How to read a peptide certificate of analysis (COA)

A certificate of analysis (COA) is the lab report for one batch of a peptide. It tells you what the material is, how pure it is, and what else is in the vial. Here is how to read one, line by line, using our own certificates as examples. Every product page on our site shows its certificate, so you can follow along.

1. Check the certificate matches the batch

Start at the top. A COA should carry a certificate or batch number, a manufacture date and a report date. Our BPC-157 certificate, for example, is number 026-B81-TSX, manufactured on 21 September 2026 and reported on 26 September 2026.

A certificate only applies to the batch it names. If a supplier shows a COA with no batch number, or one that never changes from year to year, treat it with caution.

2. Product details: is it the right molecule?

The product details section identifies the compound:

  • Sequence: the amino acids in order. BPC-157, for instance, is Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val.
  • Molecular formula and weight: what the molecule should weigh, in grams per mole.
  • CAS number: a unique registry number for the substance.
  • Appearance: usually "white powder" for a lyophilised peptide. GHK-Cu is the exception: the copper makes it blue.

3. Purity (HPLC): how clean is it?

This is the number most people look for. HPLC (high-performance liquid chromatography) separates the sample into its components and measures what share of it is the target peptide. A result of 99.04% means 99.04% of what the instrument detected was BPC-157, and the rest was related impurities.

Next to the result you will see the specification: the minimum the batch had to reach to pass, often "≥ 98.0%". Check the result is above it. Across our current range, HPLC purity runs from 99.0% to 99.41%.

4. Identity (mass spectrometry): is it the right compound?

Purity tells you how clean a sample is. It doesn't prove the sample is the compound on the label. That is what mass spectrometry (MS, often written "MS (ESI)") is for: it weighs the molecule and checks the result matches the expected molecular weight. On a COA it usually reads "Conforms".

The strongest certificates show both: high purity by HPLC and identity confirmed by MS.

5. Peptide content and water content

These two lines confuse a lot of people, because they can look like they contradict the purity figure.

  • Peptide content (N%) is how much of the powder, by weight, is actually peptide. The rest is water and counter-ions such as acetate, left over from manufacture. Our certificates specify at least 80% for most peptides.
  • Water content (Karl Fischer) is the moisture left in the powder. Lower generally means a more stable product.
  • Acetate content is the counter-ion that pairs with the peptide during purification.

So a batch can be 99% pure and 85% peptide by weight at the same time. HPLC purity compares the peptide only with the other peptide-like material the instrument detects; water and acetate don't show up in it. Peptide content measures how much of the total weight is peptide at all.

6. Mass balance

Some certificates add a mass balance line, usually with a specification of 95.0–105.0%. It checks that peptide content, water and counter-ions add up to roughly the whole sample, so nothing large is unaccounted for.

7. Storage and re-test date

The batch information usually states storage conditions (for example "−20 °C, sealed and away from light") and a re-test date, after which the manufacturer recommends testing the batch again. Lyophilised peptides are most stable kept cold, dry and dark.

8. Results and units explained

Certificates mix several units, which is where a lot of confusion starts. Here is what each one means:

  • % (percent): used for HPLC purity, peptide content, water content and mass balance. Purity is a share of what the instrument detected; peptide content is a share of the total weight.
  • mg (milligrams): the amount of powder in the vial, such as 5mg or 10mg. This is the gross weight, which is why peptide content matters.
  • g/mol or Da (daltons): molecular weight. 1 Da is the same as 1 g/mol, so BPC-157 at 1419.53 g/mol has a mass of about 1419.5 Da.
  • m/z: the mass-to-charge ratio a mass spectrometer reads. A peptide can carry more than one charge, so you may see values such as [M+H]+ or [M+2H]2+, which are the molecular weight divided by the charge (plus the added protons).
  • Retention time (min): how long the peptide takes to pass through the HPLC column. It identifies the main peak on the chromatogram.
  • Conforms / Complies / Pass: the result met the specification printed beside it.

Red flags on a certificate

  • No batch or certificate number.
  • The same certificate shown for every batch, year after year.
  • A purity figure with no specification beside it.
  • No identity test of any kind.
  • A certificate you can't download or view in full.

See it for yourself

Every peptide we stock has its certificate on its product page, with the full PDF to download. Pick any product from our research peptides range and compare the lab results box with this guide.

All products sold by Absolute Peptides are for laboratory research use only. Not for human or veterinary use.

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