Mass Analyzers for MALDI-MS

Laser desorption intrinsically is a pulsed ionization process, which is therefore ideally combined with time-of-flight (TOF) analyzers (Chap. 4.2). [16,49] Ever since the first MALDI experiments, MALDI and TOF have been forming a unit, and the majority of MALDI applications are MALDI-TOF measurements. Vice versa, it was the success of MALDI that pushed forth the tremendous delevopment of TOF mass analyzers. More recently, MALDI has also been adapted to orthogonal acceleration TOF analyzers. [147] 

The limited resolution and mass accuracy of the early MALDI-TOF instruments made the combination of MALDI with magnetic sector instruments (Chap. 4.3) desirable, [148,149] but this set-up suffered from low shot-to-shot reproducibility and poor sensitivity getting a full scan spectrum required thousands of laser shots while scanning the magnet. Even though eutectic matrix mixtures were introduced to circumvent such problems, [90,91] the MALDI-magnetic sector combination never became established. 

Fourier transform ion cyclotron resonance (FT-ICR, Chap. 4.6) is much better suited for laser desorption. [5,6] Best results are obtained when the ions are gener- 

Fenner, N.C. Daly, N.R. Laser Used for Mass Analysis. Rev. Sci. Instrum. 1966, 37, 1068-1070. 

Vastola, F.J. Pirone, A.J. Ionization of Organic Solids by Laser Irradiation. Adv. Mass Spectrom. 1968, 4, 107-111. 

Fourier transform ion cyclotron resonance (FT-ICR, Chap. 4.7) is much betto suited for laser desorption [5,6]. Best results are obtained when the ions are generated in an external ion source and subsequently transferred into the ICR cell for mass analysis [213]. MALDI-FT-ICR has become a mature combination [214,215]. Modem MALDI-FT-ICR instmments make use of collisional cooling of the plasma plume before transferring the ions into the ICR cell [216,217]. 

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