Complementary
Elucidation of the Molecular Characteristics
of Groundwater Dissolved Organic Matter Using Ultrahigh-Resolution
Mass Spectrometry Coupled with Negative- and Positive-Ion Electrospray
Ionization
posted on 2023-03-11, 14:03authored byZiqi Zhou, Qing-Long Fu, Manabu Fujii, T. David Waite
The
formula assignment of the Fourier transform ion cyclotron resonance
mass spectrometry coupled with positive-ion electrospray ionization
[ESI(+)-FT-ICR MS] is challenging because of the extensive occurrence
of adducts. However, there is a paucity of automated formula assignment
methods for ESI(+)-FT-ICR MS spectra. The novel automated formula
assignment algorithm for ESI(+)-FT-ICR MS spectra developed herein
has been applied to elucidate the composition of dissolved organic
matter (DOM) in groundwater during air-induced ferrous [Fe(II)] oxidation.
The ESI(+)-FT-ICR MS spectra of groundwater DOM were profoundly impacted
by [M + Na]+ adducts and, to a lesser extent, [M + K]+ adducts. Oxygen-poor and N-containing compounds were frequently
detected when the FT-ICR MS was operated in the ESI(+) mode, while
the components with higher carbon oxidation states were preferentially
ionized in the negative-ion electrospray ionization [ESI(−)]
mode. Values for the difference between double-bond equivalents and
the number of oxygen atoms from −13 to 13 are proposed for
the formula assignment of the ESI(+)-FT-ICR MS spectra of aquatic
DOM. Furthermore, for the first time, the Fe(II)-mediated formation
of highly toxic organic iodine species was reported in groundwater
rich in Fe(II), iodide, and DOM. The results of this study not only
shed light on the further algorithm development for comprehensive
characterization of DOM by ESI(−)-FT-ICR MS and ESI(+)-FT-ICR
MS but also highlight the importance of appropriate treatment of specific
groundwater prior to use.