Final report on key comparison CCQM-K73: Amount content of H⁺in hydrochloric acid (0.1 mol kg⁻¹)

Abstract

This key comparison (KC), CCQM-K73, was performed to demonstrate the capability of the participating National Metrology Institutes (NMIs) to measure the amount content of H+, νH+, in an HCl solution with a nominal νH+ of 0.1 mol kg−1. The comparison was a joint activity of the Electrochemical Working Group (EAWG) and Inorganic Analysis Working Group (IAWG) of the CCQM and was coordinated by NIST (USA) and CENAM (Mexico).The agreement of the results was not commensurate with the claimed uncertainties of the subset of participants that claimed small uncertainties for this determination. A workshop on technical issues relating to the CCQM-K73 measurements was conducted at the joint IAWG-EAWG meeting at the Bureau International des Poids et Mesures (BIPM), Paris (Sèvres) in April 2010. Several possible sources of bias were investigated, but none could explain the observed dispersion among the participants' results.In the absence of a specific cause for the dispersion, the IAWG and EAWG decided to assign a Key Comparison Reference Value, KCRV, and standard uncertainty of the KCRV, uKCRV, based on the DerSimonian–Laird statistical estimator. The uKCRV is dominated by the between-laboratory scatter of results in CCQM-K73. The uncertainty estimates from the participants with the lowest reported uncertainties remain unsupported by this KC.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Development of a coulometry system at the Korea Research Institute of Standards and Science and evaluation of the measurement uncertainty originating from the system

“…The performance of the first coulometry system was verified by the CCQM KC results [5][6][7][8][9][10]12] reported by the KRISS, as presented in table 9. The absolute values of the degrees of equivalences (d i ) divided by the expanded uncertainty of the d i for all results are less than 1, which indicates that all of the results obtained using the first coulometry system are consistent with the KC reference values within the associated expanded uncertainties.…”

“…By substituting equations ( 9) and (11) into equation (7), the u(i) for currents of 100 mA and 10 mA can be estimated. The estimated uncertainties are presented in tables 2 and 3.…”

“…The Electrochemical Analysis Working Group within the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM) first introduced this method in the CCQM-P7 international comparison to measure the amount content of various materials, such as K 2 Cr 2 O 7 , KCl, and NaCl [4]. Since then, national measurement institutes (NMIs) around the world have made efforts to establish national measurement standards for the amount contents of high-purity primary standards used in acid-base, redox, and precipitation titrations using this method, and numerous CCQM key comparisons (KCs) have been conducted to demonstrate the international equivalence between the established national measurement standards [5][6][7][8][9][10][11][12][13]. As part of these efforts, the Korea Research Institute of Standards and Science (KRISS) built its first coulometry system in 2000 and has recently constructed a second coulometry system to support ongoing research in the field of coulometry.…”

Candidate primary reference measurement procedure for the amount-of-substance content of a complexing agent expressed as EDTA based on the coulometric titration with electrogenerated Hg ions

“…In this method, the charge consumed or produced during the electrolysis of an analyte is measured and converted into the amount of substance using the Faraday constant as a conversion constant. This method has been successfully employed by the majority of the national measurement institutes, including the Korea Research Institute of Standards and Science (KRISS), which participated in international comparisons organized by the Electrochemical Analysis Working Group (EAWG) within the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM), in which the assay of high purity materials used as reference materials for acidbase, argentometric, and oxidation-reduction titrations was performed [2][3][4][5][6][7][8][9]. However, equivalent results from different national metrology institutes for the coulometric assay of ethylenediaminetetraacetic acid (EDTA), which is a representative substance of known high purity used as a reference for complexometric titration, have not been obtained up until the present.…”