Development of novel methods for the analyses of hydrocarbon polymers by laser-induced acoustic desorption with Fourier transform ion cyclotron resonance mass spectrometry.

摘要

An ability to quickly and accurately analyze saturated hydrocarbon polymers, such as polyethylene (PE), would be a desirable asset for the petroleum and polymer industries. Unfortunately, current analytical methods employed for polymer analysis suffer from several limitations, including long analysis times (>30 minutes), a lack of standards needed used to calibrate the techniques, the inability to provide information for individual oligomers, and, most importantly, the ability to produce stable quasimolecular ions from saturated hydrocarbon polymers. The lack of easily ionizable functional groups in these molecules mean that they cannot be ionized by either ESI or MALDI.; By desorbing neutral PE oligomers into a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer by using laser-induced acoustic desorption (LIAD) in the presence of a novel chemical ionization reagent, cyclopentadienyl cobalt radical cation (CpCo+•), produced predominantly a quasimolecular ion, [R + CpCo - 2H2] +•, for each PE oligomer or individual alkane molecule (R) that was examined. An examination of the kinetics of CpCo+•- alkane (PE oligomer) reactions revealed no bias for alkanes of differing molecular weights. However, the success of the LIAD/CpCo+• CI technique was found to depend greatly upon the LIAD sample preparation method used. Several sample preparation methods were evaluated, and pneumatically assisted spin coating was concluded to provide the best mass spectra as a result of its ability to provide uniform PE coverage on the LIAD foils. The molecular weight distributions measured for several low-molecular weight PE samples (200--655 Da) were found to be in good agreement with manufacturers' values as determined by gel permeation chromatography (GPC).