Elucidation of doubly charged ions in DOM by ultrahigh-resolution mass spectrometry
Dissolved organic matter(DOM)is a heterogeneous organic mixture ubiquitous in various environmental media,participating in many biogeochemistry and environmental chemical processes in the supergene earth system.Despite the extensive occurrence of single-charged ion peaks in the mass spectra of DOM by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS),information regarding their double-charged ion peaks is very limited.In this study,a doubly charged ions algorithm based on their singly charged precursors was developed to characterize the chemodiversity of multiply charged ions in the FT-ICR MS spectra of DOM in various environmental media.Results showed that compared with the traditional method only considering 13C isotopic peaks,the doubly charged ions method based on singly charged precursors could effectively improve 44.90％number of doubly charged ion peaks in the FT-ICR MS spectra of DOM.The doubly charged ions had higher values of O/C,minimum double-bond equivalence(DBE),modified aromaticity index(AImod),nominal oxidation state of carbon(NOSC)and lower values of H/C than those for singly charged ions,indicating that most of the doubly charged DOM were carboxyl-rich alicyclic molecules.Moreover,the number of doubly charged ions was dependent on sample type.Soil DOM was most abundant in the doubly charged ions.The number and percentage of doubly charged ions in various samples were in the order of:marine DOM(540,0.18％),natural fresh water DOM(3486,0.81％),soil DOM(6334,4.06％)and waste water DOM(41,0.13％).These results suggested that the singly charged ion peaks were dominant in the FT-ICR MS spectra of DOM for various environmental matrices.In addition to providing a novel data analysis method for FT-ICR MS data analysis,for the first time,this study reveals the properties of multiply charged ions in different types of DOM and confirms the neglectable effect of doubly charged ions on ultrahigh-resolution mass spectrometry data analysis for different types of DOM.
万方数据
维普
