Thin-layer chromatography-mass spectrometry with ionization by californium-252 fission products used for studying molecular mass distribution of oligomeric polystyrenes☆

The potential of a time-of-flight mass spectrometer with ionization by californium-252 fission products has been studied with regard to identification of oligomeric polystyrenes (PS) by means of their positive molecular ions M+. The optimized procedure for sample preparation prior to mass spectrometry consists of evaporation of PS on a substrate prepared by electrodispersion of a cellulose nitrate solution. The sensitivity of the method depends on the molecular mass of the oligomeric polymerhomologues and on the sample mass, but is in any case high enough for being used for investigating fractions obtained by thin-layer chromatography (TLC) and having molecular masses of up to 2 × 103, without the necessity of a prior sample concentration. The method enables one to identify oligomeric polymerhomologues extracted from the TLC plate and to determine the mass of the monomer unit and of the end groups from the difference in the molar mass of the ions M+ of neighbouring oligomers. These results, along with those of quantitative thin-layer chromatography (and also chromatograms obtained by means of other chromatographic methods) contain all information necessary for establishing the molecular mass distribution (MMD) of the oligomers, i.e. comprise an absolute method for determining the MMD of oligomers.