Determination of the resonance frequency ratio of the 31P and 1H NMR resonance shift standards 85% orthophosphoric acid and tetramethylsilane

✍ Scribed by Hommo T. Edzes

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 488 KB
• Volume: 30
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260300910

✦ Synopsis

Abstract

The NMR resonance frequency ratio of the ^31^P NMR resonance shift standard 85% orthophosphoric acid (H~3~PO~4~) and the ^1^H standard tetramethylsilane (TMS) was determined by means of the ‘dispersed phase’ method. The Ξ value, equal to 10^8^ times the resonance frequency ratio, was 40480737.0 ± 0.2 Hz at 25°C. A small dependence on temperature (−0.11 Hz °C^−1^) and on phosphoric acid concentration (−0.50 Hz %^−1^) was observed around 25°C. Traces of iron in phosphoric acid were found to have a negligible effect on Ξ values, although line widths increased. The determination of Ξ allows accurate referencing of ^31^P NMR spectra relative to the ^1^H resonance of internal TMS or of a secondary ^1^H shift standard. The accuracy of the ^31^P NMR resonance shift scale is primarily limited by the uncertainty of solvent‐induced ^1^H resonance shifts of TMS.