Assay of potassium hydrogen phthalate (CCQM-K34.2016)

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.