Table 4.
Proposed MS/MS fragment motifs and their tentative structures associated with amino acid residues of small peptides in mass spectra from LC–MS with electrospray ionization in the positive mode (ESI+).
| Fragment m/z | Amino acid | Tentative fragment structure |
|---|---|---|
| 44.050 | (unspecific) | |
| 55.053 | valine | unknown |
| 56.049 | (unspecific) | |
| 60.044 | serine | side chain |
| 60.055 | arginine | guanidine group |
| 69.071 | leucine, isoleucine | branched hydrocarbon chain |
| 70.065 | (unspecific) | |
| 72.080 | valine | branched hydrocarbon chain |
| 74.057 | threonine | side chain |
| 84.080 | lysine, leucine, isoleucine | side chain |
| 86.095 | leucine, isoleucine | branched hydrocarbon chain |
| 101.072 | threonine | side chain |
| 110.071 | histidine | side chain |
| 116.070 | proline, arginine | molecular ion (proline) |
| 117.032 | valine | molecular ion |
| 120.078 | phenylalanine | side chain |
| 130.048 | glutamine | side chain |
| 136.078 | tyrosine | side chain |
| 147.077 | glutamine | molecular ion |
| 175.120 | arginine | molecular ion |