Matric Assistant Laser Dersorption, Ionization, Organic Molecule, Submicroliter Volume, Nanosecond Laster Pulse, Small Nitrogen Laser

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Home >> Biotechnology and Genomics >> Mass Spectrometry - An Essential Tool for Genome and Proteome Analysis >> Matrix Assisted Laser Dersorption -Ionization(MALDI)

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Matrix Assisted Laser Dersorption-Ionization (MALDI)
MALDI was developed in the year 1988 and involved coprecipitation of large excess of a matrix material (a small organic molecule) with the analyte molecule (the molecule to be analyzed), by pipetting a submicroliter volume of a mixture of matrix and analyte onto a metal substrate, where it is allowed to dry. The dried solid having matrix and analyte is then irradiated by nanosecond laser pulse, usually supplied by a small nitrogen laser with a wavelength of 337nm, which is specific for the absorbance of the selected matrix material. The irradiation causes energy transfer and desorption, producing gas phase matrix ions. The non-absorbing intact analyte molecules are also desorbed into gas phase and ionized.

Schematic Diagram Showing Mechanism Involved In Matrix Assisted Laser Desorption-Ionization

Schematic Diagram Showing Mechanism Involved in matrix assisted Laser Desorption Ionization

The charged molecular ions that are created during a gas-phase proton transfer reaction with the matrix molecules, are detected and analysed by MALDI- TOF MS. The matrix used with biomolecules generally consists of one of several substances, some of which are listed in. The available matrix materials differ in the energy they impart to the biomolecules during desorption and ionization and hence also in the degree of fragmentation (unimolecular decay) that they cause.

The α-cyano matrix, which leads to highest sensitivity in MALDI is preferred when the ions need to be stable for only mil1isecond as in trapping experiments rather than microseconds in time of flight (TOF) experiments . Several methods are also available for sample preparation. For instance, matrix may be laid down in microcrystalline thin film on the substrate leading to better adherence and providing large crystalline surface from which the ions can be desorbed. Sometimes admixture with the matrix can also be beneficial. MALDI is generally used for study of molecules with mass above 500 daltons.

However, proteins undergo fragmentation during MALDI, resulting in broad peaks and loss in sensitivity. As a result, MALDI is mostly applied to the analysis of peptides rather than proteins.

Some Common MALDI martices having maximum absorbance at 337 nm and the corresponding analytes that can be studied.

Matrix	Analytes
α-Cyano-4-hydorxy cinnamic acid (CHCA)	Peptides, proteins, lipids, and oligonucleotides
3,5-Dimethoxy-4-hydroxy cinnamic acid (sinapinic acid)	Peptides, proteins, and glycoproteins
2,5-Dihydroxybenzoic acid (DHB)	Peptides, proteins, lipids. and oligosaccharides

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