What is Endotoxin? (Peptide Glossary)

Endotoxins are fragments of gram-negative bacterial cell walls (lipopolysaccharides, LPS) that can contaminate peptide products during manufacturing, water purification, or handling. They are invisible, heat-stable (autoclaving does not destroy them), and biologically potent - even tiny amounts trigger strong immune responses in research models, which can confound or invalidate experimental results.

Endotoxin contamination is a marker of manufacturing hygiene. Peptides synthesized in clean facilities with purified water systems and proper handling have negligible endotoxin levels. Products from sloppy operations can carry significant contamination. Because endotoxins are invisible and do not affect HPLC purity readings, a vial can be 99% pure and still heavily contaminated.

Thorough COAs include an endotoxin measurement (LAL test), reported in Endotoxin Units per milligram or milliliter. Pharmaceutical reference points are strict (typically under 5 EU/kg for injectable drugs); research peptides have no mandated limit, but responsible vendors test and report. For cell culture and in-vivo research especially, endotoxin data separates serious suppliers from the rest.