IMPROVED RESOLUTION FOR MALDI-TOF MASS SPECTROMETERS - A MATHEMATICALSTUDY

In time-of-flight (TOF) mass spectrometry with matrix-assisted laser d esorption and ionization (MALDI), the delayed acceleration of ions (so metimes called ''time-lag focusing'', ''pulsed ion extraction'' or ''d elayed extraction'') has proven to be a major breakthrough with respec t to high mass resolution. This theoretical study presents some focusi ng modes which improve either the resolution at one mass (spot focusin g) or the resolution for all masses simultaneously (wide-range focusin g), compared with the normal delayed acceleration mode. The study cons iders: (1) the case of strong correlation between ion location in spac e and ion speed at the onset of the accelerating field, observed for l ow mass MALDI ions, and (2) the case of additional spatial distributio ns disturbing the space-velocity correlation at higher masses. Improve d focusing is achieved by acceleration fields varying in time. (C) 199 7 Elsevier Science B.V.