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Peptide Modification Mass Calculator
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The modification trail and elemental delta will appear here.
Modified molecular formula
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Methods and source records
These links document the calculation conventions or laboratory context. They do not validate a catalog lot or replace a controlled laboratory method.
- 01Technical source
PeptideMass post-translational modification syntax
SIB ExPASy. Documentation for expressing discrete peptide modifications alongside a one-letter sequence.
- 02Technical source
PeptideMass calculation documentation
SIB ExPASy. Technical notes covering average and monoisotopic masses and the limits of combined modification prediction.
- 03Technical source
Unimod 35: Oxidation
Elemental increment O; monoisotopic change +15.994915 Da. Selected methionine oxidation is a theoretical modification, not evidence it occurred.
- 04Technical source
Unimod 1: Acetyl
Elemental increment C2H2O; monoisotopic change +42.010565 Da. The base mass in this tool includes the chosen terminal groups.
- 05Technical source
Unimod 21: Phosphorylation
HPO3; +79.966331 Da. This implementation supports S/T/Y only, a deliberate subset of the source record. Source mapping checked 2026-09-10.
- 06Technical source
Unimod 2020: Disulfide
H(-2); −2.015650 Da per intrapeptide Cys pair. Each cysteine may be assigned to only one pair. Source mapping checked 2026-09-10.
- 07Technical source
Unimod 3: Biotin
C10H14N2O2S; +226.077598 Da. Supports lysine or a free N-terminus, without additional linker mass. Source mapping checked 2026-09-10.
- 08Technical source
Unimod 47: Palmitoyl
C16H30O; +238.229666 Da. Simplified compatible-site model: C/K/S/T or an explicitly selected free N-terminus; not a reaction prediction. Source mapping checked 2026-09-10.
- 09Technical source
Unimod 2: Amidation
H N O(-1); −0.984016 Da. C-terminal amidation is included in the base formula when selected. Source mapping checked 2026-09-10.
- 10Technical source
Unimod 28: N-terminal Gln → pyro-Glu
Loss of NH3; −17.026549 Da. Requires N-terminal Q and excludes simultaneous N-acetylation. Source mapping checked 2026-09-10.
- 11Technical source
Unimod 27: N-terminal Glu → pyro-Glu
Loss of H2O; −18.010565 Da. Requires N-terminal E and excludes simultaneous N-acetylation. Source mapping checked 2026-09-10.
- 12Technical source
Thermo Fisher: FITC reagent composition
C21H11NO5S; calculated monoisotopic increment +389.035794 Da for addition of the FITC reagent. This linked reagent record does not describe a supplied peptide batch. Source mapping checked 2026-09-10.
- 13Technical source
Thermo Fisher: amine-reactive FITC
The supported labeling model uses lysine side-chain or free N-terminal amines. Other derivatives and spacers require their own elemental increments. Source mapping checked 2026-09-10.
- 14Technical source
Sigma-Aldrich: polyethylene glycol
Repeat-only arithmetic uses C2H4O, +44.026215 Da per unit. It excludes end groups, conjugation losses and linkers; it is not the mass of a complete PEG reagent. Source mapping checked 2026-09-10.
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