Optimal design of a continuous measurement system for endotoxin concentration in dialysate fluid

Endotoxin concentration in dialysate fluid should be frequently monitored. But conventional limulus test needs complicated operation to prevent the contamination by atmospheric endotoxin. We have developed the flow type measurement system using single tube in which sample solution reacted to limulus reagent without contact with atmosphere. The objective of the present study is to gain a sensitivity of the system to measure the endotoxin concentration ranging under 100 EU-1 accurately. Batch reaction experiments and flow type measurements were performed to determine the optimal wavelength and the reaction time for optimal operation of the continuous system. The highest sensitivity is obtained at a wavelength of 381 nm for measuring the endotoxin concentration by limulus reagent. Proper reaction time differed depending on concentration range of samples. The sensitivity of measuring the endotoxin concentration ranging under 100 EU-1 increased with reaction time. But longer reaction time in the flow type measurement system produces dispersion of the limulus reagent and lower sensitivity. Optimal reaction time of the flow type measurement system is then 45 min. Handy and exact measurements of the endotoxin concentration ranging above 50 EU-1 were able by the condition of a wavelength of 381 nm and a reaction time of 45 min.