What a 99% claim can hide
In 2024, Ashraf and colleagues (JAMA Network Open) ordered semaglutide from online sellers whose documents claimed at least 99% purity. Three of six orders arrived. LC-MS found semaglutide in all three samples at 7% to 14% purity, while the semaglutide content ran 29% to 39% above the labelled amount, and one sample carried endotoxin at 8.95 EU/mg. A follow-up paper from the same group (Journal of Medical Internet Research, 2024) reported endotoxin in all three vials.
The study makes two points about any peptide COA. A purity figure printed by a seller proves nothing until a laboratory you can identify stands behind it. And purity and content answer different questions, so a vial can fail one and overshoot the other.
Start with the lot number
A COA describes one batch. If its lot number differs from the lot printed on your vial, the document describes other material, made at another time and perhaps by another process.
A genuine report can still mislead through reuse: a seller assays one good batch and sends the same PDF with later orders. Ask for the certificate that matches the lot you will receive, and compare it with a second lot's certificate. Real assays vary from batch to batch. Identical figures across lots point to a template.
HPLC purity: area percent
Peptide purity testing on a COA uses high-performance liquid chromatography (HPLC). The column separates the components of the sample, and a UV detector draws them as peaks. Peptide labs detect in the low-UV range where the peptide bond absorbs; Bachem cites 220 nm. The purity figure is the target peak's area as a percentage of all integrated peak area.
Read the chromatogram as well as the number:
- One dominant peak on a flat baseline, with labelled axes, run time and detection wavelength.
- Small peaks beside the main one. In solid-phase synthesis these are often truncated or deletion sequences, chains with incomplete deprotection, or racemised residues. Their structures sit close to the target, so they can interfere with an assay in ways a distant impurity would not.
- Integration marks that match the visible peaks, and peak areas that add up to the stated purity.
Area percent is a relative measure. It tells you how much of the UV-absorbing material is the target peptide. It does not tell you how many milligrams the vial holds.
Mass spectrometry: is it the right molecule?
HPLC cannot name the main peak. Mass spectrometry (electrospray, MALDI-TOF or LC-MS) measures molecular mass, and a complete certificate prints the theoretical mass for the sequence next to the observed value.
For reference, the FDA labels give semaglutide a molecular weight of 4113.58 g/mol and tirzepatide 4813.53 Da. BPC-157 calculates to about 1419.5 Da from its sequence. Agreement within the instrument's tolerance supports identity. A gap of hundreds of daltons means a different molecule or a different form of it, such as a fragment sold under the full compound's name.
Mass spectrometry has a blind spot. A D-amino acid substituted for its L form has the same mass, so a mass match cannot exclude every isomer. Retention time against a reference standard covers part of that gap.
Peptide content, water and counter-ions
Net peptide content is the share of the powder's mass that is peptide. The rest consists of counter-ions left from synthesis and purification, trifluoroacetate or acetate, and residual water. Bachem measures it by amino acid analysis or by nitrogen elemental analysis; the second method works because counter-ions and water carry no nitrogen.
A vial labelled 10 mg can therefore hold less than 10 mg of peptide, depending on whether the label states gross powder mass or peptide mass. A certificate that reports content lets you do that conversion. A certificate without it leaves the peptide fraction unmeasured.
Water content by Karl Fischer titration appears on more thorough reports. Bachem notes that lyophilised peptides take up moisture and that absorbed water lowers both content and stability.
Other tests and what a blank means
Some certificates add bacterial endotoxin, reported in EU/mg, and residual solvents by gas chromatography. If a field is blank or absent, the laboratory did not test it. Treat a blank as untested rather than clean.
Signs of a fake COA
- No named laboratory, or a laboratory you cannot find anywhere outside the seller's own site.
- A purity percentage with no chromatogram, or an identity claim with no mass spectrum.
- A missing lot number, or one that does not match the vial.
- Figures identical across batches, or the same chromatogram image attached to different products.
- No way to confirm the report with the issuing lab. Some independent labs let you check a report on their own website with a code; others confirm by email if you quote the report number.
- Purity stated as exactly 100%. That figure means the lab integrated the main peak and nothing else, which deserves a question.
If a report fails one of these checks, contact the named laboratory before you rely on it.
Checking an Encodex vial
An independent laboratory assays every Encodex lot, by HPLC for purity and by mass spectrometry for identity. The certificate for the lot printed on your vial is available on request, and the /verify page confirms a lot when you enter its number. If you are comparing suppliers, ask each one for the certificate matching a specific lot number before you order.
For research use only. Everything above describes laboratory practice and published research. It is not medical advice, not dosing guidance, and carries no implication of human or veterinary use.