How to Read a Peptide COA: UK Buyer's Checklist

The short answer: a certificate of analysis (COA) is a laboratory report for a single batch of peptide. Start with the lot number and make sure it matches the vial. Next, check which laboratory analysed the sample, on what date, and whether you can verify the report with them. Then look for an identity result, normally mass spectrometry, before reading purity and content as two separate figures.

Why does a COA matter when buying research peptides in the UK?

Research peptides sold for laboratory use are not supplied as licensed medicines, so there is no marketing authorisation or product licence sitting behind the vial. In practice the COA is the main piece of evidence a supplier can offer about what a batch contains. That makes it worth reading properly rather than skimming it.

The trouble is that research COAs have no standard layout. One laboratory will send a one-line table; another will include the full chromatogram, mass spectrum and method summary. The checklist below works for either.

What should you check first on a peptide COA?

Lot number. It must match the label on your vial. If it does not, the report describes someone else’s batch.
Laboratory and verification route. A named laboratory with contact details, and ideally a unique key or QR code you can check on the lab’s own website.
Dates. Sample received and report issued. Older reports are not wrong, but they are a snapshot of the batch at that point.
Identity. A stated method and a confirmed match to the expected compound.
Purity. A percentage with the method named, ideally with the chromatogram attached.
Content. The measured amount of compound in the vial, reported separately from purity.

What is the difference between identity, purity and content?

Identity answers “is this the right molecule?” Mass spectrometry does this by measuring the mass-to-charge ratio of ions and comparing it with the expected molecular weight. Peptides often carry several extra protons in the spectrum, so the peak you see can sit at a fraction of the full mass. A published analysis of semaglutide, for instance, identified it by a characteristic peak at 1029.3 for the [M+4H]4+ ion (Ashraf et al., Journal of Medical Internet Research, 2024).

Purity answers “how much of what the detector saw was the main compound?” In HPLC it is usually the main peak’s area as a share of total integrated area. It cannot confirm identity, and it does not detect water, salts or endotoxin.

Content answers “how many milligrams are actually in the vial?” Because lyophilised peptides often contain counterions and residual moisture, content and purity rarely line up neatly.

A handy cross-check for identity is a public reference record. PubChem’s entry for BPC-157 (CID 9941957), for example, gives a molecular formula of C62H98N16O22 and a molecular weight of 1419.5 g/mol.

How much do small impurity peaks matter?

More than a headline percentage suggests. For regulated generic peptide medicines, an FDA Office of Pharmaceutical Quality presentation sets out the expectation that each peptide-related impurity at 0.10% or above is identified, and that no new peptide-related impurity exceeds 0.5%, using orthogonal chromatographic methods and high-resolution mass spectrometry. Research COAs are not held to that standard, but it is a useful reminder that a 1% gap can still contain several distinct side products.

What the evidence actually shows

Claimed versus measured. In Ashraf et al. (2024), researchers ordered from 6 online sellers; 3 lyophilised semaglutide vials arrived and each was analysed by LC-MS, pharmacopoeial sterility testing and a kinetic turbidimetric LAL endotoxin method, alongside a genuine reference product. Documentation claimed purity of at least 99%. The laboratory measured 7.70%, 8.97% and 14.37%. Measured content, by contrast, was 28.56% to 38.69% above the label. Endotoxin was found in all three samples, at up to 8.95 EU/mg; none contained viable micro-organisms. For anyone reading a COA, the point is that “more than labelled” and “pure” are separate questions.

Why the salt form is worth noticing. Cornish et al. (1999) examined trifluoroacetate (TFA), the counterion left behind by reversed-phase HPLC purification, in fetal rat osteoblast cultures, articular chondrocytes and neonatal mouse calvariae. At 10^-8 to 10^-7 M over 24 hours, TFA was associated with lower cell numbers and thymidine incorporation, and the TFA salts of amylin, amylin-(1-8) and calcitonin gave consistently lower proliferation readouts than the hydrochloride salts. The authors suggested this is relevant to cell work with purified peptides above 10^-9 M.

Endotoxin needs its own test. Neither HPLC nor mass spectrometry measures it. The FDA’s Pyrogen and Endotoxins Testing Q&A covers the gel-clot, photometric and kinetic methods used for it.

How this relates to research materials from ETHOS UK

A COA records the batch on the day it was analysed; storage looks after it afterwards. Research peptides are normally kept sealed at −20 °C, away from light and moisture.

ETHOS runs separate US and UK shops under one brand and one standard. Every batch is 8X tested, meaning eight different tests, before it ships, and batch COAs are searchable by lot number on the ETHOS public COA portal, which you can also reach from the ETHOS UK COA page. To see how a listing presents its reference identifiers, have a look at the BPC-157 listing on the UK shop or browse the wider individual peptides range.

Which warning signs should make you look twice?

The lot number is missing or does not match the vial.
There is no named laboratory, or no way to verify the report with it.
Purity is given without a method or chromatogram.
Results say “pass” or “conforms” instead of a figure.
Identity has not been tested.
One report image appears across several sizes or dates.

Frequently asked questions

Is a high purity figure enough on its own?

No. A purity percentage only tells you about the share of the main peak. Without a separate identity result, you cannot be sure the main peak is the compound on the label.

Why can the content on a COA be higher or lower than the label?

Freeze-dried peptide powders contain counterions such as trifluoroacetate and some moisture, and fill weights vary. Published testing has recorded content above the label alongside very low purity.

How do I check the COA for an ETHOS UK order?

Find the lot number on the vial label and search for it on the ETHOS public COA portal. Each batch has its own report, and the same portal serves both the US and UK shops.

Can ETHOS advise how to use a peptide?

No. ETHOS supplies materials for research purposes only and cannot advise on use. COAs document identity and quality, not use.

Research use only. ETHOS products are sold strictly for laboratory research and are not for human or veterinary use. This article explains published analytical work and how to read documentation; it is not guidance on use.