Thesis (M.Sc.)--Chulalongkorn University, 2004

This research involves the development of a method for analysis of dispersants, using matrix assisted laser desorption ionization-mass spectrometry (MALDI MS). The MALDI-MS analysis was carried out by mixing the dispersants with various types of matrix such as dithranol, 2-5-dihydroxybenzoic acid, 2-(4-hydroxyphenylazo)-benzoic acid and all-trans retinoic acid. The dispersants-matrix mixture was applied to the target and bombarded with laser to generate ionic analyte. The following MALDI-MS condition were found to provide the good MS spectrum of molecular weight distribution of the dispersants: DHB as a matrix with THF as a solvent, the dispersants solution: matrix solution of 1:50 by volume, and the laser power of 190 micro J. The MALDI MS spectrum gave the information of dispersants molecular weight distribution in 4 range of m/z. Dispersants in m/z range of 200-600, 390-1000 and 520-1260 were polyisobutenylamine and dispersants in m/z range of 1200-2300 were polyether amine. The developed MALDI-MS was used for characterization of dispersants in the commercial gasoline form 8 companies. The results showed that dispersants which added in commercial gasoline from each companies were different in type and molecular weight distribution. The types of dispersants which found in commercial gasoline were polyisobutenylamine and polyether amine.