"99% pure" is a typography choice
The purity percentage on a peptide label is typically asserted, not measured — one test-purchase study found peptide content of 7.7-14.4% against a printed 99%.
A chromatogram showing one clean peak, and "99% pure" on the label.
The peptide is a small fraction of what's actually in the vial.
- Ask for purity AND peptide content as two separate figures, not one number standing in for both.
- Request the chromatogram itself, with method, column, date and lab name, not just the percentage.
- Match the lot number on any certificate to the lot printed on your vial before trusting either.
WHY WE SAY THIS
Purity is the spec buyers rank sellers by, and the one they can't check without a lab. A peer-reviewed study bought semaglutide from three sellers and ran LC-MS: each chromatogram showed one clean signal, yet peptide mass was only 7.7%, 8.97% and 14.37% of vial powder — all three labelled 99%. A vial can be chromatographically clean and still be mostly something else by weight; purity and content differ, and stating only one picks the flattering one.
PROVENANCEPeer-reviewed LC-MS on product bought through a real buyer's ordering path (JMIR 2024). Three vials, one compound, one point in time — not a market rate.