Quantitation of polyetheramines as the active components of detergent additives in gasoline by the ninhydrin reaction

The detergent additives added into gasoline can effectively reduce the accumulation of coke deposits in engine and improve the exhaust emission pollution. The cleaning effect of detergent additives depends on the contents and compositions of the active components which usually contain a terminal amino group. In this work, a quantitative method was established to determine the polyetheramines of detergent additives in gasoline by the ninhydrin reaction. Unlike the small molecule compounds containing amino groups, such as amino acids and alkylamines, the formation of vesicles significantly increased the reactivity between polyetheramines and ninhydrin. The ninhydrin reaction was prohibited when the vesicles of polyetheramines were destroyed by adding ethanol, which was confirmed by the mass spectrometry and dynamic light scattering results. At the optimized condition, the reaction between the polyetheramines and ninhydrin generated a blue-purple dye (Ruhemann's purple) with a strong absorption at 560 nm. This reaction was highly selective, sensitive, and rapid. This quantitative method could distinguish the active components (polyetheramines) from the carrier oils (polyethers) in detergent additives. Aniline compounds in gasoline also did not interfere with the measurement of polyetheramines. The quantitative range was between 50 and 1000 mg/kg. The whole procedure could be finished in about 30 min. The accuracy of this method was verified using four different commercial polyetheramines and the results showed that the method was applicable to different types of detergent additives with relative errors lower than 10 %.