A new kinetic single-stage Limulus amoebocyte lysate method for the detection of endotoxin in water and plasma.

A convenient kinetic chromogenic Limulus amoebocyte lysate (LAL) method, based on components originally intended for a two-stage end-point method, has been developed. The components (LAL and chromogenic substrate) can be pooled and subsequently used in a single-stage kinetic procedure adapted to microplates. With the help of a kinetic software, it is possible to measure over the three log range 0.005-12 EU/ml in one test run--a range considerably wider than the range of the end-point procedure. A good linearity of the log-log standard curve, reflected by coefficients of regression between 0.997 and 1.0, is shown as well as a high-resolution (> 700 s) between the negative control and the lowest standard point. Moreover a good precision (C.V. < 10%) is obtained in both water and plasma, showing the usefulness of the method in different applications. Finally, a strong correlation (r = 0.95-0.99) to other LAL methods is demonstrated.

The importance of the quality of water in Limulus Amebocyte Lysate tests.

Commercial pharmaceutical waters were evaluated regarding their interference in the chromogenic Limulus Amebocyte Lysate (LAL) test. Two of the four tested waters strongly inhibited the U.S. Reference Standard Endotoxin, while a Control Standard Endotoxin was less affected. The inhibitory effect could be mimiced by adding trace amounts of certain metal ions to a non-interfering water. In conclusion, the water used in the LAL test must be chosen with great care.