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.

A Novel and Intuitive Method of Displaying and Interacting with Mass Difference Information: Application to Oligonucleotide Drug Impurities

“…To account for the lack of calibration standards in the higher mass ranges and the considerable reduction [38] of resolving power as a function of increasing mass using Fourier transform ion cyclotron resonance (FT-ICR) instruments, Bformula extension^approaches [39][40][41][42][43] have been developed to aid in the assignment of the most likely candidate chemical formulas from the experimental data. Using these approaches, the determination of the formulas of compounds with masses higher than approximately 500Da is based on finding peaks in the spectra differing from the lower peaks by mass differences consistent with those in a pre-established list of functional groups (e.g., gain or loss of CH 2 , H 2 , CO 2 , etc.).…”

“…In that way, compounds with unexpected functional groups cannot be determined using these approaches [39]. A significant improvement was made by Kunenkov et al [40] by the introduction of a statistical approach to determine the highmass building blocks based on the repetitive mass difference patterns in the spectra. The approach alleviates the pitfalls of the previous methods and is related to the method developed here.…”

Ion Accumulation Time Dependent Molecular Characterization of Natural Organic Matter Using Electrospray Ionization-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Different IAT values ranging from several hundred milliseconds to a few tens of seconds were set by different groups in previous studies. 20,25,38,39 IAT is the time of ions accumulating in the collision cell before entering the FTICR cell. A rational IAT extension would increase the number of ions accumulated in the collision cell and, subsequently, enhance ions intensity and sensitivity.…”

UltraMassExplorer: a browser‐based application for the evaluation of high‐resolution mass spectrometric data

“…In most previous studies, individual parts of the evaluation process such as the development and improvement of molecular formula assignment or visualization approaches have been addressed. The existing approaches differ, however, in their scope of application, performance and degree of transparency and accessibility.…”