Similarity of High-Resolution Tandem Mass Spectrometry Spectra of Structurally Related Micropollutants and Transformation Products

  • Jennifer E. Schollée
  • Emma L. Schymanski
  • Michael A. Stravs
  • Rebekka Gulde
  • Nikolaos S. Thomaidis
  • Juliane Hollender
Research Article

Abstract

High-resolution tandem mass spectrometry (HRMS2) with electrospray ionization is frequently applied to study polar organic molecules such as micropollutants. Fragmentation provides structural information to confirm structures of known compounds or propose structures of unknown compounds. Similarity of HRMS2 spectra between structurally related compounds has been suggested to facilitate identification of unknown compounds. To test this hypothesis, the similarity of reference standard HRMS2 spectra was calculated for 243 pairs of micropollutants and their structurally related transformation products (TPs); for comparison, spectral similarity was also calculated for 219 pairs of unrelated compounds. Spectra were measured on Orbitrap and QTOF mass spectrometers and similarity was calculated with the dot product. The influence of different factors on spectral similarity [e.g., normalized collision energy (NCE), merging fragments from all NCEs, and shifting fragments by the mass difference of the pair] was considered. Spectral similarity increased at higher NCEs and highest similarity scores for related pairs were obtained with merged spectra including measured fragments and shifted fragments. Removal of the monoisotopic peak was critical to reduce false positives. Using a spectral similarity score threshold of 0.52, 40% of related pairs and 0% of unrelated pairs were above this value. Structural similarity was estimated with the Tanimoto coefficient and pairs with higher structural similarity generally had higher spectral similarity. Pairs where one or both compounds contained heteroatoms such as sulfur often resulted in dissimilar spectra. This work demonstrates that HRMS2 spectral similarity may indicate structural similarity and that spectral similarity can be used in the future to screen complex samples for related compounds such as micropollutants and TPs, assisting in the prioritization of non-target compounds.

Graphical Abstract

Keywords

High-resolution tandem mass spectrometry Micropollutants Transformation products Non-target screening Spectral similarity 

Notes

Acknowledgements

Birgit Beck, Heinz Singer, and many members of the Department of Environmental Chemistry at Eawag are gratefully acknowledged for the measurement of the standards for MassBank. The authors additionally thank Nikiforos Alygizakis from the University of Athens for the measurement of the QTOFMS spectra. Uwe Schmitt (ETH Zurich) and Leon Bichmann (Eawag), Sebastian Böcker and Kai Dührkop (University of Jena), and Oscar Yanes (Center for Omic Sciences, Spain) are thanked for helpful discussions. Funding for JES was provided by the EDA-Emerge project through the EU Seventh Framework Programme (FP7-PEOPLE-2011-ITN) under grant agreement number 290100 and from the Swiss Federal Office for the Environment. ELS was supported by the SOLUTIONS project (EU FP7, grant number 603437). Funding for M.S. and R.G. was provided by the Swiss National Science Foundation.

Supplementary material

13361_2017_1797_MOESM1_ESM.docx (1.5 mb)
ESM 1 (DOCX 1501 kb)

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Copyright information

© American Society for Mass Spectrometry 2017

Authors and Affiliations

  • Jennifer E. Schollée
    • 1
    • 2
  • Emma L. Schymanski
    • 1
  • Michael A. Stravs
    • 1
    • 2
  • Rebekka Gulde
    • 1
  • Nikolaos S. Thomaidis
    • 3
  • Juliane Hollender
    • 1
    • 2
  1. 1.Eawag, Swiss Federal Institute of Aquatic Science and TechnologyDübendorfSwitzerland
  2. 2.Institute of Biogeochemistry and Pollutant DynamicsETH ZürichZürichSwitzerland
  3. 3.Laboratory of Analytical Chemistry, Department of ChemistryNational and Kapodistrian University of AthensAthensGreece

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