Four-sector instruments

With linked scan MS/MS, another analyzer is not required, but this mode gives either limited precursor selectivity with unit product-ion resolution, or unit precursor selection with poor product-ion resolution. Four-sector instruments can give very high quality data, but are costly, very space demanding, and complex. Hybrids like sector-TOF or sector-QFT are good (and cheaper) alternatives. High-energy CID MS/MS spectra are very reproducible (see Chapter 3). 

Fig. 4.15. Tandem-in-space setups for different beam instruments magnetic four-sector instrument (a), magnetic sector-quadmpole hybrid (b), triple quadmpole (c), and ReTOF (d).

Example The FAB-CID-MS/MS spectrum of thymosin-Tl [M+H] quasimolecular ions, m/z 1427.7, as obtained from a magnetic four-sector instrument [144] shows numerous fragment ions due to A-terminal, C-terminal, and internal fragmentations (Fig. 9.18). [145]... 

Bean, M. F., Carr, S. A., Thorne, G. C., Reilly, M. H. and Gaskell, S. J. Tandem mass spectrometry of peptides using hybrid and four-sector instruments a comparative study. Anal. Chem. 63 1473-1481, 1991. 

Instrumentation. HPLC isolations were performed on a Beckman 421A system using a Vydac column (C-18, 4.6 x 250 mm). Liquid secondary ion mass spectra (LSIMS) were recorded in the positive ion mode on a Kratos (Manchester, UK) MS-50S mass spectrometer equipped with a 23 kG magnet and post-acceleration detector. The LSIMS ion source has been described elsewhere (28). A Cs+ ion beam of energy 10 keV was used as the primary beam (21). Spectra were recorded (300 sec per decade) with a Gould ES-1000 electrostatic recorder. Tandem MS experiments were performed on a Kratos Concept IIHH (Manchester, UK) four sector instrument of EBEB... 

Figure 3 SIM detection of gibberellins using (A) 5000 resolution (B) 10 000 resolution (C) SRM using a sector instrument and (D) SRM using a four-sector instrument. (Reproduced with permission from Analytical Chemistry 76 1711-1716. Copyright (1995) the American Chemical Society.)...

Example The FAB-CID-MS/MS spectrum of thymosin-Tl [M-hH] ions, m/z 1427.7, as obtained from a magnetic four-sector instrument [81] shows numerous fragment ions due to TV-terminal, C-terminal, and internal fragmentations (Fig. 9.16) [82]. It would be almost inpossible to obtain sequence information from such a spectrum without generalizing rules to follow [83-88]. The most abundant ions obtained from the fragmenting peptide ion usually belong to six series named a, b, and c if the proton (charge) is kept in the TV-terminus or x, y, and z, respectively, where the proton is located in the C-terminal part. Within each series the mass difference should only be one amino acid. Ideally, one can then count down the amino acids. 

Double-focusing magnetic sector instruments represent the standard in FAB-MS, because they combine a suitable mass range with the ability to perform high-resolution and accurate mass measurements. Until the advent of ESI and MALDI, FAB-MS/MS on magnetic four-sector instruments was the method of choice for... 

More advanced possibilities for MS-MS in sector instruments can be achieved in three- and four-sector instruments. The four-sector instruments enable MS-MS with high-resolution selection/analysis for both precursor and product ions. CID is performed with high-energy collisions, i.e. in most cases by single high-energy collisions with helium. The four-sector instruments obviously are complex to operate. In addition to the three- and four-sector instruments, a... 

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