Peptide molecular weight is typically calculated from the amino acid sequence and then confirmed using analytical instruments. In research settings, the reported value may be expressed as a theoretical mass or an observed mass from testing.
How it is determined
- Sequence-based calculation: The total residue mass is summed from the peptide sequence, with adjustments for terminal groups, modifications, and counterions where applicable.
- Mass spectrometry: LC-MS or MALDI-TOF is used to compare the measured mass against the expected molecular weight.
- Documentation review: A COA may list the calculated mass, observed mass, and any known modifications or salt forms that affect the final number.
Small differences between expected and observed values can occur because of isotopic patterns, adducts, oxidation, or incomplete desolvation. For laboratory purchasing, it is important to confirm whether the stated molecular weight refers to the free base, acetate salt, trifluoroacetate salt, or another form.
Products are intended for research use only and are not intended for human consumption.