Molecular Oxygen (O2) Artifacts in Tandem Mass Spectra

Published

November 20, 2024

Author(s)

Yuxue Liang, Pedatsur Neta, Xiaoyu (Sara) Yang, Hugo Garraffo, Tallat Bukhari, Yi Liu, Stephen Stein

Abstract

The NIST 2023 tandem mass spectral library contains 1,832,086 spectra of positive ions and 541,978 of negative ions from 51,501 compounds. Peak annotation plays an important role in spectrum evaluation. While most fragment ions are formed by neutral losses, we have found ions resulting from addition reactions to these fragments. We have reported two main types of addition reactions in the collision cell, namely addition of H2O and N2. Here we report a different reaction in the collision cell, addition of O2 leading to a small peak that could only be assigned to a peroxyl radical ion. For example, some protonated iodo-aromatics lose iodine atom to form a radical cation [M+H-I]+·, which reacts with O2 to generate a peroxyl radical ion [M+H-I+O2]+·. To confirm the O2 adduction, five compounds were measured under different concentrations of O2. Indeed, higher concentrations of O2 result in higher peroxyl radical peaks, which become dominant while the precursor ion peaks are consumed. The correlation of the peroxyl radical peaks to the concentration of O2 provides a tool to estimate the trace amount of O2 within the instrument. In the NIST 2023 tandem library the peaks for [M+H-X+O2]+· are most abundant in numbers and in intensity for X = NO2 or I, much less abundant for X = Br, and rare for X = Cl. Other leaving groups in this library include SO3H, SO2NH2, CSNH2, CO2C6F5, SO2CH3, and COCH3. The O2 addition reaction is also observed with negative ions. While adducts of H2O and N2 often constitute major peaks, the peaks of the peroxyl radicals under standard conditions are mostly very small and may be mistaken for noise, but their correct annotation improves the quality of the spectra and is important when comparing spectra from different instruments or conditions.

Citation

Journal of the American Society for Mass Spectrometry

Pub Type

Journals

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Keywords

Molecular Oxygen, tandem mass spectral library, fragmentation, O2 addition.

Citation

Liang, Y. , Neta, P. , Yang, X. , Garraffo, H. , Bukhari, T. , Liu, Y. and Stein, S. (2024), Molecular Oxygen (O2) Artifacts in Tandem Mass Spectra, Journal of the American Society for Mass Spectrometry, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958265 (Accessed December 12, 2024)