Purity of at least 98.0%. Somebody chose that number. For medicines there is a published process behind it. For research material there often is not.
A spec sheet says purity must be at least 98.0%. Any single impurity must be no more than 0.5%. Round, confident numbers.
So where does 98 come from? Somebody chose it. The interesting question is who, and on what basis.
For established medicines, the numbers are not chosen by the manufacturer at all. They are published in a monograph: an entry in an official handbook covering one named substance.
The main handbooks are the United States Pharmacopeia (USP), the European Pharmacopoeia (Ph. Eur.), and the Japanese Pharmacopoeia (JP). A monograph lists the tests a batch must pass, the method for each test, and the limit it must meet. In the region that publishes it, that entry carries legal force. A batch either meets the monograph or it does not.
Most research peptides have no monograph. Nobody has written one.
Then the limits have to be built from scratch. For a compound heading toward approval, that work follows guidelines from the International Council for Harmonisation, known as ICH. It runs in four stages.
1. Work out what is tolerable. ICH Q3A and Q3B deal with impurities in a drug substance and a finished product. They set out a tiered idea. Below one level, an impurity only has to be reported. Above the next, it has to be identified. Above a third, it has to be shown to be safe. The exact percentages depend on how much of the drug a person would take in a day.
2. Find out what the process can actually do. Limits are useless if no real batch can meet them. Makers test a run of batches to see the range the process really produces. A limit is set against what the process has shown it can do, not against a hope.
3. Break the material on purpose. In forced degradation, or stress testing, a sample is deliberately exposed to heat, light, acid, base, and oxygen. The point is to make it fail. Then the lab can see what appears, and check that the test method can actually detect it. A method that cannot see the damage cannot police the limit.
4. Set the release limits. Only now do the numbers get written down. Purity at or above 98.0%. Any single impurity at or below 0.5%. Those figures are the output of the first three stages, not the starting point.
The same framework bounds the other things in the vial. ICH Q3C covers leftover solvents. ICH Q3D covers elemental impurities, which is where heavy metal limits come from. Bioburden and endotoxin are handled separately again, under their own pharmacopoeial chapters.
That is why a full specification is a page, not a line.
Here is the part worth being clear-eyed about.
That entire framework applies to medicines going through regulatory approval. A peptide sold for research use only is outside it. There is no monograph to meet and no filing to satisfy.
So the limits printed on a research COA are chosen by the supplier. Many suppliers set them sensibly, using the same logic described above. Some copy numbers that look reassuring.
The framework is still the right benchmark. It just becomes something you check for rather than something you can assume. That is why the useful question is never "what is the limit" on its own. It is which method produced the number, and against what.
This article explains published research and the rules around it. It carries no dose, no protocol, and no claim that any compound treats, cures or prevents a condition in anyone. Where the evidence is thin we say so. See our editorial standards.
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