Assesment of measurement uncertainty when determining heavy metal content in fly ash samples

Metrology is a science dealing with measurement but also a basic constituent of quality in-frastructure. Its main role is to ensure the appropriate accuracy, precision and reliability of measurement. Measurement is an activity that has been carried out since ancient times, and the results of this process may impact the quality of life to a large extent. According to Mendeleev, science begins where measurements begin. However, each measurement is loaded with corre-sponding measurement uncertainty. This problem is recognized by the international standardiza-tion organization (ISO), as well as by the International Electrotechnical Commission (IEC) in adopting the SRPS ISO/IEC 17025:2017 standard, which is used for accreditation of testing la-boratories. The assessment of measurement uncertainty ensures an increased confidence in the obtained results, especially when comparing the obtained values with legal regulations. This pa-per presents the process of determining combined uncertainty (u), as well as extended uncertainty (U) when examining the amount of heavy metals present in fly ash samples, using the bottom-up method. The identification of the processes in which measurement uncertainty arises has been de-termined using quality tools: flowcharts and cause-effect diagrams. The results obtained in this work showed that the calibration process mostly affects the measurement uncertainty. Moreover, the measurement uncertainty is highest when determining nickel, while it is lowest when determin-ing cadmium.