Electrospray ionization charge deconvolution

Data for comparison to the model were obtained via the electrospray ionization mass spectrum of a Starburst PAM AM dendrimer (core = NH3) generation = 4 between m/z 600 and 1600. The ESI mass spectrum consisted predominantly of multiple charged ions at +7, +8, +9, +10, and +11 charge states. The deconvoluted mass spectrum between 9600 and 10747 daltons suggest the presence of at least 16 components in the sample. The last significant peak at 10632 daltons corresponds with the theoretical mass 10632.96, magic number which is within one mass unit for the ideal generation = 4 structure (see Fig. 33). 

In electrospray ionization, compounds with a mass in excess of 500 Da may be prone to the formation of multiple-charge ions, either in positive-ion or in negative-ion mode [22-23], The averaging algorithm [23-24] can be used for molecular-weight determination from an ion envelope of multiple-charge ions (Ch. 16.2.2). Various automated computer-based procedures for the deconvolution or transformation of the electrospray mass spectra of proteins have been introduced. 

Intact protein mass spectrometry allows the molecular mass determination of either proteins or complexes of proteins and covalently bound ligands/other proteins. In a first step, the sample is desalted to detach from buffer components and small ions that would interfere through noncovalent complexes in the gas phase. Next, the isolated protein is ionized, for example, by electrospray ionization (ESI). The acid in the eluent causes protonation of the protein at basic sites, particularly lysine and arginine residues, so that m/z values of multiple species with different charges can be measured in a mass spectrometer. These data are then combined during the deconvolution process to yield the mass of the protein or complex. 

Progress is also made in software for mass spectral interpretation, especially for the so-called deconvolution of (mixed) ion envelopes of multiply charged protein ions generated by electrospray ionization, and for the peptide sequencing by MS-MS techniques. In that respect, the development of tools to search extensive protein and DNA databases using peptide maps, peptide molecular masses, LC retention time data, and sequence tags is an enormous... 

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