A high resolving power multiple reflection matrix-assisted laser desorption/ionization time-of-flight mass spectrometer

Two electrostatic mirrors, mounted symmetrically on the same optical axis f acing each other, are used to increase the time-of-flight of molecular ions produced in matrix-assisted laser desorption/ionization (MALDI). The mirro rs, which are used in the non-compensating mode, are located between a MALD I ion source and a stop detector. The source:is operated at 10.5 kV acceler ation voltage using the delayed extraction technique. The high voltage for the mirror arrangement is switched on after the desorption event when the m olecular ions have drifted into the region between the mirrors. The ions ar e trapped by successive reflections df the opposite electrostatic fields in the mirrors until the electric fields are switched off. The number of refl ections depends on the speed of the ions when they enter the mirror trap an d the on-time of the mirrors. When the electric fields are removed during t he motion: of the ions towards the stop detector, the ions penetrate the gr ids of the mirror,and reach that detector. The extension of the flight path due to the number of reflections is used to increase the resolving power i n time-of-flight spectra. Values of 55 000 for substance-P (MW 1346.7) and 31 000 for bovine insulin (MW 5734) were obtained for single laser shot spe ctra. Copyright (C) 1999 John Wiley & Sons, Ltd.