Routine Absorption Mode FTMS Data Display with an Ethoxylated Anionic Detergent as a Dual-Role (Mass and Phase) Calibrant.

Abstract

Absorption mode display of Fourier transform mass spectrometry (FTMS) data is known to improve both peak shape and resolution. Most FTMS data, however, are shown in magnitude mode due to the lack of a routine for determining the phase of ions that are necessary for absorption mode display. Despite the recent development of phase calibration methods, the use of absorption mode processing as a routine has been inhibited by the lack of a good phase calibration standard, particularly a standard that can be used as both a mass and a phase calibrant. A dual-role calibrant will enable the consolidation of mass and phase calibration into a single step making phase calibration as accessible as mass calibration without any incremental increase in complexity in the calibration procedure. We tested a series of detergents and found Triton QS-15, an anionic detergent, suitable as a dual-role calibrant. Additionally, Triton QS-15 produces both positive and negative ion series and thus can be used as a calibrant in both ionization modes. The establishment of a phase calibration routine helps to enable the application of FTMS in areas that require extreme mass resolution. One of the areas is the separation of the fine isotopic peaks of molecules with a large molecular mass (e.g., > 500u). For data acquired using an ion cyclotron resonance instrument with a small magnet (e.g., 7Tesla), there may not be adequate mass resolution to establish a useful isotopic fine structure if the data is displayed in the historical magnitude mode. A mere switch to the absorption mode display makes the isotopic fine structure (IFS) readily available for molecular formula determination. Graphical Abstract x.