ISOTOPE DEPLETION OF LARGE BIOMOLECULES - IMPLICATIONS FOR MOLECULAR-MASS MEASUREMENTS

Isotope depletion (or enrichment) of large biomolecules is a procedure already used in high resolution Fourier transform ion cyclotron reson ance mass spectrometry for improving the reliability and accuracy of b iomolecular mass characterization. In this work, effects of isotope de pletion on a number of mass spectrometric parameters are systematicall y studied. Implementation of the isotope depletion techniques in conju nction with lower resolution mass analyzers is discussed as well. We i nvestigate theoretically the position of the centroid of the isotopic mass distributions (centroid mass) and the shift between the monoisoto pic and the centroid masses of biopolymers as a function of the isotop e abundance (e.g., C-12:C-13 ratio). The behaviour of other additive m ass parameters, like the ratio between the monoisotopic and the first isotopic peak, is also discussed. We address by computer simulations t he effects of different instrumental parameters like mass resolution a nd ion statistics as a function of isotope abundances and from there t he achievable mass accuracy for high-mass biopolymers. We assess some of the practical issues of the isotope depletion technique, viz., to w hat degree and with what accuracy the depletion procedure should be pe rformed for achieving the desired mass accuracy. (C) 1998 American Soc iety for Mass Spectrometry.