MALDI and ESI-MS

Electro-Spray Ionization Mass Spectrometry (ESI-MS), also referred to as ES-MS, is a mass spectrometric technique that provides a similar information content to that of MALDI, i.e. is useful in the analysis of macro-molecules. ESI-MS can, however, access a greater mass range because a greater number of multiply charged ions are produced relative to MALDI. These ions are produced by dispersing, via electro-spray, a liquid containing the analyte of interest. Ions formed as a result of solvent evaporation are then directed into a mass spectrometer for molecular identification. No prior sample preparation is needed, and analysis can be carried out in close to atmospheric conditions. 

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Matrix assisted laser desorption ionisation (MALDI) and ESI-MS spectra of non-ionic surfactant blends of AE obtained after positive ionisation were compared [28]. Both the ionisation procedures, which produce [M + Na]+ ion clusters, were very useful for this purpose, but the ESI spectra generated were more complex, whereas MALDI ionisation led to simpler spectra that can be interpreted more easily [28]. 

Biomolecular mass spectrometric techniques (MALDI- and ESI-MS) for the analysis of biopolymers are leading representatives of biochemical techniques. The sensitivity of biomolecular... 

The promising use of various MALDI- and ESI-MS approaches in proteome research has accelerated many developments in the instrumental design and concepts of mass spectrometry. Novel MS techniques and intriguing combinations of existing instruments have emerged. Nonetheless, the basic principle of measuring the mass-to-charge ratios of analytes remains. 

Since the sensitivity of MS methods is similar to that of Edman chemistry, both methods will continue to be used. Because MS methods cannot determine the N- or C-terminal sequences in intact proteins, there will be a continued need for the Edman sequencer. However, MALDI- and ESI-MS methods can give accurate molecular masses for intact proteins, which when compared to their predicted sequences and databases (Eng et al., 1994), can verify a given structure, giving confidence to the N- and C-terminal sequence predicted from the peptide maps. MS-MS provides the fast and sensitive approach to sequence determination of peptides/proteins. 

As with most ionization methods, FI and FD mass spectra are most often acquired for compounds of mass <1000 Da (1 kDa). There are many examples in the literature, however, of FI/FD mass spectra for compounds/polymers in the mass range 1-5 kDa. Based on a few literature examples, the maximum practical FD mass range would appear to be 10-15 kDa thus FD-MS is a technique of intermediate mass range capability. Molecular ions can be obtained at higher masses than have been reported, for example, for El-MS and CI-MS. However, some desorption/ionization methods, such as MALDI- and ESI-MS, have demonstrated higher mass capabilities. 

Can be used both globally (intact) for screening purposes and locally (peptide level) for more detailed analysis [53]. Multiple hardware and software vendors. Compatible with both MALDI- and ESI-MS... 

Application of Protein Imaging to Disease Model Mice One of the advantages of traditional MS, including both MALDI- and ESI-MS, is that they can distinguish even slight structural variations of analyte molecules by their masses. Due to this unique advantage, MS has frequently been applied to the identification/ characterization of posttranslational modifications in modern proteome researches [12]. In this context, IMS also enables the distinct detection of the protein molecular species as well as the visualization of the distribution of these species on the tissue sections. As an excellent example, in the Stoeckli et al. study, amyloid... 

Recently, various studies have recognised MALDI and ESI as valuable techniques for analysing chemical modifications in the structure of synthetic polymers induced by degradation processes [154-158]. Even tough, MALDI and ESI MS appear considerably less extensively used in the thermal degradation of polymers than in other degradation processes [160], In fact, the study of polymer thermal degradation by MALDI has been limited to a few classes of polymers likely since it is a useful method to analyse pyrolysis products from soluble polar macromolecules. 

The Cf-PD method has been largely supplanted by MALDI and ESI MS for the analysis of complex biological molecules because these methods are more efficient and widely applicable. The method has stimulated considerable interest in the field of particle-induced desorption and understanding of the mechanisms of the desorption/ionization process. Scanning tunnelling microscopy has been used to characterize the craters produced by fission... 

This section summarizes the most important sample preparation techniques that have been developed for MALDI and ESI MS of peptides and proteins. For the study of DNA-binding proteins, this typically covers only the last steps of a long chain of sample preparation steps, which are necessary to isolate them out of their biological environment and provide them in a form that is suitable for MALDI or ESI MS. As the sample preparation of peptides and proteins for ESI or MALDI, with some exceptions, is little specific for their ability to bind to DNA or not, this section is not restricted to that feature. 

One major drawback of ESI for the analysis of synthetic polymers is the necessity of using suitable solvents, which are essential for a sufficient spray formation and ionization. The fact that most synthetic polymers are soluble in solvents such as tetrahydroftiran (THF) or chloroform rather than in typical ESI solvents (e.g., water, acetonitrile, and methanol) still limits the use of ESI for polymer analysis. Moreover, since tn/z deaeases with increasing chromatographic flow rates (which reduces the efficiency of ion formation), relatively low flow rates have to be applied. All these problems are probably the main reason for a significantly lower number of ESI-polymer publications compared to the MALDI method. Nevertheless, the nirmber of applications of MALDI and ESI-MS for polymer separation and identification increased steadily since their first reports and reached a more or less constant number in the past 5 years (see Figure 5). 

Figure 5 Number of publications with regard to MALDI and ESI-MS of polymers. Source Web of Science.

A more detailed overview on the analysis of polymers by MALDI and ESI-MS can be gained from continuative literature. " ... 

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