Quality Assurance for qNMR Supported by Reference Materials and Proficiency Testing Schemes

Jennifer Duhon, Product Manager Proficiency Testing; Kathrin Breitruck, Senior R&D Scientist

Participate in a proficiency testing quick turn study to show your competence in qNMR measurements

Quantitative NMR (qNMR) spectroscopy has evolved to become one of the most important tools for content determination of organic substances and for the quantitative evaluation of impurities in various industries such as chemistry, food and pharmacy. In NMR spectra, signal integrals are independent of the compound’s chemical nature. This opens the possibility to compare different compounds quantitatively by mixing an analyte with an internal standard (e.g. a CRM or a primary standard from a National Metrology Institute, NMI), and dissolve them in deuterated solvent to conduct a quantitative NMR experiment. The laboratory then gets a quantitative result that is traceable to internationally recognized primary material, e.g. from NIST or NMIJ. Furthermore, typical measurement uncertainties which can be achieved are very small, for example in the range of 0.2% (k=2) for pure substances.

While there is a comprehensive portfolio of certified reference materials (CRMs) available for qNMR calibration (see SigmaAldrich.com/qnmr) up to now, there have only been limited possibilities for laboratories to participate in proficiency testing (PT) schemes. We therefore developed a PT material for performance evaluation with ≥90% content of the main component. This covers a typical range in the content determination of pure neat materials. It is set up as a quick-turn study material, which means that it can be ordered any time. The laboratory does not have to wait for a Proficiency Testing campaign to start. The analytical result can be submitted online by the user, and the PT result will be provided shortly thereafter. The material is available worldwide to ensure a better comparability of all the labs performing qNMR is made possible.


Quantitative NMR (qNMR) concept


Our Laramie, WY USA site holds an ISO/IEC 17043, ISO/IEC 17025 and ISO 17034 (formerly ISO Guide 34) triple accreditation as a proficiency testing provider, testing laboratory, and manufacturer of certified reference materials. In addition, several other sites within Merck KGaA, Darmstadt, Germany hold the double accreditation ISO/IEC 17025 and ISO 17034 and can therefore produce Certified Reference Materials of the highest quality, which can also be employed in proficiency testing schemes. In addition to the comprehensive portfolio of certified reference materials, a large offering on proficiency testing can be found online on SigmaAldrich.com/pt

Process of this qNMR PT study:

  1. Place your order for Cat.No. PE5000-100MG at SigmaAldrich.com.
  2. If this is your first PT order with us, you will be contacted by a customer service representative to help you get an account set up on our online PT Portal.
  3. You will receive your PT sample and a reporting packet that gives sample preparation and reporting instructions.
  4. The sample contains Dimethylsulfone (C2H6O2S, molecular mass 94.13 g/mol) as main component, and the user has to determine the mass fraction value by quantitative 1H NMR.
  5. You will have 45 days to complete your analysis and submit your results to the PT Portal.
  6. Your qNMR evaluation report will then be emailed directly to you containing information on the performance of your analytical quality for qNMR testing.

1H-NMR spectrum of PE5000 (BCBX6075) in D2O, measured on a 600 MHz NMR spectrometer.


PE5000-NMR Spektrum2


For an overview on our complete offer for ANAB Accredited Proficiency Testing Provider ANAB Accredited TNI PT Provider


What is proficiency testing?

Proficiency Testing (PT) or Interlaboratory Comparison (ILC) is the name defined by the International Standards Organization (ISO) for a procedure that is used as a tool for external quality assessment. In simple terms, Proficiency Testing comprises a sample sent to a group of laboratories for measurement. The labs know what might be in the sample, but they don’t know exactly the content or the concentration. Their results are compared with a known reference value or against the mean value of the study. A performance score is assigned to each laboratory to show how closely their result matches with the target value.
The most common use of proficiency testing is to demonstrate to a regulatory or accreditation body that a laboratory is capable and competent to perform a specific analytical test or to apply a specific technology. This is demanded by the ISO/IEC 17025:2017 as a part of the program to ensure the validity of results. Another and sometimes overlooked benefit of proficiency testing is its use as a critical tool for quality assurance and continuous improvement since it can provide a true picture of a laboratory’s testing quality over time.