Exploration of laser-induced acoustic desorption and chemical ionization towards the analysis of underivatized polyisobutylenes with Fourier transform ion cyclotron resonance mass spectrometry

Putuma Patrice Gqamana, Purdue University

Abstract

Chemical ionization (CI) using organometallic cations coupled with laser-induced acoustic desorption (LIAD) can be used to ionize underivatized polyisobutylene oligomers (PIB) without fragmentation in the Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. CI reagents such as cyclopentadienylcobalt (CpCo+), cyclopentadienylcobalt carbonyl (CpCo(CO)+ ) and aquachloromanganese (ClMn(H2O)+) cations also ionize small aliphatic hydrocarbons, including 2,2,4,-trimethylpentene, 2,2,4,4-tetramethylpentane and 2,2,4,4,6,6,8-hexamethylnonane (PIB 226). CI agents except CpCo+ produce pseudomolecular ions with no fragmentation of the hydrocarbon. CpCo+ generally reacts by addition followed by the loss of H2 and CH4, whereas CpCo(CO)+ and ClMn(H2O)+ react largely by addition followed by the loss of the weakly bound CO and H2O ligands respectively. All the reagent cations reacted with PIB 400, a saturated and underivatized PIB sample with MW distribution from between 250 Da and 600 Da. CpCo + reacted by adduct-ion formation and adduct-ion formation followed by single and double dehydrogenation, whereas ClMn(H2O) + reacted purely by H2O displacement. Also, upon reaction with PIB550, a PIB sample with > 60 % exo-olefin content, CpCo+ produced adduct ions and adduct ions minus H2 and CH4 as expected, while ClMn(H2O)+ reacts exclusively by H2O displacement. Both CI methods produce mass spectra with a low MW bias. The use of higher laser powers in LIAD/ClMn(H2O) + analysis of PIB550 resulted in an increase in the MW distribution by three more oligomers compared to lower laser powers.

Degree

Ph.D.

Advisors

Kenttamaa, Purdue University.

Subject Area

Analytical chemistry

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