Tandem Time-of-Flight Instruments

The introduction of MALDI as an effective ionization method for peptides, proteins, and other biopolymers has provided considerable motivation for the development of tandem time-of-flight instruments that would compete favorably with electrospray ionization, which enjoys easy compatability with tandem, triple quadru-pole mass spectrometers. Tandem TOF instruments would be considerably less expensive alternatives for routine sequencing of peptides obtained from enzymatic digests or from other biological mixtures. 

FIGURE 9.1 Schematic of the ion source and linear regions of a PSD time-of-flight mass spectrometer showing the electrostatic gating system and coaxial detector. (Reprinted with permission from reference I). 

In this scheme, precnisor ipns Ww flight time i) in -the drift region (Pi) bej. the collision chamber equ to  

SO that their flight times in the second drift region (D ) arc  

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Schey, K. L. Cooks, R. G. Kraft, A. Grix, R. Wollnik, H. lon/surface coUision phenomena in an improved tandem time-of-flight instrument. Int. J. Mass Spectrom. Ion Processes 1989, 94, 1-14. 

Shevchenko, A., I. Chemushevich, et al., 2000, De Novo peptide sequencing by nanoelectrospray tandem mass spectrometry using triple quadmpole and quadrupole/time-of-flight instruments. Methods Mol. Biol. 146 1-16. 

Tandem Mass Spectrometry with Time-of-Flight Instruments... 

It should also be noted that the RF-only quadrupoles (as well as the related RF-only hexapoles and octapoles) can be operated as ion lenses, often referred to as RF-only ion guides or simply ion guides. RF-only quadrupoles (denoted as lower case q , nonitalicized, to distinguish them from the closely related quadrupole mass filters Q) also act as efficient collision cells for collision induced dissociation in triple quadrupole analyzers (QqQ, Section 6.4.3) and hybrid tandem quadrupole-time of flight instruments (QqTOF, Section 6.4.7). Discussion of these devices must be postponed imtil the principles of all hnear quadrupoles have been considered (Section 6.4.2). 

Figure 5 Overview of a tandem time-of-flight SID instrument. Reproduced with permission from Riederer Jr, DE, PhD, Department of Chemistry, University of Missouri, Columbia.

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