Laser desorption/ionization techniques

Jackson, A.T., Bunn, A., Chisholm, M.S. (2008) UtiUsing matrix-assisted laser desorption/ionization techniques for the generation of structural information from different end-gronp functionalized poly(methyl methacrylate)s. Polymer, 49,5254-5261. 

Bergman, N., Shevchenko, D., and Bergquist, J. 2014. Approaches for the analysis of low molecular weight compounds with laser desorption/ionization techniques and mass spectrometry, Ana/. Bioanal. Chem., 406 49-61. 

Recently, on-resin mass spectrometry (MS) via the MALDI (matrix-assisted laser desorption/ionization) technique has been developed. This method can be used as a semi-on-line monitoring technique during SPPS (141). An especially elegant approach for on-resin MS is to use the photolabile a-methylphenacyl ester linker (Table 5, Q -bromophenacyl entry), which is cleaved directly upon laser photolysis and MALDI ionization (142,143). 

The chemistry of the processes occurred in the above system was studied by FTIR and matrix-assisted laser desorption ionization technique with time of flight detection (MALDI-TOF). On the basis of the results obtained, a scheme of the simultaneous and sequential reactions with formation of BP, BPT, and some intermediate and additional products, including possible substituted cyanurate, isocyanurate, and mixed triazine cycles was proposed [63]. 

On the other hand, there are some ionization techniques that are very useful, particularly at very high mass, but produce ions only in pulses. For these sources, the ion extraction field can be left on continuously. Two prominent examples are Californium radionuclide and laser desorption ionization. In the former, nuclear disintegration occurs within a very short time frame to give a... 

Some solid materials are very intractable to analysis by standard methods and cannot be easily vaporized or dissolved in common solvents. Glass, bone, dried paint, and archaeological samples are common examples. These materials would now be examined by laser ablation, a technique that produces an aerosol of particulate matter. The laser can be used in its defocused mode for surface profiling or in its focused mode for depth profiling. Interestingly, lasers can be used to vaporize even thermally labile materials through use of the matrix-assisted laser desorption ionization (MALDI) method variant. 

The three techniques — laser desorption ionization, laser ablation with secondary ionization, and matrix-assisted laser desorption — are all used for mass spectrometry of a wide variety of substances from rock, ceramics, and bone to proteins, peptides, and oligonucleotides. 

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. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

Matrix-assisted laser desorption ionization (MALDI) is not yet a technique that has been used extensively for LC-MS applications. It is included here because it often provides analytical information complementary to that obtained from LC-MS with electrospray ionization, as illustrated later in Chapter 5. 

The focus of this chapter is the development of a technique often called wholecell matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) or whole-cell MALDI-TOF MS. Some groups prefer to use terms such as intact or unprocessed rather than whole, but the intended meaning is the same regardless of which word is used. As noted in the first chapter of this book, there are many different methods for the analysis of bacteria. However, for the analysis of intact or unprocessed bacteria, whole-cell MALDI-TOF MS is the most commonly used approach. This method is very rapid. MALDI-TOF MS analysis of whole cells takes only minutes because the samples can be analyzed directly after collection from a bacterial culture suspension. Direct MALDI MS analysis of fungi or viruses is similar in approach1,2 but is not covered in this chapter. MALDI-TOF MS of whole cells was developed with very rapid identification or differentiation of bacteria in mind. The name (whole cell) should not be taken to imply that the cells are literally intact or whole. Rather, it should be taken to mean that the cells that have not been treated or processed in any way specifically for the removal or isolation of any cellular components from any others. In whole-cell analysis the cells have been manipulated only as necessary to... 

The most discriminating technique for proving the identity and purity of analyte peak of a chromatogram, especially for analyzing biological samples and natural products, is by using online LC-UV/MS or GC-MS/FTIR methods [15]. Alternatively, one could use a combination of TLC and MS, where direct determination on the TLC plates is made by matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) [16]. 

Sugiura Y, Shimma S, Setou M. Two-step matrix application technique to improve ionization efficiency for matrix-assisted laser desorption/ionization in imaging mass spectrometry. Anal. Chem. 2006 78 8227-8235. 

In a separate study, a protocol for Matrix-assisted laser desorption-ionization (MALDI) imaging mass spectrometry (IMS) has been proposed.18 This IMS technique provides a new approach to visualize spatial distribution of thousands of molecular species, including peptides, proteins, and their metabolites in two- or three-dimensional levels. This approach may also provide a straightforward method of determining the tissue distribution of multiple peptides or proteins in a quantitative manner.18 Chu et al.19 reported a nondestructive molecular extraction method to obtain proteins from a single FFPE or frozen tissue section, without destroying the tissue morphology, such... 

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. 

Over the years, a lot of desorption ionization techniques have been introduced to MS, such as plasma desorption, field desorption, laser desorption, secondary ion mass spectrometry, fast atom bombardment, matrix assisted laser desorption and desorption electrospray ionization. Most of them are actually no longer used. In the following paragraphs, both matrix assisted laser desorption (MALDI) and desorption electrospray ionization (DESI) will be discussed. 

Other MS based analytical approaches have occasionally been applied to ancient resin samples, in particular for paint varnishes. Such techniques include FABS (fast atom bombardment mass spectrometry) [35], MALDI (matrix assisted laser desorption-ionization mass spectrometry) and GALDI (graphite assisted laser desorption-ionization mass spectrometry) [36 38]. 

The second advantage is the possibility of performing chemical imaging analyses. Even if other techniques, such as matrix-assisted laser desorption/ionization, also allow images to be acquired, ToF-SIMS is, for now, the mass spectrometric technique with the best spatial resolution performance. 

A modified version of 2DE and gel image analysis, with silver staining, autoradiography, and protein identification and measurement of peptide mass, uses matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) as a rapid and sensitive technique for identifying peptides. MALDI-TOF-MS applies well to protein detection in biological fluids.56 A second advantage of this technique is... 

Matrix-assisted laser desorption/ionization (MALDI) was developed by Karas, Hillenkamp, and coworkers in the late 1980s [161-163]. At the same time, a related technique was introduced by Tanaka et al. and involved mixing of the analyte with a very finely ground metal powder [164],... 

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