MALDI

There are a variety of ionization methods available, however the most commonly used methods are: Electrospray Ionization (ESI) and Matrix-assisted Laser Desorption Ionization (MALDI). In this lab we use MALDI.

There are two major steps involved in MALDI, which uses a UV-laser to ionize a sample. First, the peptide to be analyzed is dissolved in a matrix, which is a solvent containing small organic molecules. These molecules have high absorption at the laser’s wavelength. The mixture is then left to dry prior to analysis. This results in the formation of a crystal matrix that contains the peptide of interest. Second, the matrix molecule is excited to a higher energy state when it encounters the UV-laser. This eventually leads to the formation of the ion of interest. The ionized molecule enters the mass analyzer and yields the mass spectrum.