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@ARTICLE{Zherebker:180978,
      author       = {A. Zherebker and S. Kim and P. Schmitt-Kopplin and R. G. M.
                      Spencer and O. Lechtenfeld and D. C. Podgorski and N.
                      Hertkorn and M. Harir and N. Nurfajin and B. Koch and E. N.
                      Nikolaev and E. A. Shirshin and S. A. Berezin and D. S. Kats
                      and G. Rukhovich and I. V. Perminova},
      title        = {{I}nterlaboratory comparison of humic substances
                      compositional space as measured by {F}ourier transform ion
                      cyclotron resonance mass spectrometry ({IUPAC} {T}echnical
                      {R}eport)},
      journal      = {Pure and applied chemistry},
      volume       = {92},
      number       = {9},
      issn         = {0033-4545},
      address      = {Berlin},
      publisher    = {de Gruyter},
      reportid     = {DKFZ-2022-01703},
      pages        = {1447 - 1467},
      year         = {2020},
      abstract     = {Interlaboratory comparison on the determination of the
                      molecular composition of humic substances (HS) was
                      undertaken in the framework of IUPAC project 2016-015-2-600.
                      The analysis was conducted using high resolution mass
                      spectrometry, nominally, Fourier transform ion cyclotron
                      resonance mass spectrometry (FTICR MS) with electrospray
                      ionization. Six samples of HS from freshwater, soil, and
                      leonardite were used for this study, including one sample of
                      humic acids (HA) from coal (leonardite), two samples of soil
                      HA (the sod-podzolic soil and chernozem), two samples of
                      soil fulvic acids (FA) (the sod-podzolic soil and
                      chernozem), and one sample of freshwater humic acids (the
                      Suwannee River). The samples were analyzed on five different
                      FTICR MS instruments using the routine conditions applied in
                      each participating laboratory. The results were collected as
                      mass lists, which were further assigned formulae for the
                      determination of molecular composition. The similarity of
                      the obtained data was evaluated using appropriate
                      statistical metrics. The results have shown that direct
                      comparison of discrete stoichiometries assigned to the mass
                      lists obtained by the different laboratories yielded poor
                      results with low values of the Jaccard similarity score –
                      not exceeding 0.56 (not more than $56 \%$ of the similar
                      peaks). The least similarity was observed for the
                      aromatics-rich HA samples from leonardite (coal) and the
                      chernozem soil, which might be connected to difficulties in
                      their ionization. The reliable similarity among the data
                      obtained in this intercomparison study was achieved only by
                      transforming a singular point (stoichiometry) in van
                      Krevelen diagram into a sizeable pixel (a number of closely
                      located stoichiometries), which can be calculated from the
                      population density distribution. The conclusion was made
                      that, so far, these are descriptors of occupation density
                      distribution, which provide the metrics compliant with the
                      data quality requirements, such as the reproducibility of
                      the data measurements on different instruments.},
      ddc          = {540},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.1515/pac-2019-0809},
      url          = {https://inrepo02.dkfz.de/record/180978},
}