Low Endotoxin Recovery Studies

LER effects (Low Endotoxin Recovery Effects) describe a phenomenon in which the endotoxin content of a sample continuously decreases, in particular as a function of time and temperature. This is also referred to as so-called endotoxin masking effects. The criteria for this phenomenon are met if, as part of hold-time studies, the percentage endotoxin recovery rate of the initially added endotoxin quantity is < 50% for at least two consecutive test points. Furthermore, the sample matrix must not show any interference with the test system at time T0 of the study in the dilution tested. The combination of certain matrix components virtually guarantees the occurrence of masking effects. This includes:

  • Detergents (e.g. polysorbate, Triton X-100)
  • Complexing agents (e.g. citrate, phosphate, EDTA)
  • Proteins (as API or excipient)


If products contain at least two of these ingredients, the currently used test method for the detection of endotoxins should be critically questioned and evaluated. The current specification documents and guidelines as well as the competent supervisory authorities expect comprehensive process and product knowledge, as well as the checking and verification of the stability of endotoxins in the respective sample matrices within the scope of hold-time studies from the manufacturers of these products. In specific,

  • the transport
  • the storage conditions of the samples as well as
  • the time period between critical process steps and the subsequent endotoxin test

are to be analyzed and critically scrutinized.

Labor LS has long-standing expertise in the detection of masking effects. Our team of experts has already examined a wide variety of matrices and proactively developed possible strategies for the occurrence of an LER effect. In the case of products with corresponding components, studies can be conducted at Labor LS to prove or exclude a masking effect.

Your contacts on this topic

We would be pleased to advise you and prepare an individual quotation for you! For more information and enquiries, please contact our team of experts:


Dr. Enrico Barth

Examination of bacterial endotoxins
+49 9708 9100-462