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Diagnostic Ions observed at the low end of an MS/MS or source CID spectrum which are used to give clues as to the presence of specific amino acid residues in a peptide sequence. | |
| Low Mass Ions Observed in Electrosapray Triple Quad MS/MS Spectra Reported by Don Hunt's Laboratory at the University of Virginia . | ||
| Amino Acid | Low Mass Ion |
Low mass marker ions will have this general structure
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| Pro (Arg, Asn) | 70 | |
| Val | 72 | |
| Lxx | 86 | |
| Met | 104 | |
| His | 110 | |
| Phe | 120 | |
| CMC | 134 | |
| Tyr | 136 | |
| Trp | 159 | |
| Lys y1 | 147 | Look at the low end of the spectrum for these y1 ions. If you have performed a trypsin digest then one of these ions should be present in the MS/MS fragmentation spectrum and this will reveal the C-terminal residue. Hint: The N-terminal b1 ion is never observed but often the b1 ion can be observed after acetylation of the peptide. |
| Arg y1 | 175 | |
