Quantitative NMR Spectroscopy for the Analysis of Fuels: A Case Study of FACE Gasoline F

Abstract

A detailed experimental methodology is outlined, which allows for the measurement of quantitative 1H and 13C nuclear magnetic resonance (NMR) spectra of liquid hydrocarbons. Optimal experimental conditions are identified, which allow for the collection of entirely quantitative 1H and 13C NMR spectra; the most significant among these are shown to be the choice of solvent and the delay time utilized. A best practice for the interpretation of the measured spectra that utilizes heteronuclear single quantum coherence (HSQC) NMR spectroscopy is outlined. Use of the HSQC method allows for the expeditious determination of fuel-specific integral regions. Importantly, the use of HSQC is shown to be a convenient method for the identification of overlapping peaks. The fidelity of both 1H and 13C NMR spectroscopy for the analysis of liquid fuels is demonstrated through the analysis of a range of reference fuels of known composition. Atom type populations are calculated for the reference fuels using a defined set of operating equations. In general, the NMR spectroscopy measured atom type populations show a strong agreement with the known atom type populations. The uncertainty associated with these measurements is determined to be <3%; however, this does not take into account overlapping peaks. The experimental methodology is applied to the analysis of FACE Gasoline F. The NMR-derived atom type population is shown to be in good agreement with the previously reported detailed hydrocarbon analysis (DHA). Additionally, the potential for a synergistic relationship between NMR spectroscopy and DHA is highlighted through the identification of molecules present in FACE Gasoline F that were misidentified by the DHA.