Synthetic oligomer analysis using atmospheric pressure photoionization mass spectrometry at different photon energies
Résumé
Atmospheric pressure photoionization (APPI) followed by mass spectrometric detection was used to ionize a variety of polymers: polyethylene glycol, polymethyl methacrylate, polystyrene, and polysiloxane. In most cases, whatever the polymer or the solvent used (dichloromethane, tetrahydrofuran, hexane, acetone or toluene), only negative ion mode produced intact ions such as chlorinated adducts, with no or few fragmentations, in contrast to the positive ion mode that frequently led to important in-source fragmentations. In addition, it was shown that optimal detection of polymer distributions require a fine tuning of other source parameters such as temperature and ion transfer voltage. Series of mass spectra were recorded in the negative mode, in various solvents (dichloromethane, tetrahydrofuran, hexane, toluene, and acetone), by varying the photon energy from 8. eV up to 10.6. eV using synchrotron radiation. To these solvents, addition of a classical APPI dopant (toluene or acetone) was not necessary. Courtesy of the synchrotron radiation, it was demonstrated that the photon energy required for an efficient ionization of the polymer was correlated to the ionization energy of the solvent. As commercial APPI sources typically use krypton lamps with energy fixed at 10. eV and 10.6. eV, the study of the ionization of polymers over a wavelength range allowed to confirm and refine the previously proposed ionization mechanisms. Moreover, the APPI source can efficiently be used as an interface between size exclusion chromatography or reverse phase liquid chromatography and MS for the study of synthetic oligomers. However, the photoionization at fixed wavelength of polymer standards with different molecular weights showed that it was difficult to obtain intact ionized oligomers with molecular weights above a few thousands.
Mots clés
acetone
Organic solvents
Solvents
tetrahydrofuran
toluene
article
Atmospheric pressure photo ionization
Chlorinated adducts
Ionization mechanisms
Mass spectrometric detection
Optimal detection
Polymer distribution
Reverse phase liquid chromatography
Synchrotron light
Chromatography
Liquid chromatography
Mass spectrometers
Negative ions
Oligomers
Photoionization
Polymers
Polymethyl methacrylates
Silicones
dichloromethane
hexane
macrogol
oligomer
poly(methyl methacrylate)
polysiloxane
polystyrene
atmospheric pressure
atmospheric pressure photoionization
chemical analysis
fragmentation reaction
gel permeation chromatography
krypton laser
mass spectrometry
molecular weight
photon
priority journal
reversed phase liquid chromatography
synchrotron radiation