What are endotoxins, and why do they show up on a COA?
For research use only. Not for human or animal consumption.
Endotoxins are pieces of the outer membrane of Gram-negative bacteria. Chemically they are lipopolysaccharides, usually shortened to LPS: a lipid anchor (lipid A) joined to a chain of sugars. When those bacteria die or divide, LPS is shed into whatever liquid they were in.
The reason labs care is that endotoxin is a contaminant that does not behave like living bacteria. Filtering out the bacteria does not remove it. Ordinary heating does not destroy it. It sticks to glass and plastic. So a material can be free of live microorganisms and still carry measurable endotoxin.
How endotoxin gets into a peptide batch
Synthetic peptides are not grown in bacteria, so the source is the process around them rather than the peptide itself. Common routes are:
- water used in purification or rinsing
- buffers and reagents
- glassware, tubing and containers that were not depyrogenated
- handling during filling
That is why endotoxin is a process-hygiene indicator. A low figure says the water, materials and handling upstream of the vial were clean in this respect.
Why it matters in research
Endotoxin is biologically active at very low levels in many experimental systems. In cell culture, for example, LPS can trigger responses in immune-type cells that have nothing to do with the material being studied. A lab that sees an unexpected signal will often check endotoxin on the reagents before anything else. Having the figure on the COA from the start saves that step.
How it is measured
The standard assay is the LAL test, which uses a reagent made from horseshoe crab blood cells that clots or changes color in the presence of endotoxin. A newer option uses recombinant factor C (rFC), a lab-made version of the same sensing protein. Both report in endotoxin units (EU).
Reading the endotoxin line on a COA
On a report, endotoxin usually appears as one row:
| Field | Example | What to check |
|---|---|---|
| Test | Bacterial endotoxins | That it is there at all |
| Method | Kinetic chromogenic LAL, or gel-clot | Which variant was used |
| Specification | A stated limit, set by the supplier or the buyer | That a limit is printed, not just a number |
| Measured value | For example "less than 0.5 EU/mg" | The unit, and whether it is a measured figure or a "less than" value |
A "less than" figure means the lab saw nothing above the lowest level its method could reliably read under those conditions. It is not a zero.
Units need care. EU/mg, EU/mL and EU per vial describe the same thing on different bases, and a figure in one cannot be compared with another without knowing how the lab prepared the sample.
What the endotoxin line does not cover
- Live microorganisms. That is sterility or microbial count testing, a different assay.
- Chemical purity. That is HPLC.
- Identity. That is mass spectrometry.
Endotoxin is one contaminant, measured one way. A pass on this row is a pass on this row.
FAQ
Are endotoxins the same as bacteria?
No. They are fragments of bacterial cell walls. They can be present when no live bacteria are.
Does a sterility pass mean low endotoxin?
No. Sterility testing looks for growth of living organisms. Endotoxin is a molecule that remains after the organisms are gone.
Why do some COAs list endotoxin and others do not?
The panel depends on what was ordered for that lot. If the test is not printed, the report holds no endotoxin data.
Research use only
Peptira supplies materials for laboratory research. For research use only. Not for human or animal consumption. Not for diagnostic or therapeutic use. This page explains a contamination assay. It gives no acceptance limits tied to people or animals and is not medical advice.