How do I read a peptide certificate of analysis?

Read a peptide certificate of analysis (COA) in four passes. First, confirm the lot number on the document matches the lot on the container. Second, confirm identity — sequence, molecular formula, theoretical molecular weight, and a mass spectrometry result that agrees with it. Third, confirm purity against the actual HPLC chromatogram, not just a typed percentage. Fourth, read the content and contaminant panels: net peptide content, water, residual solvent and counterion, and microbial screens. A COA that cannot be tied to one specific batch, or that reports a number with no instrument trace behind it, is a marketing sheet wearing a lab coat. Everything below concerns research-use-only material evaluated for laboratory work — not human or animal use.

Start with the lot number, not the purity number

Most buyers open a COA and jump straight to the purity figure. That is the wrong first move. A certificate of analysis is a record of what one laboratory measured, on one production lot, on one date. Strip away the lot linkage and the rest of the document describes nothing in particular.

So the first check is a chain-of-custody check. The lot or batch number printed on the vial label should appear on the COA, and ideally on the packing slip as well. If a supplier sends a single PDF that accompanies every order of a given compound regardless of when it was made, you are not looking at batch documentation — you are looking at a product brochure with test-shaped content on it.

While you are in the header block, note the manufacture date and the analysis date. The analysis date should follow the manufacture date. A test date that precedes the synthesis it supposedly describes is either a clerical error or a copied template, and both are worth a direct question. Also note whether the issuing laboratory is named with contact information. An unnamed lab is an unverifiable lab.

The identity block: confirming what the material actually is

Purity answers how much of the powder is the intended compound. Identity answers whether the intended compound is what you think it is. These are separate questions and a real COA answers both.

The identity block should carry the product name, the amino acid sequence in single-letter or three-letter code, the molecular formula, the theoretical molecular weight, and where one exists, a CAS number. Compare the sequence on the COA to the published sequence for that compound. Transcription errors happen, and a mismatch in a single residue changes the molecule entirely.

Identity is then confirmed instrumentally, usually by mass spectrometry — ESI-MS or MALDI-TOF. The document should show an observed mass alongside the theoretical mass. The two should agree closely; small deviations are expected from isotope distribution and instrument calibration, large ones are not. A COA that reports purity but never confirms identity has skipped the more fundamental of the two tests, and that omission is common enough on thin documentation that it is worth looking for deliberately.

Purity, peptide content, and the chromatogram behind the percentage

Purity on a peptide COA is almost always determined by reversed-phase HPLC and expressed as the main peak area as a percentage of total peak area. That method should be spelled out: column type, mobile phase and gradient, run time, and detection wavelength. Peptide bonds are commonly detected in the low ultraviolet range, and stating the wavelength matters because impurities absorb differently at different wavelengths.

The percentage alone is a summary. The chromatogram is the evidence. A legitimate document includes the trace, with the main peak, its retention time, and the smaller impurity peaks visible around it. When you look at one, check that the baseline is shown, that the trace is not cropped to hide a shoulder or a late-eluting peak, and that the integration table matches the picture. A crisp number printed on a page with no chromatogram attached is the single most common weak point in peptide documentation.

Then there is the field most buyers skip entirely: net peptide content. Lyophilized peptide powder is not pure peptide by weight. It also contains bound water and counterion salts left over from purification. Net peptide content — determined by amino acid analysis or nitrogen determination — states how much of the gross weight is actually peptide. Two vials with identical labels and identical HPLC purity can hold measurably different quantities of compound if their net peptide content differs. For a wholesale buyer comparing suppliers on price, that field is the difference between a real comparison and a false one.

The contaminant panel and what a tested claim should cover

Beyond identity and purity, a thorough COA reports on what else is in the container. Depending on the compound and the intended laboratory application, that can include water content by Karl Fischer titration, residual organic solvents from synthesis and purification, counterion content such as acetate or trifluoroacetate, heavy metals, and microbiological screens including bioburden and bacterial endotoxin.

No single panel is universal, and it would be wrong to tell you that a fixed list applies to every compound. What is reasonable to expect is that the supplier states which panels were run, by which method, with which specification limit, and with a numerical result rather than a bare pass. The word tested, standing alone, is not information. Tested for what, by whom, against what limit, on which lot — those four answers turn a claim into a record.

A related detail worth checking is appearance and solubility notes. They are simple observational fields, but a description that contradicts the material you received is an early signal that documentation and product have drifted apart.

A field-by-field read

Red flags in the document — and in the supplier

Some problems live in the paperwork. Others live in how the paperwork is handled, and for a wholesale buyer the second category is more revealing.

Document-level red flags: no batch number, no chromatogram, no named laboratory, purity claimed without a method, a low-resolution scan that resists close reading, or specification columns filled with the word conforms and nothing else. Any of these can be innocent. All of them are answerable, and a supplier who cannot answer has told you something.

Process-level red flags matter more. Documentation released only after payment. COAs offered as a paid add-on. Test data sent as a screenshot rather than a full document. Pricing that is invisible until you have committed to a call. Refusal to provide COAs for the specific lots currently in stock, as opposed to a flattering older run. None of these practices is illegal, and none of them is unique to any one company — but each one moves verification risk from the supplier onto you, which is the opposite of what batch documentation exists to do.

One further note. A COA speaks to chemistry, not to permission. Whether your business can purchase, hold, or resell a given compound in your jurisdiction, and under what conditions, is a question for your own attorney and your state board — this article is informational and is not legal advice. Read the COA for what it is: evidence about material, not clearance for anything else.

What Real Peptides does differently

Real Peptides supplies research-use-only compounds through its Wholesale Partner Program, and its documentation practice is built around the checks described above rather than around a claim.

Batches are tested to 99%+ HPLC purity, with 6-panel batch testing applied per lot rather than as a one-time qualification of a product line. COAs are publicly verifiable — published where a prospective buyer can read the lab results before placing an order, instead of being held back behind a sales conversation or sold separately. That matters for the comparison work a wholesale buyer actually has to do: reviewing documentation across multiple lots of the same compound to see whether results hold steady, which says far more about process control than any single impressive figure.

Fulfillment is US-based, with orders shipping in 5–7 days. Onboarding runs through a 3-step wholesale application. Pricing tiers and minimums are presented as part of that process rather than discovered after commitment. Compounds are supplied for laboratory research use only, are not FDA-approved drugs, and are not sold for human consumption; supplies are never bundled with compounds.

Where this leaves a wholesale buyer

If you are stocking research peptides for your catalog, the ability to read a COA line by line is the cheapest form of quality control you have. Ask for batch-specific documents, read the chromatogram rather than the headline number, check net peptide content before you compare prices, and treat any friction around releasing test data as information in itself. Businesses ready to evaluate Real Peptides on those terms can review the published lab results and begin the three-step application to the Wholesale Partner Program.

Related pages: the wholesale peptides program overview, and the form to apply for a wholesale account.