Matrix-assisted laser desorption ionisation applications

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. 

Kolarich D, Altmann F N-glycan analysis by matrix assisted laser desorption/ionisation mass spectrometry of electrophoretically separated non-mammalian proteins. Application to peanut allergen Ara h 1 and olive pollen alleigen Ole e 1. Anal Biochem 2000 285 64-75. 

The classical area of application of mass spectrometry has been with small volatile compounds, although non-volatile samples could be analysed if they were suitably derivatised. The application of mass spectrometry to large complex molecules like proteins has been made possible by the development of novel ionisation techniques which enable large molecules (> 200 kDa) to be introduced into the mass spectrometer in an intact form suitable for analysis (Siuzdak 1996 Dass 2000). Of the various techniques that have been developed, electrospray ionisation (ESI) and matrix-assisted laser desorption ionisation (MALDI) are the ones best suited for use with macromolecules and macromolecular complexes. 

The major reason for this increase has been the use of matrix-assisted laser desorption/ionisation-MS (MALDI-MS) for numerous polymer applications. MALDI is by no means the only mass spectral method that is useful for polymer analysis, but it has provided the impetus to get polymer people interested in what mass spectrometry can do. 

The different stages of the preparation of peptide surfaces can be confirmed with surface-sensitive physical and chemical analysis techniqnes. For gold-based SAMs, Mrksich and co-workers have introduced a matrix-assisted laser desorption ionisation time-of-ftight (MALDI-TOF) mass spectrometry-based analysis procedure with which they are able to identify the presence of various surface functional groups via their mass (Yeo Mrksich, 2006 Yeo et al., 2003). Although this method is applicable to SAMs, it is not strictly a surface sensitive technique, as the desorption process in MALDI is not confined to the uppermost layer of a material. 

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