Quality control of gasoline by 1H NMR: Aromatics, olefinics, paraffinics, and oxygenated and benzene contents

A simple and fast 1H NMR method, without any pretreatment, was developed for quality control of gasoline. It is based on the average group molecular weight approach and relative-content concept involving aromatics, olefinics and paraffinics, including also ethanol and benzene contents. The ethanol content was evaluated for Brazilian samples, but the method can be easily adapted to any oxygenated compound (ex. MTBE), and to gasoline from other countries. Twenty two laboratory prepared gasoline samples (gasoline from Brazilian refineries plus hydrocarbon solvents) and thirty four real (i.e., Brazilian gas stations) gasoline samples were tested. The routine quality control carried out through the usual physicochemical analyses reached a level of confidence of 75% and 73% in detecting non conformity in laboratory and real gasoline samples, respectively. The NMR method was very superior reaching 100% and 97% of confidence, respectively. It was better suited for laboratories with high sample throughput since measurement time is short and only one NMR experiment is needed per sample.