MALDI-ToF technique

The MALDI-TOF technique was first developed for the analysis of large biomolecules (Karas and others 1987). This technique presents some interesting characteristics. Of these, the high speed of analysis and the sensitivity of the technique have been pointed out as important advantages compared with other methods. In MALDI the samples are cocrystallized with a matrix that is usually composed of organic compounds, such as 3,5-dimethoxy-4-hydroxycinnamic acid (sinapic acid), 2, 4, 6 -trihydroxyacetophenone, a-cyano-4-hydroxycinnamic acid (alpha-cyano or alpha-matrix), and 2,5-dihydroxybenzoic acid (DHB). After the cocrystallization, the laser is fired and the matrix absorbs energy and allows a soft ionization of the samples. Afterward the ions are analyzed by a TOF mass spectrometer. 

Dendrimer characterization was accomplished by 13C, NMR and FT-IR spectroscopy as well as mass spectrometry using fast atom bombardment (FAB) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) techniques. Molecular ion base peaks were observed in the MALDI-TOF MS of polyester 168 (mlz 18900 (calcd. 19044)) along with minor peaks at 37000 and 54000 mlz corresponding to ionic gasphase dimer and trimer complexes. 

There has been considerable debate over the reason why TEMPO does not work well for acrylates. CNRS researchers utilized NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) techniques to look at the terminal end-groups on poly(n-butyl acrylate) produced using TEMPO mediation [19]. They found that most of the chains were terminated by co-unsaturation resulting from either elimination or O-H TEMP from the chain-end or disproportionation between TEMPO and the polyradical (Scheme 8.7). 

MALDI-TOF precludes many previously mentioned problems and limitations of the ESI-MS technique. However, it is important to note that MALDI-TOF and ESI-MS are complementary, not alternative, techniques. Depending of the analytical goal, either one of these two methods can be more effective. MALDI-TOF technique was described in detail in the literature [282]. Fig. (21) shows a negative mode MALDI-TOF spectrum of an HA fraction composed of three individual oligomers 30-mer, 32-mer, and 34-mer [286]. In general, chemical structure, ionization, end groups, etc. are usually characterized by means of the MALDI-TOF detector [282]. 

Mass spectrometric methods are now able to assist with specific characterization of relatively long-chain oligomers, and the MALDI-TOF technique has been used in the investigation of a cell wall xylan linked by P-(l—3)-bridges and with chain length of 25. Such analysis can be carried out on impure samples. 

FAB and MALDI-TOF techniques revealed that macrocyclic oligoesters were the main condensation products of catechol or 0,0 -Bistrimethylsilyl catechol (BTSC) with adipoyl chloride, sebaroyl chloride, and sebacoyl chloride, respectively. Macrocyclic polyesters were also obtained when the noncyclic l,3-bis(tributylstannoyl)butane was used as monomer. ... 

The matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) technique is suitable to determine the presence of molecules of higher molecular weight with high accuracy, and it has been applied with success to study procyanidin oligomers and other complex phenolic mixtures [67, 141]. 

The properties of polycarbonate beside its molar mass distribution (D=Mw/Mn) depend often of type and amount of end groups, cycles, additives and branch. In particular the end chains constitute the fingerprints of its polymerization procedure, of its thermal and mechanical history and of their environmental use. Several tools such as NMR, FT-IR and Mass Spectrometry were used to determine these peculiar characteristics of PC. In particular the matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) has successfully been applied to obtain these information (49,50). MALDI-TOF technique is able to look each molecule even in a complex mixture (51-53), to obtain information on the end groups and structure (linear, cyclic or branched) of the macromlecular chains as a function of the synthesis and processing conditions. 

To an appreciably less extent, other techniques, such as scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Raman spectroscopy, and atomic force microscopy (AFM) are used in conjunction with IR or MALDI-TOF techniques. 

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