Using solvent-free sample preparation to promote protonation of poly(ethylene oxide)s with labile end-groups in matrix-assisted laser desorption/ionisation
Article first published online: 5 NOV 2008
Copyright © 2008 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry
Volume 22, Issue 23, pages 3776–3782, 15 December 2008
How to Cite
Mazarin, M., Phan, T. N. T. and Charles, L. (2008), Using solvent-free sample preparation to promote protonation of poly(ethylene oxide)s with labile end-groups in matrix-assisted laser desorption/ionisation. Rapid Commun. Mass Spectrom., 22: 3776–3782. doi: 10.1002/rcm.3798
- Issue published online: 5 NOV 2008
- Article first published online: 5 NOV 2008
- Manuscript Accepted: 26 SEP 2008
- Manuscript Revised: 25 SEP 2008
- Manuscript Received: 13 JUN 2008
- French Research Agency. Grant Number: ANR-06-JCJC-0112
Protonation is usually required to observe intact ions during matrix-assisted laser desorption/ionization (MALDI) of polymers containing fragile end-groups while cation adduction induces chain-end degradation. These polymers, generally obtained via living free radical polymerization techniques, are terminated with a functionality in which a bond is prone to homolytic cleavage, as required by the polymerization process. A solvent-free sample preparation method was used here to avoid salt contaminant from the solvent traditionally used in the dried-droplet MALDI procedure. Solvent-based and solvent-free sample preparations were compared for a series of three poly(ethylene oxide) polymers functionalized with a labile end-group in a nitroxide-mediated polymerization reaction, using 2,4,6-trihydroxyacetophenone (THAP) as the matrix without any added salt. Intact oligomer ions could only be produced as protonated molecules in solvent-free MALDI while sodium adducts of degraded polymers were formed from the dried-droplet samples. Although MALDI analysis was performed at the laser threshold, fragmentation of protonated macromolecules was still observed to occur. However, in contrast to sodiated molecules, dissociation of protonated oligomers does not involve the labile CON bond of the end-group. As the macromolecule size increased, protonation appeared to be less efficient and sodium adduction became the dominant ionization process, although no sodium salt was added in the preparation. Formation of sodiated degraded macromolecules would be dictated by increasing cation affinity as the size of the oligomers increases and would reveal the presence of salts at trace levels in the MALDI samples. Copyright © 2008 John Wiley & Sons, Ltd.