Characterization of partially transesterified poly(beta-hydroxyalkanoate)sby matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometr y (MALDI-TOFMS) was used for the characterization of a partially transester ified poly(P-hydroxyalkanoate) (PHA), a polymer produced by the bacterial s train Alcaligenes eutrophus with saponified vegetable oils as the sole carb on sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing < 10 kDa. The intact oligomers; were detected in their cationized forms, [M + Na](+) and [M + K ](+), by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicated that the oligomers obtained via acid catalysis contained a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a me thyl crotonate (olefinic) end group. In addition to hydroxybutyrate (HB), t he oligomers were found to contain a small percentage of hydroxyvalerate, w hich was independently confirmed by gas chromatography/mass spectrometry. I n comparison, analysis of a commercial PHA polymer, transesterified under i dentical conditions, showed only the presence of HB, i.e., a pure poly(HB) homopolymer.