A peptide is a molecule in which amino-acid residues are joined by amide (peptide) bonds. The repeating backbone is -NH-CHR-CO-. Identity is therefore a sequence problem, not a marketing category. Two materials with similar purity values are not interchangeable if the residue order, termini, or salt form differ.
Sequence and termini
Residues are written from the N-terminus to the C-terminus. A complete identity line states the residue sequence or an accepted fragment name; whether termini are free, acetylated, amidated, or otherwise capped; the intended salt or counter-ion if the material is supplied as a salt; and the catalog code that must reappear on the COA and the container label.
Omitting the terminus is a common source of receiving errors. An amidated C-terminus is a different chemical entity from the free acid. Acetylation of the N-terminus is likewise a different entity from the free amine.
Length classes
Oligopeptides (short, discrete sequences) and polypeptide hydrolysates are both called peptides in commerce. They are not the same analytical object. A discrete sequence should behave as a single principal species on reverse-phase HPLC and should be confirmable by mass spectrometry. A hydrolysate is a distribution of chain lengths and requires a different specification language, such as average molecular weight or degree of hydrolysis, not a single-sequence identity.
What a catalog name is allowed to do
A name is a pointer to a structure. If the supplier uses a trade name, the specification must still resolve it to a sequence or a defined fragment. If it cannot, the quote is incomplete.
Receiving implication
Before comparing price, match sequence, termini, and catalog code across the quotation, the COA, and the vial. Purity is evaluated only after identity matches.
Research-use and professional buyer information only. This note is not medical advice and does not describe personal use.