Analysis of copolymers by laser desorption fourier transform mass spectrometry (original) (raw)
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Rapid Communications in Mass Spectrometry, 2007
The results of copolymer characterization by coupling of chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) techniques and subsequent calculation of copolymer composition using a novel software tool 'MassChrom2D' are presented. For high-resolution mass analysis copolymer samples were fractionated by means of liquid adsorption chromatography (LAC). These fractions were investigated off-line by MALDI-TOF MS. Various mono-n-butyl ethers of polyethylene oxide-polypropylene oxide copolymers (PEOco-PPO) were investigated. As well as the copolymer composition presented in two-dimensional plots, the applied approach can give additional hints on specific structure-dependent separation conditions in chromatography. S. M. Weidner et al. Figure 11. MALDI-TOF MS/MS spectrum recorded for a precursor ion at m/z 2216.4 of a PEO-co-PPO polymer after chromatographic separation (top) and sections showing EO (middle) and PO distributions (bottom).
Analytical Chemistry, 1998
Glycidyl methacrylate (GMA) and butyl methacrylate (BMA) have the same nominal mass (142 Da) but differ in exact mass by 0.036 Da (CH 4 vs O). Therefore, copolymers formed from the two isobaric monomers exhibit a characteristic isobaric distribution due to different monomer compositions. Here, we show that electrospray ionization FT-ICR mass spectrometry at 9.4 T resolves the isobaric components of copolymers as large as 7000 Da with a resolving power (m/∆m 50% ) of ∼500 000 in a gel permeation chromatography fractionated polymer sample. That resolution provides for complete and unequivocal component analysis of such copolymers of the size used for high solid content automobile coatings. All five possible copolymer products predicted by the polymerization mechanism are resolved and identified in the mass spectrum. Two of those polymer series (each with saturated end group) were previously unresolved by mass spectrometry because they differ in mass from the two other unsaturated products by only 0.0089 Da. Finally, analysis of the asymmetrical isobaric distribution for the copolymer n-mers, (GMA) m (BMA) n-m , 0e m e n, in which species with adjacent values of m differ from each other in mass by 36 mDa (i.e., the mass difference, CH 4 vs O, between GMA and BMA) proves that GMA is less reactive than BMA in the polymerization process.
Structural Characterization of Multicomponent Copolyesters by Mass Spectrometry
Macromolecules, 1998
The structural characterization and composition of five random copolyesters, originating from 1,4-butanediol and mixtures of succinic, adipic, sebacic, and terephthalic acids, were obtained by analysis of their fast atom bombardment (FAB) and their matrix-assisted laser desorption ionization (MALDI) mass spectra. Multicomponent condensation copolymers may sometimes prove difficult to characterize by conventional techniques, whereas mass spectrometry is able to handle them. Once the choice between Bernoullian or Markoffian models has been made, the determination of copolymer composition, number-average sequence length, and related quantities can be achieved by applying welldefined analytical equations. The theoretical mass spectra of multicomponent copolymers are remarkably simple, and the number of peaks appearing in each copolymer mass spectrum is easily predictable. Different kinds of spectral fitting algorithms may help in the actual computations, and it has been shown that the apparent complexity of mass spectra of copolymers is due to the presence of mass series bearing different end groups. By selecting a single mass series, one obtains an experimental spectrum immediately comparable to the theoretical one. Detailed examples, together with a discussion on the reliability of results, are given to apply the computation procedures and to gain proper understanding of the concepts involved.
