Matrix Assisted Laser Desorption (MALDI) mass spectrometry technique was introduced by Karas and Hillkamp in 1988 for the ionization of peptides and proteins. Soon there after this technique was able to analyze other type of biomolecules, such as oligosaccharides, glycolipids, nucleotides, and synthetic polymers. In this technique, samples are cocrystallized with a UV-absorbing substance called matrix. For example for proteins, the matrix of choice is often sinapinic acid. A 337 nm radiation from nitrogen laser is most commonly used. The laser helps introducing energy into the molecular system in such a way preventing thermal decomposition.
MALDI is often used with time-of-flights mass spectrometers ( TOF ) due to the pulsing nature of the technique, and the mass range capability. Molecular weights up to few hundreds of daltons could be measured. Comparison of MALDI and ESI ionization techniques was attempted in the last few years. In my opinion these two techniques are not competitive but complementary. Just to name a few, for high molecular weight species, MALDI leads to the formation of singly charged molecular ions while ESI allows the formation of multiply charged molecular ions.

   Practical considerations:

-The final molar ratio sample/matrix is about or around 1/5000.

-Final concentration of the sample is from 1 to 10 pmol/ul

-Our experience with MALDI point to a dynamic range of 100 fmol/ul to few hundreds pmol/ul

-MALDI is relatively robust ionization technique that tolerates the use of salts and surfactants and buffers. Although it is best to remove them for better performance.
 

Peptide and Protein Standards for MALDI:

Angiotensin II (human)         MW: 1046.2
Substance P (human)            MW: 1347.7
Insulin (bovine)                     MW: 5733.6
Cytochrom c (equine)           MW: 12,360.1
RNase A (bovine)                 MW: 13,682.2
Apo-Myoglobin (equine)      MW: 16,951.5
Trypsinogen (bovine)           MW: 23,980.9