Charge precursors

Figure 6.15. Product ion spectrum of the doubly-charged precursor (550.1 Th) of the same peptide as shown in Fig. 6.14.

Short examination of the fragment ion spectrum from a singly charged precursor is not particularly helpful. Some previously found mass shifts can be verified but no peaks with m/z lower than 800 Th can be assigned. Detailed peak annotation is presented in Fig. 6.16. 

Figure 6.16. Annotated product ion spectra from Fig. 6.14—singly-charged precursor.

Figure 6.18. Annotated product ion spectra, doubly charged precursor.

The third idea is focused on finding the reverse ion series that might cover some additional amino acids. Masses of b-ions and y-ions emerging from the cleavage of the same bond add to the mass of the whole precursor increased by 1 Da. If the peptide is 10 AA long, the sum of masses of, for example, b8 and y2 ions is equal to the mass of the singly charged precursor +1 Da. This additional dalton is because... 

Fig. 1.45 Example of a 2D nano LC-MS/MS analysis of a C elegans extract. (A) Fraction 2, 4 mM KCI salt elution on the strong cation exchange column. (B) Full scan MS spectrum of the peak eluting at RT 26.3 min in (A). (C) product ion spectrum of the doubly charged precursor of (B) at m/z 784.8. Y fragments are typical for C-terminal fragments while b ions are typical for N-terminal fragments.

Approximately 80 pL of the remaining diluted HPLC fraction was subsequently subjected to mPC-CE-MS/MS. The doubly charged precursor ion at m/z 503.6 was subjected to collision induced dissociation and the resulting product ion spectrum (Figure 4) revealed a series of y and b ions. Interpretation of these ion series indicated a sequence of XSFKFDHX (where X is either 1 or L). The spectral data was also searched and interpreted using the Sequest database routine developed by Yates (17),... 

Figure 3. Off-line CE-nES/MS/MS of both the doubly and triply-charged precursor ions of angiotensin-1.

It is widely accepted that current ETD generally favors multiply charged precursor ions and is not effective for ions exceeding m/z 1400 or Multiply charged glycopeptides at miz above this range when acted on... 

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