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A new realization of SI for organic chemical measurement: NIST PS1 Primary Standard for quantitative NMR (Benzoic Acid)



Michael A. Nelson, Jason F. Waters, Blaza Toman, Brian E. Lang, Alexander R?ck, Kathrin Breitruck, Markus Obkircher, Anthony Windust, Katrice A. Lippa


Metrological traceability to common references supports the comparability of chemical measurement results produced by different analysts, at various times, and at separate places. Ideally, these references are realizations of base units of the International System of Units (SI). ISO/IEC 17025 (Clause 6.5) states that traceability of measurement results is a necessary attribute of analytical laboratory competence, and as such, has become compulsory in many industries, especially clinical diagnostics and healthcare. Historically, claims of traceability for organic chemical measurements have relied on calibration chains anchored on unique reference materials with linkage to the SI that is tenuous at best. A first-of-its-kind NIST reference material, ultra-pure and extensively-characterized PS1 Benzoic Acid Primary Standard for quantitative NMR serves as a definitive, primary reference (calibrant) that assuredly links the quantitative NMR (qNMR) spectroscopy technique to SI base units. As qNMR itself is a favorable method for accurate, direct characterization of chemical reference materials, PS1 is a standard for developing other traceable standards and is intended to establish traceability for the measurement of thousands of organic chemical species. It will play a critical role in directly promoting accuracy and worldwide comparability of measurement results produced by the chemical measurement community, supporting the soundness of clinical diagnostics, food safety and labeling, forensic investigation, drug development, and biomedical research. Confidence in this link to the SI was established through: (i) unambiguous identification of chemical structure; (ii) determinations of isotopic composition and molecular weight; (iii) evaluation of the respective molecular amount by multiple primary measurement procedures, including qNMR and coulometry; and (iv) rigorous evaluation of measurement uncertainty using state-of-the-art statistical methods and measurement models.
Analytical Chemistry


metrological traceability, chemical metrology, primary standard, quantitative NMR, NMR spectroscopy, organic chemical purity


Nelson, M. , Waters, J. , Toman, B. , Lang, B. , R?ck, A. , Breitruck, K. , Obkircher, M. , Windust, A. and Lippa, K. (2018), A new realization of SI for organic chemical measurement: NIST PS1 Primary Standard for quantitative NMR (Benzoic Acid), Analytical Chemistry, [online], (Accessed April 17, 2024)
Created July 30, 2018, Updated June 9, 2020