Endotoxin Testing by Limulus Amoebocyte Lysate (LAL) Turbidimetric Assay

Principle of Turbidimetric test

Bacterial endotoxin activates the factor C in Limulus amoebocyte lysate, causes a series of enzymatic reactions including the cleavage of a clotting protein by an activated clotting enzyme. The ionic interaction that occurs after the cleavage causes coalesce of cleavage products and the reaction mixture to become turbid. [1] The concentration of endotoxin is directly proportional to the increase rate of absorbance of the reaction mixture. It is a modified extension of the gel-clot test. [2]

Method of Turbidimetric test

The kinetic turbidimetric method and the endpoint turbidimetric method are the ways of turbidimetric method to determine the content of endotoxin in a sample. Both require a standard curve, which created by spiking the sample with known quantities of endotoxin in sterile water, but differ in the point for measurement.

For the kinetic turbidimetric method, by measuring the turbidity or optical density (OD) of the mixture at each specified and validated wavelength continuously throughout the incubation period, the amount of endotoxin present in a sample is inversely proportional to the time required for the mixture to reach onset OD. While the end point turbidimetric method measures the value of OD after a set incubation period to quantify the endotoxin concentration. [3]

Advantages of Turbidimetric test:

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Creative BioMart has a team of professional and well-equipped scientists dedicated to work with researchers around the world, to meet their requirements and ensure high quality of custom service. If you are interested in our services, please contact us for more details.


  1. Pyrotell-T (Limulus Amebocyte Lysate [LAL] Products) [product information]. Falmouth, MA:Associates of Cape Cod Incorporated; 1997.
  2. Alex Wheeler. Comparing Endotoxin Detection Methods, Pharmaceutical Technology, 2017 Vol.41(11), 58-62
  3. Timothy J. Joiner. Comparison of Endotoxin Testing Methods for Pharmaceutical Products, International Journal of Pharmaceutical Compounding, 2002, Vol. 6 No. 6 November/December.

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