Endotoxin and Sterility Testing
The two safety-critical tests that come up most for peptide research preparations — and what their absence implies.
Last updated: 2 April 2026
What endotoxin testing measures
Endotoxins are lipopolysaccharide components of gram-negative bacterial cell walls. Even after a sample has been sterilised, residual endotoxin can be present and is biologically active — it can provoke inflammatory responses at very low concentrations.
Endotoxin testing (LAL or recombinant Factor C) reports concentration in endotoxin units per ml or per mg. The acceptable threshold depends on the application; injectable-context preparations have stringent limits.
What sterility testing measures
Sterility testing checks for the presence of viable microorganisms. Methods vary — direct inoculation, membrane filtration, or rapid microbiological methods.
A 'sterile-filtered' label is not the same as 'sterility-tested'. Filtration removes bacteria but doesn't confirm that the final container is microbiologically clean. Reputable preparations are both filtered and tested.
What the absence of these tests implies
A COA without endotoxin or sterility data on a preparation that's sold for any sterile-context research use is incomplete. The preparation may be perfectly fine — but the document doesn't establish it.