The automated measurement of endotoxin by parallel turbidimetric time assay

Abstract

An attempt has been made to develop an automated instrument that measures the turbidity change in gelation reaction of a solution containing endotoxin and Limulus amoebocyte lysate, and quantifies endotoxin by determining gelation time of the sample. This instrument monitors the ratio R(t) of the sequential to the initial transmittance of up to 64 samples simultaneously and independently at 10s increments. As the samples are stationarily incubated at a controlled temperature of 37 ± 0.5° C, the objective judgement of gelation is provided without any disturbance from sample vibration. Defining gelation time as the time required to obtain a 5% decrease of R(t), a well correlated calibration curve was obtained for endotoxin concentration from 1 pg/ml to 100 ng/ml. The coefficients of variation of the calculated endotoxin concentration were 5.64 to 14.1%. The judgement of gelation by this method agreed well with that by the conventional gel-clot method when the proper measuring time (about half of that by the conventional method) was selected.