How to Read a Peptide Certificate of Analysis (COA)
A peptide Certificate of Analysis (COA) is the analytical record that accompanies a specific manufactured batch of a research compound, documenting what the material was found to be and how pure it was when tested. The two results that matter most are the HPLC purity figure, which estimates how much of the sample is the target peptide versus everything else, and the mass spectrometry result, which confirms the molecular identity of that target. A COA is only meaningful when it is dated, tied to a named lot number, attributed to an identifiable testing laboratory, and matched to the batch actually shipped.
What a COA is, and what it is not
A Certificate of Analysis is a snapshot of one sample drawn from one batch at one point in time. It reports measurements, not guarantees about every vial in that batch forever: a COA certifies the tested sample, and is only as representative as the sampling and the batch control behind it.
A COA is also not a safety assessment, an approval, or an endorsement of any application. It is an analytical document produced for materials handled in a laboratory setting under research-use-only terms. Peptides sold for research are not evaluated as medicines, and nothing on a COA changes that status.
The identification block: read this first
Before looking at any chromatogram, confirm the document is about the material in front of you. A usable identification block carries the product name, the peptide sequence in single-letter or three-letter amino acid code, the molecular formula, the theoretical molecular weight, the batch or lot number, the manufacture or analysis date, and the quantity per vial.
The sequence is worth reading rather than skimming. Two compounds can share a marketing name and differ in a terminal modification, such as an amidated C-terminus, and such modifications shift the expected molecular weight. If the sequence does not match what the product page describes, resolve that discrepancy before trusting anything else on the document.
HPLC purity: what the number actually measures
High-performance liquid chromatography, normally reverse-phase HPLC for peptides, separates the components of a sample as they travel through a column. Compounds that interact more strongly with the stationary phase move more slowly, so each component leaves the column at its own retention time and registers as a peak on the detector trace.
The purity percentage on a COA is almost always an area-normalization figure: the area under the main peak divided by the total area of all integrated peaks, expressed as a percentage. A result reported as 99.2 percent means the main peak accounted for 99.2 percent of the total detected peak area under those specific conditions.
Several details on the chromatogram page tell you how much weight that number deserves:
- Detection wavelength. Peptide analysis commonly uses UV detection at roughly 214 to 220 nanometres, where the peptide bond itself absorbs. Detection at 254 nanometres will under-report peptides lacking aromatic residues.
- Gradient and run time. A gradient that is too steep or a run that ends too early can hide closely eluting impurities, including deletion sequences that differ from the target by a single residue.
- Baseline quality. A drifting or noisy baseline makes integration subjective, and integration choices move the reported percentage.
- Visible minor peaks. Small peaks are normal in synthetic peptides. Their presence is not a defect; their absence on a trace that looks unnaturally flat is more suspicious than a few honest shoulders.
The mass spectrometry trace: confirming identity
HPLC tells you how much of the sample is one dominant species. It does not tell you that the dominant species is the intended peptide. Mass spectrometry answers that question by measuring the mass-to-charge ratio of ionized molecules.
Most peptide COAs use electrospray ionization (ESI-MS) or matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). The report should state the theoretical molecular weight calculated from the sequence and the observed molecular weight found by the instrument, and the two should agree within the resolution of the method.
Electrospray spectra often show a series of multiply charged ions rather than one clean peak, which is expected behaviour rather than evidence of contamination. What deserves attention is a systematic offset between observed and theoretical mass, since a consistent difference can indicate an unintended modification or a different compound entirely.
Supporting tests you may see
Not every COA includes these, and their absence is not automatically a problem, but their presence signals a more complete analytical package.
| Test | What it reports | Why it matters |
|---|---|---|
| Water content (Karl Fischer) | Residual moisture in the lyophilized solid | Moisture affects mass accuracy and solid-state stability |
| Peptide content | Proportion of the vial mass that is peptide rather than salts and water | A 99 percent pure peptide can still be well under 99 percent of the vial weight |
| Counter-ion content | Acetate or trifluoroacetate associated with the peptide | Explains discrepancies between net peptide and gross weight |
The distinction between purity and peptide content catches people out regularly. Purity describes the composition of the peptide fraction. Peptide content describes how much of the powder in the vial is peptide at all. Both are legitimate measurements of different things.
What an acceptable specification looks like
For research peptides, a purity specification of 98 percent or higher by HPLC is a common benchmark, and specifications of 99 percent or higher are widely used for well-characterized sequences. True Form Peptides supplies products to a 99 percent or higher HPLC purity specification, and batch COAs are published on many product pages.
A specification and a result are different entries. The specification is the acceptance criterion; the result is what the batch measured. A well-formed COA shows both, with a pass or fail determination, rather than a single unlabelled number.
Red flags
The following patterns should prompt questions before a batch is accepted into inventory:
- No date. An undated COA cannot be tied to a production run or evaluated for age.
- No lot or batch number. Without it, the document cannot be matched to any physical vial.
- Lot mismatch. The lot printed on the vial label differs from the lot on the COA. This is the most common and most consequential failure.
- No testing laboratory named. An analytical report with no identifiable analyst or facility cannot be followed up or independently confirmed.
- Numbers without traces. A summary table quoting 99.6 percent with no chromatogram and no spectrum is an assertion, not a measurement.
- Illegible or cropped chromatograms. Missing axes, missing retention times, or images cropped so the baseline cannot be seen prevent any independent reading.
- Identical documents across lots. If several lots share a chromatogram with pixel-identical noise, one report is being reused.
- Sequence or molecular weight that does not match the product. The identification block should be internally consistent.
- Therapeutic or outcome language. An analytical document describes measurements. Claims about effects do not belong on one.
Matching the COA to the batch you received
Reading a COA well is a two-document exercise. Put the vial label next to the certificate and confirm that the product name, the lot number, and the stated quantity agree. Check that the analysis date precedes the shipping date in a way that makes sense. If a vendor publishes COAs by lot, confirm that the published document is the one for your lot rather than a generic sample.
Where a supplier cannot produce a lot-specific document, ask for the report covering the batch shipped, including the underlying chromatogram and spectrum rather than a summary page. This is discussed further in Third-Party Peptide Testing: Independent Labs and Why Batch Testing Matters.
Recording and retaining COAs
Store the certificate with the inventory record for the batch, and reference the lot number in any notebook entry involving that material. When a vial is opened for laboratory work, carry the lot number onto the working label so results remain traceable months later. Labelling practice is covered in Lyophilized Peptides: Reconstitution, Storage and Handling in the Lab.
Comparing COAs across related sequences is also informative when evaluating compounds frequently studied alongside one another, a point touched on in BPC-157 vs TB-500: What the Research Literature Actually Says.
Research use only
All materials discussed here are supplied strictly for laboratory research use by qualified professionals. They are not drugs, foods, cosmetics, or medical devices, and they are not intended for human or veterinary use, diagnostic use, or any form of administration. Nothing in this article constitutes medical advice or a recommendation for use.