A peptide certificate of analysis (COA) is the document that links a specific batch of material to the laboratory tests performed on it. Used well, it tells you whether the peptide in your vial is what the label says and how pure it is. Used carelessly – or accepted without question – it can give false reassurance. This guide walks through each part of a typical peptide certificate of analysis, explains the main test methods in plain English and lists the warning signs that a document deserves a closer look.
Research use only. This article is educational and describes compounds sold for laboratory research. It is not medical advice, and none of the products mentioned are intended for human or veterinary use.
What is a peptide certificate of analysis?
A certificate of analysis is a formal record of test results for a particular production batch (also called a lot). For peptides, it usually reports at least two things: identity – confirmation that the molecule is the intended sequence – and purity – the proportion of the material that is that molecule rather than related impurities. Because results apply to one batch only, a peptide certificate of analysis is only meaningful when its batch number matches the vial in front of you.
The header: product, batch and laboratory
Start at the top. A useful COA identifies:
- The product – compound name and, ideally, its sequence or molecular formula.
- The batch or lot number – which should match the product label.
- Dates – of manufacture and testing, and sometimes a retest date.
- The testing laboratory – its name and contact details, and whether testing was done in-house or by an independent laboratory.
- Sign-off – who reviewed and approved the results.
Identity: mass spectrometry
Identity is most often confirmed by mass spectrometry (MS). The instrument measures the mass of the molecules in the sample, and the result is compared with the theoretical mass calculated from the peptide’s sequence. For example, BPC-157 has a molecular weight of roughly 1,419 daltons. The observed value should match the theoretical value within the instrument’s stated tolerance. A peptide certificate of analysis that reports purity but no identity result tells you only that the sample is mostly one substance – not which substance it is.
Purity: HPLC
Purity is usually measured by high-performance liquid chromatography (HPLC), most often in reversed-phase mode. The sample is separated into its components, and a detector records each one as a peak on a chart called a chromatogram. Purity is reported as the area of the main peak as a percentage of the total peak area.
When reading the HPLC section, look for the chromatogram itself, not just a number. A single dominant peak with small minor peaks is what you would expect from a well-purified peptide. The method details – column, detection wavelength and gradient – show that a real analysis was run.
Purity is not the same as peptide content
This is one of the most misunderstood points on any peptide certificate of analysis. HPLC purity describes how much of the peptide-related material is the correct peptide. It does not account for non-peptide components such as water or counter-ions (for example trifluoroacetate or acetate salts left from synthesis and purification). Some COAs therefore also report net peptide content, the percentage of the total powder weight that is peptide. A material can be 99% pure by HPLC while having a net peptide content well below 100%.
Other tests you may see
Depending on the supplier and intended use, a COA may also list appearance, solubility, water content, counter-ion content, residual solvents, heavy metals or endotoxin results. Not every research-grade COA includes these, but where they appear they should show a method, a specification and a result.
Quick reference: reading each section
| Section | What it tells you | What to check |
|---|---|---|
| Header | Which batch was tested, when and by whom | Batch number matches your label; laboratory is identifiable |
| Mass spectrometry | Identity of the molecule | Observed mass matches theoretical mass |
| HPLC | Purity of the peptide-related material | Chromatogram shown; main peak dominant; method listed |
| Net peptide content | How much of the powder is peptide | Reported separately from purity |
| Sign-off | Accountability | Named reviewer and date |
Red flags on a peptide certificate of analysis
- No batch number, or a batch number that does not match the product.
- Purity stated as a bare number with no chromatogram or method.
- No identity test at all.
- The same document reused across many different batches or products.
- A testing laboratory that cannot be identified or contacted.
- Dates that are missing, inconsistent or later than the product’s arrival.
None of these automatically means the product is poor, but each is a reason to ask questions before relying on the material.
In-house versus third-party testing
Some COAs are produced by the manufacturer’s own laboratory; others by an independent laboratory. Independent testing adds a layer of separation between the seller and the result, and some independent laboratories offer a way to verify a report using a reference number. Whichever type you receive, the same reading principles apply.
Using COAs alongside good storage
A COA describes the material at the time of testing. Poor storage afterwards can still degrade it, which is why documentation and handling go together. Our guide on how to store peptides covers the storage side, and our introduction to research peptides explains the basics. You can browse labelled products in our peptide vials range; for documentation relating to a specific order, contact support@gentlemanpeps.com.
Frequently asked questions
What purity should a research peptide have?
Requirements depend on the application. What matters most is that purity is measured by a stated method, supported by a chromatogram, and that identity is confirmed separately.
Does a peptide certificate of analysis apply to every vial?
Only to vials from the batch it describes. Always match the batch number on the COA with the one on your product.
Why does my COA show purity and net peptide content as different numbers?
Because they measure different things. Purity compares the correct peptide with related impurities; net peptide content compares peptide with everything in the powder, including water and counter-ions.