Analytica Chimica Acta 481 (2003) 261–272 Determination of uncertainty in analytical measurements from collaborative study results on the analysis of a phenoxymethylpenicillin sample P. Dehouck a , Y. VanderHeyden b , J. Smeyers-Verbeke b , D.L. Massart b , J. Crommen c , Ph. Hubert c , R.D. Marini c , O.S.N.M. Smeets d , G. Decristoforo e , W. Van de Wauw f , J. De Beer f , M.G. Quaglia g , C. Stella h , J.-L. Veuthey h , O. Estevenon i , A. Van Schepdael a , E. Roets a , J. Hoogmartens a,∗ a Laboratorium voor Farmaceutische Chemie en Analyse van Geneesmiddelen, Faculteit Farmaceutische Wetenschappen, Katholieke Universiteit Leuven, Van Evenstraat 4, 3000 Leuven, Belgium b Pharmaceutical and Biomedical Analysis, VUB, Brussels, Belgium c Department of Analytical Pharmaceutical Chemistry, Institute of Pharmacy, University of Liège, Liège, Belgium d Wetenschappelijk Instituut van de Nederlandse Apothekers, The Hague, The Netherlands e Quality Control Laboratories—Industrial Products—Betalactams, NOVARTIS Generics, Kundl, Austria f Wetenschappelijk Instituut voor Volksgezondheid—Louis Pasteur, Brussels, Belgium g Laboratory Analisi Farmaceutica, University “La Sapienza”, Rome, Italy h Laboratoire de Chimie Analytique Pharmaceutique, University Geneva, Geneva, Switzerland i Laboratoire de Chimie Analytique, Université Henri Poincaré, Nancy, France Received 27 September 2002; received in revised form 10 January 2003; accepted 17 January 2003 Abstract The correct interpretation of a measurement result requires knowledge about its uncertainty. Depending on the conditions under which the analyst is operating, different operational definitions of uncertainty have been proposed. They include: within-laboratory uncertainty, reproducibility uncertainty, bias-included uncertainty and absolute uncertainty. Here we con- sider the evaluation of the reproducibility uncertainty derived from the results obtained in an inter-laboratory experiment. Nine laboratories participated in an inter-laboratory study for the analysis of phenoxymethylpenicillin. The analyses consisted of a Karl–Fischer water determination, an acid–base titration to assay phenoxymethylpenicillin and a liquid chromatography (LC) method to determine 4-hydroxyphenoxymethylpenicillin and other impurities. The experimental set-up allowed to obtain for each determination s 2 r and s 2 L as estimates of the repeatability variance (σ 2 r ) and the between-laboratory variance (σ 2 L ), respectively. The reproducibility uncertainties for the different assays were then derived from these estimates. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Uncertainty; Collaborative study; Reproducibility; Phenoxymethylpenicillin ∗ Corresponding author. Tel.: +32-16-323-442; fax: +32-16-323-448. E-mail address: jos.hoogmartens@farm.kuleuven.ac.be (J. Hoogmartens). 1. Introduction The interpretation of a measurement result requires knowledge about its uncertainty. Many important 0003-2670/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0003-2670(03)00079-5