A rotating ball inlet for on-line MALDI mass spectrometry.

The rotating ball inlet (ROBIN) is presented in a new design for on-line matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). This 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 to 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 resulting ions are mass-separated in a linear time-of-flight mass spectrometer. The mechanical sample introduction prevents clogging of the vacuum interface by matrix crystals or frozen solvent. Preliminary results from flow injection analysis (FIA) suggest that the new interface does not introduce a significant peak-tailing or memory effect. The system is capable of 20-30 h of continuous operation with a flow rate of 2 microL/min before cleaning of the ball is needed. With the prototype inlet, concentration detection limits are at the low micromolar level.