Electrospray different charge state

Electrospray is unusual in that it produces almost exclusively multiply charged ions in a variety of different charge states. The way in which the molecular weight of an analyte may be calculated has been derived. In addition, the appearance of an electrospray spectrum may vary considerably with the conditions in the solution from which it has been generated. Eor this reason, the mechanisms leading to the production of ions using this technique have been described at some length. 

Figure 11.6 Positive ion electrospray mass spectra of an equimolar mixture of five standard proteins, under different instrumental settings, showing cases where prominent signals for the different charge states of (A) insulin, (B) ubiquitin, (C) cytochrome c, (D) lysozyme, and (E) myoglobin were preferentially observed, and (F) where signals for all the proteins were more uniformly detected.

The molecular weight of the peptide is deduced from its electrospray spectrum (Figure 9.2A). If we suppose that the observed peaks in this spectrum correspond to different charge state of the peptide, than we can calculate the number of charges z for the peak detected at m. z = j(mi - l)/( i2 -m i) where j corresponds to the number of peaks +1 separating m and m2 z has to be rounded to the nearest integer. The molecular weight is then M = zi(m - 1). 

Field desorption (FD) and fast atom bombardment (FAB) mass spectrometry provides mass spectral information about compotmds that are not very volatile but these two techniques are not used often in polymer science since they have several disadvantages. Electrospray ionization (ESI) mass spectrometry can also be used to obtain the above information about polymers, but ESI spectra are generally complicated due to differences in charge state distributions. Static secondary ion mass spectrometry (static SIMS) is a surface-sensitive MS technique, which is suitable for studying the interfaces of polymers with respect to chemical structure and molecular weight as well as end groups and surface contaminants. Laser desorption... 

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