The Chemical Characterisation Standard ISO 10993-18 Has Had An Amendment To Uncertainty Determination Published.

May 22, 2022

By M.Turner

All measurements have an inherent uncertainty. This also applies to analytical chemistry even if those PPB numbers do look incredible accurate. It is a pretty complicated field. Fortunately you don’t need to worry, MET has an expert in the field to help you through. Here James Silk explains the changes.

The latest amendment to ISO 10993-18 focuses on Annex E: Calculation and application of the analytical evaluation threshold (AET), and within that E.3: Determination of the uncertainty factor (UF). E.3 has been completely rewritten to provide more clarity on how the uncertainty factor is calculated. The value of the UF is used to calculate the AET and they are inversely proportional to each other i.e. a larger UF will give a smaller AET and vice versa. The AET is the threshold used to determine whether a chemical detected in the test sample is of a high enough concentration to be reported. The amendment details a new UF calculation method. The formula to calculate the UF now requires the relative standard deviation (RSD) of the response factors from the reference database. The reference database is internal, and the data is gathered from validated methods. A small UF is desired, because it shows that the variation in response factors is low and therefore suitable for reporting data, which is the foundation of a toxicological risk assessment. The use, value and the means of calculation of the uncertainty factor used should always be justified for each analytical method used.

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