The CCQM-K34.2016 key comparison for determination of the purity of potassium hydrogen phthalate was organized jointly by the inorganic analysis and electrochemical analysis working groups of CCQM to repeat CCQM-K34 for supporting CMC claims of participating metrology institutes in assaying the amount content of monoprotic weak acid. National Institute of Metrology P.R.China (NIM) acted as the coordinating laboratory of this comparison. Twelve NMIs participated in this key comparison. With the exception of one laboratory that used NaOH-titration, all participants used coulometry. In general a good overlap of results was observed, the suitability of coulometry for assay of high purity materials was demonstrated again, and some possible technical problems were highlighted. The comparison tested the capabilities and methods used for assay of high purity materials. Good result indicates good performance in assaying the purity (amount content) of solid weak acids. KEY WORDS FOR SEARCH CCQM-K34.2016; potassium hydrogen phthalate; coulometry 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).

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Abstract. Coulometry is a primary method for measuring high purity substances. This is used to certify the primary reference materials required in a chemical analysis process. This paper describes the coulometric titration system developed by the National Metrology Institute (NMI) of Colombia for the certification of hydrochloric acid 0,1 mol·kg -1 . In addition, it also shows preliminary studies for future development of and ethylenediaminetetraacetic acid disodium salt (EDTA-Na 2 ) certification.