Z-score, a tool for quality assurance of analytical results in neutron activation analysis

Abstract

The Nuclear and Energy Research Institute (IPEN CNEN / SP), through the Research Reactor Center (CERPq), conducts several studies using Instrumental Neutron Activation Analysis (INAA) in its Activation Analysis Laboratory (LAN). The present study performed a critical analysis of the way Certified Reference Materials (CRM) are used to assess accuracy in LAN activities, from a statistical point of view. With the wide dissemination and application of metrological concepts, the use of regulatory standards (ABNT and INMETRO) became increasingly necessary. The literature defines several approaches to the statistical principles for the use of the obtained values. CRMs are used to assess the accuracy of analytical methods, being essential for trueness assessment. There are a few ways to quantify trueness, and this can be done by percent relative error and z score, determining the trend of the analytical method, which is defined as the estimation of a systematic error. The use of z scores is interesting in evaluating the quality of analytical methods, as it is less subject to the influence of the concentration value. Theses and dissertations developed at LAN were selected as the object of study and the calculations were performed using the concepts presented to verify the data treatment, at a 95% confidence level, presenting satisfactory results.