3.1 - Introduction to Quality Assurance and Uncertainty Budget
Quality assurance in analysis is a critical aspect that guarantees the quality of the results obtained by the method used. That means, the methods proposed had to be validated extensively during its development, in order to assure the validity of the results, determine its quality parameters, but also to detect potential sources of error. Moreover, during the application of the validated methods, regular checks have to be done in order to assure the trueness of the results reported. Some of the common actions, performed in the quality assurance of analytical methods, are: periodic analysis of control samples, participation in interlaboratory exercises and proficiency tests, analysis of reference certificate materials, methods comparison, analysis of blank samples and to check of instrumental stability.
Two of the most relevant quality parameters that have to be taken into consideration, are limit of detection and uncertainty budget. Limit of detection defines the capacity of the method and which activity levels can be measured. Analysis of uncertainties associated to the analysis provides a measure of dispersion of the values, which could be reasonably attributed to the measurand. It helps understanding the method and detecting sources of errors.
In this sense, uncertainty analysis and determination of sources of errors, given for the procedures described in this Handbook, have been identified and quantified according to the recommendations made by IAEA [De Regge and Fejgelj 2004], EURACHEM [EURACHEM 2012] and the Guide of Uncertainty [JCGM 2008] for the total uncertainty budget.
The methods for the determination of Radium via Radon extraction (procedure 18.104.22.168.) as well as by means of Radium RAD Disk (procedure 22.214.171.124.) are validated below in detail. Lower Limits of Detection LLD are calculated explicitely and are presented as general examples.
De Regge P. and Fajgelj A. 2004: Quantifying uncertainties in nuclear analytical measurements; International Atomic Energy Agency, TECDOC Series No.1401
EURACHEM 2012: EURACHEM/CITAC Guide CG 4. Quantifying Uncertainty in Analytical Measurement; 3rd ed. EURACHEM/CITAC
JCGM 2008: Joint Committee on Guides in Metrology, Evaluation of measurement data – Guide to the expression of uncertainty in measurement; JCGM 101, 2008 and Supplements