CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 15 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i} (k = 2)
Red diamonds: participants in CCQMK17
Green triangle: participant in EUROMET.QMK17
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 25 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i} (k = 2)
Red diamonds: participants in CCQMK17
Green triangle: participant in EUROMET.QMK17
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 37 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i} (k = 2)
Red diamonds: participants in CCQMK17
Green triangle: participant in EUROMET.QMK17
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 15 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i }(k = 2)
BNMLNE*: participant in EUROMET.QMK17
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 25 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i }(k = 2)
BNMLNE*: participant in EUROMET.QMK17
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 37 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
Degrees of equivalence D_{i} and expanded uncertainty U_{i }(k = 2)
BNMLNE*: participant in EUROMET.QMK17
Metrology area, Subfield  Chemistry and Biology, Electrochemistry 
Description  pH measurement of phthalate buffer solutions 
Time of measurements  2001 
Status  Approved for equivalence 
Final Reports of the comparisons  
Measurand  pH 4.1 at temperature 25 °C 
Parameters  Temperature: 15 °C, 25 °C and 37 °C 
Transfer device  A phthalate buffer, containing potassium hydrogen phthalate at a molality of 0.05 mol/kg 
Comparison type  Key Comparison 
Consultative Committee  CCQM (Consultative Committee for Amount of Substance) 
Conducted by  CCQM (Consultative Committee for Amount of Substance) 
Comments  EUROMET.QMK17 results are linked to those of CCQMK17. CCQMK17 results were published on 8 September 2003, and EUROMET.QMK17 results on 28 February 2005. pH determination of a phthalate buffer at temperatures ranging from 15 °C to 37 °C. 
Pilot institute 
PTB
PhysikalischTechnische Bundesanstalt Germany 
Contact person  P. Spitzer +49 (0) 531 592 3130 
Pilot laboratory  

PTB 
PhysikalischTechnische Bundesanstalt, Germany, EURAMET 
CENAM 
Centro Nacional de Metrologia, Mexico, SIM 
CMI 
Czech Metrology Institute, Czechia, EURAMET 
GUM 
Glowny Urzad Miar, Central Office of Measures, Poland, EURAMET 
KRISS 
Korea Research Institute of Standards and Science, Korea, Republic of, APMP 
NIST 
National Institute of Standards and Technology, United States, SIM 
NMIJ AIST 
National Metrology Institute of Japan, Japan, APMP 
SMU 
Slovensky Metrologicky Ustav, Slovakia, EURAMET 
VNIIFTRI 
Institute of Physical Technical and Radiotechnical Measurements, Rosstandart, Russian Federation, COOMET 
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CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 15 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
The key comparison reference value, pH_{R}, is obtained as the varianceweighted mean of the results from the participants. The standard uncertainty, u_{R}, of pH_{R} is calculated according to the external consistency concept (see page 8 of CCQMK17 Final Report). pH_{R} = 4.0093 and u_{R} = 0.00089 
The degree of equivalence of each laboratory with respect to the key comparison reference value is given by a pair of terms: D_{i }= (pH_{i}  pH_{R}) and U_{i}, its expanded uncertainty (k = 2), U_{i} = 2(u_{i}^{2} + u_{R}^{2})^{1/2}. Note that this gives a conservative estimate of U_{i}. 
The degree of equivalence between two laboratories may be calculated using the following pair of terms: D_{ij} = D_{i}  D_{j} = pH_{i}  pH_{j} and U_{ij}, its expanded uncertainty (k = 2), U_{ij} = 2(u_{i}^{2} + u_{j}^{2})^{1/2}. No numerical values of pairwise degrees of equivalence are given. 
The PTB acted as pilot laboratory in both key comparisons.
To link the results obtained by the BNMLNE in EUROMET.QMK17 to CCQMK17 the performance of PTB within its uncertainty is assumed to be similar in both comparisons. Therefore it is assumed that the bias between the PTB results and the key comparison reference value remains constant over both comparisons.
The degree of equivalence of the BNMLNE with respect to the key comparison reference value is given by a pair of terms: D_{i } and U_{i}, its expanded uncertainty
(k = 2), see equations 1 to 4 in the EUROMET.QMK17 Final Report.
The pairwise degrees of equivalence involving the BNMLNE are not calculated. 
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 25 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
The key comparison reference value, pH_{R}, is obtained as the varianceweighted mean of the results from the participants. The standard uncertainty, u_{R}, of pH_{R} is calculated according to the external consistency concept (see page 8 of CCQMK17 Final Report). pH_{R} = 4.0156 and u_{R} = 0.00109 
The degree of equivalence of each laboratory with respect to the key comparison reference value is given by a pair of terms: D_{i }= (pH_{i}  pH_{R}) and U_{i}, its expanded uncertainty (k = 2), U_{i} = 2(u_{i}^{2} + u_{R}^{2})^{1/2}. Note that this gives a conservative estimate of U_{i}. 
The degree of equivalence between two laboratories may be calculated using the following pair of terms: 
The PTB acted as pilot laboratory in both key comparisons.
To link the results obtained by the BNMLNE in EUROMET.QMK17 to CCQMK17 the performance of PTB within its uncertainty is assumed to be similar in both comparisons. Therefore it is assumed that the bias between the PTB results and the key comparison reference value remains constant over both comparisons.
The degree of equivalence of the BNMLNE with respect to the key comparison reference value is given by a pair of terms: D_{i }and U_{i}, its expanded uncertainty
(k = 2), see equations 1 to 4 in the EUROMET.QMK17 Final Report.
The pairwise degrees of equivalence involving the BNMLNE are not calculated. 
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}Measurements at 37 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
The key comparison reference value, pH_{R}, is obtained as the varianceweighted mean of the results from the participants. The standard uncertainty, u_{R}, of pH_{R} is calculated according to the external consistency concept (see page 8 of CCQMK17 Final Report). pH_{R} = 4.0343 and u_{R} = 0.00125 
The degree of equivalence of each laboratory with respect to the key comparison reference value is given by a pair of terms: D_{i }= (pH_{i}  pH_{R}) and U_{i}, its expanded uncertainty (k = 2), U_{i} = 2(u_{i}^{2} + u_{R}^{2})^{1/2}. Note that this gives a conservative estimate of U_{i}. 
The degree of equivalence between two laboratories may be calculated using the following pair of terms: D_{ij} = D_{i}  D_{j} = pH_{i}  pH_{j} and U_{ij}, its expanded uncertainty (k = 2), U_{ij} = 2(u_{i}^{2} + u_{j}^{2})^{1/2}. No numerical values of pairwise degrees of equivalence are given. 
The PTB acted as pilot laboratory in both key comparisons.
To link the results obtained by the BNMLNE in EUROMET.QMK17 to CCQMK17 the performance of PTB within its uncertainty is assumed to be similar in both comparisons. Therefore it is assumed that the bias between the PTB results and the key comparison reference value remains constant over both comparisons.
The degree of equivalence of the BNMLNE with respect to the key comparison reference value is given by a pair of terms: D_{i }and U_{i}, its expanded uncertainty
(k = 2), see equations 1 to 4 in the EUROMET.QMK17 Final Report.
The pairwise degrees of equivalence involving the BNMLNE are not calculated. 
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}
Measurements at 15 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
pH_{i} : result of measurement carried out by laboratory i
u_{i} : combined standard uncertainty (k = 1) of pH_{i}U_{i }: expanded uncertainty (k = 2) of pH_{i}, U_{i} = 2u_{i}

