Aromaticity Index with Improved Estimation of Carboxyl Group Contribution for Biogeochemical Studies

Alexander Zherebker, Gleb D. Rukhovich, Anastasia Sarycheva, Oliver J. Lechtenfeld, Evgeny N. Nikolaev

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Natural organic matter (NOM) components measured with ultrahigh-resolution mass spectrometry (UHRMS) are often assessed by molecular formula-based indices, particularly related to their aromaticity, which are further used as proxies to explain biogeochemical reactivity. An aromaticity index (AI) is calculated mostly with respect to carboxylic groups abundant in NOM. Here, we propose a new constrained AIcon based on the measured distribution of carboxylic groups among individual NOM components obtained by deuteromethylation and UHRMS. Applied to samples from diverse sources (coal, marine, peat, permafrost, blackwater river, and soil), the method revealed that the most probable number of carboxylic groups was two, which enabled to set a reference point n = 2 for carboxyl-accounted AIcon calculation. The examination of the proposed AIcon showed the smallest deviation to the experimentally determined index for all NOM samples under study as well as for individual natural compounds obtained from the Coconut database. In particular, AIcon performed better than AImod for all compound classes in which aromatic moieties are expected: aromatics, condensed aromatics, and unsaturated compounds. Therefore, AIcon referenced with two carboxyl groups is preferred over conventional AI and AImod for biogeochemical studies where the aromaticity of compounds is important to understand the transformations and fate of NOM compounds.

Original languageEnglish
Pages (from-to)2729-2737
Number of pages9
JournalEnvironmental Science and Technology
Issue number4
StatePublished - 15 Feb 2022
Externally publishedYes


  • aromaticity index
  • carboxylic groups
  • deuteromethylation
  • humic substances
  • isotopic labeling
  • NOM

ASJC Scopus subject areas

  • Chemistry (all)
  • Environmental Chemistry


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