Friday, December 3, 2010
MALDI (matrix-assisted laser desorption/ionization), a laser-based soft ionization method has proven to be one of the most successful ionization methods for mass spectrometric analysis and investigation of large molecules.[1,2] In addition analysis of post source decay (decay of proteins following the ionization) in many cases allows rapid sequencing of proteins. Thus MALDI has gained a crucial importance for protein analysis.
Its constituting feature is that the sample is embedded in a chemical matrix (ca. 1000 x molar excess) that greatly facilitates the production of intact gas-phase ions from large, nonvolatile, and thermally labile compounds such as proteins, oligonucleotides, synthetic polymers. and large inorganic compounds. The matrix plays a key role in this technique by absorbing the laser light energy and causing a small part of the target substrate to vaporize.
The most important applications of MALDI mass spectrometry are (in decreasing order of importance): peptides and proteins, synthetic polymers, oligonucleotides, oligosaccharides, lipids, inorganics.
In its current state, MALDI is primarily based on the laser desorption of solid matrix-analyte deposits . The technique suffers from some disadvantages such as low shot-to-shot reproducibility, short sample life time and strong dependence on the sample preparation method.
MALDI MS-based systems have been developed to rapidly characterize microorganisms, such as intact proteins in the 5K-20K Da range in a top-down proteomics. In such experiments, proteins are identified either by conducting a homology search of extracted sequence tags or by comparison of MS/MS spectra with fragmentations predicted from protein sequences in existing protoeme database.