How to Read a Certificate of Analysis (COA) for Research Peptides

When you acquire a compound for laboratory use, the only objective document that tells you what is actually inside the vial is the Certificate of Analysis — the COA (Certificate of Analysis). Not marketing, not a photo of the label, not the seller's assurance. Hard measurement results from analytical instruments. For anyone working with research material, the ability to read a COA matters more than any product description.

This guide breaks the COA down to its fundamentals: what “purity ≥99%” really means, how mass identification differs from a purity measurement, why an endotoxin test matters and why the batch number is the heart of the whole document. At the end you will find a 60-second checklist.

What a Certificate of Analysis (COA) is

A COA is a report of analytical testing on a specific batch of material. It is issued by the manufacturer's laboratory or — in the stronger variant — an independent, third-party laboratory. The document describes the compound's identity, its purity and the presence or absence of defined impurities. Crucially: a COA describes a batch, not “the product in general”. Two vials with the same name on the label may come from different syntheses and have different purity profiles — which is why a credible COA is always tied to a batch number.

An important caveat: a COA is a document of chemical quality for research material. It is not a ruling on the safety of use in humans or animals and does not change the status of the compound — the material remains for research purposes only.

The four pillars of a COA you need to be able to read

1. HPLC purity — what “≥99%” really means

HPLC (high-performance liquid chromatography) separates a mixture into its individual components and measures what percentage of the total signal is accounted for by the main peak — that is, the target molecule. The notation “purity ≥99% (HPLC)” means that the main peak corresponds to at least 99% of the area of all detected peaks. The remaining roughly 1% is process-related impurities: truncated sequences, synthesis by-products, trace reagents.

Importantly — and often overlooked — HPLC purity is a value relative to what the detector sees. Water, buffering salts or counterions (e.g. acetate, TFA) may not be counted within the same measurement window. That is why “99%” is information about the proportion of organic substances separated on the column, not a declaration that the vial contains 99% dry peptide mass. A good COA states the assay conditions (column, UV detection at a given wavelength) so that the result can be verified.

2. Mass identification (MS) — is this really the right molecule

Purity tells you “how pure”, but not “whether correct”. Identity is confirmed by mass spectrometry (MS) — most often ESI-MS or MALDI-TOF. The instrument measures the molecular mass of the compound and compares it with the theoretical mass derived from the sequence formula. Agreement between the measured and the calculated mass is proof that the main peak really contains that molecule, and not another peptide with a similar retention time. HPLC without MS shows the purity of an anonymous peak; only MS gives it an identity.

3. Endotoxin test (LAL)

Endotoxins are lipopolysaccharides from the membranes of Gram-negative bacteria — a residue of microbiological contamination at the production stage. The standard method for measuring them is the LAL test (Limulus Amebocyte Lysate), and the result is reported in endotoxin units per milligram or per vial (EU/mg, EU/vial). This parameter is particularly important for research materials intended for injectable applications in experimental models, where microbiological purity affects the reproducibility of results. The presence of an LAL result on a COA is a signal that the manufacturer controls not only the chemistry but also the hygiene of the process.

4. Batch number (LOT) and date

The batch number (LOT / batch number) is an identifier linking a specific vial to a specific synthesis and its analytical results. It is what turns a COA from a pretty PDF into a verifiable document — it lets you check that the certificate you are holding refers to exactly the material you have. The date (of production or analysis) completes the picture: it tells you when the measurements were taken. A COA without a batch number, or the same COA “attached” to every sale, is worthless — because it cannot be tied to the vial in your hand.

Why batch-to-batch matters

Peptide synthesis is a chemical process, not the printing of copies. Each run may differ slightly in coupling efficiency, in the profile of truncated sequences or in the level of residual impurities. That is why each batch should have its own, fresh COA. Reproducibility between batches — comparable purity, the same confirmed MS, controlled endotoxins — is in practice the best measure of a manufacturer's maturity. A single high result means nothing; consistently reproducible results batch after batch mean everything.

“Chinese origin” does not differentiate — quality control does

The common mental shortcut goes: “it's from China, so it's worse”. In practice, a significant share of the world's peptide raw materials (API) — including those that reach reputable laboratories — is made in a small number of specialised facilities, including in China. Geographic origin alone is not a quality parameter. What differentiates is something entirely different: whether every batch is tested, whether the result covers HPLC and MS and LAL, whether the COA is tied to a batch number and whether — in the stronger variant — it is confirmed by an independent laboratory.

In other words: you don't care where the reactor stands. You care about the chain of evidence between that reactor and the vial on your desk. That chain is built with documentation, not with a flag on a map.

“You don't know what's in the vial until you test it”

This sentence is sometimes used as a scare tactic. We treat it as a description of the standard, not a source of fear. It is right about one thing: without an analytical measurement, the label is only a declaration. That is precisely why an analytical document — and not the seller's assurance — is the only sensible point of reference. The answer is not distrust of the entire category, but the requirement that verifiable analysis stand behind every material. That is how we set the bar, and that is how we ask you to judge every supplier — ourselves to the same measure.

How PurePoint documents quality

At PurePoint we treat documentation as part of the product, not an add-on. We declare purity determined by the HPLC method as a standard and maintain a set of safety data sheets for the substances we offer, describing their physicochemical properties and the rules for safe handling of the material under laboratory conditions. You will find them in the safety data sheets section. We supply the material in lyophilisate form, and we describe its storage and handling in the context of research work — not use in humans.

Checklist: how to read a COA in 60 seconds

• Batch number (LOT) — is it present and does it match the vial label? If not, the rest doesn't matter.
• HPLC purity — stated with a value (e.g. ≥99%) and the assay conditions?
• MS identification — does the measured mass match the theoretical one? This confirms identity.
• Endotoxins (LAL) — is there a result in EU/mg or EU/vial?
• Date and source — when was it tested and by whom (in-house or independent laboratory)?

If all five items are filled in and mutually consistent, you are holding a document that actually means something. A missing one — that's a question for the supplier, before anything else.

For research purposes only. Not for consumption by humans or animals.