MALDI is an ionisation technique used for medium to large molecules such as peptides, proteins, and some organo- metallic compounds.
The samples are dissolved in a solvent at about 1mg/ml and 1 microlitre is applied to a stainless steel plate and allowed to dry to a thin film. A matrix is applied on top of the dried sample and allowed to dry. The matrix varies from sample to sample but is chosen for its ability to desorb laser energy. The slide is placed in the instrument and laser beam is fired at the sample slide and the sample ionised. A charged plate propels the ions down a flight tube and if the instrument has been calibrated with a known compound an accurate spectrum can be obtained.