Delayed-extraction MALDI mass spectra

FIGURE 7.27 Delayed-extraction MALDI mass spectra of the molecular-ion region of bovine insulin (MW 5733.4) obtained on three separate reflectron TOP instruments having effective path lengths of (a) 2.0 m, (b) 3.0 m, and (c) 6.6 m. (Reprinted with permission from reference 44). 

Applications MALDI-ToFMS is at its best as a rapid screening technique for quick identification of known additives. However, this screening is rendered slightly more complicated by the fact that MALDI-ToFMS spectra of pure additives and of additives in the presence of excess macromolecules are not always identical (matrix effect) [55]. For unknown additives, the relation MALDI-ToFMS spectrum-chemical structure is not easily established, and the use of FD or MALDI-MS/MS is then needed. As MALDI-MS shows a sensitivity difference for the various additives, it cannot easily quantify them unless the analytes are very similar. For differentiation of additives with the same mass number (e.g. Tinuvin 315 and Cyasorb UV3638 with m/z = 368) high resolution is required, as provided by delayed extraction MALDI-ToFMS. 

Figure 5-5. A. MALDI mass spectrum of the anthocyanin pigments in the grape variety Marechal Foch. This figure is from the article Matrix-assisted laser desorption ionization mass spectrometry analysis of grape anthocyanins , Am. J. Enol. Vitic. 50 199-203 by Sugui, J. A., Wood, K. V., Yang, Z., Bonham, C. C. and Nicholson, R. L. 1999. Reprinted by permission of the American Society for Enology and Viticulture. B. MALDI mass spectrum of grape anthocyanins acquired on a MALDI mass spectrometer with delayed extraction capabilities. Peak identities are discussed in the text.

FIGURE 7.9 Delayed extraction MALDI-TOF mass spectrum of melittin. (Reprinted with permission from reference 21). 

More recently, delayed orthogonal extraction has been utilized to observe peptide fragmentation on MALDI time-of-flight instnmients. Figure 7.9 shows the high irradiance MALDI mass spectrum of melittin obtained by Standing et al., following an I8-ps delay. 

FIGURE 7.28 MALDI in-source decay (ISD) mass spectrum of the oxidized B chain of bovine insulin obtained with delayed ion extraction.The extraction pulse was 1.5 kV applied 350 ns after the laser pulse. (Reprinted with permission from reference 45). 

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