Abstract
CI mass spectra of twentyfour alkylbenzenes, C11H16~C25H44, were measured in order to elucidate the characteristic correlation between their molecular structures and the CI mass spectra. Approximately 2 μg of each sample dissolved in acetone or benzene were introduced into a Finnigan 3300E GC/QMS equipped with an OV-1 GC column. Pressure of methane or isobutane as a reagent gas in an inonization chamber was 1.0 and 0.5 Torr, respectively. The ion source temperature was maintained at 70°C. The molecular weights of all alkylbenzenes were clarified securely by (M±H)+, M+ and adduct ions appeared in methane and isobutane CI, especially in the latter. Alkyl substituents could be determined by observing ions formed by olefin displacement reactions, e. g., (M-13)+, (M-27)+, (M-41)+ and the fragment ions such as CnH2+n⌉+ and (M-CmH2m+1)+, especially by methane CI. The C7H8+ (m/z 92) ions and its homologous ions gave the same information as that in EI. Numbers of substituents could also be successfully estimated. Positions of substituents in di-substituted benzene isomers could be determined by observing ions such as (M+57)+ in isobutane CI. It was generally very difficult to determine the positions of substituets in tri-substituted benzenes owing to insufficient information.
