Aplicação da incerteza de medição e carta controle em análises de mercúrio por TDA-AAS

Abstract

Scientific and technological advances have promoted the emergence of metrology in the search for traceable standards to reliably compare results from different locations. In Brazil, INMETRO was created to facilitate the traceability of standards by supporting the accreditation process of laboratories according to ISO/IEC 17025:2017. This technical standard outlines the procedures that laboratories must follow to ensure the reliability and safety of the results they provide to their customers. Among the procedures to be followed, the determination of the measurement uncertainty associated with chemical testing is essential, as it seeks to identify the factors influencing the result so that they can be quantified, minimised or eliminated - as these factors can cause the measured value to deviate from the true value of the measurand. It is also essential to monitor the stability of the method used to determine the measurand, which can be done using control charts. These charts define a central limit (CL), an upper control limit (UCL) and a lower control limit (LCL). These limits establish a range within which data points should fall to ensure that the process remains under control. This assessment can be performed using a certified reference material (CRM), provided it has a defined and certified associated uncertainty, or an appropriate internal reference material (IRM), if the uncertainty is determined by the laboratory itself. In view of this, the present study aimed to evaluate the quality and reliability of results obtained for the determination of mercury using the DMA-80, as mercury is a hazardous analyte for public and environmental health due to its high biomagnification and bioaccumulation capacity. Monitoring was carried out using an internal reference material obtained by diluting a CRM. The calibration curve did not fully comply with the manufacturer's recommendations and the adopted method, the evaluation of the measurement uncertainty showed a significant contribution from reproducibility and repeatability, and the control chart indicated that the procedure was out of control. The results presented indicate that the procedure is not suitable for the accreditation process of the laboratory, with factors such as laboratory air quality and the quality of the water used in solution preparation being the main contributors to the uncertainty of results in this chemical test.