Linked scan mass spectra

Franski, R. et al., Differentiation of interglycosidic linkages in permethylated flavonoids from linked-scan mass spectra (B/E), J. Agric. Food Chem., 50, 976, 2002. 

An example of linked scanning on a triple quadrupole instrument. A normal ion spectrum of all the ions in the ion source is obtained with no collision gas in Q2 all ions scanned by Q1 are simultaneously scanned by Q3 to give a total mass spectrum (a). With a collision gas in Q2 and with Q1 set to pass only m+ ions in this example, fragment ions (f, fj ) are produced and detected by Q3 to give the spectrum (b). This CID spectrum indicates that both f, and fj are formed directly from m+. 

The importance of linked scanning of metastable ions or of ions formed by induced decomposition is discussed in this chapter and in Chapter 34. Briefly, linked scanning provides information on which ions give which others in a normal mass spectrum. With this sort of information, it becomes possible to examine a complex mixture of substances without prior separation of its components. It is possible to look highly specifically for trace components in mixtures under circumstances in which other techniques could not succeed. Finally, it is possible to gain information on the molecular structures of unknown compounds, as in peptide and protein sequencing (see Chapter 40). 

By automating the linked scanning under computer control, a complete mass spectrum can be scanned for metastable ions in just a few seconds. 

Chlornitrofen and nitrofen conditions for GC/MS column, cross-linked methyl silicone capillary (12 m x 0.22-mm i.d., 0.33- am film thickness) column temperature, 60 °C (1 min), 18 °C min to 265 °C inlet, transfer line and ion source temperature, 260, 200 and 200 °C, respectively He gas column head pressure, 7.5 psi injection method, splitless mode solvent delay, 3 min electron ionization voltage, 70 eV scan rate, 0.62 s per scan cycle scanned mass range, m/z 100-400. The retention times for chlornitrofen and nitrofen were 11.8 and 11.3 min, respectively. The main ions of the mass spectrum of chlornitrofen were at m/z 317, 319 and 236. Nitrofen presented a fragmentation pattern with the main ions at m/z 283, 202 and 285. ... 

Mechanistic pathways for the formation of the fragments encounteted in the mass spectrum of compound 40 were proposed. The sequences were validated by linked scans at constant B/E and high-resolution accurate MS <2000RCM1077>. 

This analytical mode has a resolution sufficient for the fragment ions. For instance, the B/E linked scan spectrum of the unimolecular decomposition of the MH ion (m/z 259) of biotin methyl ester, produced by Cl ammonia, has a good resolution (< 1 u). The m/z 221, 241 and 243 ions are due to the elimination of neutral fragments (CH3OH, HjO and CH4), which characterize Cl mass spectra (Fig. 21). 

Figure 24. Cl mass spectrum and BjE — E/Eo) linked scan spectrum of neutral loss of ketene (42 amu) for a mixture of various acetylated phenols [149].

Neutral-loss scan The first and third quadrupoles are linked and scanned at the same speed over the same mass range with a constant mass difference between the two analyzers. Because of the mass offset at any time quadrupole 3 will transmit product ions (if any) with a fixed lower m/z value than the mass selected precursor ions transmitted by quadrupole 1. The result is a mass spectrum containing all the precursor ions that loose a neutral species of selected mass. 

Fig. 3. B/E constant linked scan spectrum of [MH-GlcOH] ion at m/z 548 in positive ion mode FAB mass spectrum of 1...

---