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Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique used in mass spectrometry, allowing, among other things, the ionization of biomolecules (biopolymers such as proteins, peptides and sugars) and long, organic polymers, both of which tend to be more fragile and quickly lose structure when ionized by more conventional ionization methods. It is most similar in character to electrospray ionization both in relative softness and ions produced.

The matrix consists of crystallized molecules, of which the three most commonly used are 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid), a-cyano-4-hydroxycinnamic acid (alpha-cyano or alpha-matrix) and 2,5-dihydroxybenzoic acid (DHB). A solution of one of these molecules is made, in a mixture of highly purified water and another organic compound (normally acetonitrile (ACN) or ethanol). Normally some trifluoroacetic acid (TFA) is also added. A good example of a matrix-solution would be 20 mg/mL sinapinic acid in ACN:water:TFA (50:50:0.1).

The matrix-solution is then mixed with the analyte molecule (e.g. protein-sample) which you wish to investigate. The organic compound ACN allows for the hydrophobic proteins in the sample to dissolve into the solution, while the water allows for water-soluble (hydrophilic) proteins to do the same. This solution is spotted onto a MALDI plate (usually a metal plate designed for this purpose). The solvents vaporize, leaving only the recrystallized matrix, but now with proteins spread throughout the crystals. The matrix and the analyte are said to be co-crystallized in a MALDI spot. (from Wikipedia)


Virginia Tech Center for Genomics

Institute for Biomedical and Public Health Sciences (IBPHS)

Fralin Biotechnology Center

Department of Biochemistry

College of Agriculture and Life Sciences
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