Analytical Chemistry, 2008
Complex copolymers are heated to slowly increasing temperatures on a direct probe (DP) inside the plasma of the atmospheric pressure chemical ionization (APCI) source of a quadrupole ion trap. Slow heating allows for temporal separation of the thermal degradation products according to the stabilities of the bonds being cleaved. The products released from the DP are identified in situ by APCI mass spectrometry and tandem mass spectrometry. DP-APCI experiments on amphiphilic copolymers provide conclusive information about the nature of the hydrophobic and hydrophilic components present and can readily distinguish between copolymers with different comonomer compositions as well as between cross-linked copolymers and copolymer blends with similar physical properties. The dependence of DP-APCI mass spectra on temperature additionally reveals information about the thermal stability of the different domains within a copolymer. Electrospray ionization (ESI) 1 and matrix-assisted laser desorption/ionization (MALDI) 2,3 have made it possible to form intact gas-phase ions from most classes of synthetic polymers, enabling mass spectrometry (MS) analyses on such macromolecules. 4-20 MS experiments provide the masses of the individual oligomers contained in a polymer, from which important compositional and structural information about the polymer can be deduced, for example, its (co)monomer composition, end groups, compositional heterogeneity, and molecular weight distribution. Still, numerous synthetic polymers designed for important industrial or biomedical applications cannot be analyzed by MS, because they are too large or too polar to be dissolved (for ESI) or desorbed (for MALDI), or they are unable to form gas-phase ions due to the lack of functional groups that can attract and bind a charged particle, such as a proton or metal cation. Fortunately, most large or unionizable polymers become amenable to MS analysis by pyrolysis, i.e., thermal degradation. 9,21-30 Depending on the thermal stability of the polymer and the temperature used (typically within 150-1000°C), pyrolysis leads either to small fragments that can be ionized by electron ionization, chemical ionization (CI), field ionization, or photoionization, or to higher-mass pyrolyzates that can be subjected to ESI, MALDI, or both. The resulting mass spectra unveil the composition of the polymer sample. Molecular weight information is lost, but information about the thermal stability and degradation pathways of the polymer is gained. Rapid heating of the sample to a high temperature, via hightemperature Curie-point or resistive heating flash pyrolysis,
Macromolecules, 1992
Statistical modeling of the mass spectral intensities of copolymers has been used to derive information on the distribution of monomers along the copolymer chain, and an automated procedure to find the composition and the sequence of the copolymers analyzed has been developed. A deconvolution method to determine the microstructure of copolymers when different chemical species contribute to the same mass spectral peak (that is, when a mass spectroscopic peak has an equivocal structural assignment) is presented. The effect of the partial degradation process on the mass spectra of copolymers is discussed, and a theory is given for the interpretation of the mass spectra of copolymers when the cleavage of the copolymer chain occurs by a selective or nonselective mechanism. A method is also reported to obtain the copolymer composition by direct analysis of the mass spectra. All these theories have been applied to determine the composition and microstructure of several copolymers (both addition and condensation types) whose mass spectra have been reported in the most recent literature.
Journal of Applied Polymer Science, 2018
ABSTACT: Poly(styrene-co-4-vinylpyridine) random copolymers with different molar composition were synthesized by nitroxidemediated controlled-radical polymerization using 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) as a mediator. We record the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) spectra under various conditions, and we find (at last) that they show mostly intact ions [using 2(-4-hydroxyphenylazo-)benzoic acid as MALDI matrix]. Spectra are highly resolved, and thus they allow for the determination of all end-groups, even some less-abundant ones. Spectra are dominated by intact "dormant" copolymer chains terminated with TIPNO at one end and with (4-Bromo-phenyl)ethyl group (starting fragment) at the other one. Applying the mass analysis of copolymers (MACO) statistical model to the spectra, we show that the MACO/MALDI-TOF mass spectrometry (MS) analysis can be successfully applied to copolymers having a difference between the mass of the comonomers as small as 1 g mol −1 (the styrene and 4-vinylpyridine units are 104.15 and 105.15 g/mol, respectively), which results in overlapping isotopic patterns. The results are accurate: chemical composition evaluated by means of MS agrees with that calculated by 1 H-nuclear magnetic resonance, for all copolymers investigated. This analytical method allows to extract detailed information on the composition of the copolymer samples and their structure. Glass transition temperatures of copolymers were also determined by differential scanning calorimetry.
Structural characterization of polyester copolymers by MALDI mass spectrometry
Progress in Organic Coatings, 2002
A polyester copolymer is produced by step-growth polymerization of neopentyl glycol (50 mol%), trimethylol propane (1%), terephthalic acid (45%) and adipic acid (5%) and its microstructure is characterized by gel permeation chromatography and matrix-assisted laser desorption ionization mass and tandem mass spectrometry. The combination of these analytical methods is shown to yield detailed insight about the composition, end groups, molecular weight, and sequence of the product.
Interference from multiple cations in MALDI–MS spectra of copolymers
International Journal of Mass Spectrometry, 2004
A matrix-assisted laser desorption/ionization Fourier transform mass spectral (MALDI-FTMS) investigation of copolymers of methyl methacrylate (MMA) and butyl methacrylate (BMA) is reported here. A key to the analysis of copolymers by mass spectrometry is the accurate assignment of a unique composition to each ion signal observed in a spectrum. In the present case, the spectra reveal numerous ions with nominal mass separations of 16 Da. This results from the presence of oligomers differing in composition by three extra MMA units and two lesser BMA units. Lithium-sodium and sodium-potassium adduct pairs produce ions that also differ by a nominal mass of 16 Da. Therefore, ambiguous assignments of compositions are possible, especially when the identities of the cations are unknown. When cesium ions are added to the sample, the adducts produced allow high resolution Fourier transform mass spectra to be used for assignment of unambiguous compositions to ions. Spectra with overlap from multiple cations were compared with the cesium adduct spectra using a mathematical analysis of relative ion abundances to determine the fraction of ionization that each cation contributed. When two cations were simultaneously added to a sample, the resulting fraction of ionization by one of the cations was related to the ratio of the two added salts. This relationship is well described by an empirical equation that allows the prediction of the ionization fraction for a given ratio and vice versa.