A MALDI Probe for Mass Spectrometers

Abstract

A new MALDI probe has been designed that uses transmission geometry. This geometry allows the probe to be fashioned after typical EI/CI solid probes which enables it to be introduced into spatially constrained ion source regions such as encountered in quadrupole ion trap mass spectrometers. In the probe design demonstrated here, light from a fiber optic irradiates the backside of a sample through a small piece of quartz on which the sample has been directly deposited. The performance characteristics exhibited by utilizing this probe for MALDI on a quadrupole ion trap mass spectrometer are similar to those which can be obtained through the traditional methods of implementing MALDI. Spectra have been obtained from 50 fmol of total loading of bombesin, MS/MS has been performed on 5 pmol of des-Arg⁹-bradykinin, and the analyte ion signal is shown to last for over 2500 laser shots for 2 pmol of bombesin. Optical micrographs showing the crystal distribution of a sample containing 2 pmol of bombesin have been obtained as a function of the number of laser shots for a single sample loading. Although this probe was designed for use with the quadrupole ion trap, it can be adapted for use with all types of mass spectrometers. Thus, with only one laser, one fiber optic, and this probe, MALDI can be performed on multiple instruments in a lab.