses of Interest,” which are identified by suspect screening or data filtering, two common forms of feature prioritization. This confidence scale is consistent with general criteria for communicating confidence in the identification of small organic molecules by HRMS (e.g., through a match to analytical reference standards, library MS/MS, and/or retention times) but incorporates the specific conventions and tools used in PFAS classification and analysis (e.g., detection of homologous series and specific ranges of mass defects). Our scale clarifies the level of certainty in PFAS identification and, in doing so, facilitates more efficient identification.

FindPFΔS: Non-Target Screening for PFAS─Comprehensive Data Mining for MS2 Fragment Mass Differences

“…All identified compounds in paper and soil samples discussed in this section have MS/MS information and one standard per homologous series and are therefore considered as level 2a for homologues and level 1 if a reference standard is available according to the identification levels by Schymanski et al. 2014 and to the new levels for PFAS. ,, …”

“…40,51 Considering all pieces of information, the identification level is 2b. 50 Besides being present in the paper sample, some FTMAP sulfoxides/ sulfones have been retrospectively found (by accurate mass, Figure S23) in a contaminated soil sample where FTMAPs and FTSAs were previously identified, 40 indicating their presence also in environmental samples. Similar observations were made for diPAPs in paper extract P2.…”

“…All identified compounds in paper and soil samples discussed in this section have MS/MS information and one standard per homologous series and are therefore considered as level 2a for homologues and level 1 if a reference standard is available according to the identification levels by Schymanski et al 2014 and to the new levels for PFAS. 8,49,50 PFAS Standards. When using ΔCF 2 , ΔC 2 F 4 , ΔHF, and ΔC 2 F 4 SO 3 together (tolerance ±1 mDa, absolute intensity threshold = 1000 counts), 94% of all compounds were correctly assigned by FindPFΔS.…”

IDSL.UFA Assigns High-Confidence Molecular Formula Annotations for Untargeted LC/HRMS Data Sets in Metabolomics and Exposomics

“…IDSL.UFA can only confirm isotopic profile match (Figure S6); however, a confirmatory in-source fragment ([M-C 3 F 6 O] − ) was consistent with the published MS/MS fragmentation (Figure S8). Authentic standards for Cl-PFTrEAs are not readily available; therefore, a confidence level 3b (isotopic profile match combined with fragmentation-based candidates) is suggested for these annotations according to a recently proposed PFAS identification confidence level by Charbonnet et al Levels of Cl-PFTrEAs were similar to those of the commonly known legacy halogenated compounds for human serum samples (Figure ). These findings also show that IDSL.UFA software can potentially detect chemicals of public health concerns in a human biospecimen and can be helpful in expanding the existing database of exposome chemicals …”

IDSL.UFA assigns high confidence molecular formula annotations for untargeted LC/HRMS datasets in metabolomics and exposomics

“…IDSL.UFA can only confirm isotopic profiles match (Figure S.6); however, a confirmatory in-source fragment ([M-C 3 F 6 O] - ) was consistent with the published MS/MS fragmentation (Figure S.8). 37 Authentic standards for Cl-PFTrEAs are not readily available; therefore a confidence level 3b (isotopic profile match combined with fragmentation-based candidate) is suggested for these annotations according to a recently proposed PFAS identification confidence level by Charbonnet et al 38 Levels of Cl-PFTrEAs were similar to the commonly known legacy halogenated compounds 14 for human serum samples (Figure 4). These findings also show that IDSL.UFA software can potentially detect chemicals of public health concerns in a human biospecimen and can be helpful in expanding the existing database of exposome chemicals.…”