Federal Institute for Materials Research and Testing,
Analytical Chemistry; Reference Materials,
Richard-Willstaetter-Strasse 11, D-12489 Berlin/Germany
Tel. +49 30 8104 1100, Fax +49 30 8104 1117
Certificate no. U2-0113 for reference material
Supplier of the reference Sigma-Aldrich Production GmbH, Industriestrasse 25, CH-9471 Buchs/Switzerland
material:
Object of certification:
Product no. 60357, Potassium Hydrogen Phthalate: KHC8H4O4 acidimetric standard in 50
ml glass bottles, screw caps; batch no.BCBH6361V
Certification report no. 1170/IX2, BAM Berlin
Intended use:
This reference material is intended for use as acidimetric standard and cannot be
employed as purity standard or pH standard.
Storing and handling
Ensure that the reference material is stored in the dark (i.e. within the packaging of the
flask) at temperatures in the range of 5°C to 30°C. Before any use as a reference material
it has to be dried for 3 hours at 120°C. After the flask is opened it should be used
according to established rules in analytical chemistry (i.e. to guarantee that no
contamination can take place). The use of samples less than 175 mg is prohibited in order
to avoid possible inhomogeneities with smaller sample sizes (see part. 2 of certification
report).
Number of pages of this
certificate:
1
Annex:
Certification report no. 1170/IX2 (2 pages), BAM Berlin, as part of this certificate
Expiry date:
25 January 2018 5
Certified value and its measurement uncertainty according to ISO Guide 35:
Constituent (formula) and relative
Expanded uncertainty 1
Certified value
molar mass for reporting
Coverage factor = 2
Potassium Hydrogen Phthalate
(KHC8H4O4)
Mr = 204.2212 4
1
2
3
4
5
w = 99.970 % 2
0.99970 mol/mol
± 0.070 % 2
± 0.00070 mol/mol 3
Methods of analysis
volumetric acid-base
titration
Eurachem / CITAC Guide „Quantifying Uncertainty in Analytical Measurement“, Third Edition, 2012
Mass content of acid, calculated as potassium hydrogen phthalate
Fraction of measured molar amount in relation to the theoretical value referring to 100% potassium hydrogen phthalate
Relative molecular mass: Pure Appl. Chem., Vol. 78, No. 11, pp. 2051–2066, 2006
Expiry date is based on stability tests carried out at Empa, Swiss Federal Laboratories for Materials Testing and Research, St. Gallen/Switzerland
The responsibility for this certificate in case of any inquiry lies only with BAM Berlin.
Berlin, 25 January 2013
BAM Berlin/Germany
Head of Department Analytical Chemistry; Reference Materials
Prof. Dr. U. Panne
This certificate is valid for the mentioned batch of the originally sealed containers only, under the condition that the storing and handling
instructions are adhered to. The use of certificates for purposes of advertising, including a mere reference as well as a partial publication, require
the approval of BAM. Certificates together with the respective documents will be kept in the archive for ten years. For sale or other distribution of
the certified product the relevant laws and regulations apply.
Federal Institute for Materials Research and Testing,
Analytical Chemistry; Reference Materials,
Richard-Willstaetter-Strasse 11, D-12489 Berlin/Germany
Tel. +49 30 8104 1100, Fax +49 30 8104 1117
Certification report no. 1170/IX2
This report comprises two pages.
Sigma-Aldrich Production GmbH produced Product no. 60357, Potassium Hydrogen Phthalate (KHC8H4O4),
batch no. BCBH6361V as acidimetric standard. Sigma-Aldrich Production GmbH filled a total number of 1195 glass
bottles each with 50 g of batch material. The sampling of the randomly chosen flasks for certification analyses was
done by Sigma-Aldrich Production GmbH.
Combined standard uncertainty:
The determination of the content of the acidimetric standard and the assessment of the homogeneity of the whole
production of 1195 glass bottles was performed on thirty-five randomly chosen flasks applying the volumetric
neutralization titration as primary analysis method. The content analysis of the acidimetric standard was done on
three randomly chosen flasks employing the coulometric acid-base titration as primary analysis method4. All
measurements were carried out between November 05, 2012 and January 24, 2013 in a temperature range of 22°C
± 2°C.
Content of the acidimetric standard:
u
c
=
u
Expanded uncertainty 2 uc :
2
BAM
2
+ u Inhom = 0.029 2 + 0.019 2 = 0.035%
99.970 % 1
0.99970 mol/mol 2
0.070 % 1
0.00070 mol/mol 2
1. Content of the acidimetric standard by volumetric acid-base titrations
The volumetric acid-base titrations with freshly prepared carbonate free NaOH-solution using the combined pHelectrode were performed by S. Just with a fully automatic sample preparation and data acquisition system. The
work was carried out under supervision of Dr. S. Recknagel. Samples of each of the thirty-five randomly chosen
flasks and of eight separately prepared reference materials were dissolved and then titrated in one set. The results
are based on seven sets with titration of the weighed samples of potassium hydrogen phthalate. All the
measurements are traced gravimetrically to National Bureau of Standards (NIST) Standard Reference Material 84k
acidimetric standard, potassium hydrogen phthalate (99.9911%). At the time of the certification measurements the
two NIST SRM lots 84k (99.9911%) and 84l (99.9934 %) were compared to each other. No significant difference to
the certified value of SRM 84k was measured which means that both references are equivalent. All samples of
acidimetric standard were dried for 3 hours at 120°C.
Content of the acidimetric standard:
Standard uncertainty:
99.970 % 1
0.029 % 1
Berlin, 25 January 2013
BAM Berlin/Germany
Head of Division Inorganic Reference Materials
0.99970 mol/mol 2
0.00029 mol/mol 2
2. Homogeneity of the acidimetric standard
The homogeneity was investigated simultaneously with the content assessments using acidimetric titration during
the seven experimental sets as described in part 1. For each of the thirty-five randomly chosen samples a content of
the acidimetric standard was established. The inhomogeneity contribution to the uncertainty uInhom is set to the
experimentally determined between-bottle standard deviation as the best estimate of the uncertainty due to
between-bottle heterogeneity 3. The studies were performed by weight of contents using approximately 175 mg
samples of the acidimetric standard. Therefore any use as a reference material below this limit is prohibited.
Standard uncertainty uInhom value:
0.019 % 1
0.00019 mol/mol 2
Dr. S. Recknagel
1
2
3
4
Mass content of acidimetric standard, calculated as potassium hydrogen phthalate
Fraction of measured molar amount in relation to the theoretical value referring to 100% potassium hydrogen phthalate
Accred. Qual. Assur., Vol. 6, pp. 274-277, 2001
Analytica Chimica Acta 599 (2007) 256–263
The test results are valid solely for the batch of reference material tested. The use of the test reports for the purpose of publicity, the mere
reference to them or publication of excerpts require the approval of BAM. Test reports and supporting documents are retained for 10 years.