Almost every research peptide sold in the UK comes with a Certificate of Analysis, and almost nobody reads it properly. A COA is the only objective evidence you have that the vial contains what the label says. It is also easy to fake, easy to recycle across batches, and easy to misunderstand. This guide explains what each section of a peptide COA actually tells you, what it does not, and how to spot a certificate that is not worth the PDF it is printed on.
Important: Research peptides are not licensed medicines. A COA describes chemical identity and purity for laboratory purposes. It is not a safety assessment and says nothing about suitability for any use outside in-vitro research.
What a Certificate of Analysis Is
A COA is a document issued by a testing laboratory that records the results of specified analytical tests on a specific batch of material. For synthetic peptides the two tests that matter are:
- HPLC (high-performance liquid chromatography) for purity
- Mass spectrometry (usually LC-MS or ESI-MS) for identity
A good COA answers two questions: is this the molecule it claims to be? and how much of the sample is that molecule rather than something else? Everything else on the certificate is context that lets you check those two answers are trustworthy.
Section by Section
1. Product name and sequence
The certificate should name the peptide and, ideally, give its amino-acid sequence and molecular formula. For a compound like BPC-157 the sequence is published and can be checked. For blends, each component should be listed separately with its own results.
2. Batch or lot number
This is the single most important line on the document. The batch number on the COA must match the batch number on the vial label. A COA without a batch number, or with a number that does not appear on the product you received, is a generic template and tells you nothing about your material.
3. Testing laboratory and date
The certificate should identify who ran the tests and when. Independent third-party testing carries more weight than in-house results, though many synthesis labs run credible in-house QC. A test date more than a year or two before your purchase is a reason to ask whether the material has been re-tested or stored appropriately.
4. HPLC purity
Reverse-phase HPLC separates the components of a sample by how strongly they interact with a column, then measures each as it elutes, typically by UV absorbance at 214 or 220 nm where the peptide backbone absorbs. The result is a chromatogram: a trace with peaks. The purity figure is the area of the main peak expressed as a percentage of the total area of all peaks.
Three things to check:
- The chromatogram is present. A purity number with no trace behind it cannot be evaluated. You should be able to see the main peak, the baseline and any minor peaks.
- The method is stated. Column type, gradient, flow rate and detection wavelength. Different methods resolve impurities differently, and a lazy method can hide them.
- The number is plausible. Synthetic peptide purity of 95 to 99 percent is typical for research grade. Figures of 99.9 percent or higher on longer peptides, with no visible minor peaks, deserve scepticism rather than confidence.
5. Mass spectrometry identity
Mass spec measures the mass-to-charge ratio of ions produced from the sample. For a peptide, the certificate will show a theoretical (calculated) molecular weight and an observed one. They should agree closely, usually within a fraction of a Dalton on modern instruments. For larger peptides you may see multiply charged species, for example the same molecule detected at [M+2H]2+ and [M+3H]3+, which is normal.
This test confirms the molecule is the right size, which is strong evidence it is the right molecule. It does not confirm purity; that is what HPLC is for. A COA that reports mass spec alone has told you what the main component is but not how much of the sample it represents.
6. Appearance and solubility
Usually a one-line description: white lyophilised powder, soluble in water or a stated solvent. Useful as a sanity check against what you received.
What a Standard COA Does Not Measure
This is where most misreading happens. "98 percent pure by HPLC" is often taken to mean 98 percent of the vial's mass is peptide. It does not.
Net peptide content
Lyophilised peptides contain bound water and counter-ions, most commonly trifluoroacetate (TFA) left over from purification, or acetate if the supplier has exchanged it. These can account for 10 to 30 percent of the gross weight. HPLC purity measures the peptide fraction relative to other UV-absorbing impurities; it says nothing about how much of the powder is peptide versus salt and water. Net peptide content requires a separate assay (amino-acid analysis or nitrogen determination) and is rarely reported on research-grade COAs. When it is, that is a mark of a serious supplier.
Sterility and endotoxin
Standard peptide COAs do not test for microbial contamination or bacterial endotoxin. Research-grade material is not manufactured under sterile conditions and is not represented as sterile. If a certificate claims sterility, look for the method (typically USP 71 for sterility and LAL testing for endotoxin) and the lab that performed it.
Residual solvents and heavy metals
Not usually reported at research grade. Pharmaceutical-grade material would include them.
Biological activity
A COA confirms chemistry, not function. Correct mass and high purity do not demonstrate that a peptide is folded correctly or biologically active. That requires a functional assay, which is outside the scope of a supplier COA.
Red Flags
- No batch number, or a batch number that does not match the vial.
- Identical COAs across different products or batches. Compare the chromatograms. Genuine traces are never pixel-identical.
- A purity figure with no chromatogram.
- No testing lab named, or a lab that cannot be found.
- Round-number purity such as 99.9 or 100 percent.
- Observed mass that differs from theoretical by more than a Dalton or two, or a mass spec section that simply repeats the theoretical value without an observed one.
- Claims of sterility or endotoxin testing with no method stated.
- A COA supplied only as a low-resolution image where the batch number and trace cannot be read.
A Quick Checklist
| Check | What good looks like |
|---|---|
| Batch number | Present, matches the vial label |
| Testing lab | Named, with test date |
| HPLC purity | Figure plus visible chromatogram plus stated method |
| Mass spec | Theoretical and observed mass, close agreement |
| Sequence | Stated and matches the published sequence |
| Counter-ion | Stated (TFA or acetate) if the supplier knows it |
| Sterility / endotoxin | Either not claimed, or claimed with a method |
Frequently Asked Questions
Is 98 percent purity good for a research peptide?
Yes. Research-grade synthetic peptides are typically supplied at 95 to 99 percent purity by HPLC. Higher figures are possible for short peptides but become less plausible as chain length increases.
What is the difference between purity and net peptide content?
Purity is the proportion of the peptide fraction that is the target molecule, measured by HPLC. Net peptide content is the proportion of the total powder weight that is peptide rather than water and counter-ions. A sample can be 98 percent pure and 75 percent net peptide content at the same time.
Does a COA prove a product is safe?
No. A COA describes chemical identity and purity. It does not assess toxicity, sterility, or suitability for any use, and research peptides are not licensed for use in humans.
Should I trust in-house COAs?
In-house QC from a synthesis lab can be entirely credible, but independent third-party testing removes the conflict of interest. If a supplier only provides in-house results, ask whether third-party testing is available for the batch.
Can I request the COA before buying?
A reputable supplier will provide the current batch COA on request. Reluctance to do so is itself a data point.
This article is for informational purposes only. It does not constitute medical, legal or professional advice. Research peptides are sold for in-vitro laboratory use and are not licensed for human use.
