title: Total mass difference statistics algorithm: a new approach to identification of high-mass building blocks in electrospray ionization Fourier transform ion cyclotron mass spectrometry data of natural organic matter.
abstract: The ultrahigh-resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrum of natural organic matter (NOM) contains several thousand peaks with dozens of molecules matching the same nominal mass. Such a complexity poses a significant challenge for automatic data interpretation, in which the most difficult task is molecular formula assignment, especially in the case of heavy and/or multielement ions. In this study, a new universal algorithm for automatic treatment of FTICR mass spectra of NOM and humic substances based on total mass difference statistics (TMDS) has been developed and implemented. The algorithm enables a blind search for unknown building blocks (instead of a priori known ones) by revealing repetitive patterns present in spectra. In this respect, it differs from all previously developed approaches. This algorithm was implemented in designing FIRAN-software for fully automated analysis of mass data with high peak density. The specific feature of FIRAN is its ability to assign formulas to heavy and/or multielement molecules using "virtual elements" approach. To verify the approach, it was used for processing mass spectra of sodium polystyrene sulfonate (PSS, M(w) = 2200 Da) and polymethacrylate (PMA, M(w) = 3290 Da) which produce heavy multielement and multiply-charged ions. Application of TMDS identified unambiguously monomers present in the polymers consistent with their structure: C(8)H(7)SO(3)Na for PSS and C(4)H(6)O(2) for PMA. It also allowed unambiguous formula assignment to all multiply-charged peaks including the heaviest peak in PMA spectrum at mass 4025.6625 with charge state 6- (mass bias -0.33 ppm). Application of the TMDS-algorithm to processing data on the Suwannee River FA has proven its unique capacities in analysis of spectra with high peak density: it has not only identified the known small building blocks in the structure of FA such as CH(2), H(2), C(2)H(2)O, O but the heavier unit at 154.027 amu. The latter was identified for the first time and assigned a formula C(7)H(6)O(4) consistent with the structure of dihydroxyl-benzoic acids. The presence of these compounds in the structure of FA has so far been numerically suggested but never proven directly. It was concluded that application of the TMDS-algorithm opens new horizons in unfolding molecular complexity of NOM and other natural products.
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Moscow, Russia.
authors.forename: Erast V
authors.initials: EV
authors.lastname: Kunenkov
authors.forename: Alexey S
authors.initials: AS
authors.lastname: Kononikhin
authors.forename: Irina V
authors.initials: IV
authors.lastname: Perminova
authors.forename: Norbert
authors.initials: N
authors.lastname: Hertkorn
authors.forename: Andras
authors.initials: A
authors.lastname: Gaspar
authors.forename: Philippe
authors.initials: P
authors.lastname: Schmitt-Kopplin
authors.forename: Igor A
authors.initials: IA
authors.lastname: Popov
authors.forename: Andrew V
authors.initials: AV
authors.lastname: Garmash
authors.forename: Evgeniy N
authors.initials: EN
authors.lastname: Nikolaev
mesh_terms: D000465:Algorithms; D001578:Benzopyrans / Q000737:chemistry*; D015233:Models, Statistical; D011109:Polymethacrylic Acids / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*; D012984:Software; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods / Q000706:statistics & numerical data*
chemical_list: D001578:Benzopyrans; D011109:Polymethacrylic Acids; D011137:Polystyrenes; C030613:polymethacrylic acid; C003321:polystyrene sulfonic acid; C005023:fulvic acid