Endotoxin

Endotoxins are lipopolysaccharide fragments from the outer membrane of gram-negative bacteria. They survive sterilisation that kills the bacteria themselves, and even tiny amounts injected into an animal or a person trigger fever and inflammation. A sterile solution can therefore still be contaminated with endotoxin, which is why it is tested separately from sterility.

The standard test is the limulus amebocyte lysate assay, which uses a clotting reaction from horseshoe crab blood that is exquisitely sensitive to endotoxin. Results are reported in endotoxin units per milligram or per millilitre against a limit appropriate to the intended use. A certificate of analysis for injectable-grade research peptide should include this figure; a certificate that reports only HPLC purity has not addressed it.

Endotoxin is a property of the manufacturing environment rather than of the peptide, which is why two lots of the same compound can differ. The lab-testing page sets out the checks applied to lots sold here, including endotoxin and sterility.