Molecular Weight
Molecular weight is the mass of one molecule of a compound, usually written in daltons (Da) or grams per mole (g/mol). It is a fixed number for any given molecule.
Where the word comes from
“Molecular” comes from the Latin molecula, meaning “a small mass” — a little piece of the larger Latin word moles, “mass.” So molecular weight is, at its root, the weight of a very small mass. The dalton (Da), the unit chemists use for it, is named after John Dalton, the English chemist who developed atomic theory in the early 1800s.
What it means here
Every peptide has a set molecular weight determined by its chain of amino acids. Labs use that number to confirm identity: when mass spectrometry measures a sample and the result matches the expected molecular weight, that match is evidence the vial holds the right compound. The number also appears on certificates of analysis and in the specification table on our product pages, alongside the sequence and CAS number.
Words you’ll see together
- Da (dalton) — the mass unit used for single molecules
- g/mol — the same number written as grams per mole
- molecular formula — the count of each kind of atom in the molecule
- sequence — the amino-acid order that fixes a peptide’s weight
Related terms
- Mass spectrometry — the lab method that measures a sample’s actual mass
- Amino acid — the building blocks whose sum sets a peptide’s molecular weight
- CAS number — another fixed identifier listed next to molecular weight
- Certificate of Analysis — the document where the measured value is reported
Where it appears in our catalog
- Reading a Certificate of Analysis — walks through the molecular-weight line on a COA
- BPC-157 — molecular weight listed in the product specification table
- Semax — same specification format, different peptide
References
- PubChem, National Library of Medicine — compound records listing computed molecular weight and identifiers: pubchem.ncbi.nlm.nih.gov
