Fragmentation pathways of polymer ions (original) (raw)
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Analytical Chemistry, 2000
Chemical structures of polymer end groups play an important role in determining the functional properties of a polymeric system. We present a mass spectrometric method for determining end group structures. Polymeric ions are produced by electrospray ionization (ESI), and they are subject to source fragmentation in the ESI interface region to produce low-mass fragment ions. A series of source-fragment ions containing various numbers of monomer units are selected for high-energy collision-induced dissociation (CID) in a sector/time-offlight tandem mass spectrometer. It is shown that highenergy CID spectra of source-induced fragment ions are very informative for end group structure characterization. By comparing the CID spectra of fragment ions with those of known chemicals, it is possible to unambiguously identify the end group structures. The utility of this technique is illustrated for the analysis of two poly-(ethylene glycol)-based slow-releasing drugs where detailed structural characterization is of significance for drug formulation, quality control, and regulatory approval. Practical issues related to the application of this method are discussed.
Polymers
Several families of polymers possessing various end-groups are characterized by ion mobility mass spectrometry (IMMS). A significant contribution of the end-groups to the ion collision cross section (CCS) is observed, although their role is neglected in current fitting models described in literature. Comparing polymers prepared from different synthetic procedures might thus, be misleading with the current theoretical treatments. We show that this issue is alleviated by comparing the CCS of various polymer ions (polyesters and polyethers) as a function of the number of atoms in the macroion instead of the usual representation involving the degree of polymerization. Finally, we extract the atom number density from the spectra which gives us the possibility to evaluate the compaction of polymer ions, and by extension to discern isomeric polymers.
Secondary ion formation from functional polymer systems in static secondary ion mass spectrometry
Applied Surface Science, 1990
The process of emission of structurally related secondary ions from functional polymers under keV ion bombardment is investigated. Competition between ion formation mechanisms IS apparent in static SIMS analysis of functionalired polymer systems. Complementary positive and negative "ion pair" emission is favorable when the fragmentation of the polymer structure results in charge stabilized ions. These processes are illustrated by SIMS analysis of poly(ary1 methacrylates) and by comparison to previous laser desorption mass spectrometry results of the same materials. The generation of n-mer fragment ions. from bond breaking along the chain of a polymer, is illustrated by the analysis of a series of functionalized nitrogen containing polymers and from poly(styrene sulfonic acid). In these cases, pre-existing localized charge at the surface of a polymer has a direct effect on the measured peak intensities and the presence or absence of structurally related ions. The analysis of polymeric surface reactivity due to different solid state isomeric structures at the surface is investigated through the surface modification of isomeric poly(viny1 pyridines) (PZVP and P4VP). This allows for differentiation of these systems as well as insight into the extent of static SIMS primary ion modification of the material under analysis
International Journal of Mass Spectrometry, 2011
Tandem mass spectrometry is increasingly applied to polymer ions in the context of in-depth structural characterization. In particular, the well-known collision-induced dissociation (CID) methodology is nowadays advantageously used to characterize end-groups and to distinguish isomeric polymer ions. When applied to sodium-cationized polyesters, CID was demonstrated to mainly involve charge remote fragmentation processes and consecutive as well as competitive dissociation pathways. In the present report, an experimental and theoretical study of collision induced dissociation of isomeric sodium cationized polylactide was investigated. The investigated polymers were designed to obtain oligomers only differentiated on the basis of regioisomeric end-groups, using ortho-, meta-, and para-methylbenzyl alcohols as initiators. The CID spectra revealed the presence of competitive charge driven and charge remote fragmentations. In particular, the charge induced fragmentations allowed the minute distinction between the three isomeric end-groups. The intermediacy of an ion/neutral complex was proposed to account for the observed decomposition and some theoretical calculations were performed to support the proposal.
Mass Spectrometry of Synthetic Polymers
Analytical Chemistry, 2004
The aim of this review is to give a compact overview about the literature on mass spectrometry (MS) of polymers published during 2006/2007. The citations are drawn from SciFinder January 25, 2008, using the search terms "poly*" and "mass spectrometry" with restrictions to review and journal contributions in the English language including refined searches in Web of Science. More than 750 relevant papers, reviews, (1, 2) and historical summaries were published in these two years, demonstrating the importance of MS for polymer analysis. We were therefore forced to select the most important references. This is always a subjective decision and may not always represent the best choices. In contrast to the previous review in this series (5), which focused on MS principles, including matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF), electrospray ionization (ESI) TOF, TOF secondary ion mass spectrometry (SIMS), etc., in this paper, we categorize according to applications of MS for polymer analysis. Even this choice is arbitrary.
