How to read a peptide spec sheet: formula, molar mass, purity

A peptide specification sheet condenses everything you need to identify and work with a compound onto a single page of numbers and codes. Reading it quickly is a basic laboratory skill. Here are the fields that matter most and what each one tells you.

Molecular formula

The molecular formula — a string such as C₄₅H₇₃N₁₃O₁₀ — lists the exact atomic composition of the peptide and is the ground truth for its identity. Salt forms are sometimes shown separately, because a trifluoroacetate or acetate counterion adds its own atoms.

Molar mass

Molar mass, or molecular weight, is given in grams per mole and lets you convert between mass and moles. Spec sheets usually quote the average mass, while a mass spectrometer reports the monoisotopic mass; the two differ slightly, so know which you are reading when comparing a certificate of analysis to an MS trace.

Purity

Purity is typically expressed as an HPLC area percentage, for example ≥98%, reflecting the proportion of target peptide relative to related impurities. Our article on how peptide purity is measured explains how that number is generated.

Sequence and modifications

The sequence appears in one- or three-letter amino acid code. Modifications such as N-terminal acetylation, C-terminal amidation or cyclisation are noted here, because each one changes the mass and behaviour of the molecule.

Salt form and net content

Finally, note the counterion and the net peptide content — the fraction of the vial's mass that is actually peptide rather than salt or residual water. This matters for accurate work. Every Vela order includes a free 3 mL bacteriostatic water vial; see our reconstitution guide for the calculation.