Reference
Sterility and endotoxin
Both are named on almost every peptide certificate discussion as “a separate assay” and almost never explained. They are separate, they are different from each other, and a purity figure tells you nothing about either.
They are not the same thing
Sterility is the absence of viable microorganisms — nothing alive and able to multiply.
Endotoxin is a molecule: lipopolysaccharide, a component of the outer membrane of Gram-negative bacteria. It is released when those bacteria break apart.
The distinction that matters follows from that. Endotoxin is a chemical, not an organism, and it is remarkably heat-stable — considerably more so than the bacteria that produced it. A process that kills every organism present does not necessarily remove what they left behind. Sterile does not imply endotoxin-free.
How each is tested
Sterility testing means attempting to grow something. Sample is introduced to growth media and incubated, and the absence of growth over a defined period is the result. It takes time by its nature — you cannot rush an incubation.
Endotoxin testing is more unusual. The standard method uses Limulus amebocyte lysate, derived from the blood of horseshoe crabs, whose clotting system reacts to remarkably small amounts of bacterial endotoxin. That reaction — measured as clotting, turbidity or colour change — is the assay. Recombinant alternatives now exist that do not require the animal source.
Why neither is on a peptide certificate
A peptide certificate of analysis typically reports purity by chromatography and identity by mass spectrometry. Both are chemistry performed on a small sample, and neither has any bearing on microbiological content.
They are different tests, run by different methods, often at different laboratories, and commissioned separately. A supplier is not concealing anything by not including them — but equally, a purity figure of 99% says precisely nothing about either. The two facts are unrelated, and it is a common and understandable error to read one as implying the other.
What this means when reading a report
- Purity and identity are chemical measurements. They establish what the molecule is and how much of the sample is it.
- Sterility and endotoxin are microbiological measurements. They are absent unless explicitly reported.
- An absent test is not a failed test — it is an unasked question, and the certificate is the wrong place to look for the answer.
We publish the analytical reports we hold and describe exactly what they cover. We make no claim about anything they do not, and nothing on this site is guidance about use — if that is what you need, the person to ask is a registered prescriber.
