Theoretical molecular weight is calculated from a defined sequence and terminal chemistry. Counterions, hydration, adducts, isotopic conventions and charge states can alter what appears in calculations, mass spectra and weighed material.
What procurement and laboratory teams should review
Declare average or monoisotopic mass where the distinction matters
Confirm N- and C-terminal chemistry and modifications
Interpret MS charge states and adducts using the method context
Do not use gross vial mass as molecular identity evidence
Define the molecular form before comparing offers
Sequence alone may not fully define a peptide material. Termini, modifications, disulfide pattern, counterion, hydration state and presentation can affect molecular-weight calculations, analytical reporting, solubility and handling.
- Record sequence, termini and every modification explicitly.
- State the requested salt or counterion form.
- Treat solubility and stability as material- and condition-specific.
Questions to resolve before quotation or release
- Which molecular formula and terminal groups were used?
- Does the theoretical mass exclude counterions?
- How was the MS result deconvoluted or assigned?
Technical review should align sequence, modification, salt form and mass calculation before the analytical result is evaluated.
Source material and further reading
This guide is informed by the following primary guidance and established technical resources. Always confirm the current version and its applicability to your material and jurisdiction.
HK PEPTIDES materials are supplied for laboratory research and documentation workflows only. They are not intended for human consumption, diagnostic use, therapeutic use, veterinary use or clinical application.