Matrix assisted laser applications

Matrix-assisted laser desorption/ionization (MALDI) is widely used for the detection of organic molecules. One of the limitations of the method is a strong matrix background in low-mass (up to 500-700 Da) range. In present work an alternative approach based on the application of rough matrix-less surfaces and known as surface-assisted laser desoi ption/ionization (SALDI), has been applied. 

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. 

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. 

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. 

The development of soft ionization methods (electrospray ionization and matrix-assisted laser desorption ionization, and others not discussed here) has contributed to the remarkable progress seen in mass spectrometry applied to biochemistry and molecular biology research progress, and is beginning to find applications in archaeology. 

While fast atom bombardment (FAB) [66] and TSI [25] built up the basis for a substance-specific analysis of the low-volatile surfactants within the late 1980s and early 1990s, these techniques nowadays have been replaced successfully by the API methods [22], ESI and APCI, and matrix assisted laser desorption ionisation (MALDI). In the analyses of anionic surfactants, the negative ionisation mode can be applied in FIA-MS and LC-MS providing a more selective determination for these types of compounds than other analytical approaches. Application of positive ionisation to anionics of ethoxylate type compounds led to the abstraction of the anionic moiety in the molecule while the alkyl or alkylaryl ethoxylate moiety is ionised in the form of AE or APEO ions. Identification of most anionic surfactants by MS-MS was observed to be more complicated than the identification of non-ionic surfactants. Product ion spectra often suffer from a reduced number of negative product ions and, in addition, product ions that are observed are less characteristic than positively generated product ions of non-ionics. The most important obstacle in the identification and quantification of surfactants and their metabolites, however, is the lack of commercially available standards. The problems with identification will be aggravated by an absence of universally applicable product ion libraries. 

Zhou, G. H., Luo, G. A., Zhou, Y, Zhou, K. Y, Zhang, X. D., and Huang, L. Q. (1998). Application of capillary electrophoresis, liquid chromatography, electrospray mass spectrometry and matrix-assisted laser desorption/ionization time of flight mass spectrometry to the characterization of recombinant human erythropoietin. Electrophoresis 19, 2348—2355. 

API offers unique opportunities for the implementation of new sources or to develop new applications. Atmospheric pressure matrix assisted laser desorption (AP-MALDI) [21] can be mounted on instruments such as ion traps which were originally designed only for electrospray and LC-MS. New API desorption techniques such as desorption electrospray (DESI) [22] or direct analysis in real time (DART) [23] have been described and offer unique opportunities for the analysis of surfaces or of solid samples. 

Petkovic, M., Muller, J., Muller, M., Schiller, J., Arnold, K., Arnold, J. Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for monitoring the digestion of phosphatidylcholine by pancreatic phospholipase A2. Anal. Biochem. 2002, 308, 61-70. 

Kang, M.-J., Tholey, A., Heinzle, E. Application of automated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the measurement of enzyme activities. Rapid Commun. Mass Spectrom. 2001, 15, 1327-1333. 

This proposal describes the development of a new, systematic approach for qualitatively and quantitatively studying surface-biomolecule interactions by matrix-assisted laser desorption ionization (MALDl) mass spectrometry (MS). This methodology is being developed because of the profound importance that surface-biomolecule interactions play in applications where biomaterials come into contact with complex biological fluids, it can readily be shown that undesired reactions occurring in response to surface-biomolecule contact (protein adsorption, biofouling, immune response activation, etc.) lead to enormous economic and human costs. Thus, the development of analytical methodologies that allow for efficient assessment of the properties of new biomaterials and/or the study of detailed fundamental processes initiated upon surface-biomolecule contact are of critical value ... 

The exception to this is the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). In 1981, Barber and Liu and coworkers independently introduced the concept of employing MALDI where the absorption of the matrix is chosen to coincide with the wavelength of the employed laser to assist in the volatilization of materials. In 1988, Tanaka, Hillenkamp, and coworkers employed the laser as the energy source, giving birth to MALDI-MS. 

Nonier, M.F. et al., Application of off-line size-exclusion chromatographic fractionation-matrix assisted laser desorption ionization time of flight mass spectrometry for proanthocyanidin characterization, J. Chromatogr. A, 1033, 291, 2004. 

Tholey, A. and Fleinzle, E., Ionic (liquids) matrices for matrix-assisted laser desorption/ionization mass spectrometry - applications and perspectives. Anal Bioanal. Chem., 386, 24-37, 2006. 

The third focus is the use of IL as supports for MS. The application of the IL enabling electrospray ionization (ESI) using nonpolar solvents will be demonstrated. A major emphasis will be put on the use of ILs as matrices for matrix-assisted laser desorption/ionization (MALDI) MS, a field gaining emerging interest in the last few years. 

Nicola, A. J. et al.. Application of the fast-evaporation sample preparation method for improving quantification of angiotensin II by matrix-assisted laser desorption/ionization. Rapid Commun. Mass Spec., 9, 1164,1995. 

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