Dry heat inactivation of endotoxin on the surface of glass

The thermal inactivation of three endotoxin preparations on the inner surface of glass capillary tubes was studied. The samples were exposed to precisely controlled dry heat conditions at study temperatures ranging from 170 degrees to 350 degrees C, and were assayed using the gel-clot method of the Limulus Amebocyte Lysate test. Plots of the log of the amount of pyrogenic material remaining versus heating time revealed apparently biphasic destruction curves. The initial slopes were linear to a minimum 3-log unit reduction, and were followed by slower destruction rates for the terminal slopes. D values were calculated from the initial slopes of the destruction data, and Z values were estimated from the D values. The D and Z values were found to vary with the initial charged amounts of endotoxin. A second-order equation was found to be an inappropriate model for the inactivation process at temperatures between 170 degrees and 250 degrees C, but was found to be suitable for temperatures between 250 degrees and 325 degrees C. The data were successfully fit to a biexponential equation for all the temperatures studied. The overall inactivation rate of the endotoxin material formulated with fillers was apparently faster than that for the pure endotoxin preparations.