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Degrees of Equivalence for Chemical Measurement Capabilities: Primary pH

Published

Author(s)

David L. Duewer, Kenneth W. Pratt, Chainarong Cherdchu, Nongluck Tangpaisarnkul2 Nongluck Tangpaisarnkul2, Akiharu Hioki, Masaki Ohata, Petra Spitzer, Michal M?ri?ssy, Leo¿ Vysko¿il

Abstract

The Key Comparison (KC) studies of the Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM) help ensure the reliability of chemical and biochemical measurements relevant to international trade and environmental , health , and safety related decision making. The Working Groups of the CCQM are responsible for selecting and conducting KCs that enable national metrology institutes (NMIs) and related organizations to publicly document their measurement capabilities. The usual result for each measurement result reported in a KC is a result specific “degree of equivalence” (DEq) that quantitatively specifies how consistent the result is relative to a reference value. Recognizing the impossibility of conducting separate KCs for all important analytes in all important sample matrices at all important analyte levels, several of the CCQM Working Groups are now designing KCs to document broadly applicable critical or “core” measurement competencies in addition to specific measurement challenges. Successful participation in a combination of these “core competency” KCs will enable participants to document their measurement capabilities for broad classes of measurement tasks. To better accomplish the required synthesis of results, data analysis methods must be developed for objectively and quantitatively combing individual DEqs. The pH measurements reported in the Final Reports of KCs conducted by the CCQM Electroanalytical Working Group (EAWG) and two regional metrology organizations provide an excellent initial model for “core competency” studies. To date, primary method pH results are publicly available for 11 KCs involving 20 NMIs, 5 buffer systems, and 3 evaluation temperatures. This report proposes data analysis and display tools for combining the result specific DEqs for these measurements into summaries that document the expected measurement performance of the NMIs for primary pH measurements between pH 1 to pH 11 and from 15 °C to 37 °C.
Citation
Accreditation and Quality Assurance
Volume
19

Keywords

Consultative Committee for Amount of Substance – Metrology in Chemistry, degree of equivalence, Electroanalytical Working Group, key comparison, leave one out, parametric bootstrap Monte Carlo, pH
Created September 10, 2014, Updated November 10, 2018