Post-source decay mass spectra

Figure 8.14 Post-source decay mass spectra of metal ion adducts. Reprinted by permission of Elsevier from Ref. [140] American Society for Mass Spectrometry, 2001.

FIGURE 8.9 Post-source decay mass spectra of Substance P recorded at different values of the reflectron voltage. (Reprinted with permission from reference 8). 

FIGURE 8.11 Post-source decay mass spectra of a mixture of Substance P and bombesin, (a) Mass spectrum without precursor-ion selection at full reflectron voltage, (b) Selection of the MK ion of Substance P. (c) Selection of the MH ion of bombesin. (Reprinted with permission from reference 3). 

FIGURE 8.25 General form of the calibration curve used for calibrating post-source decay mass spectra on a curved-field reflectron TOR (Reprinted with permission from reference 15). 

RNase digestion products of 5S rRNA of S. acidocaldarius (b) Post-source decay mass spectrum obtained from the precursor ion... 

FIGURE 8.15 Post-source decay mass spectrum of coli thioredoxin obtained from a single-stage reflectron TOP mass spectrometer in two reflectron voltage segments. (Reprinted with permission from reference 10). 

FIGURE 10.18 Post-source decay mass spectrum of the peptide angiotensin-converting enzyme inhibitor (MW = 1100.5) obtained using a curved-field reflectron. 

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].)...

We have implemented scanning methodologies using MALDI-TOF mass spectrometry to partially purified venom from C. striatus and C. ermineus. We have carried out specific derivatizations in order to deduce composition and sequence information. Together with an intact mass these measurements are used to determine whether an ionized species observed in the MALDI mass spectrum corresponds with the intact protonated molecule of a previously characterized conotoxin. The information obtained from derivatizations is also important when the ionized species does not correspond with the intact mass of peptides of known sequence. In that case, post source decay of the native and derivatized species may help assign the fragment ions. 

Figure 4. Tryptic peptide digest spectrum of spot 6 and post source decay spectrum of a tryptic peptide (T8), MYSPTSILDIR, with mass at m/z 1295.94 from the protein at spot 6. (A) MALDI reflector mass spectrum of tryptic peptide mixture derived from spot 6. (B) Mass spectrometric determination of partial peptide sequence of a tryptic peptide (T8). Y" series ions were observed.

Figure 8 Positive ion matrix-assisted laser desorption (MALDI) time-of-flight mass spectrum of P-cryptoxanthin paknitate isolated from tangerine juice. Post source decay was used to enhance detection of structurally significant fragment ions such as loss of toluene (m/z 698), loss of palmitic acid (m/z 534), and loss of both toluene and palmitic acid (m/z 442). (From Ref. 320.)... 

FIGURE 8.13 Product-ion mass spectrum resulting from the post-source decay of the Ml-f ion of Substance P with the reflection voltage optimized for the precursor ion. (Reprinted with permission from reference 9)... 

Some Examples. Earlier in this chapter, we discussed the isolation and identification of an antigen AMAPBTLLL bound to a novel murine Class IB MHC molecule Qa-1. In that example, the amino acid sequence was determined from the MALDI mass spectra of ladder peptides obtained from aminopeptidase M, carboxypeptidase P, and chymotrypsin digestions. As shown in Figure 10.19, the amino acid sequence can also be determined from the post-source decay MALDI mass spectrum of the intact peptide. In this case, a curved-field reflectron was used, so that the entire mass spectrum was recorded without changing the reflectron voltage. 

The post-source decay technique suffers from some limitations, such as the limited selectivity obtainable on the parent ion, modest mass accuracy of the daughter ions (compared to the accuracy achieved for parent ions), and the frequently incomplete information obtained from the metastable decay spectrum. These factors have stimulated the development of various tandem instruments, as discussed below. 

The loss of 44 5 uma was also observed in the mass spectrum of poly-BFl synthesized by anionic polymerization with PhLi as the initiator (Fig. 39), recorded using the dithranol as matrix. In this case, the difference between the two most intense peaks belonging to each cluster is about 77 Da, suggesting that the most intense peaks correspond to the macromolecular chains terminated with a phenyl group (Ph) at one end, as expected since PhLi was used as initiator [23]. Since very similar mass spectra were recorded using other matrices, such as CHCA (a-cyano-4-hydroxycinnamic acid), DCTB [tra/25-2-[3-(4-t rt-butylphenyl)-2-methyl-2-pro-penylidene]malononitrile], and HABA [2-(4-hydroxylphenylazo)benzoic acid], the question about the loss of a compound with a mass 44 5 requires appropriate investigations by means of post-source decay (PSD) and CID (collision induced dissociation) MALDI-TOF/TOF tandem mass spectrometry methods. 

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