Determination of a reference value in the analysis of the key comparison data of CCQM-K9 on pH

摘要

The first international key comparison for the quantity pH, CCQM-K9 [0], was organised by the Working Group on Electrochemical Analysis (EAWG) within the Consultative Committee of Amount of Substance (CCQM) at BIPM. This comparison demonstrates the capability of ten national metrology institutes (NMIs) to determine the pH of primary reference buffer solutions at different temperatures. A high degree of agreement of the measurement results of the NMIs was evident. According to the high degree of overlap of the uncertainties stated by the participants, the individual laboratory uncertainties played a major part in determining the uncertainty of the key comparison reference value (KCRV). Assuming that all participants of the key comparison are equally competent, there was no reason to doubt their uncertainty statements, so these had been regarded as credible. Different approaches to assign the KCRV and the uncertainty associated with were taken into consideration and will be discussed. One participant discovered a calculation error which influenced the measurement result. A follow-up bilateral comparison was therefore agreed by the participants and the pilot laboratory. The result of the bilateral comparison allows a new line of data to be included for the participant in the table of matrices of equivalence of CCQM-K9. It will be demonstrated that the result of the pilot laboratory in CCQM-K9 acts as a link between the subsequent bilateral and the original key comparison.