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Ethylene Oxide Residual Analysis

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Ethylene Oxide (EtO) is known to exhibit a number of biological effects which include irritation, organ damage, mutagenicity and carcinogenicity in human and animals, and reproductive effects in animals. When determining the suitability of ethylene oxide for sterilization of medical devices, it is important to ensure that the levels of residual EtO, ethylene chlorohydrin (ECH) and ethylene glycol (EG) pose a minimal risk to the patient in normal product use.

The biological evaluation and testing requirements, combined with the EtO-sterilization process residue limits, form the justification that an EtO-sterilized device is acceptable for use.



The maximum allowable daily doses of EtO and ECH for a medical device is calculated based on the duration of contact. Devices can be categorized as:

  1. Limited exposure – devices whose cumulative single, multiple or repeated use or contact is up to 24 hours.
  2. Prolonged exposure – devices whose cumulative single, multiple or repeated long-term use or contact is likely to exceed 24 hours but not 30 days.
  3. Permanent contact – devices whose cumulative single, multiple or repeated use or contact exceeds 30 days.

The guiding principle in selecting appropriate extraction methods for the determination of EtO is the evaluation of the dose to the patient in order to show compliance with the requirements set out in ISO 10993-7:2008, using simulated use wherever possible. For devices in the prolonged exposure category, it is important to note that the device must also meet the residue requirements of the limited exposure category, and that devices in the permanent contact category must also meet the residue requirements of the prolonged exposure and limited exposure categories, whichever extraction condition is used. Where residues are shown to be within these requirements for products tested by exhaustive extraction, there is no need to further challenge the device by simulated-use extraction.



  1. Exhaustive Extraction using Ethanol
  2. Simulated-Use Extraction using Deionised Water


  1. ISO 10993-7:2008(E): Biological evaluation of medical devices - Part 7: Ethylene oxide sterilization residuals.
  2. NATA Technical Note 17: Guidelines for the Validation and Verification of Chemical Test Methods, June 2012.
  3. NATA Technical Note 33: Guidelines for Estimating and Reporting Measurement Uncertainty of Chemical Test Results, December 2009.


Three blank samples (unsterilised) of each product are required for controls and validation work. Client decides how many sterilised samples for each product to test. The more replicate of results, the more analytically sound the result will be. As a minimum, two replicates for each product from each aeration time are recommended.



Five working days from receipt of samples and signed submission form given no further aeration time is needed.