Matrix-assisted laser desorption/ionization polymers

Barton, Z., Kemp, T. J., Buzy A., and Jermings, K. R. Mass spectral characterization of the thermal degradation of polyjpropylene oxide) by electrospray and matrix-assisted laser desorption ionization. Polymer, 36, 4927, 1995. 

Electrospray and Matrix-Assisted Laser Desorption Ionization, Polymer, 36, 4927,1995. 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

The growing interest for the identification and characterization of polar and large compounds caused the development and the introduction of new ionization techniques, such as electrospray ionization (ESI)[4], and matrix assisted laser desorption ionization (MALDI),[5] and their more recent improvements, thus establishing new MS based approaches for studying large molecules, polymers and biopolymers, such as proteins, carbohydrates, nucleic acids. 

Since the discovery, in the early 1990s that polymers can be ionized by matrix-assisted laser desorption/ionization (MALDI see Section 2.1.22) in a fashion similar to proteins, MALDI is rapidly becoming a standard tool in polymer characterization [4-6]. 

The advantages of supercritical fluid chromatography for polymer separations have been illustrated in the literature for many years. A recent example is the separation of long-chain polyprenols using SFC with matrix-assisted laser-desorption ionization TOF mass spectrometry [10]. The generic name for 1,4-polyprenyl alcohols is polyprenol these compounds generally have smaller polymerization chains of less... 

Even if relatively new, HF FIFFF has been used to separate supramicrometer particles, proteins, water-soluble polymers, and synthetic organic-soluble polymers. Particle separation in HF FIFFF has recently been improved, reaching the level of efficiency normally achieved by conventional, rectangular FIFFF channels. With these channel-optimized HF FIFFF systems, separation speed and the resolution of nanosized particles have been increased. HF FIFFF has recently been examined as a means for off-line and on-line protein characterization by using the mass spectrometry (MS) through matrix-assisted laser desorption ionization time-of-flight mass spectrometry (M ALDl-TOF MS) and electrospray ionization (ESl)-TOF MS, as specific detectors. On-line HF FIFFF and ESl-TOF MS analysis has demonstrated the viability of fractionating proteins by HF FIFFF followed by direct analysis of the protein ions in MS [38]. 

A toluene solution of polymer 15 was added to an aqueous mixture of peptides. After effective equUibration, the heterogeneous mixture was allowed to separate and the organic layer was analyzed by matrix assisted laser desorption ionization mass spectrometry analysis. Because the pH of the aqueous solution was 7.1, the peptides with pis above 7.1 were extracted and the peptides with pis below 7.1... 

Finally, another method commonly used to characterize these copolymeric materials is that of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. When using this technique, it is possible to investigate the molecular weight distributions, end groups, and polymer constitution of low-molecular-weight samples [63], MALDI-TOF may also provide vital... 

Mass spectra are used to determine molecular weights and molecular composition (from the parent or molecular ion) and to obtain structural information from the fragmentation of the molecular ion into daughter ions. Electrospray ionization (ESI-MS) and matrix-assisted laser desorption ionization (MALDI-MS) mass spectroscopy can be used to obtain structural information about macromolecules, including proteins, polymers, and drug-DNA complexes. 

The most creative application of the secondary cathode approach was described by Schelles and Van Grieken [24], who investigated its ability to determine the elemental constituents of polymeric materials. Mass spectrometric analysis has almost exclusively been directed at the determination of molecular weights and disparity characteristics secondary ion mass spectrometry (SIMS) [53,54] and matrix assisted laser desorption ionization (MALDI) [55,56] have carried the major share of the workload. Growing concerns over the fate of polymeric materials in the environment and the leaching of heavy metals into ground waters have necessitated the development of methods that permit the elemental analysis of bulk polymers. In addition, the use of polymers as immobilization media for waste remediation is also pressing these developments. 

Most analytical studies using FT-ICR mass spectrometry, where ions have been produced inside (or just outside) the analyzer cell, have used lasers as ionization sources. Other than some very limited Cs secondary ion mass spectrometry (SIMS) studies [77], most research utilized direct laser desorption to form various organic [78] and inorganic [79] ions, including metal [80] and semiconductor [81] (including carbon) clusters. More recently matrix assisted laser desorption ionization (MALDI) has been used to form ions of high molecular weight from polymers [82] and many classes of biomolecules [83]. 

MALDI-MS refers to matrix-assisted laser desorption-ionization mass spectroscopy, It is also called MALFI-TOF, because the mass spectrometer is a time-of-flight version. In this technique, the polymer is mixed with a molar excess of a salt, for cationization, and deposited on a probe surface. A UV laser is pulsed... 

Laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MSs have become useful tools for the characterization of various conducting polymers. For instance, analysis of poly[2,5-di(thien-2-ylidene)-l,3,4,6-tetrathiapentalene] 56 (DT-TTP) showed ions above mlz = 500 corresponding to oligomers of DT-TTP with up to five monomer units <2000JMP550>. 

On-line MS detectors for SEC offer great promise for serving simultaneously as an absolute detector, concentration-sensitive detector (i.e., total ion current), and composition detector, especially for oligomers and low-MW polymers. Successful developments in the use of matrix-assisted laser desorption ionization (MALDI) MS for high-MW polymers are extremely encouraging, and on-line MALDI MS should... 

Cryoscopy and ebulioscopy can be used for the measurement of Mn for polymers in a similar way to the application on smaller molecules, and the procedure is used mainly when Mn < 2 10. I LDI-MS (matrix-assisted laser desorption ionization-mass spectroscopy) allows the measurement of both Mn and M , as well as the molecular weight distribution, which indicates the variation of w, (weight fraction of the component i ), as a function of M,. 

For natural poly-APS alkaloids (77), matrix assisted laser desorption ionization-time-of-flight (MALDI-TOF) spectrometric analysis showed that the compounds comprised a mixture of two polymers with molecular weights centred at around 5520 Da and 18900 Da and with a low degree of polydispersity [34]. 

Matrix-assisted laser desorption ionization (MALDI), like ESI, is capable of ionizing and launching very large molecules (e.g, polysaccharides, synthetic polymers, peptides, and proteins) into the gas phase and is a major analytical tool for high-throughput proteomic studies.17,53 In many respects, MALDI is a complementary technique to ESI and both techniques are often applied to the same sample when determining protein identity. ESI produces macromolecular ions from solution, whereas MALDI produces them from the solid state. 

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