Guides & comparisons
What a COA Cannot Tell You
If you buy research peptides, know what a COA leaves out: it describes one sample of one batch on one test date. It does not establish sterility, endotoxin, heavy metals or residual solvents — those are separate tests — and it records nothing about how the vial was shipped or stored afterwards.
A certificate of analysis is a snapshot, at a test date, of a sample from a batch. That sentence contains three limits, and most of what people expect a COA to establish falls outside all three of them.
This isn’t an argument against certificates. A certificate is the best documentary evidence available about research material. It just answers a narrower question than its reputation suggests, and knowing the edges of it is more useful than treating the document as a general guarantee.
What exactly does a COA describe?
Sample. A portion was drawn and analysed. The result describes that portion. Extending it to the whole batch assumes homogeneity — a fair assumption for well-mixed lyophilised bulk, and less fair the more handling steps happened afterwards.
Batch. Every unit in the batch inherits the certificate. Not one of them was analysed individually. Anything specific to one unit — a stopper that didn’t seat properly, a vial that took a knock — sits outside the document’s reach by construction.
Date. The result describes the material as it was when it was run. It is a historical statement, and it gets older every day.
Which tests are not on a standard COA?
A standard peptide certificate is a purity-and-identity document. Several questions people assume it answers have their own methods, their own cost, and are frequently just absent:
| Question | What answers it | On a typical purity COA? |
|---|---|---|
| How much of the detected material is the target? | HPLC-UV | Usually |
| Is it the right molecule? | Mass spec — ESI or MALDI-TOF | Usually |
| How much peptide is in the vial by weight? | Amino acid analysis | Sometimes |
| How much water is in the powder? | Karl Fischer or thermogravimetric analysis | Sometimes |
| What synthesis solvents remain? | Gas chromatography | Rarely |
| Are there elemental or heavy-metal impurities? | ICP-MS | Rarely |
| Is bacterial endotoxin present? | LAL assay | Rarely |
| Is it sterile? | Microbiological sterility testing | Rarely |
Two of those rows get confused constantly. Endotoxin is a heat-stable fragment of bacterial cell wall; it persists after the organisms that produced it are gone and survives conditions that kill them. Sterility is the absence of viable microorganisms. Material can be sterile and still carry endotoxin, and a low endotoxin result says nothing about viability. Neither is implied by purity — a chemically pure preparation can be microbiologically anything at all, because HPLC and mass spectrometry are not looking for organisms.
The most important thing about every “rarely” in that table: not tested is not the same as failed. It means unknown. A certificate that doesn’t mention endotoxin is not reporting a bad endotoxin result; it is not reporting an endotoxin result. Reading absence as reassurance is the single most common misreading of these documents.
The purity figure and the content figure are similarly distinct questions, and only one of them is usually answered.
What happens after the sample was tested?
The laboratory analysed material at a bench on a particular day. Between that bench and your shelf sits a chain of events no certificate records: bulk handling, aliquoting into vials, lyophilisation and sealing, packaging, warehousing, customs, one or more couriers, and however long the package sat somewhere before anyone opened it.
Peptides degrade by well-characterised chemical routes — hydrolysis of the backbone, oxidation of methionine, cysteine and tryptophan residues, deamidation of asparagine and glutamine, and aggregation. These are time-and-temperature processes. They don’t have a threshold that gets crossed; they accumulate. A lyophilised powder is far more robust than material in solution, sometimes dramatically so — but robust is not unaffected, and early degradation generally leaves no visible mark.
Nothing about a week in an unrefrigerated vehicle in August appears on the certificate. The thermal history of a specific package is real data with no custodian at all, unless you become one.
Does a COA still describe the material once it is in solution?
Material in solution is a different physical system from the powder that was analysed. The degradation routes above run faster there, and the certificate describes a state that no longer exists.
That is a statement about chemistry, not a recommendation — this site carries no reconstitution or handling instructions and won’t. The narrow point for reading a COA is this: the document’s relevance to a particular vial declines from the moment the batch left the laboratory, and drops sharply once the material is no longer in the form that was tested.
What is the difference between a retest date and an expiry date?
A retest date means “re-analyse after this point to know where you stand”. An expiry date implies a stability conclusion. Many peptide certificates carry a date derived from general expectations for the compound class rather than from a stability study on that specific batch, which is a reasonable estimate and not a measurement. Where a certificate states an expiry with no supporting stability data, read it as a convention rather than a result.
What should you record yourself?
The document covers a sample, a batch and a date. The rest is yours to keep:
- Date received, and condition on arrival
- Storage location and conditions since
- Any known excursion — a delayed delivery, a package left outside, a fridge that failed
- Date first opened
- The lot number that ties all of the above back to the certificate
That is the second half of provenance, and it is the half no laboratory can supply. It is also why the certificate belongs attached to the item rather than filed by product name, and part of what a tracking system that actually holds up is for. Peppies keeps lot number, certificate and intake record on one shelf entry for exactly this reason — not because an app improves the material, but because the record has to live somewhere and memory isn’t a location.
Related: every field on a certificate, line by line, what the purity percentage hides, and how a genuine certificate ends up on the wrong vial.
Everything here concerns documentation for research-use-only laboratory materials. A certificate describes a sample; it makes no statement about anything else, and neither do we.