Matrix associated laser desorption ionisation

Mass spectroscopy [electron ionisation (El), chemical ionisation (Cl), electrospray ionisation (ESI), fast atom bombardment (FAB), matrix-associated laser desorption ionisation (MALDI), inductively coupled plasma-mass spectrmetry (ICP-MS, cf and ), etc]... 

Figure 9.5 Schematic of Matrix Assisted Laser Desorption Ionisation (MALDI). The laser is fired at the sample analyte of interest admixed with a crystalline matrix that readily absorbs laser energy and allows the sputtering of analyte into the vapour phase in association with matrix molecules of solvation. Desolvation and proton transfer leads to naked molecular ion species, ready for mass analysis.

Szabados F, Becker K, von Eiflf C, Kaase M, Gatermann S. The matrix-assisted laser desorption/ ionisation time-of-flight mass spectrometry (MALDI-TOF MS)-based protein peaks of 4448 and 5302 Da are not associated with the presence of Panton-Valentine leukocidin. Int J Med Microbiol. 2011 301(l) 58-63. doi 10.1016/j.ijmm.2010.05.005. 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

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