MALDI-TOF MS Bergdís Björk Bæringsdóttir Daníel Arnar Tómasson Kristján Einar Guðmundsson

Theory Large analyte molecules and smaller matrix molecules are dissolved in a solvent which is allowed to evaporate once spotted on a plate The molecular structure of the matrix molecules contains conjugated pi bonds which absorb in the uv region. To drive the ionization of the analyte molecules, the matrix molecules are acidic. When the matrix molecules absorb the energy from the uv pulse they evaporate and carry the larger ionized analyte molecules with them.

Theory In the acceleration region there is a constant electric field that accelerates the ionized molecules towards the TOF unit In the TOF unit there is no field acting on the particles and the time of flight (velocity) depends only on the mass and the charge of the particles.

Theory The mass to charge ration of the time of flight function means that doubly charged single mass molecules arrive at the detector first and the singly charged double mass particles last. Furthermore, the square root of the function makes it so that time difference is less when masses get larger and spectra is less resolved.

How it works Matrix solution is mixed with the analyte, spotted onto the metal MALDI plate and left to dry so the matrix can recrystallize with analyte molecules embedded into MALDI crystals.  There may be some dust particles on the plate that need to be removed Also fingerprints may interfere with the measurements

Ions Laser is fired at the matrix crystals in the dried-droplet spot. The matrix absorbs the laser energy and the analyte molecules come flying as neutral molecules, but are ionized due to proton transfer from the matrix The matrix is then thought to transfer protons to the analyte molecules thus charging the analyte. An ion observed after this process will consist of the initial neutral molecule [M] with ions added or removed. MALDI is capable of creating singly charged ions or multiply charged ions (mostly +2,+3) depending on the nature of the matrix, the laser intensity, and/or the voltage used.

Measurements The ions move in an electric field and their time of fligh is measured by TOF The flight time is different for each ion because of their mass and charge, m/z.

Data from MALDI-TOF measurement of unkown sample

Maldi-Tof Symulation