Mass Spectrometry MALDI-TOF

Since it is a less laborious technique than GPC or NMR, MALDI-TOF has attracted interest as a possible technique for characterizing commercial polymers such as polyethylene. However, polyolefins cannot be analyzed using MALDI-TOF, since they lack a functional group that can be cationized. Bauer et al. [88] proposed a technique for overcoming this problem in the case of polyethylene by the chemical modification of the polymer prior to analysis. 

The use of NMR to elucidate the structure of polyolefins was pioneered by Randall, who has reviewed the capabilities of this technique [89]. Structural features that can be probed include the identity of the repeat unit and its chirality, copolymer sequence structures and their distributions, identity of end groups, degree of polymerization, and branching. Carbon-thirteen is a naturally-occurring isotope that represents about one percent of the carbon atoms present in a polymer. In a typical experiment, a sample is excited by a series of radio frequency pulses, which alter local nuclear moments by a certain angle, after which they decay to their undisturbed (equilibrium) state. The decay is monitored by a detector coil, and the output curve shows the frequencies at which resonance occurred. In order to achieve sufficient precision for the applications mentioned above, experiments of quite long duration are required, often many hours, or even several days. 

The NMR resonances are sensitive to structural contributions of carbon atoms up to about four atoms away from a given atom. As a result, this technique is unable to detect, for example, the difference between a short-chain branch resulting from the presence of octene comonomer in polyethylene and a branch long enough to be entangled. When dealing with a polymer that contains both types of branch, additional techniques are required to elucidate the structure. 

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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 molecular weights and molecular weight distributions (MWD) of phenolic oligomers have been evaluated using gel permeation chromatography (GPC),23,24 NMR spectroscopy,25 vapor pressure osmometry (VPO),26 intrinsic viscosity,27 and more recently matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).28... 

Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF)... 

Foret et al.98 collected fractions of model proteins and variants of human hemoglobins after fractionation by CIEF, and then analyzed them by matrix-assisted laser desorption-time-of-flight-mass spectrometry (MALDI-TOF-MS). As the authors point out, MS is an orthogonal method to CIEF because it separates according to molecular mass. 

Matrix-Assisted Laser Desorption/lonization Time-of-liight Mass Spectrometry (MALDI-TOF MS, PerSeptive Biosystems Voyager-DE STR) was used to characterize the molecular weight distribution and the number average molecular weight (M ) of the poly(methacrylic acid) (PMAA) degradation products as described elsewhere [25]. 

Below we report methodological studies based upon HPLC, GC/FID, GC-MS, LC-MS, matrix-assisted laser desorption ionisation coupled with time-of-flight mass spectrometry (MALDI-ToF/MS), CE, proton nuclear magnetic resonance ( I INMR), RIA and enzymatic colorimetric techniques. 

Matrix-assisted Laser Desorption/lon ization Time-of-f I ig ht Mass Spectrometry (MALDI ToF) for Parasite Analysis... 

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI ToF) for parasite analysis 337... 

They screened seven libraries, each containing 19 peptides of different masses, and found the sequences that bound most tightly to Tom20. Matrix-assisted laser desorp-tion/ionization time-of-flight mass spectrometry (MALDI-TOF MS) served as a readout that allowed the ionized peptides to be observed directly. Using this approach, Kohda and colleagues discovered that the recognition site spans six residues, not the previously established five, and were able to refine sequence preferences further. 

Direct evidence of the existence of organomagnesium compounds with a cluster metal core has been obtained by matrix-assisted laser desorption/ ionizaiton time-of-flight mass spectrometry (MALDI-TOF MS). This method allows one to record the spectra of molecular ions [MH]+ of pro-tonated molecules M. The major advantage of this method is that the use of volatile matrices makes it possible to measure the mass spectra of compounds that hardly transform to the gas phase under other conditions. This is true in full measure for organomagnesium compounds. The method does not provide detailed information on the geometry of corresponding... 

MALDI-Fourier transform ion cyclotron resonance mass spectrometry MALDI-Q-ion mobility-TOFMS MALDI-Quadrupole-ion-trap-TOF mass spectrometry MALDI-TOF-imaging mass spectrometry MALDI Time-of-flight mass spectrometry Magnetic resonance imaging Matrix solution fixation Moxifloxacin... 

A fast-growing application of the MALDI technique is use in combination with Time-of-Flight mass spectrometry (MALDI-TOF-MS) and has been applied to the determination of molecular weight for biological macromolecules [2-4], Currently, analytes that have molecular weights of <1,000 Da can be analyzed by MALDI-TOF-MS [5-7],... 

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry MALDI-TOF appears the newest technique particularly suitable for the study of oligomers and dendrimers because, under appropriate conditions, the parent peak is obtained uncontaminated by fragmentation species. However, in some cases supramolecular clusters have been observed which could be misinterpre-tated as dimers and higher multiplets [13]. The molecular weight range available reaches 50,000 D with a potential resolution between 0.01 and 0.05%. 

Because of expected electrical, electrochemical, optical, chemo-sensor, and other properties of the ball-type Pcs, several metallo and metal-free ball-type Pcs with different linkers have been reported. Metallo and metal free ball-type Pcs containing four calyx[4]arene units as linkers have been synthesized, Fig. 1 [37], The structures of compounds 1-3 were confirmed by UV-vis, IR, 1II-NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and elemental analysis. Because of their unique structure and versatile complexation properties [38], calixarenes were found to be one type of interesting compounds to be incorporated into Pc. The cone conformation of the t-butylcalix[4]arene direct... 

Recently, matrix-assisted laser desorption ioniza-tion/time-of-flight/mass spectrometry (MALDI/TOF/ MS) of intact adducted hemoglobin was explored as a diagnostic tool for the confirmation of exposure to sulfur mustard (23). Multiple alkylated species were observed from incubates of hemoglobin with sulfur mustard however, the methodology has not yet been reported for diagnostic purposes. 

Since then, many novel methods have been developed to analyze gene expression and mutation by using electrochemical techniques [1,2], matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MASS) [3], polymerase chain reaction (PCR) [4,5], bacterial magnetic particles [6], and microbeads [7]. 

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