Fine Structure in Isotopic Peak Distributions Measured Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: A Comparison between an Infinity ICR Cell and a Dynamically Harmonized ICR Cell

Abstract

The fine structure of isotopic peak distributions of glutathione in mass spectra is measured using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) at 12 and 15 T magnetic field, with an infinity cell and a dynamically harmonized cell (DHC) respectively. The resolved peaks in the fine structure of glutathione consist of 2 H, 13 C, 15 N, 17 O, 18 O, 33 S, 34 S, 36 S, and combinations of them. The positions of the measured fine structure peaks agree with the simulated isotopic distributions with the mass error less than 250 ppb in broadband mode for the infinity cell and no more than 125 ppb with the DHC after internal calibration. The 15 T FT-ICR MS with DHC cell also resolved around 30 isotopic peaks in broadband with a resolving power (RP) of 2 M. In narrowband (m/z 307−313), our current highest RP of 13.9 M in magnitude mode was observed with a 36 s transient length by the 15 T FT-ICR MS with the DHC and 2ω detection on the 15 T offers slightly higher RP (14.8 M) in only 18 s. For the 12 T FT-ICR MS with the infinity cell, the highest RP achieved was 15.6 M in magnitude mode with a transient length of 45 s. Peak decay was observed for low abundance peaks, which could be due to the suppression effects from the most abundant peak, as result of ion cloud Coulombic interactions (space-charge).

Natural Abundance Isotope Ratio Measurements of Organic Molecules Using 21 T FTICR MS

“…In 2013, a method to correct for ion signal damping improved isotope ratios with FTICR to errors below 1% . More recently, higher field (12 and 15 T) FTICR has been evaluated for fine isotopic pattern fidelity, showing that the modern dynamically harmonized cell is capable of significantly improved spectrum quality …”

“…26 More recently, higher field (12 and 15 T) FTICR has been evaluated for fine isotopic pattern fidelity, showing that the modern dynamically harmonized cell is capable of significantly improved spectrum quality. 27 The recent successes of Orbitrap FTMS have prompted a reinvestigation of the utility of FTICR in this space. Here, we sought to evaluate the potential applicability of ICR-MS as a stable isotope measurement platform.…”