Harned cell pH T measurements were performed on 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) buffered artificial seawater solutions in the salinity range 5-20, at three equimolal buffer concentrations (0.01, 0.025, 0.04 mol·kg-H 2 O −1 ), and in the temperature range 278.15-318.15 K. Measurement uncertainties were assigned to the pH T values of the buffer solutions and ranged from 0.002 to 0.004 over the investigated salinity and temperature ranges. The pH T values were combined with previous results from literature covering salinities from 20 to 40. A model function expressing pH T as a function of salinity, temperature and TRIS/TRIS·H + molality was fitted to the combined data set. The results can be used to reliably calibrate pH instruments traceable to primary standards and over the salinity range 5-40, in particular, covering the low salinity range of brackish water for the first time. At salinities 5-20 and 35, the measured dependence of pH T on the TRIS/TRIS·H + molality enables extrapolation of quantities calibrated against the pH T values, e.g., the dissociation constants of pH indicator dyes, to be extrapolated to zero TRIS molality. Extrapolated quantities then refer to pure synthetic seawater conditions and define a true hydrogen ion concentration scale in seawater media.
Key Comparison CCQM-K36.2016 was a follow-up comparison for K36 and provided updated support for the corresponding calibration and measurement capability (CMC) entries in the BIPM CMC database. It aimed to demonstrate the capabilities of the participating NMIs to measure electrolytic conductivity of aqueous electrolyte solutions in the conductivity range 0.15 S m−1 to 1.5 S m−1 and in the conductivity range 1.5 mS m−1 to 15 mS m−1. To this end electrolytic conductivity of a potassium chloride solution (nominal conductivity 0.5 S m−1) and of a HCl solution (nominal conductivity 5 mS m−1) had to be measured. 17 NMIs participated in the comparison. The key comparison reference value (KCRV) of the KCl solution was (0.50999 +/-0.00032) S m−1 and the KCRV of the HCl solution was (4.9877 +/-0.012) mS m−1. Both values were estimated from the medians of the results considered eligible for KCRV calculation. They were given with their expanded uncertainties (95% coverage). The majority of the 0.5 S m-1 results were consistent with the KCRV. Two institutes showed a small inconsistency, one outlier was observed. The conductivity of the HCl solution showed a small, but steady linear drift of 0.00006843 mS m−1 per day during the measurement period and was corrected for KCRV calculation. Some institutes reported unstable measurement conditions for this solution. The results of seven participants have been inconsistent with the KCRV. 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).
Main text The CCQM key comparison K73.2018 is a follow-up comparison of CCQM-K73. It was performed to demonstrate the capability of the participating institutes to measure the amount content of H+ in hydrochloric acid of 0.1 mol·kg−1 molality. 16 NMIs participated in this comparison. The comparison was coordinated by PTB. The sample showed a slight but significant instability by loss of water of around 0.11 μmol kg−1d−1 corresponding to 0.02 % over the measurement period. Therefore, the results were corrected for this instability. The results of this key comparison show good equivalence between the majority of participants. The equivalence is significantly better compared to the first comparison CCQM-K73. 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).
Main text This key comparison is being performed to evaluate the degree of equivalence of measurement procedures to support the participants' claims of Calibration and Measurement Capabilities (CMCs) and to evaluate the capabilities of participants for the determination of the pH of carbonate buffer solutions. This is the fourth APMP key comparison on pH measurement following APMP.QM-K9/P16 (phosphate), APMP.QM-K19/P25 (borate) and APMP.QM-K91/P29 (phthalate). The results have the linkage to CCQM-K18.2016 (carbonate buffer) and were evaluated by comparing the results of the Physikalisch-Technische Bundesanstalt (PTB) and the National Metrology Institute of Japan (NMIJ) performing Harned cell method. The results of PTB and NMIJ were used for the definition of the Key Comparison Reference Value (KCRV). The ensuing pH value was calculated based on the Bates-Guggenheim convention to compare the results of primary and secondary methods. In this comparison measurements of pH were performed only at the temperature of 25 °C. The results demonstrated by most participants are in better agreement than those in CCQM-K18.2016. 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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