MALDI source ion & laser optics

Exhibit no. 983

In MALDI-TOF, a pulsed laser is focused on a target with a thin layer of a sample. A high voltage is applied between the target and a grounded counter electrode, thus accelerating the ions into the flight tube. The lighter ions fly faster and reach the detector before the heavier ions. The m/z values are calculated from the time of flight of the ions. The mass resolution in MALDI-TOF is limited by the relatively broad distribution of the ion energy. The resolution can be improved by a delay between the generation and extraction/acceleration of the ions. Faster ions, which have traveled further, receive less energy from the electric field than the slower ions. Thus, ions of the same mass arrive at the detector at the same time, irrespective of their initial velocities. The technique is known as “time-lag focusing” or “delayed extraction”.