Absorption-Mode: The Next Generation of Fourier Transform Mass Spectra

Abstract

The Fourier transform spectrum can be presented in the absorption-mode (commonly used in FT-NMR), magnitude-mode (FT-ICR), and power-mode (engineering applications). As is routinely used in FT-NMR, it is well-known that the absorption-mode display gives a much narrower peak shape which greatly improves the spectrum; recently, the successful solution of the phase equation allowed broadband phase correction which makes it possible to apply the absorption-mode routinely in FT-ICR. With the empirical evidence provided herein, it has been confirmed that in addition to the improvement on resolving power, compared to the conventional magnitude-mode, the new absorption-mode improves the signal-to-noise ratio (S/N) of a spectrum by 1.4-fold and can improve the mass accuracy up to 2-fold with no extra cost in instrumentation. Therefore, it is worthwhile to apply and promote absorption-mode in routine FT-ICR experiments.

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].…”

Autophaser: An Algorithm for Automated Generation of Absorption Mode Spectra for FT-ICR MS

“…18 and which show the expected improvements in resolving power (√3 – 2 fold), signal to noise ratio (√2 fold), and mass accuracy, over the same spectra when processed in magnitude mode. 17, 21 An example spectrum phased by both methods is provided in the Supplementary Information.…”

Data processing in Fourier transform ion cyclotron resonance mass spectrometry

“…Many types of modern mass spectrometers (ion trap, quadrupole, time‐of‐flight) offer the mass accuracies in the level of at best tens of ppm in a limited mass range, whereas FT‐ICR can achieve mass accuracy in sub‐ppm, or even ppb (parts per billion) level in state‐of‐the‐art instruments (Kaiser et al, ; Nikolaev et al, ). With such extraordinary performance, the ion's elemental composition can be revealed without tandem MS experiments (Qi et al, ).…”

“…Bottom: Details of peak assignment (peaks used for mass calibration are in bold). Reprinted from Qi et al (), with permission from Wiley, copyright 2012.…”

“…Phase correction aligns the data points (vectors) with the real axis of the complex space, and the noise from the imaginary part of the complex number does not get added into the absorption‐mode spectrum. As the absorption‐mode does not change the intensity of a peak, phase correction decreases the noise baseline level by √2 compared to magnitude‐mode (Qi et al, ). Such an improvement is equivalent to have a “quadrature detection” which requires two separate receiver coils for the instrument (Marshall & Hendrickson, ), but here it is just data processing without the cost of extra hardware.…”