Comparison Display

CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

pH at 15 °C

D_i

Participating institutes

Enlarged graph

CCQM-K99_T15_Graph

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

pH at 25 °C

D_i

Participating institutes

Enlarged graph

CCQM-K99_T25_Graph

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

pH at 37 °C

D_i

Participating institutes

Enlarged graph

CCQM-K99_T37_Graph

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

LAB_i	D_i	U_neg,i	U_pos,i
	dimensionless	dimensionless	dimensionless
BIM	-0.001	0.004
CENAM	0.000	0.004
CMI	0.002	0.003
DFM	0.000	0.002
GUM	-0.009	0.003
INDECOPI	-0.002	0.004
INMETRO	0.002	0.003
MKEH	0.000	0.006
NIMT	-0.055	0.039
NIST	0.002	0.002
NMIJ	0.000	0.003
PTB	-0.001	0.003
SMU	-0.001	0.004
UME	-0.022	0.002
SE "Ukrmetrteststandard"	0.012	0.006
VNIIFTRI	-0.004	0.004
KRISS	-0.001	0.004

Participating institutes

CCQM-K99

CCQM-K99.1

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

LAB_i	D_i	U_neg,i	U_pos,i
	dimensionless	dimensionless	dimensionless
BIM	-0.002	0.004
CENAM	-0.001	0.006
CMI	0.004	0.003
DFM	-0.001	0.002
GUM	-0.007	0.003
IBMETRO	0.003	0.010
INDECOPI	-0.004	0.004
INMETRO	0.001	0.003
LATU	-0.004	0.010
MKEH	-0.002	0.007
NIMT	-0.057	0.029
NIST	0.001	0.002
NMIJ	-0.001	0.002
PTB	-0.001	0.003
SMU	-0.003	0.003
UME	0.005	0.002
SE "Ukrmetrteststandard"	0.005	0.004
VNIIFTRI	-0.006	0.004
KRISS	-0.002	0.004

Participating institutes

CCQM-K99

CCQM-K99.1

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

Degrees of equivalence represented by D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence.

LAB_i	D_i	U_neg,i	U_pos,i
	dimensionless	dimensionless	dimensionless
BIM	-0.006	0.004
CENAM	-0.004	0.005
CMI	-0.006	0.004
DFM	0.001	0.002
GUM	-0.010	0.004
INDECOPI	0.000	0.004
INMETRO	-0.001	0.005
LATU	0.002	0.010
MKEH	-0.004	0.007
NIMT	-0.053	0.022
NIST	0.002	0.002
NMIJ	0.001	0.003
PTB	0.001	0.003
SMU	-0.001	0.004
UME	-0.020	0.003
SE "Ukrmetrteststandard"	0.004	0.005
VNIIFTRI	-0.004	0.005
KRISS	0.001	0.004

Participating institutes

CCQM-K99

CCQM-K99.1

Comparison

Comparison close

CCQM-K99.1

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Information & contact
Participants

Metrology area, Sub-field	Chemistry and Biology, Electrochemistry
Description	pH of a phosphate buffer
Time of measurements	2025
Status	Approved for equivalence

Final Reports of the comparisons	CCQM-K99.1 Final report 2025 18pp DOI:10.59161/YSBU4088
Measurand	Acidity function at zero chloride molality of an phosphate buffer
Parameters	pH ~ 7.5 Measurement temperatures: 15 °C, 25 °C, 37 °C

Comparison type	Key Comparison
Consultative Committee	CCQM (Consultative Committee for Amount of Substance)
Conducted by	CCQM (Consultative Committee for Amount of Substance)
Comments	This key comparison is a bilateral, subsequent key comparison to CCQM-K99 on the pH of an unknown phosphate buffer. PTB will be the linking laboratory. pH is one of the fundamental properties of aqueous solutions and is measured routinely in laboratories. This study aims to evaluate the degree of equivalence of the primary pH measurements at KRISS with the key comparison value of CCQM-K99, and aims to support respective CMCs in the KCDB. Results published 02 February 2026
Pilot institute	KRISS Korea Research Institute of Standards and Science Korea, Republic of
Contact person	Min-Ah Oh +820428685779
Additional	Kyungmin Jo, Korea Research Institute of Standards and Science

Pilot laboratory
KRISS	Korea Research Institute of Standards and Science, Korea, Republic of, APMP

PTB	Physikalisch-Technische Bundesanstalt, Germany, EURAMET

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

The key comparison reference value x_R and its associated standard uncertainty u_R is obtained by calculating the weigthted mean including the institutes using primary standards for which the results passed a previously defined consistancy filter.

x_R = 7.5561 u_R = 0.0009

The degree of equivalence of laboratory i relative to the key comparison reference value x_R is given by a pair of terms:

D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence where U_i = 2 ( (1 − 2w_i) u_i² + u_R²)^1/2 where w_i represents the weight of laboratory i.

