Quantitative NMR (qNMR)
Quantitative NMR (qNMR) is a potential primary reference measurement procedure for quantifying the main component within an organic compound. Its use for rapid, SI-traceabile purity assignment of primary calibrators is becoming increasingly widespread amongst NMIs and more broadly in the organic measurement community.
The BIPM's qNMR facility results from a collaborative agreement between the BIPM and the NMIJ (Japan) for the development and application of qNMR for organic primary calibrator comparisons. This collaborative agreement supports the BIPM's activity in coordinating key comparisons and will lead to improved qNMR analytical methods and procedures being made available to all Member States and Associates of the CGPM.
The current focus of the BIPM's qNMR programme is:
- to improve qNMR methodology so that international comparability at levels of parts in 103 can be achieved for a broad range of compounds,
- to establish and publish best-practice guidelines for performing qNMR measurements, and
- to identify a small suite of compounds that in principle would constitute a set of Primary Internal Standards applicable to the mass fraction purity assignment by qNMR for the majority of organic compound/solvent combinations.
The qNMR programme contributed to the IUPAC Technical Report "Methods for the SI Value Assignment of the Purity of Organic Compounds", which was published in 2023. The writing group for the report was prepared chaired by the BIPM with contributions from eleven NMIs (BAM, LGC, LNE, NIM, NIST, NMIA, NMIJ, NRC, PTB, VSL, UME) and two international organizations (IAEA and JRC Geel).
qNMR Internal Standard Reference Data (ISRD)
Any laboratory performing a qNMR experiment to value-assign the purity of organic compounds requires well characterized Certified Reference Materials (CRMs) to use as internal standards. The BIPM–NMIJ/AIST research programme has established Internal Standard Reference Data (ISRD) for the eight compounds listed below. For the vast majority of potential organic analyte/solvent combinations, at least one of these will be suitable for use as a CRM in qNMR measurements.
The reference data documents provide guidance on the use and limitations of each Internal Standard Reference Material for qNMR measurements, and general recommendations for the design, implementation and treatment of data from a quantitative 1H NMR measurement calibrated using the reference materials.
Related reference data documents are being prepared for reference materials and best practice for quantitative 19F NMR measurements.
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