Understanding uncertainty to weighing by electronic-analytical balances

Weighing with electronic-analytical balances (EABs) is the most precise operation of measurement in the analytical laboratory, but the determination of the uncertainty of measurement remains an issue of some controversy. Manufacturers’ specifications are not always met during routine measurements, and method validation of weighing is therefore required to arrive at the true level of uncertainty. The aim of this study is to revisit concepts introduced by the Bureau International de Poids et Mesures, which are supposed to provide a level of uncertainty that corresponds to the observed uncertainty associated with those of the samples. Through the use of pooled calibrations, it is shown that the uncertainty of repetition should not be included in the uncertainty because it hampers the prediction of observed uncertainty. The principle of pooled calibrations was also used to show that certified-calibration masses had gained mass, on average, by approximately 0.001% since the date of production. The uncertainty of EABs, which was predicted in one laboratory, was found to correspond to the uncertainty observed for EABs in another laboratory situated in another part of the world. Accordingly, the principle of pooled calibrations was important to the prediction of the observed uncertainty of samples, which simplifies calculations and underpins scientific methodology.