The LAL assay (Limulus amebocyte lysate assay) is the pharmacopoeial standard for detecting and quantifying bacterial endotoxin. It exploits the fact that amebocytes from the horseshoe crab (Limulus polyphemus) contain a clotting-cascade enzyme system that is activated by picogram quantities of endotoxin.
LAL is performed in three principal formats: gel-clot (a semi-quantitative pass/fail at a defined sensitivity), turbidimetric and chromogenic (both quantitative). Results are reported in Endotoxin Units per millilitre (EU / mL) and converted to EU / mg based on the peptide concentration. Recombinant Factor C (rFC) assays offer an equivalent, animal- free alternative.
LAL is the assay behind every endotoxin figure reported on a Certificate of Analysis for a research peptide.