Source decay

This is an approximation to the complete dispersion equation [131]. The amplitude of a train of waves originating from an infinitely long linear source decays exponentially with the distance x from the source... 

Requires shielding and special procedures to avoid exposure of personnel to radiation Frequent recahbration is required to compensate for source decay over time Electrical power and power line transient protection required... 

Matrix-assisted laser desorption ionization post-source-decay mass spectrometry... 

In instrnments withont a reflectron (see Figure 3.7 above), both the precursor and prodnct ions reach the detector at the same time and are not separated. The reflectron, however, is an energy analyser and product ions with different energies, after passage through the reflectron, will have different flight times to the detector and may be separated and their m/z ratios determined. This is known as post-source decay (PSD) [11]. 

Experimentation showed that the protein was not glycosylated and that the sequence at the iV-amino acid terminus corresponded to that expected. The C-terminus sequence, however, did not correspond to that predicted and these data were interpreted in terms of the presence of a heterogeneous, truncated, protein. A study of the tryptic digest fragments from this protein with matrix-assisted laser desorption ionization (MALDI) with post-source decay enabled the authors to suggest the positions at which the parent protein had been truncated. 

Post-source decay The term used to describe the production of product-ion MS-MS spectra in a time-of-flight mass analyser. 

Post-source decay RT.TF Remote laser-induced fluorescence... 

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Figure 6 Partial MALDI-TOF mass spectrum from PMMA generated by ATRP with ethyl-2-bromoisobutyrate as initiator (inset shows theoretical isotope distribution for lithiated 18-mer of structure 3). (Peak labelled 3 arises from post-source decay of 3 [10].)...

Further plate-out studies were conducted using radon progeny and thoron progeny reference sources, models Rn-190 and Th-190, respectively, manufactured by Pylon Electronic Development (Ottawa), hereafter referred to as Pylon sources, for simplicity. These are small cylindrical containers (<40 cm3 volume) provided with a Ra-226 source or Th-228 source. The containers can be opened at their base and some suitable material can be placed in it for exposure purposes (Vandrish et al., 1984). The Ra-226 and Th-228 sources decay, respectively, to Rn-222 and Rn-220 which in turn, decay into their progeny. In this respect, the above sources can be considered miniature RTTFs quite suitable or plate-out studies, in which air flow pattern effects are minimized. 

J. J. Lennon and K. A. Walsh. Locating and Identifying Posttranslational Modifications by In-Source Decay During MALDI-TOF Mass Spectrometry. Protein Sci., 8(1999) 2487-2493. 

B. Spengler. Post-Source Decay Analysis in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Biomolecules. J. Mass Spectrom., 32(1997) 1019-1036. 

The development glycopeptide libraries obtained by the split-mix method is severely hampered by the lack of concurrent development of a general, facile separation and characterization technology. Some headway has been made with chemical coding of the libraries, but very few direct methods of analysis exist. One promising method that could be applied to the direct characterization of both types of libraries is mass spectrometry. More specifically, post-source-decay matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (PSD-MALDI-TOF-MS) and CID-FAB/MS/MS have been used to characterize glycopeptides.53-55... 

PAGE Phe Pro PSD QC Q-ToF Q-ToF-LC-MS-MS polyacrylamide gel electrophoresis phenylalanine proline post-source decay quality control quadrupole time-of-flight mass analyser quadrupole time-of-flight mass analyser in combination with (high performance) liquid chromatography and tandem mass... 

Several original papers must be mentioned that deal with mass spectrometric techniques which the numerous reviews do not comprise. Kaufmann and coworkers268,288 studied the mass spectrometric analysis of carotenoids and some of their fatty acid esters using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and its post-source-decay (PSD) variant. Some advantages concerning the thermal instability and limited solubility were discussed, but the fragmentation paths of the carotenoid cations were found to be essentially the same as those observed with conventional techniques. 

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. 

Cordero, M.M. Cornish, T.J. Cotter, R.J. Lys, LA. Sequencing Peptides Without Scanning the Reflectron Post-Source Decay With a Curved-Field Reflectron TOF Spectrometer. Rapid Commun. Mass Spectrom. 1995, 9, 1356-1361. 

Schnaible, V. Wefing, S. Resemann, A. Suckau, D. Biicker, A. Wolf-Kiimmeth, S. Hoffmann, D. Screening for Disulfide Bonds in Proteins by MALDI in-Source Decay and LlFT-TOF/TOF-MS. Anal Chem. 2002, 74, 4980-4988. 

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