The principles of MALDI is use laser light irradiating the sample with a matrix formed of the crystalline film, the matrix to absorb energy from the laser is passed to the biological molecules, while the ionization process will proton transfer the biological molecules or biological molecules to the proton of the biomolecule ionization process. Therefore, it is a soft ionization technique, applicable to the mixture and the determination of biological macromolecules.
In proteomics, MALDI is used for the rapid identification of proteins isolated by using gel electrophoresis: SDS-PAGE, size exclusion chromatography, affinity chromatography, strong/weak ion exchange, isotope coded protein labelling (ICPL),and two-dimensional gel electrophoresis. Peptide mass fingerprinting is the most popular analytical application of MALDI-TOF mass spectrometers. MALDI TOF/TOF mass spectrometers are used to reveal amino acid sequence of peptides using post-source decay or high energy collision-induced dissociation (further use see mass spectrometry).
Some synthetic macromolecules, such as catenanes and rotaxanes, dendrimers and hyperbranched polymers, and other assemblies, have molecular weights extending into the thousands or tens of thousands, where most ionization techniques have difficulty producing molecular ions. MALDI is a simple and fast analytical method that can allow chemists to rapidly analyze the results of such syntheses and verify their results.
In polymer chemistry MALDI can be used to determine the molar mass distribution. Polymers with polydispersity greater than 1.2 are difficult to characterize with MALDI due to the signal intensity discrimination against higher mass oligomers. A good matrix for polymers is dithranol and AgTFA.
MALDI/TOF spectra are used for the identification of microorganisms such as bacteria or fungi. A colony of the microbe in question is smeared directly on the sample target and overlayed with matrix. The mass spectra generated are analyzed by dedicated software and compared with stored profiles. Species diagnosis by this procedure is much faster, more accurate and cheaper than other procedures based on immunological or biochemical tests. MALDI/TOF may become the standard method for species identification in medical microbiological laboratories over the next few years.