An endotoxin test measures the level of bacterial endotoxin contamination in a research compound. Endotoxins are lipopolysaccharide (LPS) fragments from bacterial cell walls that can contaminate any peptide synthesis. Even at sub-nanogram-per-milliliter levels, endotoxins activate inflammatory pathways and can completely confound cell-based research results.
The Standard Test
The most common endotoxin assay is the Limulus Amebocyte Lysate (LAL) test, named for the horseshoe crab cells used to detect endotoxin presence. Results are reported in EU/mg (Endotoxin Units per milligram of compound) or EU/mL (per milliliter of solution).
Endotoxin Tiers
- <0.5 EU/mg: low-endotoxin grade — suitable for cell culture and in vivo work
- 0.5–5 EU/mg: standard research grade — fine for most in vitro biochemistry
- 5–50 EU/mg: elevated — non-cell-based work only
- >50 EU/mg: high — not suitable for biological assays
Why It’s Separate from Purity
HPLC purity measures the organic chemistry — what fraction of the UV-detectable material is the target peptide. It doesn’t catch endotoxin contamination, which sits at concentrations far below HPLC’s detection threshold but can still ruin a cell-based assay.
A complete COA includes both an HPLC chromatogram (for purity) AND an LAL endotoxin result. If a supplier publishes only purity, half the QC picture is missing.
Matte’s COA library includes endotoxin results on every lot.
Research use only. Not for human consumption. Statements not evaluated by the US FDA.