A comparison of quantitative nuclear magnetic resonance methods: internal, external, and electronic referencing
Article first published online: 3 SEP 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Magnetic Resonance in Chemistry
Volume 51, Issue 11, pages 705–713, November 2013
How to Cite
Cullen, C. H., Ray, G. J. and Szabo, C. M. (2013), A comparison of quantitative nuclear magnetic resonance methods: internal, external, and electronic referencing. Magn. Reson. Chem., 51: 705–713. doi: 10.1002/mrc.4004
- Issue published online: 4 OCT 2013
- Article first published online: 3 SEP 2013
- Manuscript Accepted: 8 AUG 2013
- Manuscript Revised: 5 AUG 2013
- Manuscript Received: 24 MAY 2013
- purity determination;
- internal reference;
- external reference
The performance of three quantitative NMR methods was compared in terms of short-term and long-term precision and accuracy, robustness, linear range, and general applicability. The Internal Reference method employs a reference material co-dissolved with sample; the External Reference method employs a reference material contained in a separate solution; and the third method, known as Electronic REference To access In vivo Concentrations (ERETIC), employs an externally calibrated digital reference peak. The Internal Reference method results were the most precise and remained stable within 0.1% for at least 4 weeks. The results from the External Reference and ERETIC methods were practically equivalent to each other during this time. These methods exhibited small differences relative to the standard set by the Internal Reference method and slightly lower precision, establishing them as practical alternatives to the Internal Reference method. In contrast to the Internal Reference method, the External Reference and ERETIC methods possess several advantages that address peak overlap, flexibility of calibration, and duration of applicability. The study was designed such that each spectrum contained the information needed to compare the three methods while all other variables were kept constant. Applicability of pulse width compensation is addressed. ERETIC software compensation and minor adjustments to 90° pulse width were concluded to be unnecessary for this system. Although each of the methods was applied here to specifically calculate and compare chemical purity values, this evaluation applies generally to absolute quantitation by NMR. Copyright © 2013 John Wiley & Sons, Ltd.