Matrix-assisted laser desorption/ionization

Matrix-assisted Laser-Desorption/Ionisation (English matrix -assisted laser desorption / ionization, MALDI ) is a method for the ionization of molecules. It proved since its development in the 1980s to be particularly effective for mass spectrometry of large molecules, polymers and biopolymers (eg proteins ).

Most of the term MALDI is also as shorthand for MALDI mass spectrometry ( MALDI -MS, MALDI -TOF -MS ) was used. Due to the high sensitivity, and applicability to large and complex molecules is the MALDI-MS in particular in biology as well as in chemical analysis, is very important.

Operation

MALDI based on the co-crystallization of the matrix and analyte with a 100 - to 100,000 - fold molar excess of matrix molecules. Analyte molecules must be " built into" the crystals of the MALDI matrix, while the crystals form. Typically, the successful co-crystallization requires a matrix to analyte ratio of approximately 5000:1 (mol / mol). As the matrix materials, small organic molecules are chosen which at the laser wavelength used (e.g. a nitrogen laser at a wavelength of 337.1 nm) strongly absorb energy (e.g., sinapic acid, 2,5- dihydroxybenzoic acid, α - Cyanohydroxyzimtsäure ). With short, high-energy laser pulses of 2-5 ns pulse duration, the stimulus that leads to relaxation of the crystal lattice leads to explosive Teilchenablösungen on the surface of the crystal takes place. The entrapped analyte molecules are thereby converted by the vacuum of the mass spectrometer and thus available to the mass spectrometric analysis in conjunction with the matrix.

Essential for MALDI measurement, the sample preparation and application to the sample tray. There are various ways for example, the Dried Droplet Method ( = mixing the analyte and the matrix solution, followed by evaporation of the solvents used ), or the thin film preparation.

The MALDI ionization is not completely understood. There are currently two favored options: