MICROSTRUCTURE OF BACTERIAL POLY(BETA-HYDROXYBUTYRATE-CO-BETA-HYDROXYVALERATE) BY FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY ANALYSIS OF THE PARTIAL PYROLYSIS PRODUCTS

The microstructure of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (P(HB-co-HV)) has been studied by mass spectrometry. We describe a novel method for the structural analysis of P(HB-co-HV) copolymers, based on the direct FAB-MS analysis of the partial pyrolysis products. The FAB spectra obtained allow the identification of the copolymer microstructure up to the hexads level, and a comparison between the experimental and calculated peak intensities makes it possible to discern clearly if the sample is made of a single random copolymer or of a mixture of two random copolymers. In addition, an algorithm has been developed that also allows the determination of both the amount of the random copolymers in the binary P(HB-co-HV) mixtures, as well as the copolymer composition of the individual copolymers. The highly discriminating power of the method developed here is due to the possibility of fitting the calculated statistical abundances with the MS experimental values corresponding to higher oligomers, i.e., hexamers as compared to diad and triad monomer sequences seen by C-13 NMR.