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International Comparison of Carbonate pH Primary Measurement Method
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摘要: 简述了我国水溶液酸度(pH)基准3次参加碳酸盐pH测量国际比对的过程。在2006年CCQM.K18和2007年CCQM.K18.1比对中发现基准存在系统误差。经分析，认为这个负的系统误差是由于基准Harned-Cell电池的结构造成电极电势持续飘移，采用斜率倒推得到的平衡电势偏低而产生的。2009年基准进行了改造完善，采用了新的Harned-Cell电池结构，并在2020年APMP.QM-K18.2016国际比对中取得了国际等效一致，等效度DoE(di, U(di)) 为DoE(−0.0014, 0.0030)。Abstract: The process of the Chinese aqueous solution acidity (pH) primary standard participating in three international comparisons of carbonate pH measurements is briefly described. A systematic error in the benchmark was found in the 2006 CCQM.K18 and 2007 CCQM.K18.1 comparisons. It was concluded that the negative systematic error was caused by the continuous drift of the electrode potential due to the structure of the primary standard’s Harned-Cell and the low equilibrium potential obtained by using slope inversion. In 2009, the pH primary standard device was modified and improved with a new Harned-Cell structure, and in the international comparison of APMP.QM-K18.2016 in 2020, the international equivalence agreement was achieved, and the degree of equivalent DoE(di, U(di)) was DoE(−0.0014, 0.0030) .
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Key words:
- international comparison /
- pH /
- carbonate buffer /
- primary measurement method /
- degree of equivalent
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图 1 2009年基准改造前Harned-Cell电池结构图
Figure 1. The Harned-cell structure before the modification of primary standard in 2009
图 2 2009年基准改造后Harned-Cell电池结构图
Figure 2. The Harned-cell structure after the modification of primary standard in 2009
图 3 CCQM-K18（2006）和CCQM-K18.1（2007）国际比对等效度图
Figure 3. DoEs of CCQM-K18 (2006) and CCQM-K18.1 (2007)
图 4 APMP.QM-K18碳酸盐比对结果图
（2020，25 ℃，*为基准方法，×为次级方法）
Figure 4. Results of APMP.QM-K18
(2020，25 ℃，*primary，× secondary)
图 5 APMP.QM-K18碳酸盐比对等效度图
（2020，25 ℃，*为基准方法，×为次级方法）
Figure 5. DoEs of APMP.QM-K18
(2020，25 ℃，*primary，× secondary)
表 1 APMP.QM-K18的比对结果（2020）
Table 1. Results of APMP.QM-K18 (2020)
实验室简称 校准用标准 $p{({\alpha _{\rm{H}}}{\gamma _{{\rm{Cl}}}})^0}$ $\lg {\gamma _{{\rm{Cl}}}}^0$ CENAM 基准方法 10.1236 −0.10956 GLHK 玻璃电极法 / / NIST 186 g，NIST 191d IBMETRO 比较法 / / NIST 191d INMETRO 基准方法 10.1261 −0.10956 MUSSD 玻璃电极法 / / DAKKS/DIN 19266 ZENTRUM和Xylem NIM 基准方法 10.1259 −0.10956 NIMT 基准方法 10.11614 −0.10956 NMIJ 基准方法 10.12807 −0.10956 PTB 基准方法 10.13110 −0.10956 UMTS 基准方法 10.1168 −0.10956 VNIIFTRI 基准方法 10.12892 −0.10956 
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表 2 链接实验室PTB与NMIJ在CCQM-K18.2016的比对结果和比对等效度
Table 2. Results and DoEs of linking lab. PTB and NMIJ in CCQM-K18.2016
实验室简称 $p{a^0}:{\rm{CCQM}}$ $U(p{a^0}):{\rm{CCQM}}$ ${d_i}:{\rm{CCQM}}$ $u({d_i}):{\rm{CCQM}}$ $u'({d_i}):{\rm{CCQM}}$ NMIJ 10.1172 0.0024 0.0015 0.0035 0.0031 PTB 10.1187 0.0016 0.0030 0.0034 0.0029 KCRV 10.1157 0.0034 / / / ${d_{{\rm{mean}}}}:{\rm{CCQM}}$ / / 0.0023 / 0.0021
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表 3 APMP.QM-K18的等效度和扩展不确定度
Table 3. DoEs and expanded uncertainties of APMP.QM-K18
实验室简称 ${d_i}{\rm{:APMP}}$ $u({d_i}{\rm{):APMP}}$ $\begin{gathered} U({d_i}{\rm{):APMP}} \\ {\rm{ }}k = {\rm{2}} \\ \end{gathered} $ $ \begin{array}{l}U(\rm{CMC})\\ k=2\end{array}$ CENAM −0.0037 0.0063 0.0126 0.0113 GLHK −0.0013 0.0082 0.0164 0.0154 IBMETRO −0.0098 0.0057 0.0115 0.0100 INMETRO −0.0012 0.0029 0.0059 0.0018 MUSSD −0.0074 0.0080 0.0159 0.0149 NIM −0.0014 0.0032 0.0064 0.0030 NIMT −0.0112 0.0046 0.0093 0.0097* UMTS −0.0105 0.0034 0.0069 0.0089* VNIIFTRI 0.0016 0.0034 0.0068 0.0039
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[1] Measurement comparisons in the CIPM MRA. Guidelines for organizing, participating and reporting: CIPM MRA-G-11[S]. BIPM, 2021. [2] RP Buck, S. Rondinini, A. K. Covington, et al. Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002)[R]. IUPAC, 2002. [3] Bates R. G. “Determination of pH: Theory and Practice”[M]. Second Edition. United of States of America, 1954. [4] Rachel. “Metrology of pH at LNE: State of the art and perspectives”[J]. REVUE FRANÇAISE DE MÉTROLOGIE n°5, 2006(1): 13-21. [5] L. Vyskočil, M Máriássy, Susumu Nakamura, et al. Report of key comparison CCQM-K18: pH of carbonate buffer[R]. CCQM, 2006. [6] L. Vyskočil, M Máriássy, Marcela Monroy, et al. Final report on subsequent key comparison CCQM-K18.1: pH of carbonate buffer[R]. CCQM, 2007. [7] Toshiaki Asakail, Igor Maksimov, Sachiko Onuma, et al. APMP. QM-K18.2016: Key Comparison on pH Measurement of Carbonate Buffer Draft B report (November 16, 2020)[R]. APMP, 2020. [8] Jason F. Waters, Michal Máriássy, Frank Bastkowski, et al. Key Comparison CCQM–K18.2016: pH of carbonate buffer final report[R]. CCQM, 2016. -
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