17O quantitative nuclear magnetic resonance spectroscopy of gasoline and oxygenated additives.

Abstract

17O Nuclear magnetic resonance (NMR) spectroscopy allows exclusive detection and direct quantification of oxygenates in gasoline unaffected by its hydrocarbon content, using the internal standard quantitative NMR (QNMR) method. Chemical shifts of 24 oxygen-containing compounds as potential additives and contaminants have been measured in gasoline and corrected values of deltaO 18.1 and 3.9 determined for neat methyl tert-butyl ether (MTBE) and neat di-n-butyl ether, respectively. Quantification of ethanol in gasoline can be readily achieved by 17O QNMR with dimethyl sulfone as an internal standard reference material, at the levels currently used in retail gasolines (1-20%). In addition, the simultaneous detection and quantification of the oxygenates methanol, ethanol, 2-propanol, tert-butyl alcohol, and MTBE in gasoline has been established to further demonstrate the specificity of the method. 17O NMR has distinct advantages over 1H and 13C QNMR methods, and although it cannot reliably differentiate 1-propanol, 1-butanol, 1-pentanol, and isopentyl alcohol, 17O NMR does allow the rapid and unambiguous identification of unexpected oxygenates such as acetates and ketones found as contaminants in some retail gasoline.