A picture of the MALDI source is shown below. The sample of interest (along with the matrix and any desired salts) is applied onto a stainless steel cylindrical target that is 1.25 cm long and 1.25 cm in diameter. This sample target is then fitted onto a screw-threaded device and inserted into the ion source housing. A small motor turns the screw-threaded device so that the sample rotates and translates, exposing a fresh sample area for each laser shot. The screw device allows ~15-16 revolutions, providing enough sample for several hours.
A Lambda Physik 210i excimer laser, refitted for use as a nitrogen laser (wavelength = 337 nm) is used to desorb the sample and generate ions. The laser is typically operated at 50-100 Hz and has a pulse energy of 1.5-3 mJ and pulse duration of 10-20 ns. The laser beam is steered into the source by two dielectric mirrors and focused onto the sample by a 300 mm concave lens, hitting the target at a 45o angle normal to the sample surface. A set of extraction plates and focusing lenses located 5 mm and 7.5 mm from the sample (and insulated from the source housing) direct the formed ions toward the mass spectrometer.