MALDI

MALDI creates ions by firing a laser at the sample. The trick is that the sample is mixed into a large excess of a light-absorbing matrix. The matrix absorbs the laser energy and carries the sample up with it, so the sample itself is not destroyed — making MALDI a soft ionization technique well suited to proteins and other large biomolecules.

How it works

Turn the laser on and watch — the plume rises straight up into the analyzer inlet above.

1. Crystallize: the sample is mixed with an excess of matrix and dried into crystals on a target plate, with sample molecules embedded throughout.
2. Laser hit: a pulsed UV laser strikes the spot; the matrix — not the sample — absorbs the energy.
3. Desorption: the matrix bursts into a plume that rises and carries the intact sample with it.
4. Ionization: proton transfer in the plume turns sample molecules into ions, which are accelerated into the analyzer.

Why the matrix matters

By absorbing the laser energy itself, the matrix shields the sample from a direct, destructive hit and gently lofts it into the gas phase. MALDI is often paired with a TOF analyzer, because the pulsed laser gives a clear start time for measuring flight time.