A rotating ball inlet for on-line MALDI mass spectrometry

The rotating ball inlet (ROBIN) is presented in a new design for on-line ma trix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). T his method uses a capillary to deliver a matrix and analyte solution to the surface of a rotating ball upon which MALDI is carried out. The ball is in contact with a polymer gasket surrounding the capillary. Sample adhering t o the surface of the ball is dragged past the gasket into the vacuum of the mass spectrometer where it is irradiated by a pulsed UV laser, and the res ulting ions are mass-separated in a linear time-of-flight mass spectrometer . The mechanical sample introduction prevents clogging of the vacuum interf ace by matrix crystals or frozen solvent. Preliminary results from now inje ction analysis (FIA) suggest that the new interface does not introduce a si gnificant peak-tailing or memory effect. The system is capable of 20-30 h o f continuous operation with a now rate of 2 mu L/min before cleaning of the ball is needed. With the prototype inlet, concentration detection limits a re at the low micromolar level.