Thesis (M.Sc.)--Chulalongkorn University, 2002

This research involves the development of a method for determination of molecular weight distribution of polyisobutenylsuccinimide dispersant, using matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS). The MALDI-MS analysis was carried out by mixing the dispersant with various types of matrix such as dithranol, alpha-hydroxycyanocinnamic acid (CCA), 2,5-dihydroxy benzoic acid, all-trans retinoic acid, indole acrylic acid, and 2-(4-hydroxyphenylazo)-benzoic acid. After the dispersant-matrix mixture was dried to form a solid solution, the dried mixture was bombarded with laser light to obtain ionic analyte. The following MALDI-MS conditions were found to provide the good MS spectrum of molecular weight distribution of the polymer dispersant: sample preparation using a dried droplet method, CCA as a matrix with tetrahydrofuran as a solvent, the dispersant solution: matrix solution of 1:5 by volume, and the laser power of 170 to 180 micro J. The developed MALDI-MS was used to be an excellent method for determination of the molecular weight distribution of polyisobutenylsuccinimide dispersant in the commercial diesel oils.