Gasoline analysis by 1H nuclear magnetic resonance spectroscopy

High-resolution proton nuclear magnetic resonance ( 1 H n.m.r.) spectroscopy allows the rapid and exact quantitative determination of the composition and quality of gasolines. For this study about 140 gasolines from Austrian filling stations were analysed. The amounts of methanol, methyl tert -butyl ether (MTBE), benzene and aromatics were determined quantitatively using an internal standard. These results were compared with data obtained by fluorescent indicator adsorption and g.c. analyses. Each n.m.r. spectrum was subdivided into 12 regions and the integrals were correlated with the octane number using multiple linear regression. This allowed the calculation of the octane number of small amounts of unleaded gasolines from the 1 H n.m.r. spectra in only a few minutes. The structural groups that produce the n.m.r. signals were determined by two-dimensional measurements. Their different influences on octane number were evaluated by chemometric methods (cluster and factor analyses). Nine of these structural groups were used to describe quantitatively the influence of structure on RON and MON. Thus the importance of chemical substructures, determined by n.m.r. spectroscopy, in determining the octane number was confirmed for the first time.