Enhancement of the effective resolution of mass spectra of high-mass biomolecules by maximum entropy-based deconvolution to eliminate the isotopic natural abundance distribution

Although high-resolution Fourier transform ion cyclotron resonance mass spectrometry can resolve individual isotopic masses for biomolecules of more than 100 ku, its effective mass accuracy is limited by the distribution of naturally occurring rare isotopes (¹³C, ¹⁵N, ¹⁸O, ³⁴S, etc.). In this article, we compare least-squares and maximum entropy methods for deconvolution of the isotopic natural abundance distribution to narrow the mass spectral isotopic abundance envelope for greatly enhanced effective mass resolution. We apply both methods to yield deconvolved high-resolution deuterium distributions for peptides and proteins subjected to H/D exchange prior to electrospray Fourier transform ion cyclotron resonance mass analysis. In addition, we show that even unresolved isotopic envelopes from a quadrupole mass spectrometer can be narrowed for considerably improved resolution there as well.