Phase Correction of Fourier Transform Ion Cyclotron Resonance Mass Spectra Using MatLab

Abstract

FT-ICR mass spectrometry has been limited to magnitude mode for almost 40 years due to the data processing methods used. However, it is well known that phase correction of the data can theoretically produce an absorption-mode spectrum with a mass-resolving power that is as much as twice as high as conventional magnitude mode, and that it also improves the quality of the peak shape. Temporally dispersed frequency sweep excitation followed by a time delay before detection results in a steep quadratic variation in the signal phase with frequency. Viewing this, it is possible to find the correct phase function by performing a quadratic least squares fit, modified by iterating through phase cycles until the correct quadratic function is found. Here, we present a robust manual method to rotate these signals mathematically and generate a "phased" absorption-mode spectrum. The method can, in principle, be automated. Baseline correction is also included to eliminate the accompanying baseline drift. The resulting experimental FT-ICR absorption-mode spectra exhibit a resolving power that is at least 50% higher than that of the magnitude mode.

Unit Mass Baseline Resolution for an Intact 148 kDa Therapeutic Monoclonal Antibody by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Thus, FT-ICR mass spectra have conventionally been displayed in magnitude mode, which is independent of phase. As described in detail elsewhere, 38–40 broadband phase correction yields an absorption-mode spectrum with significantly higher resolving power and higher mass accuracy (after one zero-fill of the time-domain data) without loss in S/N. Figure 5 illustrates magnitude-mode and absorption-mode spectra for the 57+ charge state for the IgG1k antibody.…”

“…The measurement also benefits from in-source collisional dissociation to remove adducts; implementation of an electrically compensated open cylindrical cell for improved DC potential tunability to reduce destructive shearing force on the ion cloud; 33, 37 and phase correction to yield absorption-mode spectra with significantly higher resolving power. 38–40 …”

Resolving Isotopic Fine Structure to Detect and Quantify Natural Abundance- and Hydrogen/Deuterium Exchange-Derived Isotopomers

“…A handful of specialized groups, including our own, have detected isotopic fine structure of peptides and even proteins, but required considerable time of tuning, long transient times, specialized parameters, and even specialized data processing. 28–30 It is therefore noteworthy that the combination of the dynamically harmonized ICR cell (trade name “ParaCell”) 25 and integrated data processing methods for generating phased absorption-mode spectrum 31–33 makes the acquisition of such data routine.…”

Differentiating Fragmentation Pathways of Cholesterol by Two-Dimensional Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…The mass spectrum was phase-corrected using the Autophaser 6.0 phase correction software [25][26][27][28][29][30][31][32]. All onedimensional (1D) spectra were first externally calibrated in the solariXControl software (Bruker Daltonics, Billerica, MA, USA) using Agilent ESI-L Low Concentration Tuning Mix (Agilent Technologies, Stockport, United Kingdom), and then internally calibrated against the theoretical m/z values of the ions generated by cholesterol using the quadratic calibration function within Data Analysis 4.0 (Bruker Daltonik GmbH, Bremen, Germany) [33].…”