Reading a Peptide Certificate of Analysis, Line by Line
Every research peptide should arrive with a paper trail, and the Certificate of Analysis (CoA) sits at the centre of it. It records what a testing laboratory found when it analysed one particular batch. Without it, you have no direct way to check that the powder in the vial is the compound on the label.
Below we go through the sections a typical peptide CoA contains, explain what each test measures, and list the signs that separate a careful report from one that is mostly decoration.
On this page
What a CoA is, and what it is not
A CoA is an analytical report for a single production lot, signed off by the lab that ran the tests. It is specific by design: it names one batch by its lot number and gives the date the testing took place. It is not a brochure. When a seller attaches an identical certificate to every order of a product, treat that as a warning.
Reports carry the most weight when they come from an independent, third-party laboratory, meaning a lab that earns nothing from the sale. A seller grading its own stock has an obvious conflict of interest. An outside lab takes that conflict away.
Section by section
Layouts differ from lab to lab, but the core content is much the same. Here is what each part tells you.
Product name and lot number
Everything else on the page hangs on the lot, or batch, number. It has to be identical to the number on your vial. If the two differ, the report is about some other material, not yours.
HPLC purity
HPLC, short for High-Performance Liquid Chromatography, pulls the target peptide apart from everything else in the sample and expresses purity as a percentage. Research-grade material usually reads 98–99%+. A solid report attaches the chromatogram itself: a plot with one tall main peak and only small traces around it. A bare percentage with no plot behind it is far weaker evidence.
Mass spectrometry (identity)
HPLC says how clean a sample is. It says nothing about which molecule it is. Mass spectrometry fills that gap by weighing the molecule. The measured mass should land within a narrow tolerance of the mass calculated for the intended peptide. A purity result with no identity result answers only one of the two questions.
Appearance and net peptide content
Appearance records the physical form, which for most peptides is a white freeze-dried (lyophilized) powder. Net peptide content, sometimes called peptide loading, gives the share of the vial's contents that is peptide rather than leftover salts and moisture. It often comes in below the gross fill weight, and it matters whenever a study needs precise amounts.
Endotoxin / LAL and sterility
The LAL assay checks for bacterial toxins called endotoxins and reports them in endotoxin units per milligram (EU/mg). The smaller the number, the better. Contamination is a leading cause of unreliable results in sensitive cell-culture work, so a certificate that adds endotoxin and sterility data protects you better than one that leaves them out.
Water content and date of analysis
Residual moisture, commonly measured by Karl Fischer titration, influences how stable the powder is. The analysis date shows how recently the batch was characterised.
Signs of a weak or invented CoA
- No laboratory listed. If the issuer is not named, nobody can check the report.
- Figures without plots. A line reading "99% pure", with neither a chromatogram nor a mass spectrum behind it, is a claim rather than proof.
- The same CoA for every lot. Real certificates belong to one batch. A recycled report should make you cautious.
- Lot numbers that disagree. When the vial and the report show different numbers, the report tells you nothing about your material.
- No identity test at all. A purity figure on its own cannot show that you received the peptide you ordered.
Checking the certificate against the vial
When a parcel arrives, a one-minute check is worth the time. Compare the lot number on the vial with the one on the certificate. Make sure the product name and quantity agree with your order. Then check that the purity and identity figures match the specification you were expecting. Labelling and packing mistakes get caught here, before they can find their way into your data.
Certificates at NordPeps
Certificates from an independent third-party laboratory are published per batch on our certificates page as they become available, so you can compare each one with the lot number on your vial. The way we approach testing is described on the quality page.
Common questions
Purity versus identity: what is the difference on a CoA?
Purity, measured by HPLC, is the share of the sample that is the target compound rather than impurities. Identity, measured by mass spectrometry, shows that the sample is the peptide that was ordered. A complete certificate gives both results.
Does it matter whether the CoA comes from a third-party lab?
Yes. A lab with no stake in the sale has no reason to flatter the result. That independence removes the conflict of interest that arises when a seller tests its own stock, which makes third-party reports the strongest kind.
What is EU/mg on a certificate?
It stands for endotoxin units per milligram. It is the output of the LAL endotoxin test and measures contamination by bacterial toxins. Lower is better, and it matters most in sensitive cell-culture research.