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Figure 1 | BMC Bioinformatics

Figure 1

From: QUDeX-MS: hydrogen/deuterium exchange calculation for mass spectra with resolved isotopic fine structure

Figure 1

Resolving power and acquisition time required to observe deuterium-associated isotopic fine structure is charge state dependent. A. In order to resolve deuterium-associated peaks, it is necessary to detect a mass difference m HDX of ~2.922 mDa, where m HDX is the mass difference between 2H and 1H minus the mass difference between 13C and 12C. Increasing charge states require higher resolving power at a given m/z. Plotted are the resolving powers (m/∆m 50% where ∆m50% is the full width at half-maximum peak height) required to observe deuterium-associated isotopic fine structure for z = 1, 2, and 3 (Eq. 2). ∆m50% was calculated assuming two peaks separated by m HDX/z of equal height and Lorentzian peak shape are resolved with a valley between them reaches half-maximum height for either peak (Eq. 3). Also plotted (in black diamonds) are the resolving powers required to observed various peptide ions we previously monitored in a HDX experiment [9] to help illustrate the range of resolving powers necessary for one representative set of data. B. Theoretical minimum acquisition time required in order to resolve deuterium-associated isotopic fine structure as a function of absolute mass for various charge states. For a 9.4 T FTICR-MS operating in absorption mode, we assumed a conservative ~1.45-fold improvement in resolving power over the magnitude mode low-pressure limit (Eq. 1, effective field B 0 = 13.6 T [47]). For the 12 T FTICR-MS operating in absorption mode, we assumed the maximum 2-fold improvement in resolving power over the magnitude mode low-pressure limit, which can be valid for acquisition times of less than a few seconds [46],[47]. Again plotted (in black diamonds) are peptide ions monitored from an actual HDX experiment [9] to help illustrate the range of acquisition times that would be necessary without further optimization.

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