Setting and Using Target Uncertainty in Chemical Measurement

A measurement procedure is valid, i.e. is fit for the intended purpose, if measurement uncertainty is small enough for the performed assessment on the measured quantity. Therefore, the last stage of measurement procedure validation involves assessing if procedure can produce measurements, in a relevant quantity range, with adequately low uncertainty.
In some analytical fields, maximum uncertainty values, i. e. target measurement uncertainties [1], are set to allow an adequate validation of the measurement procedure. Typically target uncertainty is set for the maximum and/or minimum limit values for the measured quantity. However, in many relevant fields no target values are defined for the uncertainty.
In this communication, criteria proposed in a Eurachem/CITAC guide for setting and using the target measurement uncertainty [2], when this parameter is not defined in a regulation or by the customer, are presented. Criteria are presented from the supported on available target values for some performance parameters, more likely to be consensual, to the ones where information about measurement use or performance in related analytical fields is considered.
The role of the target measurement uncertainty in measurement procedure validation indicates it must be defined, presented and compared with estimated measurement uncertainty.

1. Joint Committee for Guides in Metrology, International vocabulary of metrology – basic and general concepts and associated terms (VIM), 3rd edition – 2008 edition with minor corrections, JCGM 200, BIPM, 2012 (www.bipm.org).

2. R. Bettencourt da Silva, A. Williams (Eds), Eurachem/CITAC Guide: Setting and Using Target Uncertainty in Chemical Measurement, 1st edition, Eurachem, 2015 (www.eurachem.org).