How to Read a Certificate of Analysis (and What It Does Not Tell You)

Foundations

The short version

A typical peptide COA reports identity, purity and net content, usually by LC-MS.
It does not test sterility, bacterial endotoxin, particulates or container integrity.
A 99.9 percent pure peptide can still cause a serious reaction.
Most COAs certify one sample somebody chose to send, not the vial you received.
Independent testing has found problems in roughly 30 percent of gray market vials.

What the tests actually mean

Identity confirms the molecule is what the label says, usually by mass spectrometry. Useful, and it catches outright substitution.

Purity reports what percentage of the peptide content is the target molecule rather than truncated sequences or synthesis byproducts. This is the number everybody quotes.

Net content reports how much is actually in the vial. Worth reading closely, because underfilling is common and a vial labelled 10mg containing 8mg is a 20 percent dosing error you would never notice.

The gap that matters

None of those tests detect bacterial endotoxin. Endotoxin is a fragment of gram-negative bacterial cell wall. It survives sterilisation, it is invisible to LC-MS, and it causes fever, rigors and systemic inflammatory response at very small injected doses. It is the most common failure mode for non-GMP injectables and it is absent from every standard peptide COA.

Sterility, particulate matter and container closure integrity are similarly untested. Those are USP 71, 788 and 1207 respectively, and they are what a compounding pharmacy runs on every lot.

The two phrases to look for

Most legitimate labs include language along the lines of "for informational purposes only" and "specific to the sample submitted." Read both carefully.

The first is the lab declining to certify fitness for any use. The second means they tested one sample somebody chose to send them. There is no chain of custody connecting that sample to the vial in your hand, and no reason to assume they came from the same batch.

What a pharmacy does differently

A licensed compounding pharmacy performs its own release testing on every lot, under USP 797, covering potency, sterility, endotoxin and particulates, with documented chain of custody. And it carries the liability, backed by a licence a regulator can suspend. That is the actual product you are buying. See safety and sourcing.

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