Endotoxin
Endotoxins are fragments of the outer wall of certain bacteria. They can end up in lab materials during manufacturing, so quality labs test every batch for them.
Where the word comes from
From Greek endon, “within,” and toxikon, “poison” — a toxin held inside the bacterial cell wall. Greek toxikon itself traces to toxon, “bow”: toxikon pharmakon was poison for arrows, which is how a word for archery became the root of “toxic.” Bacteriologists coined “endotoxin” in the late 1800s to separate the poisons locked inside a bacterial cell from exotoxins, the ones bacteria release.
What it means here
A peptide can be highly pure and still carry endotoxin, because purity testing and endotoxin testing look for different things — one measures the peptide, the other measures a contaminant. Even small amounts of endotoxin can interfere with sensitive experiments, especially work with living cells. The standard test is the LAL assay, which uses a substance from horseshoe crab blood that reacts when endotoxin is present. Endotoxin results are reported per batch, alongside purity, on a certificate of analysis.
Words you’ll see together
- LAL assay — the standard lab test that detects endotoxin
- EU/mg — endotoxin units per milligram, the unit a result is reported in
- batch — the unit of production each endotoxin result applies to
- lot-specific — a label meaning the result belongs to one tested batch only
Related terms
- Purity — a separate measurement; high purity does not rule out endotoxin
- Certificate of Analysis — where a batch’s endotoxin result is reported
- Lot number — the code that ties a vial to its tested batch
Where it appears in our catalog
- Purity and testing FAQ — how endotoxin testing fits into batch quality checks
- Certificates of Analysis FAQ — reading the endotoxin line on a COA
- How to read a certificate of analysis — a walkthrough of a real report
