In-source decay , fragmentation

Lemaire, R, Debois, D., Smargiasso, N., et al. (2013) Use of 1,5-diaminonaphthalene to combine matrix-assisted laser desorption/ionization in-source decay fragmentation with hydrogen/deuterium exchange. Rapid Commun Mass Spectrom, 27 (16), 1837-1846. 

Figure 123. A 2D plot of MALDI-IM-MS conformation space for a short oligonucleotide (CATG), a peptide (dynorphin 1, YGGLFRRl), a lipid (sphingomyelin), and their respective in-source decay fragment ions. Lines are overlaid on signals arising for particular molecular classes for visuaUzation purposes. The gray spectrum (bottom) illustrates the mass spectrum obtained by integrating over the entire IM dimension. (Adapted with permission bom Anal. C/icm.2004, 76, 2187-2195. Copyright 2004 American Chemical Society.)...

Note In particular the MALDI-TOF community has coined some sort of an own terminology, e.g., in-source decay (ISD) for all fragmentations occurring within the ion source, post-source decay (PSD) instead of metastable ion dissociation and fragment analysis and structural TOF (FAST) for the specific mode of operation of a ReTOF to detect metastable ions. 

T. Yamagaki, Y. Ishizuka, S.-I. Kawahara, H. Nakanishi. Analysis of glycosidic linkages in saccharide compounds by post-source decay fragment methods in matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy. Rap. Comm. Mass. Spec. 1999, /1,527-531. 

Bache, N., Rand, KD., Roepstorff, P., J0igensen, T.J.D. (2008) Gas-phase fragmentation of peptides by MALDl in-source decay with limited amide hydrogen (H-l/H-2) scrambling. Anal Chem, 80 (16), 6431-6435. 

Kocher, T, Engstrom, A., Zubarev, R.A. (2005) Fragmentation of peptides in MALDl in-source decay mediated by hydrogen radicals. Anal Chem, 77 (1), 172-177. 

Several gas-phase fragmentation techniques have found a niche as a possible means to sequence oligonucleotides. These include ESI in-source CID (nozzle-skimmer voltage to induce fragmentation), IRMPD in an FT-ICR MS instrument, MALDI in-source decay and post-source decay, and CID-MS/MS of the ESI-produced ions. CID generates complementary (a — B )- and in-type ions, which can provide bidirectional sequencing from the 5 3 direction and 3 5 ... 

Sakakura, M. and Takayama, M. (2010) In-source decay and fragmentation characteristics of peptides using... 

Asakawa, D. and Takayama, M. (2012) Fragmentation processes of hydrogen-deficient peptide radicals in matrix-assisted laser desorption/ionization in-source decay mass spectrometry. J. Phys. Chem. B, 116,4016 23. 

For the metastable decay fragments, groups conducting research into MALDl-TOF have made a rather arbitrary distinction between in-source decay (ISD) [24,... 

Laine, O., Trimpin, S., Raeder, H.J., and Muellen, K. (2003) Changes in post-source decay fragmentation behavior of poly(methyl methacrylate) polymers with increasing molecular weight studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Eur. J. Mass Spectrom., 9, 195-201. 

In-Source Decay (ISD). In the next chapter we will describe a method for amino acid sequencing of peptides on reflectron TOF instruments known as post-source decay (PSD). This method exploits the considerable metastable fragmentation that occurs in the drift region after the ions are extracted from the ion source. The resulting product ions spend a shorter time in the reflectron, and therefore arrive at the detector sooner than their precursors. 

However, compared to ESI, MALDI has always been limited by the fact that desorbed ions become vibrationaUy excited on desorption (i.e., they are hot ). This metastable activation is often sufficient to cause them to fragment, often on a > 1 -ps timescale. In 1994, Spengler et al., first took advantage of this metastable activation to sequence peptides and coined the two terms post-source decay and in-source decay . The differentiation between fragmentation post-source and in-source is instrument-dependent because the two terms simply refers to metastable fragmentation that occurs after the ion leaves the MALDI source and enters the mass analyzer or before the ion extraction voltage pulse is applied. 

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