How to Read a Peptide Certificate of Analysis (Using Two of Ours)

A certificate of analysis is the one document that tells you whether a research peptide is actually what its label says. Most buyers glance at a purity number and stop there. That number matters, but on its own it is the easiest thing on the page to fake. This is a walkthrough of everything else, using two of our own lab reports as the examples so you can open the PDFs and follow along.

We will use two lots: a BPC-157 10 mg vial tested by BT Labs in West Palm Beach, Florida, and a Retatrutide 10 mg vial tested by Krause Analytical in Austin, Texas. Two independent labs, two different report layouts. If you can read both, you can read almost any COA you will come across.

A COA answers two separate questions

Purity and identity are not the same test, and a real certificate reports them separately.

Identity asks: is this molecule the one on the label? That is answered by mass spectrometry, which weighs the molecule. Purity asks: of everything in the vial's active fraction, how much is the target compound versus related impurities? That is answered by high-performance liquid chromatography (HPLC).

A report that gives you a purity percentage but never confirms identity has skipped half the job. You can have a 99% pure sample of the wrong peptide.

HPLC purity: what the percentage actually measures

HPLC pushes the dissolved sample through a column that separates compounds by how they interact with it. Each compound leaves the column at its own time, its retention time, and registers as a peak. The area under the target peak divided by the area of all peaks is the purity percentage.

On our BPC-157 report the HPLC purity reads 99.6%, against a specification of at least 98%. The target peak comes off at 4.055 minutes, and the chromatogram shows one clean peak with a flat baseline around it. That baseline is the part people skip. A high headline number sitting above a noisy baseline full of small unlabeled peaks is a very different thing from a genuinely clean trace.

The Retatrutide report, from the other lab, reads greater than 99.9% purity with the peak at 8.78 minutes. Different compound, different column conditions, different retention time, same logic.

Two things to check on any purity result: the wavelength it was read at (both of ours are measured at 220 nm, standard for peptide bonds) and whether the method is even named. "99%+" with no trace behind it is marketing, not data.

Mass spec: confirming it is the right molecule

The Retatrutide report lists Mass Spectral Match: ID Confirmed and prints the actual spectrum, with a base peak at 1586.1 m/z and the CAS number 2381089-83-2, retatrutide's registry number, right on the certificate. When the measured mass fingerprint lines up with the known compound, identity is confirmed. This is the test that catches a mislabeled or substituted peptide, and it is the one weak certificates leave out.

Potency and the excipient ratio: reading past the purity number

Here is where the two reports get interesting, and where most guides stop too early.

Purity is a percentage of the peptide fraction. Potency is how many milligrams of actual peptide are in the vial. They are different, and a vial can be highly pure but underfilled.

Our Retatrutide lot measured 9.97 mg against a 10 mg label, which is 99.7% of label: essentially exact. Our BPC-157 lot measured 12.2 mg of peptide against a 10 mg label, or 122.3%. That over-label reading is not an error; that lot was filled above its stated mass. Either way, the honest thing a potency test does is report the real number instead of trusting the sticker.

The BPC-157 report also lists a peptide-to-excipient ratio of 1:8.5: 12.2 mg of peptide alongside 103.8 mg of filler, for 116 mg total in the vial. Lyophilized peptides are almost always freeze-dried with a bulking agent, usually mannitol, so there is something visible to reconstitute; a few bare milligrams of peptide would be an invisible film on the glass. A filler ratio is normal and expected. What you are checking is that the report accounts for it honestly rather than hiding a light peptide fill behind a heavy total mass.

Red flags on a peptide COA

• No identity test. Purity without a mass-spec confirmation is half a certificate.
• No named method or wavelength. Real labs cite the method; both of ours reference USP monographs and HPLC-UV/MS.
• A number with no chromatogram. If you cannot see the actual trace, you are trusting a typed figure.
• The lab and the seller are the same entity. Independent means a third party ran it.
• A certificate that does not match the lot. It should correspond to the specific batch you are buying, not a generic sample from a year ago.

How to check ours

Every lot we stock has its own page with the full third-party report attached as a downloadable PDF: the same BT Labs and Krause Analytical documents quoted above, not a screenshot or a retyped summary. You can open the certificate, read the method, and see the chromatogram yourself. The lab, the date, the purity, the potency, and the identity confirmation are all there.

That is the point of publishing them per lot. You should not have to take our word for the number; you should be able to read the same document the lab issued.

*All products are supplied as laboratory reagents for research use only. Not for human or veterinary use. This article covers analytical methodology only.*