Mass Spectrometry of Synthetic Polymers (original) (raw)
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Journal of Visualized Experiments, 2018
There are many techniques that can be employed in the characterization of synthetic homopolymers, but few provide as useful of information for end group analysis as matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). This tutorial demonstrates methods for optimization of the sample preparation, spectral acquisition, and data analysis of synthetic polymers using MALDI-TOF MS. Critical parameters during sample preparation include the selection of the matrix, identification of an appropriate cationization salt, and tuning the relative proportions of the matrix, cation, and analyte. The acquisition parameters, such as mode (linear or reflector), polarization (positive or negative), acceleration voltage, and delay time, are also important. Given some knowledge of the chemistry involved to synthesize the polymer and optimizing both the data acquisition parameters and the sample preparation conditions, spectra should be obtained with sufficient resolution and mass accuracy to enable the unambiguous determination of the end groups of most homopolymers (masses below 10,000) in addition to the repeat unit mass and the overall molecular weight distribution. Though demonstrated on a limited set of polymers, these general techniques are applicable to a much wider range of synthetic polymers for determining mass distributions, though end group determination is only possible for homopolymers with narrow dispersity.
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
Current Trends in Matrix-Assisted Laser Desorption/Ionization of Polymeric Materials
European Journal of Mass Spectrometry, 2005
In the last few years, mass spectrometry has rapidly become indispensable in polymer analysis and complements, in many ways, the structural data provided by nuclear magnetic resonance. Mass spectrometry of polymers is emerging as a revolutionary technique, capable of challenging the techniques and protocols established for years for the characterization of synthetic polymers. Matrix-assisted laser desorption/ionization (MALDI) has become a widely applied method for the structural characterization of synthetic polymers. The primary aim of this review is to illustrate some recent advances in the study of macromolecular systems by MALDI. MALDI allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers and the estimate of composition and sequence for co-polymers. MALDI is also quite useful for the measurement of molar mass and bivariate distributions in polymers and for the detection of self-association in macromolecules, performed b...
Quantitative mass spectrometry of technical polymers: a comparison of several ionization methods
European Mass …, 1998
The development of soft ionization methods such as matrix-assisted laser desorption/ionization (MALDI), electrospray ionization (ESI) and secondary ion mass spectrometry (SIMS) has led to an increased use of mass spectrometry in characterizing technical (synthetic) polymers. In this paper, we compare the relative performance of these three ionization methods for characterizing the molecular weights, polydispersities and quantification of relative amounts of polymer components in mixtures. Two polymers used in biomaterials, poly(dimethylsiloxane) and poly(ethylene glycol), are employed as the model polymer systems for our survey because of their well-defined molecular weights and importance as surfactants in biomaterials and because many of their surface and solutionphase properties are well understood. Matrix-assisted laser desorption/ionization can be used to examine the surface and bulk composition of biomaterials, whereas secondary ion mass spectrometry is used for examining monolayer and submonolayer coverage of polymers on surfaces and electrospray ionization is suited for examination of extractables from biomaterials. Secondary ion mass spectrometry and electrospray show discriminate behavior against ionization of higher molecular weight oligomers, especially of poly(dimethylsiloxane). Matrix-assisted laser desorption/ionization appears to exhibit the best performance for reliable molecular weight determination at higher masses and polydispersity characterization as well as for quantification of components in polymer mixtures. The results are discussed within the context of the ionization mechanisms by which each soft ionization technique operates and by the attributes of the mass analyzers (time-of-flight and Fourier transform mass spectrometers) employed.
European Journal of Mass Spectrometry, 1998
A simple, low-cost, air-spray technique has been evaluated for the preparation of matrix-assisted laser desorption/ionisation (MALDI) sample slides. Hydroxyl end groups of poly(ethylene glycol) M n = 600 were functionalised by esterification using acetyl and butyryl chlorides. Air-spray deposition gave excellent shot-to-shot and spot-to-spot reproducibility; the observed compositions by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) being in agreement with those obtained from 1 H NMR. Compressed air-spray is an excellent, inexpensive, sample preparation procedure for simple routine MALDI-TOF MS which increases the reproducibility of this increasingly important technique for synthetic polymer analysis.
Journal of the American Society for Mass Spectrometry, 1996
Matrix-assisted laser desorption-ionization (MALDI) time of flight is shown to give a molar peak area response for isolated methylmethacrylate oligomers that have 25 and 50 repeat units when run on three different instruments in reflectron or linear mode and using three different matrix materials. In addition, fragmentation was not observed in any of the three different matrices or at higher laser power. No spectral differences were observed for syndiotactic and isotactic methylmethacrylate oligomers. These results suggest that the low most probable peak values observed for narrow distribution polytmethylmethacrylate) standards by MALDI mass spectrometry are not the result of mass discrimination or fragmentation.
The application of nonpolar matrices for the analysis of low molecular weight nonpolar synthetic polymers using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is demonstrated. Anthracene, pyrene, and acenaphthene were utilized as nonpolar matrices for the analysis of polybutadiene, polyisoprene, and polystyrene samples of various average molecular weights ranging from about 700 to 5000. The standard MALDI-MS approach for the analysis of these types of polymers involves the use of conventional acidic matrices, such as all-trans-retinoic acid, with an additional cationization reagent. The nonpolar matrices used in this study are shown to be as equally effective as the conventional matrices. The uniform mixing of the nonpolar matrices and the nonpolar analytes enhances the MALDI-MS spectral reproducibility. Silver salts were found to be the best cationization reagents for all of the cases studied. Copper salts worked well for polystyrene, poorly for polyisoprene, and not at all for polybutadiene samples. These matrices should be useful for the characterization of hydrocarbon polymers and other analytes, such as modified polymers, which may potentially be sensitive to acidic matrices. (J Am Soc Mass Spectrom 2000, 11, 731-737)