Analytical Chemistry, 1999
Matrix-assisted laser desorption/ionization has been combined with high-energy collision-induced dissociation for the analysis of poly(ethylene glycols) with butanoyl, benzoyl and acetyl end groups, using novel technology comprising a magnetic-sector mass spectrometer and ion buncher with an in-line quadratic-field ion mirror. Highenergy (>8 keV) collision-induced dissociation facilitated unambiguous end-group determination of these polymers, providing masses of end groups and structural information. The high-energy collision-induced dissociation also provided information regarding repeat units. Mass spectrometry of synthetic polymers is gaining in popularity due to the unprecedented high-quality information accessible to the synthetic polymer chemist. Matrix-assisted laser desorption/ionization (MALDI) has been shown to be an especially useful tool for the direct analysis of synthetic polymers. 1-8 The results obtained for polymers from MALDI mass spectrometry experiments typically give qualitative molecular weight information but normally not structural information. Nevertheless, MALDI has been utilized to gain information on monomer reactivity ratios, 9 end groups, 10-13 and mechanisms of polymerization. 14-16 Many attempts, with a variety of success, have also been made to use MALDI-time-of-flight (TOF) mass spectrometry to obtain values for molecular mass averages, M n and M w , especially in combination with size exclusion chromatography. 17-20 Techniques of polymer synthesis are becoming increasingly sophisticated with a move toward the attempt to design macromolecules for specific application. This has usually been centered around living, or pseudoliving, polymerization which allows the incorporation of different functionalities at precise positions by judicious choice of reaction conditions. 28-34 For example, R and terminally functional polymers may have very different proper
Control of fragmentation products for the mass spectrometric analysis of polymeric mixtures
European Journal of Mass Spectrometry, 1995
The concept of controlled fragmentation for the analyses of mixtures is developed in the fast atom bombardment/Fourier transform mass spectrometry of a new oligomeric class of cyclic β-keto lactones. These cyclic oligomers produce fragments during ionization with masses that are identical to smaller homologues. By using the proper alkali metal ion, dissociation reactions are limited to loss of the metal ions. In this way, fragments do not interfere with the identification of quasimolecular ions. From competition experiments involving several alkali metals, Cs + was identified as the best candidate to analyze mixtures. It enhances the quasimolecular ion signal but does not produce Cs + coordinated fragments. The metal was then used to analyze a reaction mixture to elucidate the oligomerization mechanism.
Journal of Mass Spectrometry, 2012
In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization-quadrupole-time of flight (ESI-Q-TOF) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2-oxazoline via a living cationic ring-opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI-Q-TOF and MALDI-TOF MS in combination with collision-induced dissociation (CID) experiments. In ESI-MS as well as MALDI-MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2-hydride shift with a charge-remote rearrangement via a four-membered cyclic transition state, as well as charge-induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4-hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks.
Rapid Communications in Mass Spectrometry, 1998
A poly(amino)ester dendrimer, bearing tert-butyl ester terminations and used as the precursor of an acid-terminating poly(amino)ester dendrimer, was studied by electrospray ionization tandem mass spectrometry to establish its fragmentation rules upon collision-induced dissociation. Mechanisms for dissociation reactions experienced by protonated molecules were proposed and supported by accurate mass measurements. The release of 2-methylprop-1-ene was observed as many times as tert-butyl groups were available. Each of these steps was followed by elimination of carbon dioxide and ethylene within the so-deprotected branches. Detachment of an entire arm, released as a neutral or as a protonated molecule, was found to be a useful complementary process but it mainly proceeded from the singly charged precursor. Three targeted dendritic impurities were structurally characterized by monitoring the occurrence of these reactions together with any deviation from the reference behavior. Detection of these compounds in the precursor sample could account for the presence of defective molecules previously characterized in the acid-terminating poly(amino)ester dendrimer sample.
Polymer Journal, 1997
Spectra of eight polymers [(CH2-CHR). (R=H, OH, F, Cl, OCH3, and CONH2), (CF2-CF2).] and (CH 2-CHCN). in time-of-flight (TOF)-and static(S)-secondary ion mass spectrometry (SIMS), respectively, were analyzed by semiempirical and ab initio molecular orbital (MO) calculations. We predicted where the cleavage of the polymers occurs on sputtering, due to two-center bond energies of the model pen tamers by a semiempirical MO calculations using AMI program; a) the cleavage can occur in any bonds (polyethylene, poly(vinyl methyl ether), polyacrylonitrile), b)the cleavage of the main chain occurs in any bonds, after side chain groups cleaved first (poly(vinyl chloride, poly(acrylamide)), c) the main chain carbons with the side chain group cleave at any bonds of the main chain (poly(vinyl fluoride, poly(tetrafluoroethylene), poly(vinyl alcohol)). We also determined the possible structural formulas of the secondary positive-ion fragments in the range of 0-100 amu by ab initio MO calculations using the HONDO7 program.