The other fragment strikes a detector and triggers the start of data acquisition. This ionization method is especially useful for large biological molecules. Ions can be focused and accelerated to higher kinetic energies than are possible for neutral beams, and sensitivity is improved for higher masses. A spark source ionizes analytes in solid samples by pulsing an electric current across two electrodes. If the sample is a metal it can serve as one of the electrodes, otherwise it can be mixed with graphite and placed in a cup-shaped electrode.
Thermal ionization is used for elemental or refractory materials.
A sample is deposited on a ribbon of Pt, Re The ribbon is often coated with graphite to provide a reducing effect.