How to Read a Peptide Certificate of Analysis (COA)

If you’ve ever ordered a research peptide and received a Certificate of Analysis alongside it, you’ll know the document can look more intimidating than it needs to. A wall of numbers, abbreviations, and testing methodology references that, without context, tells you very little. The COA is one of the most important documents in the peptide sourcing process, but only if you know what you’re actually looking at.

This guide breaks down what a COA is, what each section means, and what to do when something doesn’t look right. It’s written for researchers who want to move past taking a supplier’s word for it and start reading the evidence themselves.

What a Certificate of Analysis Actually Is

A Certificate of Analysis is a document produced by an independent third-party laboratory that verifies the identity, purity, and potency of a compound. The operative word is independent. A COA produced by the same facility that manufactures the product is not independent verification — it’s self-reporting, and it carries significantly less weight as a quality assurance document.

A legitimate COA comes from an accredited analytical laboratory that has no commercial relationship with the outcome of the test. The lab tests a sample of the product, runs it through one or more analytical methods, and reports what it found. What you’re looking at when you read a COA is the lab’s findings, not the supplier’s claims.

Northern Peptides publishes third-party COAs directly on product pages for compounds where results are available. You’ll find them linked on individual product listings — the BPC-157 page, the TB-500 page, and others carry them as results come through from the testing lab.

The Key Sections of a COA and What They Mean

Identity Confirmation

The first thing a COA should tell you is that the compound in the vial is actually what it claims to be. Identity testing typically uses mass spectrometry or another technique capable of confirming the molecular structure of the compound. If identity confirmation is absent from a COA, that’s a significant gap — purity data means very little if the compound hasn’t been confirmed as the right molecule in the first place.

Look for a clear statement that the compound’s molecular weight and sequence match the expected values for the peptide in question. Any deviation or asterisk here warrants follow-up.

Purity by HPLC

High-Performance Liquid Chromatography, almost always abbreviated to HPLC, is the standard method for measuring peptide purity. The technique separates the components of a sample and quantifies what percentage of the total is the target compound versus everything else. The result is expressed as a percentage.

For research-grade peptides, the accepted standard is 98% purity or above. A result below 98% doesn’t necessarily mean a product is unusable for all research contexts, but it does mean the remaining percentage is made up of impurities, degradation products, or synthesis byproducts whose presence should be accounted for in any experimental design. Anything below 95% is generally considered substandard for serious research purposes.

When reading the HPLC section, look for a chromatogram if one is included — this is the visual representation of the separation, showing the target compound as a dominant peak with smaller peaks representing everything else. A clean chromatogram with one dominant peak and minimal noise is what you want to see.

Water Content

Many COAs for lyophilised peptides include a water content measurement, typically expressed as a percentage by weight. This matters because peptide powders absorb moisture from the environment, and water weight contributes to the total mass of the product. A vial labelled as 10mg of peptide that contains 8% water actually contains somewhat less active compound than the label suggests, which has direct implications for accurate reconstitution and dosing in research settings.

Water content is measured by Karl Fischer titration in most laboratory settings. A figure below 6% is generally considered acceptable for lyophilised peptide powders.

Endotoxin Testing

Not all COAs include endotoxin data, but the ones that do are providing meaningfully more information than those that don’t. Endotoxins are bacterial cell wall fragments, specifically lipopolysaccharides, that can persist in a product even after the bacteria that produced them have been eliminated. They are a known contaminant risk in peptide manufacturing and can cause significant physiological responses at low concentrations.

Endotoxin levels are measured in Endotoxin Units per milligram (EU/mg). The acceptable threshold varies by application, but COAs reporting low or undetectable endotoxin levels represent a higher standard of manufacturing quality than those that don’t test for it at all.

What a COA Cannot Tell You

Understanding the limits of a COA is just as important as reading the data it contains. A COA tests a sample — it does not test every vial in a batch. Batch-to-batch consistency is a manufacturing question, not a testing question, and a COA from one batch does not guarantee the same results in the next.

A COA also cannot tell you how a product has been stored since it left the testing lab. Peptides are sensitive to temperature, light, and moisture. A product that tested at 99% purity at the time of manufacture may have degraded if the cold chain was broken during shipping or storage. This is why sourcing from suppliers with documented storage and fulfilment protocols matters alongside COA data.

Finally, a COA date matters. A certificate issued two years ago on a product being sold today is not current verification. Look for COA dates that correspond to recent production batches.

Red Flags to Watch For

When reviewing any COA, the following should prompt serious scrutiny before proceeding:

• No independent laboratory name or accreditation details listed
• Identity confirmation absent or vague
• HPLC purity below 95%
• COA date significantly older than the product batch date
• The document is produced by the supplier rather than a third-party lab
• No batch or lot number linking the COA to a specific production run

Any single one of these doesn’t automatically disqualify a product, but each one reduces your confidence in the data and should be investigated before the compound is used in any research context.

How to Use a COA Alongside the Peptide Mixing Calculator

Once you’ve confirmed the purity and water content of a compound, that data feeds directly into accurate reconstitution. If your compound has a water content of 7% and an HPLC purity of 98.5%, those figures affect the actual concentration of active peptide in your working solution. Northern Peptides’ Peptide Mixing Calculator is designed to support accurate reconstitution, and using it in conjunction with COA data gives you a more precise starting point than relying on label weight alone.

For researchers working across multiple compounds, cross-referencing COA data with the Shop All page and its linked certificates is a practical first step in any protocol design process. Compounds currently carrying published COAs include BPC-157, TB-500, GHK-Cu, Retatrutide, and KPV, with additional results being added as batches complete testing.

All products available through Northern Peptides are sold strictly for research purposes only. Nothing in this article constitutes medical advice, and no compound referenced here is approved by Health Canada for human therapeutic use. Researchers are responsible for ensuring their use of any compound complies with applicable laws and institutional guidelines.