TY - JOUR
T1 - Aromaticity Index with Improved Estimation of Carboxyl Group Contribution for Biogeochemical Studies
AU - Zherebker, Alexander
AU - Rukhovich, Gleb D.
AU - Sarycheva, Anastasia
AU - Lechtenfeld, Oliver J.
AU - Nikolaev, Evgeny N.
N1 - Funding Information:
This work was supported by Russian Science Foundation grant 21-47-04405 the German Research Foundation (grant 445025664) and the Rudolf und Helene Glaser-Stiftung in the frame of project “Influence of natural factors on concentration, quality and impact of dissolved organic carbon in the Bavarian Forest National Park” (Project No. T0083\30771\2017\kg) in part of soil sample extraction. The authors are grateful to Maria P. da Silva (UFZ) for providing the soil pore water and the staff of the Bavarian Forest National Park (BFNP) administration for access to the national park, Boris P. Koch (AWI) for providing and Rebecca Matos (UFZ) for labeling the marine sample, as well as for using the analytical facilities of the Centre for Chemical Microscopy (ProVIS) at the Helmholtz Centre for Environmental Research, Leipzig, which is supported by the European Regional Development Funds (EFRE─Europe funds Saxony) and the Helmholtz Association.
Publisher Copyright:
© 2022 American Chemical Society
PY - 2022/2/15
Y1 - 2022/2/15
N2 - 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.
AB - 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.
KW - aromaticity index
KW - carboxylic groups
KW - deuteromethylation
KW - FTICR MS
KW - humic substances
KW - isotopic labeling
KW - NOM
UR - http://www.scopus.com/inward/record.url?scp=85124159333&partnerID=8YFLogxK
U2 - 10.1021/acs.est.1c04575
DO - 10.1021/acs.est.1c04575
M3 - Article
C2 - 35084826
AN - SCOPUS:85124159333
SN - 0013-936X
VL - 56
SP - 2729
EP - 2737
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 4
ER -
