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NIST PS1

Primary Standard for quantitative NMR 

(Benzoic Acid)

CERTIFICATE OF ANALYSIS

Purpose: This NIST Certified Reference Material is intended for use as a primary standard for quantitative nuclear 

magnetic resonance (qNMR) methods. 

Description: A unit of NIST PS1 consists of two vials, each containing approximately 500 mg of purified crystalline

benzoic acid.

Certified Values: Certified values, valid for use of quantities ≥5 mg, are provided in Table 1. A NIST certified value 

is a value for which NIST has the highest confidence in that all known or suspected sources of bias have been 

accounted for. Confidence in the certified values was achieved through acidimetric titration and qNMR primary 

measurement procedures.

Table 1. Certified Values for Benzoic Acid in NIST PS1

Values are metrologically traceable to the International System of Units (SI) mole and kilogram.

Mass fraction, 

g/g(a,b,c)

Specific amount, 

mol/kg(a,b,c)

Benzoic Acidd 0.99992

−0.00006 +0.00004

8.1880

−0.0005 +0.0004

(a) Values are expressed as xx −UULL95% +UUHH95%, where x denotes the certified value and UULL95% and UUHH95% indicate 

the low and high boundaries of a 95% coverage interval for the true value of the measurand.

(b) The standard uncertainty may be approximated as u(xx) = UULL95% /2.

(c) If a Monte Carlo method, as described in the GUM Supplement 1 [1], is employed to propagate the 

uncertainty of the certified value, this may be accomplished via “The NIST Uncertainty Machine” 

(https://uncertainty.nist.gov/)[2], whereby the certified mass fraction is assigned a beta distribution,

Beta (Shape1, Shape2), with parameters Shape1=88873.7, Shape2=7.11. The assignment for the certified 

specific amount may be derived from this distribution using the molar mass (MM) of benzoic acid.

(d) The value of MM was evaluated empirically through stable isotope relative abundance measurements as 

122.12204 g/mol with an associated standard uncertainty u(MM) = 0.00019 g/mol.

Expiration of Certification: The certification of NIST PS1 is valid, within the stated measurement uncertainties, 

until 31 December 2037, provided the CRM is handled and stored in accordance with the instructions given in this 

certificate. The certification is nullified if the CRM is damaged, contaminated, or otherwise modified.

Carlos A. Gonzalez, Chief

Chemical Sciences Division

Material Measurement Laboratory Date of Issue: 1 January 2018
NIST PS1 Page 2 of 2

Source: The benzoic acid used in this CRM was provided, prepared and packaged by Sigma-Aldrich Production 

GmbH and in collaboration with NIST. 

Storage and Handling: Until required for use, NIST PS1 should be stored at room temperature in its original 

packaging. After use, this CRM should be stored in its original bottle at room temperature. It must be tightly recapped after use, protected from moisture and light, and placed in a desiccator for long term storage. The certified 

value should not be considered valid if remaining material is not stored in this manner. 

Supporting Measurements: Direct 1

H-qNMR comparisons of NIST PS1 were made to SRM 350b that established 

confidence in traceability for historical use of SRM 350b for 1

H-qNMR calibrations. Confirmatory 1H-qNMR analysis 

by an external standard approach was performed by the National Research Council (NRC) Canada. Confirmatory 1

HqNMR analysis of bulk purity by an internal standard approach was performed by Sigma-Aldrich Production GmbH. 

Mass spectrometric determinations of stable isotope ratios were performed by the United States Geological Survey, 

Reston, VA and NRC Canada. Isotope atom fractions (x) of 1

H and 13C are derived from the isotope delta values of 

δ2

HVSMOW-SLAP and δ13CVPDB as x(

1

H) = 0.999 860, u(x(

1

H)) = 0.000 003 and x(

13C) = 0.010 74, u(x(13C)) = 0.000 09, 

respectively [3,4,5].

Certain commercial equipment, instruments or materials may be identified in this Certificate of Analysis to adequately 

specify the experimental procedure. Such identification does not imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are 

necessarily the best available for the purpose.

Distribution of this NIST CRM will occur only via Material Transfer Agreement. For more information, contact the 

Technology Partnerships Office, 100 Bureau Drive, Stop 2200, Gaithersburg, Maryland 20899-2200; telephone 

(301) 975-2573; e-mail tpo@nist.gov. 

Technical queries regarding the certification and usage of this material may be directed to the NIST PS1 Technical 

Project Leader, Michael Nelson; e-mail michael.nelson@nist.gov.

Users of this CRM should ensure that the Certificate of Analysis in their possession is current. NIST will monitor this 

CRM until its certification expires. If substantive technical changes occur that affect the certified values before this 

certificate expires, NIST will notify the signatory of the Material Transfer Agreement. 

Reference

[1] Joint Committee for Guides in Metrology (2008) "Evaluation of measurement data --- Supplement 1 to the 

``Guide to the expression of uncertainty in measurement'' --- Propagation of distributions using a Monte Carlo 

method", JCGM 101:2008, International Bureau of Weights and Measures (BIPM), Sevres, France, 

www.bipm.org/en/publications/guides/gum.html.

[2] T. Lafarge and A. Possolo (2015) "The NIST Uncertainty Machine", NCSLI Measure Journal of Measurement 

Science 10(3): 20-27

[3] Coplen, T. (1994) Reporting of stable hydrogen, carbon, and oxygen isotopic abundances (Technical Report). 

Pure and Applied Chemistry 66(2): 273-276

[4] Brand W.A., Coplen T.B., Vogl J., Rosner M., Prohaska T. (2014) Assessment of international reference materials

for isotope-ratio analysis (IUPAC Technical Report), Pure and Applied Chemistry 86(3): 425 

[5] Coplen T.B., Hopple J.A., Böhlke J.K., Peiser H.S., Rieder S.E., Krouse H.R., Rosman K.J.R., Ding T., Vocke 

R.D. Jr., Révész K.M., Lamberty A., Taylor P., De Bièvre P. (2002) “Compilation of Minimum and Maximum 

Isotope Ratios of Selected Elements in Naturally Occurring Terrestrial Materials and Reagents”, U.S. Geological 

Survey Water-Resources Investigations Report 01-4222.