pH_{i}  u_{i}  Date of measurement 
NRCCRM  4.0070  0.0020  Aug 01 
PTB  4.0100  0.0011  Jul 01 
Radiometer A/S  4.0074  0.0008  Jul 01 
KRISS  4.0033  0.0015  Jul 01 
NMIJ  4.0024  0.0032  Jul 01 
CENAM  4.0020  0.0024  Jul 01 
GUM  4.0123  0.0015  Jul 01 
VNIIFTRI  4.0130  0.0013  Jul 01 
SMU  4.0095  0.0011  Sep 01 
CMI  4.0014  0.0017  Sep 01 
NIST  4.0108  0.0005  Jul 01 

pH_{i}  U_{i}  Date of measurement 
BNMLNE  3.9919  0.0024  Feb 03 
PTB  3.9985  0.0024  Jan 03 
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}
Measurements at 25 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
pH_{i} : result of measurement carried out by laboratory i
u_{i} : combined standard uncertainty (k = 1) of pH_{i}U_{i }: expanded uncertainty (k = 2) of pH_{i}, U_{i} = 2u_{i}

pH_{i}  u_{i}  Date of measurement 
NRCCRM  4.0150  0.0020  Aug 01 
PTB  4.0168  0.0011  Jul 01 
Radiometer A/S  4.0150  0.0008  Jul 01 
KRISS  4.0104  0.0017  Jul 01 
NMIJ  4.0108  0.0030  Jul 01 
CENAM  4.0050  0.0022  Jul 01 
GUM  4.0183  0.0015  Jul 01 
VNIIFTRI  4.0193  0.0013  Jul 01 
SMU  4.0174  0.0011  Sep 01 
CMI  4.0050  0.0017  Sep 01 
NIST  4.0170  0.0006  Jul 01 

pH_{i}  U_{i}  Date of measurement 
BNMLNE  4.0002  0.0038  Feb 03 
PTB  4.0052  0.0024  Jan 03 
CCQMK17 and EUROMET.QMK17
MEASURAND : pH value of phthalate buffer
Sample: Potassium hydrogen phthalate, KHC_{8}H_{4}O_{4}
Measurements at 37 °C
NOMINAL VALUE : pH = 4.0 at 25 °C
pH_{i} : result of measurement carried out by laboratory i
u_{i} : combined standard uncertainty (k = 1) of pH_{i}U_{i }: expanded uncertainty (k = 2) of pH_{i}, U_{i} = 2u_{i}

pH_{i}  u_{i}  Date of measurement 
NRCCRM  4.0370  0.0020  Aug 01 
PTB  4.0360  0.0015  Jul 01 
Radiometer A/S  4.0351  0.0008  Jul 01 
KRISS  4.0296  0.0017  Jul 01 
NMIJ  4.0261  0.0039  Jul 01 
CENAM  4.0290  0.0020  Jul 01 
GUM  4.0355  0.0015  Jul 01 
VNIIFTRI  4.0380  0.0013  Jul 01 
SMU  4.0397  0.0015  Sep 01 
CMI  4.0272  0.0011  Sep 01 
NIST  4.0371  0.0013  Jul 01 

pH_{i}  U_{i}  Date of measurement 
BNMLNE  4.0209  0.0046  Feb 03 
PTB  4.0225  0.0024  Jan 03 