Abstract
Mass spectrometry enables the study of increasingly larger biomolecules with increasingly higher resolution, which is able to distinguish between fine isotopic variants having the same additional nucleon count, but slightly different masses. Therefore, the analysis of the fine isotopic distribution becomes an interesting research topic with important practical applications. In this paper, we propose the comprehensive methodology for studying the basic characteristics of the fine isotopic distribution. Our approach uses a broad spectrum of methods ranging from generating functions—that allow us to estimate the variance and the information theory entropy of the distribution—to the theory of thermal energy fluctuations. Having characterized the variance, spread, shape, and size of the fine isotopic distribution, we are able to indicate limitations to high resolution mass spectrometry. Moreover, the analysis of “thermorelativistic” effects (i.e., mass uncertainty attributable to relativistic effects coupled with the statistical mechanical uncertainty of the energy of an isolated ion), in turn, gives us an estimate of impassable limits of isotopic resolution (understood as the ability to distinguish fine structure peaks), which can be moved further only by cooling the ions. The presented approach highlights the potential of theoretical analysis of the fine isotopic distribution, which allows modeling the data more accurately, aiming to support the successful experimental measurements.Graphical ᅟElectronic supplementary materialThe online version of this article (doi:10.1007/s13361-015-1180-4) contains supplementary material, which is available to authorized users.
Highlights
An important challenge in mass spectrometry (MS) is to extend the technology to enable detection of large organic particles, biomolecules, and nano-particles
Variance, entropy, spread, and size of the fine isotopic distribution of an aggregated isotopic variant, we investigate if the fine isotopic distribution can be approximated by a normal distribution
We analyzed: (1) moment generating functions for calculating the variance and information theory entropy; (2) theoretical spread and number of peaks of the center-mass within the most abundant aggregated peaks; (3) the normality of the fine structure distribution for the most abundant aggregated variants; (4) thermorelativistic effects corresponding to the high-resolution measurements
Summary
An important challenge in mass spectrometry (MS) is to extend the technology to enable detection of large organic particles, biomolecules, and nano-particles. P. Dittwald et al.: On the Fine Isotopic Distribution methodology could be useful in experimental practice. The investigation of theoretical limits for the applicability of the isotopic distribution, especially for heavy particles, can be useful to the mass spectrometry community for improving experimental design and data processing. This could help to avoid planning experiments that will be unable to succeed because of these limits, or to plan experiments with the purpose of overcoming these limits [5]
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