Measurement uncertainty evaluation and traceability assurance for total fluorine determination in vegetation by fluoride ion selective electrode

Abstract

The evaluation of measurement uncertainty (MU) according to the Guide to the Expression of Measurement Uncertainty (GUM) is of great importance, because in addition to random effects, which are estimated by one standard deviation, also systematic effects are included. Furthermore, all uncertainty components are quantified and traceability to SI units is assured. In research laboratories, there is a lack of knowledge on how to introduce the GUM principles into analytical measurements, which is also illustrated by the scarcity of papers reporting results together with the MU. In order to clarify some of the issues related to this topic, a procedure for the MU evaluation based on the GUM for determination of fluorine in solid samples was suggested. The procedure was applied to determination of fluorine in tea as a model sample, because it is known to accumulate large amounts of fluorine in the leaves. Fluoride was determined with fluoride ion selective electrode after preceding total decomposition by alkaline carbonate fusion. The uncertainties according to the GUM represent 7–15% of the reported result. They are larger than standard deviations (1–5%) but only such results are trustworthy and have metrological value.