Linking CCQM-K99.1 to CCQM-K99

PTB provides the link between the key comparison CCQM-K99 and CCQM-K99.1, having participated in both comparisons. The linking process is described in Section 9 of the CCQM-K99.1 Final report.

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

x_R = 7.5246 u_R = 0.0008

The degree of equivalence of laboratory i relative to the key comparison reference value x_R is given by a pair of terms:

D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence where U_i = 2 ( (1 − 2w_i) u_i² + u_R²)^1/2 where w_i represents the weight of laboratory i.

Linking CCQM-K99.1 to CCQM-K99

PTB provides the link between the key comparison CCQM-K99 and CCQM-K99.1, having participated in both comparisons. The linking process is described in Section 9 of the CCQM-K99.1 Final report.

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

x_R = 7.5013 u_R = 0.0009

The degree of equivalence of laboratory i relative to the key comparison reference value x_R is given by a pair of terms:

D_i = (x_i - x_R) and its expanded uncertainty U_i at a 95 % level of confidence where U_i = 2 ( (1 − 2w_i) u_i² + u_R²)^1/2 where w_i represents the weight of laboratory i.

Linking CCQM-K99.1 to CCQM-K99

PTB provides the link between the key comparison CCQM-K99 and CCQM-K99.1, having participated in both comparisons. The linking process is described in Section 9 of the CCQM-K99.1 Final report.

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

x_i measurement value submitted by institute i, Lab_i

u_i combined standard uncertainty of x_i

CCQM-K99

Lab_i	x_i	u_i
Lab_i	x_i	u_i
BIM	7.5553	0.0020
CENAM	7.5561	0.0016
CMI	7.5585	0.0013
DFM	7.5563	0.0008
GUM	7.5474	0.0013
INDECOPI	7.5542	0.0020
INMETRO	7.5582	0.0013
MKEH	7.5558	0.0030
NIMT	7.5006	0.0197
NIST	7.5578	0.0008
NMIJ	7.5561	0.0010
PTB	7.5553	0.0011
SMU	7.5554	0.0016
UME	7.5337	0.0010
SE "Ukrmetrteststandard"	7.5683	0.0028
VNIIFTRI	7.5520	0.0020

CCQM-K99.1

Lab_i	x_i	u_i

KRISS	7.3265	0.0013

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

x_i measurement value submitted by institute i, Lab_i

u_i combined standard uncertainty of x_i

CCQM-K99

Lab_i	x_i	u_i
Lab_i	x_i	u_i
BIM	7.5228	0.0020
CENAM	7.5239	0.0027
CMI	7.5287	0.0013
DFM	7.5232	0.0008
GUM	7.5178	0.0014
IBMETRO	7.5276	0.0050
INDECOPI	7.5209	0.0020
INMETRO	7.5255	0.0013
LATU	7.5206	0.0050
MKEH	7.5226	0.0033
NIMT	7.4679	0.0143
NIST	7.5255	0.0008
NMIJ	7.5236	0.0010
PTB	7.5235	0.0011
SMU	7.5220	0.0015
UME	7.5291	0.0010
SE "Ukrmetrteststandard"	7.5295	0.0021
VNIIFTRI	7.5190	0.0021

CCQM-K99.1

Lab_i	x_i	u_i

KRISS	7.2936	0.0014

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CCQM-K99 and CCQM-K99.1

MEASURAND pH value of an unknown phosphate buffer

NOMINAL VALUE pH = 7.5

x_i measurement value submitted by institute i, Lab_i

u_i combined standard uncertainty of x_i

CCQM-K99

Lab_i	x_i	u_i
Lab_i	x_i	u_i
BIM	7.4951	0.0020
CENAM	7.4973	0.0024
CMI	7.4954	0.0020
DFM	7.5021	0.0008
GUM	7.4917	0.0016
INDECOPI	7.5014	0.0020
INMETRO	7.5006	0.0022
LATU	7.5029	0.0050
MKEH	7.4973	0.0034
NIMT	7.4482	0.0110
NIST	7.5036	0.0008
NMIJ	7.5025	0.0010
PTB	7.5027	0.0011
SMU	7.5005	0.0019
UME	7.4812	0.0010
SE "Ukrmetrteststandard"	7.5055	0.0021
VNIIFTRI	7.4970	0.0023

CCQM-K99.1

Lab_i	x_i	u_i

KRISS	7.2725	0.0014

KCDB

CIPM MRA

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Key and supplementary comparisons - Print out