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.

根据测量不确定度表达指南对测量不确定度（MU）进行评估（GUM）非常重要，因为除了通过一个标准偏差估算的随机效应之外，还包括系统效应。此外，所有不确定因素均已量化，并确保了对SI单位的可追溯性。在研究实验室中，缺乏如何将GUM原理引入分析测量的知识，这也可以通过与MU一起报告结果的论文匮乏来说明。为了阐明与该主题相关的一些问题，建议了一种基于GUM的MU评估方法，用于测定固体样品中的氟。该方法用于测定茶叶中的氟作为模型样品，因为已知在茶叶中会积累大量的氟。在通过碱金属碳酸盐熔融完全分解之前，用氟离子选择性电极测定氟化物。根据GUM的不确定性占报告结果的7-15％。它们大于标准偏差（1-5％），但是只有这样的结果才是可信赖的并且具有计量价值。