Postsource Decay

Reflectron time-of-flight mass spectrometers can be used to generate fragment spectra. Before the introduction of delayed extraction, it was observed that the ions had a tendency to disassemble into fragments while they were traveling to the reflectron (Spengler et al., 1992). This behavior is called postsource decay (PSD). The ions collide with matrix ions in the gas phase when they are accelerated with several kilovolts. Their decay occurs in the first field-free drift region. 

De novo Sequencing Using MALDI and Postsource Decay Fragmentation... 

Postsource decay is used to sequence peptides de novo. However, the fragment spectra of peptides are inherently more complex than fragment... 

Kaufmann, R. Kirsch, D. Spengler, B. Sequencing of Peptides in a TOF Mass Spectrometer Evaluation of Postsource Decay Following MALDL Int. J. Mass Spectrom. lonProc. 1994, 757,355-385. 

Yau, P.M. and Burlingame, A.L. (2002) Identification of acetylation and methylation sites of histone H3 from chicken erythrocytes by high-accuracy matrix-assisted laser desorption ionization-time-of-flight, matrix-assisted laser desorption ionization-postsource decay, and nanoelectrospray ionization tandem mass spectrometry. Analytical Biochemistry, 306, 259-269. 

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer with UV laser (i.e., 337-nm nitrogen laser), MALDI probe, and optional delayed extraction and postsource decay... 

Abundant molecular ions, M+, will be observed as the base peaks in the MALDI-TOF mass spectra. Delayed extraction will enhance the abundance of the molecular ions relative to background noise, and the use of postsource decay will facilitate the detection of structurally... 

Wingerath, T., Kirsch, D., Kaufmann, R., Stahl, W., and Sies, H. 1999. Matrix-assisted laser desorption ionization postsource decay mass spectrometry (Review). Methods Enzymol. 299 390-408. 

Describes sample preparation and matrix requirements for analyzing carotenoids using MALDI-TOF MS and discusses the use of postsource decay for obtaining structurally significant fragment ions of carotenoids during MALDI-TOF MS. 

Mo, W., Takao,T, Shimonishi, Y. (1997). Accurate peptide sequencing by postsource decay matrix-assisted laser... 

Hsieh, S., Dreisewerd, K., Van der Schoors, R.C., Jimenez, C.R., Stahl-Zeng, J., Hillenkamp, F., Jorgenson, J.W., Geraerts, W.P.M. and Li, K.W. (1998) Separation and identification of peptides in single neurons by microcolumn liquid chromatography-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and postsource decay analysis. Anal. Chem. 70, 1847-1852. 

The following ion-activation techniques have been used at one time or other to sequence peptides (1) fast atom bombardment (FAB) ionization, (2) CID—tandem MS (MS/MS), (3) ESI in-source CID, (4) MALDI ion-source decay, (5) MALDI postsource decay (PSD), (6) electron-capture dissociation (ECD) and electron-transfer dissociation, and (7) peptide ladder sequencing. Because of the lack of space, only (2) and (4) will be discussed further. 

Pevsner, P.H. et al., Direct identification of proteins from T47D cells and murine brain tissue by matrix-assisted laser desorption/ionization postsource decay/collision-induced dissociation, Rapid Commun. Mass Spectrom., 21,429, 2007. 

Pesticides in grape and wine 279 Polyphenols 163 Postsource decay (PSD) 89 Procyanidins 165,214 Production ion scan 81 Proteins 323 Proton affinity 12... 

Sullivan, A. G., Garner, R., and Gaskell, S. J., Structural analysis of sulfonated monoazo dyestuff intermediates by electrospray tandem mass spectrometry and matrix-assisted laser desorption/ ionization postsource decay mass spectrometry, Rapid Commun. Mass Spectrom., 12, 1207-1215, 1998. 

Several desorphon and spray ionization methods can be used to convert S5mthehc polymers into intact molecular or quasimolecular ions (vide supra), whose exact m/z ratio identifies the composition of the polymer. For structural informahon about the polymer, the dissociation behavior or ion-molecule reactions of the polymer ions must be studied. Such reactions, which rarely take place during the soft ionization processes necessary to generate intact gas phase ions from synthetic macromolecules, are most conveniently assessed by tandem mass spectrometry (MS/MS). With MS/MS, a specific precursor ion is mass-selected, so that its reactivity can be investigated without perturbation from the other ions formed upon ionization. The reaction products of this ion are then mass-analyzed and collected in the MS/MS spectrum. MS/MS studies on polymer ions have so far focused on their spontaneous ("metastable") or collision-induced fragmentation. The fragments arising in these reactions are displayed in metastable ion (MI) or collisionally activated dissociation (CAD) spectra, respectively. Customarily, MI spectra acquired with a TOF mass analyzer have been named "postsource decay (PSD)" spectra similarly, CAD is often referred to as CID (collision-induced dissociation). ... 

Spengler, B., Kirsch, D., and Kaufmann, R., Fundamental Aspects of Postsource Decay in Matrix-Assisted Laser Desorption Mass Spectrometry. 1. Residual Gas Effects, /. Phys. Chem., 96, 9678, 1992. 

Keough, T. Youngquist, R.S. Lacey, M.P. A method for high-sensitivity peptide sequencing using postsource decay matrix-assisted laser desorption ionization mass spectrometry. Proc. Natl. Acad Sci. USA. 1999, 96, 7131-7136. 

D. J. Harvey, Postsource decay fragmentation of N-linked carbohydrates from ovalbumin and related glycoproteins, 7. Am. Soc. Mass Spectrom. 11, 572-577 (2000). 

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