Measurements Recovery Evaluation from the Analysis of Independent Reference Materials: Analysis of Different Samples with Native Quantity Spiked at Different Levels

Rui Cordeiro, Chemistry and Biochemisty Department, Faculty of Sciences of the University of Lisbon, Lisboa, Portugal
Constantino Rosa, Laboratório, Labelec, Sacavém, Portugal
Ricardo Bettencourt da Silva, Chemistry And Biochemisty Department, Faculty Of Sciences Of The University Of Lisbon, Lisboa, Portugal

The measurement uncertainty evaluation involves combining uncertainty components reflecting all relevant random and systematic effects: the precision and trueness uncertainty components respectively. Typically, trueness is assessed from the analysis of various materials with a known reference value, such as Certified Reference Materials or spiked samples, from which it should be decided about the relevance and the need to correct result for systematic effects. Algorithms proposed so far to assess systematic effects are only applicable to the analysis of the same reference material type or assumes some uncertainty components affecting evaluations are negligible or constant. This work presents detailed algorithms for the assessment of systematic effects, through the determination of recovery and respective uncertainty, applicable the analysis of various independent reference materials such as Certified Reference Materials and spiked samples with native analyte. These algorithms are applicable to cases where native analyte determinations and/or spiking are associated with relevant and significantly different uncertainties allowing for a reliable assessment of systematic effects and measurement uncertainty. This methodology was successfully applied to the quantification of Na, K, Mg, Ca, Cr, Mn, Fe and Cu in waters from two proficiency tests, by ICP-OES, where recovery was estimated from the analysis of samples with different native concentrations and spiked at different levels. Results relative expanded uncertainty ranged from 28.9 % to 3.9 % and are fit for the monitoring of environmental water taking performance criteria set in the European Union legislation.