The design of a reliable endotoxin test.

An endotoxin assay utilizing Limulus lysate (LAL) and a chromogenic peptide substrate is described. The assay of picograms of a compound, present in significant quantities almost everywhere, is obviously associated with a serious risk of contamination. Measures to avoid and detect contamination have been considered. When a quantitative assay like the present one is used, the inhibitory effects of samples analyzed are obvious and also possible to quantify. Methods to avoid such inhibitory effects have been studied and the simplest procedure seems to be dilution with endotoxin-free water, in some cases also combined with heat treatment (75 degrees C for 5 min).